How to choose a valve?
Valve is the control part of the fluid conveying system. It has the functions of cut-off, regulation, diversion, countercurrent prevention, stabilization, diversion and overflow relief. In the field of industrial production, choosing the right valve is particularly important for the overall control of the production process. With the continuous development of valve technology, the application field of valves is expanding, and the functions are becoming more and more perfect. In the face of various valve types and different application conditions, how will you choose valves correctly?
Characteristics of Valves
1.1 Use characteristics:
It determines the main performance and scope of use of valves, belonging to the characteristics of the valve: the type of valves (closed-circuit valves, regulating valves, safety valves, etc.); product types (gate valves, globe valves, butterfly valves, ball valves, etc.); the main parts of valves (valve body, cover, stem, disc, sealing surface) materials; valve transmission mode, etc.
1.2 Structural characteristics:
It determines some structural characteristics of valve installation, maintenance and other methods. It belongs to the structural characteristics of the length and overall height of the valve, the connection form with pipeline (flange connection, threaded connection, clamp connection, external thread connection, welding end connection, etc.), the form of sealing surface (ring, threaded ring, surfacing, spray welding, valve body body), etc. Form (rotating rod, lifting rod) etc.
Valve Selection Steps
- (1) Define the use of the valve in the equipment or device, determine the working conditions of the valve: suitable medium, working pressure, working temperature and so on.
- (2) Determine the nominal diameter and connection mode of the pipe connecting with the valve: flange, thread, welding, etc.
- (3) Determine the way to operate the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical or hydraulic linkage, etc.
- (4) According to the medium, working pressure and working temperature of pipeline transportation, the materials of the shell and inner parts of the selected valve are determined: grey cast iron, malleable cast iron, nodular cast iron, carbon steel, alloy steel, stainless acid-resistant steel, copper alloy, etc.
Select the types of valves: closed-circuit valves, regulating valves, safety valves, etc.
Determine the type of valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure relief valve, steam trap, etc.
Determine the parameters of valves: For automatic valves, the allowable flow resistance, discharge capacity, back pressure and so on are determined according to different needs, and then the nominal diameter of pipeline and the diameter of valve seat hole are determined.
Determine the geometric parameters of the selected valve: structure length, flange connection form and size, valve height direction after opening and closing, bolt hole size and number of connections, the size of the whole valve shape, etc.
Use the existing information: valve product catalogue, valve product samples, etc. to select appropriate valve products.
- (1) The use, operating conditions and control mode of the selected valve.
- (2) The properties of working medium: working pressure, working temperature, corrosion performance, whether it contains solid particles, whether the medium is toxic, whether it is flammable, explosive medium, medium viscosity and so on.
- (3) Requirements for fluid characteristics of valves: flow resistance, discharge capacity, flow characteristics, sealing grade, etc.
- (4) Installation size and outline size requirements: nominal diameter, connection mode with pipeline and connection size, outline size or weight limitation, etc.
- (5) Additional requirements for reliability of valve products, service life and explosion-proof performance of electric devices.
According to the above-mentioned basis and steps for selecting valves, when selecting valves reasonably and correctly, it is necessary to have a detailed understanding of the internal structure of various types of valves in order to make the right choice for the preferred valves.
The final control of the pipeline is the valve. Valve opener controls the flow pattern of medium in the pipeline. The shape of the valve runner makes the valve have certain flow characteristics. This must be taken into account when selecting the most suitable valve for installation in the pipeline system.
Valves for cut-off and open media
The flow channel is a straight-through valve, and its flow resistance is small. Valves used as cut-off and open media are usually chosen. Downward closed valves (globe valves, plunger valves) are seldom selected because of their tortuous flow passages and higher flow resistance than other valves. Closed valves can be used when high flow resistance is allowed.
Valves for flow control
Valves that are easy to regulate flow are usually chosen for flow control. Downward closed valves (such as globe valves) are suitable for this purpose because their seat size is proportional to the stroke of the closure. Rotary valves (cock valves, butterfly valves, ball valves) and flex body valves (clamping valves, diaphragm valves) can also be used for throttling control, but usually only within a limited valve caliber range. Gate valve is a circular valve seat orifice with a disc gate to do cross-cutting movement. It can better control the flow only when it is close to the closed position, so it is usually not used for flow control.
Valves for reversing diversion
The valve can have three or more channels according to the need of reversing diversion. Cock valves and ball valves are more suitable for this purpose, therefore, most of the valves used for reversing diversion are selected one of these valves. However, in some cases, other types of valves can also be used as directional diversion as long as two or more valves are properly connected to each other.
Valves for Medium with Suspended Particles
When there are suspended particles in the medium, it is most suitable to use the sliding valve with wiping action along the sealing surface of its closing parts. If the closure is vertical to the back and forth movement of the seat, particles may be clamped, so the valve is only applicable to a basically clean medium unless the sealing surface material allows the insertion of particles. Ball valves and cock valves have wiping effect on the sealing surface during the opening and closing process, so they are suitable for use in medium with suspended particles.
Selection of valves according to flow characteristics
The shape of valve opening and closing parts and valve runner makes the valve have certain flow characteristics. This must be taken into account when selecting valves.
1. Valves for cutting off and connecting Media
Valves with small flow resistance and straight flow passage are usually chosen. These valves include gate valves, globe valves and plunger valves. Downward closed valves are seldom used because of the tortuous flow passage and higher flow resistance than other valves. However, closed valves can also be used when high flow resistance is allowed.
2. Valves for flow control
Valves that are easy to regulate flow are usually chosen. For example, control valve, throttle valve, plunger valve, because its seat size is proportional to the travel of the opening and closing parts. Rotary (e.g. cock, ball, butterfly) and flex (pinch, diaphragm) valves can also be used for throttling control, but usually only within a limited valve caliber range. In most cases, people usually change the shape of the globe valve disc for throttling. It should be pointed out that it is extremely unreasonable to change the opening height of gate valve or globe valve to achieve throttling effect. Because the medium in the pipeline is in the throttling state, the flow rate is very high, and the sealing surface is easy to be washed and worn, thus losing the function of cutting off and sealing. Similarly, it is unreasonable to use the throttle valve as the cutting device.
3. Valves for reversing diversion
According to the need of directional diversion, the valve can have three or more channels, suitable for the selection of cock valves and ball valves. Most valves for reversing and diverting use this type of valve. In some cases, other types of valves are properly connected with each other by two or more valves, and can also be used as directional diversion of media.
4. Valves for Medium with Suspended Particles
If the medium has suspended particles, it is most suitable to use its opening and closing parts sliding along the sealing surface with wiping valve. Such as flat gate valve.
Selection of valves according to connection form
There are many types of connection between valve and pipeline, among which the main threads, flanges and welding connections are the most important.
1. Thread connection
This connection usually processes the end of the valve inlet and outlet into tapered or straight pipe threads, which are screwed into the tapered pipe threaded joints or pipes. Because this connection may have larger leakage channels, these channels can be blocked with sealants, sealants or fillers. If the material of the valve body can be welded, it can also be sealed after thread connection. If the material of the connecting parts is allowed to be welded, but the coefficient of expansion varies greatly, or the working temperature varies greatly, the threaded joints must be sealed only. The threaded valves are mainly valves with nominal diameter less than 50 mm. If the diameter is too large, it is very difficult to install and seal the connecting part.
In order to facilitate the installation and disassembly of threaded valves, pipe joints can be used at appropriate locations in the pipeline system. Valves with nominal diameter less than 50 mm can be fitted with sleeve joints. The threads of the sleeve joints connect the two parts of the connection.
2. Flange connection
Flanged valves are easy to install and disassemble, but they are heavier than threaded valves, and the corresponding price is higher. Therefore, it can be applied to pipeline connections of various sizes and pressures. However, when the temperature exceeds 350℃, the bolts, gaskets and flange creep relaxation will significantly reduce the load of bolts, which may lead to leakage of flanged connections with great stress.
3. Welding Joints
This kind of connection is suitable for all kinds of pressure and temperature. It is more reliable than flange connection when used under more harsh conditions. However, the disassembly and reinstallation of welded valves are difficult, so their use is limited to situations where they can normally operate reliably for a long time, or where the service conditions are harsh and the temperature is high. Such as thermal power plants, nuclear power projects, ethylene projects on the pipeline.
Welded valves with nominal sizes less than 50 mm usually have welded sockets to support pipes with flat ends. Because socket welding forms a gap between the socket and the pipeline, it is possible to cause the gap to be corroded by some media. At the same time, the vibration of the pipeline will make the joint fatigue, so the use of socket welding is limited to a certain extent.
The groove butt welding is often used for valve body in the case of large nominal condition, harsh use condition and high temperature. At the same time, the welding seam is strictly required.
Selecting Valves Based on Medium Performance
Many media have certain corrosiveness; the same medium has different corrosiveness with the change of temperature, pressure and concentration. Therefore, valves suitable for the medium should be selected according to the corrosion resistance of the material.
1. cast iron valves
(1) Gray iron valves
Suitable for water, steam, petroleum products, ammonia can work in the most alcohol, aldehyde, ether, ketone, lipid and other corrosive medium. It is not suitable for medium such as hydrochloric acid and nitric acid. But it can be used in concentrated sulfuric acid, because concentrated sulfuric acid can produce a passive film on its metal surface. To prevent the corrosion of cast iron by concentrated sulfuric acid.
Ductile Iron Valve
Strong corrosion resistance, can work in a certain concentration of sulfuric acid, nitric acid, sulfuric acid, acid salt. But it is not resistant to corrosion of fluoric acid, strong alkali, hydrochloric acid and ferric trichloride hot solution. Avoid sudden heat and cold when using, otherwise it will burst.
Nickel cast iron valves
The alkali resistance is stronger than that of gray cast iron and nodular cast iron valves. Nickel cast iron is an ideal valve material for dilute sulfuric acid, dilute hydrochloric acid and caustic alkali.
2. Carbon steel valves
The corrosion resistance of carbon steel valves is similar to that of gray cast iron and slightly inferior to that of gray cast iron.
3. Stainless steel valves
Stainless steel valves have excellent atmospheric resistance, nitric acid and other oxidizing media, and alkali resistance.
It can resist the corrosion of non-oxidizing acids and salts such as hydrochloric acid, dilute sulfuric acid and phosphoric acid. But it is not resistant to the corrosion of strong oxidizing acids, alkalis and some organic solvents such as nitric acid and chromic acid.
Also known as polychlorinated ether, is a linear, high crystallinity thermoplastic. It has excellent corrosion resistance, second only to fluoroplastics. It can resist the corrosion of various acids, alkalis, salts and most organic solvents except concentrated sulfuric acid and concentrated nitric acid, but not liquid chlorine, fluorine and bromine.
Like other fluoroplastics, it has excellent corrosion resistance and other properties, and its corrosion resistance is slightly lower than that of PTFE. It has good corrosion resistance to organic acid, inorganic acid, alkali, salt and various organic solvents. Some solvents containing halogen and oxygen at high temperatures can swell them. It is not resistant to high temperature fluoride, fluoride, fused alkali, concentrated nitric acid, aromatic hydrocarbons, fuming nitric acid, fused alkali metals, etc.
Polytetrafluoroethylene (PTFE) has excellent corrosion resistance. It can resist almost all chemical media except molten metal lithium, potassium, sodium, chlorine trifluoride, oxygen trifluoride at high temperature and liquid oxygen at high flow rate.
Plastic Lining Valve
Because of the low strength of plastics, many valves use metal lining as shell and plastic as lining. Plastic lined valves have different corrosion resistance with different lined plastics. The corrosion resistance of the plastic lining is the same as that of the corresponding plastic in the above plastic valves. However, the corrosion resistance of other materials used in plastic lined valves should be considered when selecting.
Rubber is soft, so many valves use rubber as lining to improve the corrosion resistance and sealing performance of valves. The corrosion resistance of rubber varies greatly with the type of rubber. The vulcanized natural rubber can resist the corrosion of non-oxidizing acids, alkalis and salts, but not strong oxidants, such as nitric acid, chromic acid and concentrated sulfuric acid, and also the corrosion of petroleum products and some organic solvents. Therefore, natural rubber is gradually replaced by synthetic rubber. NBR in synthetic rubber has good oil resistance, but it is not resistant to strong solvents such as oxidizing acid, aromatic hydrocarbon, grease, ketone and ether; fluorine rubber has excellent corrosion resistance, and can resist various acids, alkalis, salts, petroleum products, hydrocarbons, etc., but less solvent resistance than fluoroplastics; polyether rubber can be used in water, oil, ammonia, alkali and other media.
Lead is an active metal, but it is often used as a lining for special valves because of its soft material. Lead corrosion product film is a strong protective layer. It is a well-known sulfuric acid-resistant material. It has high corrosion resistance in phosphoric acid, chromic acid, carbonate and neutral solution, seawater and other media, but it is not alkali-resistant, hydrochloric acid corrosion, nor suitable for working in their corrosion products.
Selection of Valves Based on Temperature and Pressure
In addition to considering the corrosion performance, flow characteristics and connection form of the medium, the temperature and pressure of the medium are important parameters in selecting the valve.
1. Valve service temperature
The service temperature of the valve is determined by the material used to make the valve. The temperature of commonly used materials for valves is as follows:
- The service temperature of gray iron valves is – 15 – 250℃.
- The service temperature of malleable cast iron valves is – 15 – 250℃.
- The service temperature of nodular cast iron valves is – 30 – 350℃.
- The maximum service temperature of high nickel cast iron valves is 400℃.
- The service temperature of carbon steel valves is – 29 – 450℃. The recommended service temperature T < 425℃ in JB / T3595 – 93 standard.
- The maximum service temperature of 1Cr5Mo and alloy steel valves is 550℃.
- The maximum service temperature of 12Cr1MoVA and alloy steel valves is 570℃.
- The service temperature of 1Cr18Ni9Ti and 1Cr18Ni12Mo2Ti stainless steel valves is – 196 – 600℃.
- The service temperature of copper alloy valves is – 273 – 250℃.
Maximum service temperature of plastic valves:
- Nylon is 100℃.
- The chlorinated polyether is 100℃.
- The temperature of polyvinyl chloride is 60℃.
- Polytrifluorochloroethylene – 60 – 120℃;
- Polytetrafluoroethylene – 180 – 150℃.
- Rubber diaphragm valves have different operating temperatures due to different types of rubber.
- The natural rubber is 60℃.
- Nitrile butadiene rubber and chloroprene rubber are 80℃.
- Fluorine rubber is 200℃.
When using rubber and plastics for valve lining, the temperature resistance of rubber and plastics shall prevail.
Ceramic valves, because of their poor temperature resistance and rapid change, are generally used in working conditions below 150℃. Recently, a super performance ceramic valve has appeared, which can withstand the high temperature below 1000℃.
Glass valves, with poor temperature resistance and rapid change, are generally used in working conditions below 90℃.
The temperature resistance of enamel valves is limited by the sealing ring material, and the maximum service temperature is not more than 150℃.
2. Valve pressure
The service pressure of the valve is determined by the material used to make the valve.
- The maximum nominal pressure allowed for gray iron valves is 1 MPa.
- The maximum nominal pressure allowed for malleable iron valves is 2.5 MPa.
- The maximum nominal pressure allowed for ductile iron valves is 4.0 MPa.
- The maximum nominal pressure allowed for copper alloy valves is 2.5 MPa.
- The maximum nominal pressure allowed for titanium alloy valves is 2.5 MPa.
- The maximum nominal pressure allowed for carbon steel valves is 32 MPa.
- The maximum nominal pressure allowed for alloy steel valves is 300 MPa.
- The maximum nominal pressure allowed for stainless steel valves is 32 MPa.
- The maximum nominal pressure allowed for plastic valves is 0.6 MPa.
- The maximum nominal pressure allowed for ceramic, glass and enamel valves is 0.6 MPa.
- The maximum nominal pressure allowed for FRP valves is 1.6 MPa.
3. Relation between Valve Temperature and Pressure
Valve operating temperature and pressure have a certain internal relationship, but also affect each other. Among them, temperature is the dominant factor. Valves with a certain pressure are only suitable for a certain temperature range. The change of valve temperature can affect the pressure of the valve.
For example, the nominal pressure of a carbon steel valve is 10 MPa, the maximum working pressure P20 is 10 MPa when the working temperature of the medium is 200℃, the maximum working pressure P40 is 5.4 MP when the working temperature of the medium is 400℃, and the maximum working pressure P54 is 4.5 MPa when the working temperature of the medium is 450℃.
Determining Valve Size Based on Flow Rate and Flow Rate
The flow rate and flow rate of the valve mainly depend on the diameter of the valve, and also on the resistance of the structure of the valve to the medium. At the same time, it has a certain internal relationship with the pressure, temperature and concentration of the medium of the valve.
The flow area of the valve is directly related to the flow rate and flow rate, and the flow rate and flow rate are two interdependent quantities. When the flow rate is constant, the area of the runner will be smaller if the flow rate is large, and the area of the runner will be larger if the flow rate is small. On the contrary, the area of the runner is large and its velocity is small, while the area of the runner is small and its velocity is large. Medium flow rate is high, valve diameter can be smaller, but the resistance loss is large, the valve is easy to damage. High flow rate will produce electrostatic effect on flammable and explosive media, causing danger; too low flow rate, low efficiency and uneconomical. For medium with high viscosity and explosive property, a smaller flow rate should be adopted. Oil and liquids with high viscosity choose flow rate with the size of viscosity, generally 0.1-2m/s.
In general, the flow rate is known and the flow rate can be determined by experience. See Table 2-2 for the flow velocities commonly used in various media. The nominal diameter of the valve can be calculated by flow rate and flow rate.
Valve size is the same, its structure is different, fluid resistance is also different. Under the same conditions, the greater the resistance coefficient of the valve, the more the flow rate and flow rate of the fluid through the valve decrease; the smaller the resistance coefficient of the valve, the less the flow rate and flow rate of the fluid through the valve decrease. The flow velocities of common media are shown in Table 2-2.
Table 2-2 Velocimeters commonly used in various media
|Liquid name||Conditions of use||
|Liquid name||Conditions of use||Flow rate (m/s)|
DN > 200
DN=200 ~ 100
DN < 100
Rho < 0.01 (gauge pressure)
Rho < 0.15 (gauge pressure)
Rho < 2.5 (gauge pressure)
DN > 200
DN=200 ~ 100
DN < 100
One point six
One point five
|Low pressure steam||P < 1 (absolute pressure)||15~20|
|Medium pressure steam||=1.0 ~ 4 (absolute pressure)||20~40||liquid ammonia||
Less than 0.6 (gauge pressure)
Less than 2 (gauge pressure)
0.05 to 0.3
0.3 to 0.8
0.8 to 1.5
|High pressure steam||=4.0 ~ 12 (absolute pressure)||40~60|
Less than 0.3 (gauge pressure)
=0.3 ~ 0.6 (gauge pressure)
=0.6 ~ 1 (gauge pressure)
=1.0 ~ 2 (gauge pressure)
=2.0 ~ 3 (gauge pressure)
=3.0 ~ 30 (gauge pressure)
0.5 to 3
Concentration 0 to 30%
Concentration 30% to 505
Concentration 50% to 73%
One point five
One point two
Concentration 88% to 93%
Concentration 93% to 100%
One point two
One point two
|hydrochloric acid||One point five|
=0 ~ 0.05 (gauge pressure)
=0.05 ~ 0.6 (gauge pressure)
=0.6 ~ 1 (gauge pressure)
=1.0 ~ 2 (gauge pressure)
=2.0 ~ 3 (gauge pressure)
|Water and viscosity similar liquids||
=0.1 ~ 0.3 (gauge pressure)
Less than 1 (gauge pressure)
Less than 8 gauge pressure)
Less than 20~30 (gauge pressure)
Circulating water and cooling water in heat supply network
No pressure backwater
0.5 to 2
0.5 to 3
2 to 3.5
0.3 to 1
0.5 to 2
0.5 to 1.2
|coal gas||2.5 to 15|
|Semi water gas||=0.1 ~ 0.15 (gauge pressure)||10~15|
|Natural gas||Thirty||tap water||
Supervisor =0.3 (gauge pressure)
Branch tube =0.3 (gauge pressure)
1.5 to 3.5
1 to 1.5
|nitrogen||=5 ~ 10 (absolute pressure)||15~25|
< 0.3 (gauge pressure)
< 0.6 (gauge pressure)
Less than 2 (gauge pressure)
|Boiler feed water||> 3|
|Steam condensate||0.5 to 1.5|
|Condensate water||Gravity flow||0.2 to 0.5|
|Seawater and slightly alkaline water||< 0.6 (gauge pressure)||1.5 to 2.5|
Note: The unit of DN value is mm; the unit ofvalue is MPa.
- The resistance coefficient of the gate valve is small, only in the range of 0.1-1.5; the resistance coefficient of the gate valve with large caliber is 0.2-0.5; and the resistance coefficient of the shrinkage gate valve is larger. The resistance coefficient of globe valve is much larger than that of gate valve, generally between 4 and 7. Y-type globe valve (DC) has the smallest resistance coefficient, ranging from 1.5 to 2. Forged steel globe valves have the greatest resistance coefficient, even up to 8.
- The resistance coefficient of the check valve depends on the structure: the swing type check valve is usually about 0.8-2, and the multi-lobe swing type check valve has a larger resistance coefficient; the lift type check valve has the largest resistance coefficient, up to 12.
- The resistance coefficient of the cock valve is small, usually about 0.4-1.2.
- The resistance coefficient of the diaphragm valve is generally about 2.3.
- The resistance coefficient of butterfly valve is small, generally less than 0.5.
- The resistance coefficient of the ball valve is the smallest, generally around 0.1.
- The resistance coefficient of the above-mentioned valve is the value of the valve in full open state.
Valve diameter selection should take into account the processing accuracy and size deviation of the valve, as well as other factors. Valve size should have a certain amount of affluence, generally 15%. In practice, the valve diameter depends on the diameter of the process pipeline.
Confirming the structure type of the valve according to the working condition and process operation
1. Process requirements
Ammonia has corrosive effect on copper. Valves made of copper can not be selected. In the process of containing ammonia in medium, the structure of globe valve is different from that of general valve, and its sealing surface is made of pasteurized alloy.
Non-directional valves should be selected for double-flow pipelines. In refineries, when heavy oil pipes stop operating, steam should be used to reverse purge the pipeline to prevent heavy oil from clogging the pipeline, so it is not appropriate to use shutoff valve. Because when the medium flows in the opposite direction, it is easy to erode the sealing surface of the globe valve. Gate valve should be chosen as the best choice.
Globe valves and gate valves are not suitable for some media with crystallization or sediment, because their sealing surfaces are easy to be worn by crystallization and sediment. Therefore, ball valves or cock valves should be selected; flat gate valves can also be selected, but pinch valves are preferred.
In the selection of gate valves, the open bar single gate is more suitable for corrosive medium than the dark bar double gate; the single gate is more suitable for medium with high viscosity; the wedge double gate is better than the wedge single gate for high temperature and deformation of sealing surface, and it will not be stuck due to temperature changes, especially superior to the non-elastic single gate.
When it is necessary to regulate small flow accurately, stop valves should not be required, needle valves or throttle valves should be used. Pressure relief valves should be used when it is necessary to maintain pressure stability behind the valves.
For high-pressure and ultra-high-pressure media, right-angle globe valves are often used, because right-angle globe valves are usually made of forged steel, and the pressure resistance of forged steel is relatively stronger than that of cast steel.
2. Economic Rationality
For corrosive media, if the temperature and pressure are not high, non-metallic valves should be used as far as possible; if the temperature and pressure are high, lining valves can be used to save precious metals. When choosing non-metallic valves, economic rationality should still be considered. For example, polytetrafluoroethylene (PTFE) is not needed when polyvinyl chloride (PVC) can be used, because the price of PTFE is higher than that of polyvinyl chloride (PVC).
For high temperature and high pressure occasions, should be based on the thermobarometer, if ordinary carbon steel valves can meet the use requirements, it is not appropriate to use alloy steel valves, because alloy steel valves are much more expensive.
For medium with higher viscosity, smaller flow resistance is required. Valves with smaller flow resistance such as Y-type direct current globe valve, gate valve, ball valve and plug valve should be adopted. Low flow resistance valve, less energy consumption.
It is reasonable to choose large-caliber gate valves and butterfly valves for medium such as water and air with low pressure and large flow. The butterfly valve can be used for cutting off and throttling.
3. Safety and reliability
Ductile iron valves and cast steel valves can be used in steam pipes. But in the outdoor steam pipeline, if the gas supply is stopped, the water will easily freeze and the valve will burst, especially in the north of China. Therefore, it is advisable to use cast steel or forged steel valves, while doing a good job in the frost-proof and heat preservation of the valves.
Acetylene is flammable and explosive, which requires high sealability. When the pressure is below 0.6 MPa, the diaphragm valve should be used, but it should not be used in the pipeline of vacuum equipment. Corrugated pipe valves should be used for radioactive and highly toxic media in order to prevent leakage of media from packing box.
For the valves with driving devices (electric, hydraulic and pneumatic), besides the safety and reliability of the driving devices, the corresponding driving devices should be selected according to the different working conditions. For example, in the case of fire protection, the valves of hydraulic and pneumatic devices should be selected; when the valves of electric devices must be selected, their electric devices should be explosion-proof in order to avoid arc-induced fire.
4. Convenient operation and maintenance
For large valves and valves at high altitude, high temperature, high pressure, dangerous and long distance, gear drive, chain drive or valves with electric, pneumatic and hydraulic devices should be selected.
When the operating space is limited, it is not suitable to be in the open-rod gate valve. It is better to choose the dark-rod gate valve. It’s better to use butterfly valve.
For valves that need fast closing and opening, it is not suitable to be in general gate valves and globe valves. Ball valves, cock valves, butterfly valves and fast opening gate valves should be required according to other requirements.
Gate valves and globe valves are the two most widely used types of valves. When selecting, it should be considered comprehensively. Gate valve has small flow resistance and less energy consumption of conveying medium, but it is difficult to maintain. Globe valve has simple junction and convenient maintenance, but it has large flow resistance. From the maintenance point of view, globe valve maintenance is more convenient than gate valve; water and steam in globe valve, pressure drop is not big, so globe valve is widely used in medium pipelines such as water and steam. However, in the medium with high viscosity such as petroleum products, gate valves are still widely used despite the difficulty of maintenance. In the pipeline of welding connection, the globe valve of welding connection should be selected as far as possible, and the gate valve of welding connection should not be selected. It is much more difficult to repair the sealing surface of the gate valve in pipeline than that of the globe valve, and the gate plate and seat are easily jammed when the temperature of the gate valve varies greatly.
Selection of Driving Valves
Gate valves, globe valves, ball valves, butterfly valves, cock valves, throttle valves, diaphragm valves and other valves as pipeline closure devices are widely used, among which gate valves and globe valves are the most used.
Chapter 1, Section 6, systematically describes the terms, structure and scope of application of valves, which can be used as the basis for the selection of valve types and models. When the type and model of the valve are determined, the shell material, sealing surface material, applicable temperature, suitable medium and nominal diameter of the valve are determined. Under the circumstances, the following steps can be taken.
1. Steps for valve selection
- (1) According to the characteristics of medium, working pressure and temperature, the material of valve body and sealing surface are selected according to the data provided in the two sections of “Selecting valves according to medium performance” and “Selecting valves according to temperature and pressure”, as well as tables 2-3a and 2-3b.
- (2) The nominal pressure level of the valve is determined according to the working pressure and temperature of the valve body material and medium.
- (3) According to nominal pressure, medium characteristics and temperature, the sealing surface material is selected. The maximum service temperature is not lower than the working temperature of the medium.
- (4) Determine the nominal diameter according to the calculation value of pipe diameter. Normally, the nominal diameter of the valve is the diameter of the pipe.
According to the use of the valve and the requirements of the production process, choose the driving mode of the valve.
According to the connection method of pipeline and nominal diameter of valve, choose the connection form of valve.
According to the nominal pressure, medium characteristics, working temperature and nominal diameter of the valve, select the type, structure and type of the valve.
Table 2-3a Selection Table of Common Valve Body Materials
|Material Science||Common working conditions||Main medium|
|category||Material grade||Code name||PN/MPa||T/ C|
|Gray cast iron||HT200||Z||Less than 1.6||Less than 200||Water, steam, oil, etc.|
|HT250||Ammonia is less than 2.5.||Ammonia or more – 40|
|Malleable iron||KT30-6||K||Less than 2.5||
Ammonia or more – 40
|Ductile iron||QT400-18||Q||Less than 4||Less than 350|
|High silicon cast iron||NSTSi-1S||G||Less than 0.6||Less than 120||Nitric acid and other corrosive media|
|High quality carbon steel||ZG200, ZG250, WCB||C||Less than 16||Less than 450||
Water, steam, oil, etc.
Ammonia, nitrogen, hydrogen, etc.
|A3, 10, 20, 25, 35||Less than 32||Less than 200|
|Chrome molybdenum steel||
12CrMo, WC6, 15CrMo
|I||P5410||Five hundred and forty||Steam, etc.|
|Cr5Mo, ZGCr5Mo||Less than 16||Less than 550||oils|
|Chromium molybdenum vanadium alloy steel||
ZG12Cr1MoV, ZG15Cr1MoV, WC9
|V||P5714||Five hundred and seventy||Steam type|
Nickel, chromium, titanium,
Acid resistant steel
|P||Less than 6.4||
Less than 200
– 100 – 196
Less than 600
|Nitric acid and other corrosive media|
|Ethylene and other low temperature medium|
|High temperature steam, gas, etc.|
Nickel chromium molybdenum titanium
Acid resistant steel
|R||Less than 20||Less than 200||Urea, acetic acid, etc.|
|High quality manganese vanadium steel||
|I||Less than 16||Less than 450||Water, steam, oil, etc.|
|Copper alloy||HSi80-3||T||Less than 4||Less than 250||Water, steam, gas, etc.|
Table 2-3b selection of commonly used sealing surface materials
|Material Science||Code name||Common working conditions||Applicable valves|
|rubber||X||Less than 0.1||Less than 60||Globe valves, diaphragm valves, butterfly valves, check valves, etc.|
|nylon||N||Less than 32||Less than 80||Ball valves, globe valves, etc.|
|ptfe||F||Less than 6.4||Less than 150||Ball valves, globe valves, cock valves, gate valves, etc.|
|Babbitt alloy||B||Less than 2.5||– 70~150||Stop valve for ammonia|
|T||Less than 1.6||Less than 200||Gate valves, globe valves, check valves, stopcocks, etc.|
|H||Less than 3.2||Less than 450||Medium high pressure valve|
|Nitriding steel 38CrMoALA||D||P5410||Five hundred and forty||Station gate valves, general conditions not used|
|Cemented carbide||WC, TiC||Y||Determined by valve body material||High temperature valve and ultra high pressure valve|
|Determined by valve body material||
High pressure and ultra high pressure valve
High temperature and low temperature valve
|Processing in noumenon||cast iron||W||Less than 1.6||Less than 100||Gas and oil use gate valves, cut-off valves, etc.|
|High quality carbon steel||Less than 4||Less than 200||Valve for oil|
|Less than 32||Less than 450||Valves for acid and other corrosive media|
2. Examples of Driving Valve Selection
[Example 1] Steam pipeline working pressure is 1.3 MPa, temperature is 350 C, nominal diameter is 100 mm, try to choose closed-circuit valve.
[Solution] Valve body material: Known steam pressure 1.3 MPa, temperature 350 C, valve body material according to Table 2-3a can choose ductile iron or high quality carbon steel. Considering that 350 has reached the maximum service temperature of ductile iron, high quality carbon steel (WCB, ZG230-450) valves should be selected for safe use.
Nominal pressure: According to the pressure and temperature of high quality carbon steel and steam, the nominal pressure PN of the valve is 2.5 MPa, which is found in Table 1-3.
Sealing surface material: According to nominal pressure and medium temperature of valve, stainless steel should be selected as sealing surface material according to Table 2-3b.
Driving mode: According to the given nominal diameter DN100mm, because the diameter of the pipe is small, the required moment of opening and closing is not big. This example does not put forward the special requirements of operating mode, so the handwheel drive is selected.
Connection form: According to the given steam pressure and temperature, seamless steel pipe should be used, and seamless steel pipe should be welded. However, in order to facilitate the loading and unloading and maintenance of the valve, its connection form should not be welded, and flange connection should be adopted.
Valve type and model: According to medium characteristics, nominal pressure and nominal diameter, globe valve or gate valve can be selected. Because the price of the gate valve is higher than that of the globe valve under the same pressure level, the globe valve should be preferred. However, in the globe valve parameter table, there is no carbon steel product with nominal pressure PN2.5MPa, so gate valve is still used in this case. Select valve model Z40H-25 DN100 according to gate valve parameter table.
[Example 2] For an oil pipeline, the working pressure of the medium is 11.5 MPa, the temperature is 340 C, and the inner diameter of the pipeline is 107 mm; try to select a suitable closed-circuit valve.
[Solution] Valve body material: According to medium characteristics and parameters, high quality carbon steel (WCB, ZG230-450) can be selected according to Table 2-3a.
Nominal pressure: According to the quality and medium parameters of high quality carbon steel, the nominal pressure of the valve is PN=16MPa, which is found in Table 1-3.
Sealing material: According to nominal pressure and medium temperature of valve, stainless steel or carbide steel can be selected according to Table 2-3b.
Driving mode: This case does not require special requirements, can be driven by handwheel.
Connection form: flange connection.
Nominal diameter: According to the medium parameters, 50 high quality carbon steel seamless steel pipe can be selected. According to the allowable stress of 107mm inner diameter, 11.5MPa nominal pressure and 20 steel at 340C, and 14mm wall thickness, the calculated outer diameter of the pipe is DW=107+2*14=135mm, 140 mm outer diameter, DN=125mm at this time. The nominal diameter of the valve shall be the same as that of the pipe.
Type and type of valve: Gate valve should be selected for oil pipeline. According to the parameters of the valve parameter table, when PN = 16MPa, the maximum nominal diameter of the globe valve is 40 mm, and the maximum nominal diameter of the gate valve is 200 mm under the same pressure level, so the gate valve should also be selected. According to the gate valve parameter table, the carbon steel handwheel flange gate valve models under PN16MPa are Z41H-160 and Z41Y-160. However, the maximum nominal diameter of the former is 40 mm, while the maximum nominal diameter of the latter is 200 mm. Therefore, Z41Y-160 gate valve should be selected, and its sealing surface is carbide. The selected furan is called open-rod wedge single gate valve (Z41Y-160DN125).
The selection of automatic valves is the same as that of general valves. In addition to economic rationality and durability, the performance of automatic valves such as sensitive, reliable and accurate regulation is also required.
1. Selection of Check Valves
The function of the check valve is to allow the medium to flow in only one direction and to prevent the reverse flow. The common check valves are divided into lifting type and swing type (see Fig. 1-28-Fig. 1-32).
Lifting check valves are usually used in high pressure and small caliber equipment or pipelines. For pipelines requiring low pressure drop, it is not appropriate to choose lift check valve, because of its high flow resistance, butterfly check valve or swing check valve should be selected. On pipelines with high pressure fluctuation and special requirements. In order to prevent valve disc from damaging by water hammer, swing check valve with buffer device should be selected. When the caliber is large, multi-valve swing check valve is selected. At the outlet of boiler feed pump, special empty check valve should be selected to prevent medium backflow and improve pump efficiency. Bottom valves should be selected for check valves at the bottom of pump suction pipes.
Ordinary swing check valve or lift check valve should avoid excessive caliber as far as possible. In order to make the check disc fully open or in suitable position at the minimum flow rate, the caliber of the check valve must be smaller than that of the corresponding pipe in some cases.
In order to meet the needs of various uses, check valves also have a variety of, such as: spherical check valves. Threaded lifting stop check valve, swing check valve without impact, inclined check valve, conical diaphragm check valve, etc.
Depending on the medium, the disc can be made entirely of metal, or it can be inlaid with leather, rubber or other alloy materials by synthetic covering or thermal spraying.
2. Selection of relief valve
Pressure relief valve is a valve that reduces the import pressure to a certain required outlet pressure by throttling the opening and closing parts, and can keep the outlet pressure basically unchanged by using its own medium energy when the import pressure and flow rate change.
Pressure relief valves are divided into direct acting type and pilot type.
(1) Direct action
Direct acting relief valve is loaded with compression spring, weight or gravity lever and compressed air. Valves directly controlled by pressure through diaphragm, piston or bellows. The valve is simple in structure and durable. In relatively bad working conditions, as long as properly maintained, it can also have a long life. Although the direct-acting pressure regulation is not as accurate as the pilot type, it is inexpensive. It can be widely used in situations where precise control is not necessary.
The commonly used direct acting pressure relief valves can be divided into spring film pressure relief valve, piston pressure relief valve, bellows pressure relief valve and lever pressure relief valve. Spring film pressure relief valve is a pressure relief valve which uses diaphragm as a sensitive element to drive the disc movement. It has high sensitivity and is suitable for water and air medium pipelines with low temperature and pressure.
Piston type pressure relief valve is a pressure relief valve which uses piston as sensitive element to drive disc movement. Because the piston bears more friction in the cylinder, its sensitivity is not as good as that of the membrane pressure relief valve. Therefore, it is suitable for pipelines and equipment with high temperature and pressure and working media such as steam and air.
Bellows pressure relief valve is a pressure relief valve which uses bellows as sensitive elements to drive the disc movement. It is suitable for pipelines with clean media such as steam and air with low medium parameters. Can not be used for decompression of liquids. It can not be used in pipes containing solid particles. Therefore, it is advisable to add a filter before the bellows pressure relief valve. When choosing relief valve, attention should be paid not to exceed the relief range of relief valve. It is guaranteed to be used under reasonable conditions.
Leverage pressure relief valve is a pressure relief valve which uses the weight or gravity lever as the sensitive element to drive the disc movement. This form is simple and durable, but not accurate. At present, it is seldom used.
(2) Pilot type
Pilot relief valve is composed of main valve and pilot valve. The change of outlet pressure is controlled by pilot valve amplification. In this kind of valve, the function of the guide valve is to assist or completely control the main valve. The pilot valve itself can be a small direct acting pressure relief valve. The precise control of such valves depends on their specific structure. In essence. The purpose of the pilot valve is to regulate the opening of the main valve by maintaining the flow rate under the preset pressure. The pressure control accuracy of the pilot type pressure relief valve is very accurate, and the structure is compact. For the same function pressure relief valve, the pilot type is usually much smaller than the direct acting type. In this form, the pilot valve and the main valve can be integrated, or can be used as a separate device for remote pressure signal control. It can also be used for remote switch control, that is, components in a complete system controlled by a control center. In addition, equipment directly controlled by temperature can be obtained by installing proper type of guide valve. Because of the complex structure of the pilot relief valve, frequent maintenance and clean working conditions are required. Clean working conditions often install filters at the valve entrance. The commonly used Pilot-type pressure relief valves can be divided into three types according to their structure: pilot piston type pressure relief valve, pilot bellows type pressure relief valve and pilot film type pressure relief valve.
Several problems that should be paid attention to when choosing pressure relief valve
Pressure relief valves are widely used, including steam, compression opening, industrial gas, water, oil and other liquid media can be used. Therefore, in view of many possible structural changes, when the particles are selected to relieve pressure valve, the most important is the exact performance of the valve, first of all, it should be fully tested to ensure good use effect. In testing, the pressure relief valve shall meet the following performance requirements:
(1) Within the given spring pressure level, the outlet pressure should be continuously adjusted between the maximum and minimum, and there should be no obstruction or abnormal vibration.
(2) For soft-sealed pressure relief valves, no leakage shall occur within a specified time; for metal-sealed pressure relief valves. The leakage should be no more than 0.5% of the maximum flow rate.
(3) When the outlet flow rate changes, the negative deviation of the outlet pressure is less than 20% for the direct-acting type and less than 10% for the pilot type.
(4) When the inlet pressure changes, the negative deviation of the outlet pressure is less than 10% in the direct-acting mode and less than 5% in the pilot mode.
For unused relief valves, adjust the spring to keep them in a free state. Closure shall be applied at the inlet and outlet ends.
The names, types and technical parameters of commonly used pressure relief valves are listed in the section and appendix of Chapter I, Section VI.
The nominal diameter and orifice area of commonly used pressure relief valves are shown in Table 2-4.
Table 2-4 Valve Hole Area of Pressure Relief Valve
|Nominal diameter DN (mm)||Twenty-five||Thirty-two||Forty||Fifty||Sixty-five||Eighty||One hundred||One hundred and twenty-five||One hundred and fifty|
|Seat access area f (cm2)||Two||Two point eight||Three point four eight||Five point three zero||Nine point four five||Thirteen point two||Twenty-three point five||Thirty-six point eight||Fifty-two point two|
The flow rate of the relief valve is related to the nature of the fluid and the pressure ratio. The smaller the pressure ratio, the larger the flow rate; but when the pressure ratio decreases to a certain value, the flow rate does not increase with the decrease of the pressure ratio.
The valve hole area listed in the product specification of pressure relief valve is the maximum cross-section area, and the runner area under the working condition is less than this value. The valve hole area selected should be slightly larger than that of the technical valve hole area.
Selection of pressure relief valves under a certain working condition can also refer to product samples and instructions to strive for scientific and reasonable.
3. Selection of Safety Valves
Safety valve is an automatic valve, it does not rely on any external force but uses the force of the medium itself to discharge a rated amount of fluid, in order to prevent the pressure in the system from exceeding the predetermined safety value. When the pressure returns to normal, the valve closes again and prevents the medium from flowing out. Safety valves are used in boilers, pressure vessels and other pressurized equipment as safety protection against overpressure. For some important pressure systems, sometimes more than two kinds of overpressure protection devices are needed. In this case, the safety valve is often used as the last protection device. Therefore, its reliability has a special significance for the safety of equipment and people.
The development of safety valve technology has gone through a long process, from the micro-open type with small displacement to the full-open type with large displacement, from the heavy hammer type (static weight type) to the lever-heavy hammer type, spring type and the pilot type with indirect action after the direct action type.
Commonly used safety valves are direct load safety valves, power assistant safety valves, supplementary load safety valves and pilot safety valves.
In modern industry, heavy hammer safety valve and lever heavy hammer safety valve have been used less and less because of their limited load, sensitivity to vibration and low return pressure. Spring direct load relief valve and pilot relief valve have their own characteristics which can not be replaced each other, and both of them have been developed at the same time.
(1) Lever-weight safety valve. Pressure is regulated by moving the position of the hammer or changing the weight of the hammer. The safety valve can only be fixed on the equipment. The weight of the weight of the hammer itself generally does not exceed 60 kg, so as to avoid difficult operation. The lever-weight safety valve made of cast iron is suitable for working conditions of nominal pressure PN < 1.6MPa and medium temperature T < 200 C. The lever-weight safety valve manufactured from carbon steel is suitable for working conditions of nominal pressure PN < 4.0MPa and medium temperature T < 450 C. The lever weight hammer safety valve is mainly used for working media such as water and steam.
(2) Spring direct load relief valve. The pressure of the disc is balanced and sealed by the force of the compression spring. Spring direct load safety valve has the advantages of simple structure, sensitive response and good reliability. However, due to the spring loading, its load size is limited, so it can not be used in high pressure and large caliber occasions. In addition, when the protected system is in normal operation, the specific pressure on the sealing surface of the safety valve closure depends on the difference between the normal operation pressure of the valve and the system. It is a small value, so it is difficult to achieve a good seal. This is especially true when the valve closure is metal seal and when the setting pressure of the valve is close to the normal operating pressure of the system. At this time, in order to ensure the necessary sealing, it is often necessary to adopt special structural types and carry out extremely fine processing and assembly. Spring direct load relief valve has closed and non-closed two kinds. Generally flammable, explosive or toxic media are sealed. Steam or inert gas, etc. can not be closed. Spring direct load relief valves have wrenches, and some do not. The function of the wrench is to check the sensitivity of the disc.
(3) Pilot safety valve. It is a safety valve driven or controlled by the medium discharged from the pilot valve. The pilot valve itself should be a direct load safety valve that meets the standard requirements. Because the main valve of pilot safety valve is usually loaded by working medium pressure, its load is not limited. Therefore, it can be used in high pressure and large caliber occasions. At the same time, because the main valve can be designed to rely on the working medium pressure seal form, or can impose a much larger load on the disc direct load safety valve, so the sealing of the main valve can be easily guaranteed. In addition, the operation of this kind of safety valve can be less affected by the change of back pressure, but the reliability of pilot safety valve is related to the main valve and the pilot valve, and the structure is more complex. In order to improve the reliability, the specification often requires the use of multiple pilot control pipelines. This increases the complexity of the whole protection system. Based on the above reasons, pilot safety valve and spring direct load safety valve are widely used in both process industry and power industry, and their respective development and common constitute the mainstream of the development of safety valve structure.
(4) Requirements for selection of safety valves. When selecting a safety valve, the nominal pressure of the safety valve is usually determined by the operating pressure, the temperature range of the safety valve is determined by the operating temperature, the pressure range of the spring or lever is determined by the fixed pressure value of the calculated safety valve, the material and structure of the safety valve are determined by the using medium, and the nozzle cross-section area or diameter of the safety valve are calculated according to the discharge amount of the safety valve. Select the type and number of safety valve.
The working pressure level of spring direct load relief valve is shown in Table 2-5. There are five working pressure levels. When selecting, the pressure level of the spring should be indicated in addition to the type, name, medium and temperature of the product.
Table 2-5 Working Pressure Level of Spring Safety Valve
|Working pressure /MPa|
|Rho I||Rho II||Rho III||Rho IV||Rho V|
One point six
Two point five
Six point four
> 0.05 ~ 0.1
> 0.25 ~ 0.4
> 0.1 ~ 0.25
> 0.4 ~ 0.6
> 0.25 ~ 0.4
> 0.6 ~ 1
> 1 ~ 1.3
> 1.6 ~ 2.5
> 3.2 ~ 4
> 5 ~ 6.4
> 8 ~ 10
> 0.4 ~ 0.6
> 1 ~ 1.3
> 1.3 ~ 1.6
> 2.5 ~ 3.2
> 4 ~ 5
> 6.4 ~ 8
> 0.6 ~ 1
> 1.3 ~ 1.6
> 1.6 ~ 2.5
> 3.2 ~ 4
> 5 ~ 6.4
> 8 ~ 10
The inlet and outlet of the safety valve are respectively located on both sides of high pressure and low pressure, so the connecting flange also adopts different pressure grades, as shown in table 2-6.
Table 2-6 safety valve inlet and outlet flange pressure level MPa
|Nominal pressure of safety valve||One||One point six||Four||Ten||Sixteen||Thirty-two|
|Inlet flange pressure level||One||One point six||Four||Ten||Sixteen||Thirty-two|
|Outlet flange pressure level||One||One point six||One point six||Four||Six point four||Sixteen|
When the medium is discharged through the relief valve, the pressure decreases, the volume expands and the flow rate increases, so the outlet diameter of the safety valve is larger than the inlet diameter. For the micro start safety valve, the outlet diameter can be equal to the inlet diameter because of its small displacement and liquid medium. The full open safety valve has large displacement and is mainly used for gas medium, so its outlet diameter is generally larger than nominal diameter. The import and export routes are selected according to table 2-7.
Table 2-7 safety valve inlet and outlet diameter mm
|Nominal diameter||Ten||Fifteen||Twenty||Twenty-five||Thirty-two||Forty||Fifty||Eighty||One hundred||One hundred and fifty||Two hundred|
|Import path||Ten||Fifteen||Twenty||Twenty-five||Thirty-two||Forty||Fifty||Eighty||One hundred||One hundred and fifty||Two hundred|
|Outlet path||Micro opening||Ten||Fifteen||Twenty||Twenty-five||Thirty-two||Forty||Fifty||Eighty|
|Full open type||Forty||Fifty||Sixty-five||One hundred||One hundred and twenty-five||Two hundred||Two hundred and fifty|
According to the standard: the direct load safety valve made of carbon steel and alloy steel is suitable for working conditions of PN less than 32MPa and DN less than 150mm. It is mainly used in water, steam, ammonia, petroleum and oil products. The safety valve made of carbon steel is used for medium temperature T or less than 450 C. the safety valve of alloy steel is used for medium temperature T or less than 600 C.
The safety valve should have enough sensitivity. When the opening pressure is reached, it should be opened without obstruction. When the discharge pressure is reached, the disc should be fully opened and the rated discharge is achieved. When the pressure drops to the pressure of return seat, the valve should be closed in time and kept sealed. The pressure of the safety valve shall comply with the requirements of table 2-8.
Table 2-8 safety valve pressure regulation MPa
|Site of use||Working pressure||Opening pressure a||Return pressure H||Emission pressure V||purpose|
1.3 to 3.9
0.94 p H
0.92 p H
0.93 p H
0.90 p H
1.03 p V
1.03 p V
1.03 p V
Less than 1
0.90 p H
0.85 p H
Rho =1.1 p V
Rho V > 1.15 p V
When two safety valves are installed, one is the control safety valve and the other is the working safety valve. The opening pressure of the control safety valve should be slightly lower than that of the working safety valve in order to avoid excessive exhaust due to the simultaneous opening of the two safety valves.
Due to the progress of science and technology, some safety valves for special environment and special working conditions are constantly appearing, such as safety valves for large-scale thermal power plants, safety valves for petrochemical plants, safety valves for primary loop devices of nuclear power plant pressurized water reactor, etc. The safety valves on these devices ensure the normal operation and safety of the system. For more information, please refer to the monograph on this subject.
4. Selection of traps
The trap is an automatic control device that automatically discharges condensate water from a closed vessel containing steam while keeping fresh steam from leaking. It also allows steam to pass through at a predetermined flow rate when necessary. In modern society, steam is widely used in industrial, agricultural production and living facilities. Whether in the steam pipeline system, or in the process of heating, drying, heat preservation, disinfection, cooking, concentration, heat transfer, heating, air conditioning and other processes, condensate generated by steam traps need to be eliminated, and steam leakage is not allowed.
According to the driving mode of opening and closing parts, steam traps can be divided into three categories: mechanical steam traps driven by the change of condensate level; thermostatic steam traps driven by the change of condensate temperature; and thermodynamic steam traps driven by the dynamic characteristics of condensate water. The structure type of trap is shown in Table 1-25.
Steam trap is an important accessory of steam use system. Its performance is good or bad for the normal operation of the system. The improvement of equipment thermal efficiency and the rational utilization of energy play an important role.
Mechanical steam trap
This kind of trap mainly has closed float type, open upward float type, open downward float type and so on. The working principle of this type of steam trap is based on the old Archimedes principle. It has reliable performance and can remove saturated water, but it is bulky and bulky. Because the turbulent and rolling environment has a considerable impact on its steam resistance and drainage performance, it can not adapt to the use of trains, ships and devices with greater vibration.
(2) Thermostatic steam trap
The main types of steam traps are steam pressure steam traps, bimetal sheet or thermoelastic element type steam traps, liquid or solid expansion type steam traps. This kind of trap almost appears at the same time as mechanical trap. At first, it is metal expansion steam trap. It can prevent steam and drain water by utilizing the physical properties of stem material and the change of condensate water temperature. However, this type of steam trap can not adapt to the situation where the steam pressure changes greatly and the condensate water volume is unstable. Later, a pressure balanced bellows steam trap using liquid expansion was developed. The above problems have been preliminarily solved. With the development of material science and technology, bimetal sheet has been widely used. A bimetal sheet steam trap has been developed. It uses the deformation of bimetal sheet caused by temperature change to achieve the function of steam resistance and drainage. The trap is small in size and light in weight, and can remove a lot of air, but it costs a lot.
Thermal power steam trap
These traps include disc steam traps, pulse steam traps, hollow steam traps and orifice plate steam traps. Disc steam trap is a kind of steam-blocking and drainage operation, which takes advantage of the difference between steam flow rate and condensate flow rate. This kind of steam trap is small in size, light in weight, simple in structure, but its air-exhausting performance is poor. Pulse steam trap also has the characteristics of small size and light weight, but its structure is complex, high manufacturing accuracy and high price.
Selection of traps
Because various types of steam traps have different advantages and disadvantages and different application conditions, so for many years, various types of steam traps coexist for a long time and are applied in various industrial pipelines. Among many types of traps, it is necessary to choose the right one for a certain system, because it has a great impact on the normal operation of the system, and to choose the right one can improve the thermal efficiency and save fuel. Correct selection should be based on the following criteria:
The nominal pressure and working temperature of steam traps shall be greater than or equal to the maximum working pressure and temperature of steam pipes and steam equipment.
(2) Steam traps must be selected according to their working performance, conditions and condensate discharge, and the nominal diameter of steam traps should not be used as the basis for selection.
(3) In condensate water recovery system, steam traps with high back pressure ratio (such as mechanical steam traps) should be selected when working back pressure is used to recover condensate water.
(4) When condensate water cannot be accumulated in steam equipment, steam traps (such as floating ball steam traps) that can continuously discharge saturated condensate water should be selected.
In condensate water recovery system, when saturated condensate water is discharged by steam from steam equipment and non-condensable gas is discharged by steam in time, the steam trap with saturated water in parallel with the exhaust device or the steam trap with both drainage and exhaust functions (e.g. special manager steam trap) should be adopted.
When the working pressure of steam equipment fluctuates frequently, steam traps that do not need to adjust the working pressure should be selected.
The determination of the actual maximum working back pressure of steam trap.
- Mechanical steam trap: p’MOR = 0.8 p’o(1)
- Thermostatic steam trap: p’MOR=0.3 p’o(2)
- Thermodynamic steam trap:
- Disc steam trap: p’MOR = 0.5 p’o(3)
- Pulse steam trap: p’MOR = 0.25 p’o(4)
- The actual maximum working back pressure of type P’MOR – steam trap, Pa;
- The actual working pressure of the steam trap, Pa.
The determination of the actual working pressure of steam trap. When condensate water is discharged from the steam pipeline system, the actual working pressure of the steam trap is equal to the working pressure of the steam pipeline.
When the condensate water is discharged from the steam equipment, the actual working pressure of the steam trap is determined by the following formula:
P’o= (0.9-0.95) P (5)
The actual working pressure of type P’o-steam trap, Pa;
P – Steam pressure of steam equipment, Pa, its value is measured data or data provided by the manufacturer.
The actual working back pressure of steam trap is determined by pressing down the formula:
P’OR = G P. (H3 + Delta Z3) +p 3 (6)
The actual working back pressure of type P’OR – steam trap, Pa;
H3 – The total hydraulic resistance of the pipeline system behind the steam trap valve, Pa;
Z3 – The height of the steam trap rises or falls after lifting, rises to a positive value and falls to a negative value, m;
3 Pressure of condensation tank, Pa;
G-gravity acceleration, m/s 2;
The condensate discharge for selecting steam traps shall be determined according to the following principles. It is necessary to accurately grasp the condensate discharge Gt and steam pressure of steam equipment.
The condensate discharge Gt of the steam trap is calculated according to the following formula:
Gt = . Gc (7)
The condensate discharge of Gt-steam trap, t/h;
Safety ratio, the value of which is selected according to the sample of steam trap, or reference table 2-9;
Gc – Condensate discharge from steam equipment, t/h.
Choosing a good trap is an important energy-saving measure. According to the statistics of relevant departments in China. At present, there are about 5 million steam traps in China. About 80% of the products fail to meet the requirement of less than 3% steam leakage in the current national standard. 15 million tons of standard coal will be lost every year. Therefore, it is necessary to select suitable traps under different working conditions in the country.
The performance of traps commonly used in China is shown in Table 2-10.
Due to the influence of various factors, the theoretical calculation of the technical parameters of the trap is different from the actual use. The actual drainage is greater than the theoretical drainage. The safety rateis shown in Table 2-9.
When condensate water needs to be removed immediately, such as turbine steam engine, steam pump, steam main pipe, etc., it is not appropriate to use supercooled traps, such as pulse traps and thermostatic bellows traps.
Table 2-9 Recommended table for safety factorof steam traps
|Serial number||Heating system||Usage situation||ETA|
|One||Bottom drain of sub cylinder||Under all kinds of pressure, we can quickly remove condensate.||Three|
|Two||Steam master drain||
For main pipes conveying saturated steam, the steam traps should be installed at intervals of about 100m every time. When the steam supply is continuously supplied, the reverse slope pipe should be installed at intervals of 200 to 300m. The steam traps should be installed at intervals of 400 to 500m. The main steam pipes for transporting superheated steam can be determined according to the degree of superheat and the degree of superheat reduction in the process of transportation, referring to saturated steam.
The drain points of steam piping should be selected at the lowest part of the pipe, the bottom of the riser, the end of the pipeline, the front of the pressure reducing valve and the automatic regulating valve.
|Three||Branch pipe||The front of each control valve with a branch length greater than or equal to 5M has a drain point.||Three|
|Four||Steam separator||Drain at the bottom of the steam separator.||Three|
|Five||Heater||The general heat pipe diameter is DN15, and the drain point is less than or equal to 50m.||Two|
|Six||Heater||When pressure is constant||Three|
Pressure adjustable: less than or equal to 100KPA
|Seven||Single coil heating (liquid)||Rapid heating||Three|
|No quick heating is required.||Two|
|Eight||Multiple parallel coil heating (liquid)||Two|
|Nine||Drying room (box)||
Using higher pressure PN16
When pressure is constant
When the pressure is adjustable
|Ten||Hydrophobicity of evaporator for LiBr refrigeration equipment||
The single effect pressure is less than or equal to 100KPA.
Double effect pressure is less than or equal to 1MPa
|Eleven||Hot coils immersed in liquid||When pressure is constant||Two|
Pressure adjustable: 1~200 kPa
Greater than 200 kPa
|Twelve||Tubular heat exchanger||When pressure is constant||Two|
Pressure adjustable: less than or equal to 100 kPa
Greater than 200 kPa
|Thirteen||Jacketed pot||The air valve must be arranged above the jacket pot.||Three|
|Fourteen||Single effect or multi effect evaporator||
Condensation water is less than or equal to 20t/h
Greater than 20t/h
|Fifteen||Laminator||Drain valve should be layered, pay attention to water hammer.||Three|
|Sixteen||Sterilizer||The upper part of the cabinet is equipped with an air valve.||Three|
|Seventeen||Rotary drying cylinder||
Surface linear velocity: less than or equal to 300m/s
|Eighteen||Two steam cans||The diameter of the tank should be kept at two steam speeds of V or less than 5 m/s, and air valves should be arranged on the tank.||Three|
Note: the air heating part of the heating machine can be seen in the JBJ10-83 “technical regulations for heating ventilation and air conditioning design of machinery plants”.
Table 2-10 performance comparison of commonly used steam traps
|project||Thermal power steam trap||Mechanical steam trap||Thermostatic trap valve|
|Thermal power type||Pulse type||Bell float type||Floating ball type||Buoy type||Bellows type||
|Drainage performance||Intermittent drainage||Near continuous||Intermittent drainage||Near continuous||Intermittent drainage||Same left||Same left||Same left|
|Exhaust performance||preferably||good||preferably||not good||not good||good||good||good|
|When conditions of use change||Automatic adaptation||Need to be adjusted||Automatic adaptation||Weight of buoy needs to be adjusted.||Generally not adjusted||Appropriate adjustment|
|Allowable backpressure||Allowable backpressure 50% minimum working pressure 0.05MPa||Allowable backpressure 25%||Delta P > 0.05MPa||Same left||Same left||Allowable backpressure is very low.||No adjustment is allowed when the backpressure is 50%.||Allowable backpressure is very low, but it can be improved after adjustment.|
|Action performance||Sensitive and reliable||Sensitive control cylinder easy to jam.||Slow but steady and reliable||Same left||Same left||Slow and unreliable||Same left||Same left|
|Scope of application||Can be used for superheated steam.||Same left||Suitable for low pressure (0.2MPa) only.|
|Steam leakage||< 3%||1% to 2%||2% to 3%||nothing||nothing||nothing|
|Do you want to prevent frost?||Vertical installation prevents icing.||Do not||want||want||want||Do not||Vertical installation prevents icing.||Same left|
|Start operation||Water filling||Open vent valve and fill water.|
|Installation direction||level||level||level||Same left||Same left||Bellows telescopic direction||level||Same left|
|Drainage temperature||Near saturation temperature||Same left||Same left||Same left||Same left||Below saturation temperature||Same left||Same left|
|Durability||preferably||Poor||The valve and pin tip wear faster.||Valve parts wear faster||Poor||good||good|
|Structure size||Small||Small||more||large||large||Very small||Small||Small|
Pulse traps should not be used when condensate water is less than 15% of the rated maximum discharge, because fresh steam is easily lost from the discharge hole under such conditions. In office buildings, schools, scientific research institutes and other buildings around the need for quiet environment, should not choose thermal power traps with high noise, but should choose thermal managers like traps and floating ball traps, because it is slow, low impact, low noise.
Intermittent operation of indoor steam heating equipment and pipelines requires the selection of traps with good exhaust performance, such as inverted bucket or thermostatic traps.
Mechanical traps are generally not suitable for outdoor work. When it must be selected, there should be anti-freezing protection measures.
The parameter tables of gate valve, globe valve, throttle valve, ball valve, butterfly valve, diaphragm valve, cock valve, check valve, pressure reducing valve and safety valve are shown in tables 2-11 to 2-20, respectively.
Table 2-11 Gate Valve Parameters
Less than / C
|Wedge type double gate valve||Z42W-1||Zero point one||coal gas||One hundred||300~500|
|Bevel gear drive wedge type double gate valve||Z542W-1||600~1000|
|Electric wedge type double gate valve||Z942W-1||600~1400|
|Electrically operated hidden rod wedge type double gate valve||Z946T-2.5||Zero point two five||water||Sixteen million one thousand and eight hundred|
|Electrically operated hidden rod wedge gate valve||Z945T-6||Zero point six zero||Twelve million one thousand and four hundred|
|wedge gate valve||Z41T-10||One||Steam and water||Two hundred||50~450|
|wedge gate valve||Z41W-10||Oils||Two hundred||50~450|
|Electric wedge gate valve||Z941T-10||Steam and water||Two hundred||100~450|
|Parallel double gate valve||Z44T-10||50~400|
|Parallel double gate valve||Z44W-10||Oils||One hundred||50~400|
|Hydraulic wedge gate valve||Z741T-10||water||100~600|
|Electric parallel double gate valve||Z944T-10||Steam and water||Two hundred||100~400|
|Electric parallel double gate valve||Z944W-10||Oils||One hundred||100~400|
|Wedge gate valve with hidden rod||Z45T-10||water||50~700|
|Wedge gate valve with hidden rod||Z45W-10||Oils||50~450|
|Spur gear drive wedge gate valve||Z455T-10||water||Eight billion nine million and one thousand|
|Electrically operated hidden rod wedge gate valve||Z945T-10||water||100~1000|
|Electrically operated hidden rod wedge gate valve||Z945W-10||Oils||One hundred thousand four hundred and fifty|
|wedge gate valve||Z40H-16C||One point six||Oil, steam and water||Three hundred and fifty||200~400|
|Electric wedge gate valve||Z940H-16C||200~400|
|Pneumatic wedge gate valve||Z640H-16C||200~500|
|wedge gate valve||Z40H-16Q||65~200|
|Electric wedge gate valve||Z940H-16Q||65~200|
|wedge gate valve||Z40W-16P||Nitric acid||One hundred||Two hundred million two hundred and fifty thousand and three hundred|
|wedge gate valve||Z40W-16I||Acetic acid||Two hundred million two hundred and fifty thousand and three hundred|
|wedge gate valve||Z40Y-16I||Oils||Five hundred and fifty||200~400|
|wedge gate valve||Z40H-25||Two point five||Oil, steam and water||Three hundred and fifty||50~400|
|Electric wedge gate valve||Z940H-25||50~400|
|Pneumatic wedge gate valve||Z640H-25||50~400|
|wedge gate valve||Z40H-25Q||50~200|
|Electric wedge gate valve||Z940H-25Q||50~200|
|Bevel gear drive wedge type double gate valve||Z542H-25||Two point five||Steam and water||Three hundred||300~500|
|Electric wedge type double gate valve||Z942H-25||300~800|
|Socket welding wedge type gate valve||Z61Y-40||Four||Oil, steam and water||Four hundred and twenty-five||15~40|
|wedge gate valve||Z41H-40||15~40|
|wedge gate valve||Z40H-40||50~250|
|Spur gear wedge gate valve||Z400H-40||Three hundred million three hundred and fifty thousand and four hundred|
|Electric wedge gate valve||Z940H-40||50~400|
|Pneumatic wedge gate valve||Z640H-40||50~400|
|wedge gate valve||Z40H-40||Three hundred and fifty||50~200|
|Electric wedge gate valve||Z940H-40Q||50~200|
|wedge gate valve||Z40Y-40P||Nitric acid||One hundred||Two hundred thousand two hundred and fifty|
|Spur gear wedge gate valve||Z440Y-40P||300~500|
|wedge gate valve||Z40Y-40I||Oils||Five hundred and fifty||50~250|
|wedge gate valve||Z40H-64||Six point four||Oil, steam and water||Four hundred and twenty-five||50~250|
|Spur gear wedge gate valve||Z440H-64||Three hundred million three hundred and fifty thousand and four hundred|
|Electric wedge gate valve||Z940H-64||50~800|
|Electric wedge gate valve||Z940Y-64I||Oils||Five hundred and fifty||Three hundred trillion and three hundred and fifty billion four hundred million four hundred and fifty thousand and five hundred|
|wedge gate valve||Z40Y-64I||Ten||Oil, steam and water||Four hundred and fifty||50~250|
|wedge gate valve||Z40Y-100||50~200|
|Spur gear wedge gate valve||Z440Y-100||Two hundred and fifty thousand and three hundred|
|Electric wedge gate valve||Z940Y-100||50~300|
|Socket welding wedge type gate valve||Z61Y-160||Sixteen||Oils||15~40|
|wedge gate valve||Z41H-160||15~40|
|wedge gate valve||Z40Y-160||50~200|
|Electric wedge gate valve||Z940Y-160||50~300|
|wedge gate valve||Z40Y-160I||Five hundred and fifty||50~200|
|Electric wedge gate valve||Z940Y-160I||50~200|
Table 2-12 globe valve parameters
Less than / C
|Nominal diameter DN/mm|
|Rubber lined DC cut-off valve||J45J-6||Zero point six||Acids and alkaloids||Fifty||40~150|
|Lead lined DC stop valve||J45Q-6||Sulphuric acid||One hundred||25~150|
|Welded bellows globe valve||WJ61W-6P||Nitric acid||10~25|
|BELLOWS GLOBE VALVE||WJ41W-6P||32, 40, 50|
|Internal thread globe valve||J11W-16||One point six||Oils||One hundred||15~65|
|Internal thread globe valve||J11T-16||Steam and water||Two hundred||15~65|
|Globe valve||J41W-16||Oils||One hundred||25~150|
|Globe valve||J41T-16||Steam and water||Two hundred||25~150|
|Globe valve||J41W-16P||Nitric acid||One hundred||80~150|
|Globe valve||J41W-16R||Acetic acid||80~150|
|External thread globe valve||J21W-25K||Two point five||Ammonia and ammonia solution||-40 ~ 150||Six|
|External thread angle cut-off valve||J24W-25K||Six|
|External thread globe valve||J21B-25K||10~25|
|External thread angle cut-off valve||J24B-25K||10~25|
|Angle stop valve||J44B-25Z||32, 40, 50|
|BELLOWS GLOBE VALVE||WJ41W-25P||Two point five||Nitric acid||One hundred||25~150|
|Direct current stop valve||J45W-25P||25~100|
|External thread globe valve||J21W40||Four||Oils||Two hundred||6, 10|
|Card stop valve||J91W-40||6, 10|
|Card stop valve||J91H-40||Four||Oil, steam and water||Four hundred and twenty-five||15, 20, 25|
|Clip angle stop valve||H94W-40||Oils||Two hundred||6, 10|
|Clip angle stop valve||J94H-40||Oil, steam and water||Four hundred and twenty-five||15, 20, 25|
|External thread globe valve||J21H-40||Oil, steam and water||Four hundred and twenty-five||15, 20, 25|
|External thread angle cut-off valve||J24W-40||Oils||Two hundred||6, 10|
|External thread angle cut-off valve||J24H-40||Oil, steam and water||Four hundred and twenty-five||15, 20, 25|
|External thread globe valve||J21W-40P||Nitric acid||One hundred||6~25|
|External thread globe valve||J21W-40R||Acetic acid||6~25|
|External thread angle cut-off valve||J24W-40P||Nitric acid||6~25|
|External thread angle cut-off valve||J24W-40R||Acetic acid||6~25|
|Socket welding stop valve||J61Y-40||Oil, steam and water||Four hundred and twenty-five||10~25|
|Globe valve||J41W-40P||Nitric acid||One hundred||32~150|
|Globe valve||J41W-40R||Acetic acid||32~150|
|Electric globe valve||J941H-40||Oil, steam and water||Four hundred and twenty-five||50~150|
|Globe valve||J41H-40Q||Three hundred and fifty||32~150|
|Angle stop valve||J44H-40||Four hundred and twenty-five||32, 40, 50|
|Globe valve||J41H-64||Six point four||50~100|
|Electric globe valve||J941H-64||50~100|
|Globe valve||J41H-100||Ten||Four hundred and fifty||10~100|
|Electric globe valve||J941H-100||50~100|
|Angle stop valve||J44H-100||32, 40, 50|
|Socket welding stop valve||J61Y-160||Sixteen||Oils||Four hundred and fifty||15~50|
|Globe valve||J41Y-160I||Five hundred and fifty||15~50|
|External thread globe valve||J21W-160||Two hundred||6, 10|
Table 2-13 throttle valve parameters
Less than / C
|Nominal diameter DN/mm|
|External thread throttle valve||L21W-25K||Two point five||Ammonia and ammonia solution||-40 ~ 150||10, 25|
|External thread angle throttle valve||L24W-25K||10, 25|
|External thread throttle valve||L21B-25K||20, 25|
|External thread angle throttle valve||L24B-25K||20, 25|
|throttle valve||L41B -25Z||Two point five||Ammonia and ammonia solution||-40 ~ 150||32, 40, 50|
|Angle throttle valve||L44B-25Z||32, 40, 50|
|External thread throttle valve||L21W-40||Four||Oils||Two hundred||6, 10|
|Throttle throttle valve||L91W-40||6, 10|
|External thread throttle valve||L21W-40P||Nitric acid||6~25|
|External thread throttle valve||L21W40R||Acetic acid||6~25|
|External thread throttle valve||L21H-40||Oil, steam and water||Four hundred and twenty-five||15, 20, 25|
|Throttle throttle valve||L91H-40||15, 20, 25|
|throttle valve||L41H-40Q||Three hundred and fifty||32, 40, 50|
|throttle valve||L41H-40||Four hundred and twenty-five||10~50|
|throttle valve||L41W-40P||Nitric acid||One hundred||32, 40, 50|
|throttle valve||L41W-40R||Acetic acid||32, 40, 50|
|throttle valve||L41H-100||Ten||Oil, steam and water||Four hundred and fifty||10~50|
Table 2-14 ball valve parameters
Less than / C
|Nominal diameter DN/mm|
|Internal thread ball valve||Q11F-16||One point six||Oil and water||One hundred||15~65|
|Globe valve||Q41F-16P||Nitric acid||One hundred million one hundred and twenty-five thousand one hundred and fifty|
|Globe valve||Q41F-16FR||Acetic acid||One hundred million one hundred and twenty-five thousand one hundred and fifty|
|L shape three way ball valve||Q44F-16Q||Oil and water||15~150|
|T shape three way ball valve||Q45F-16Q||15~150|
|Worm gear drive fixed ball valve||Q347F-25||Two point five||One hundred and fifty||200~500|
|Pneumatic fixed ball valve||Q647F-25||200~500|
|Electric fixed ball valve||Q947F-25||200~500|
|External thread ball valve||Q21F-40||Four||10~25|
|External thread ball valve||Q21F-40P||Nitric acid||One hundred||10~25|
|External thread ball valve||Q21F-40R||Acetic acid||10~25|
|Globe valve||Q41F-40Q||Oil and water||One hundred and fifty||32~100|
|Globe valve||Q41F-40P||Nitric acid||One hundred||32~200|
|Globe valve||Q41F-40R||Acetic acid||32~200|
|pneumatic valve||Q641F-40Q||Oil and water||One hundred and fifty||50~100|
|Globe valve||Q41N-64||Six point four||Oil, natural gas||Eighty||50~100|
|Pneumatic fixed ball valve||Q647F-64||One hundred and twenty-five million one hundred and fifty thousand and two hundred|
|Electric fixed ball valve||Q947F-64||125~500|
|Electric hydraulic fixed ball valve||Q247F-64||125~500|
|Gas-liquid fixed ball valve||Q847F-64||125~500|
|Pneumatic hydraulic welding fixed ball valve||Q867F-64||400~700|
|Electro hydraulic welding fixed ball valve||Q267F-64||400~700|
Table 2-15 butterfly valve parameters
Less than / C
|Nominal diameter DN/mm|
|Hydraulic butterfly valve||D741X-2.5||Zero point two five||Oil and water||Fifty||2200~3000|
|Electric butterfly valve||D941X-2.5||1600~3000|
|Electric butterfly valve||D941X-6||Zero point six||12001400,|
|Electric butterfly valve||D941X-10||One||250~1000|
|pneumatic butterfly valve||D641X-10||250~1000|
|Worm gear butterfly valve||D341X-10||250~1000|
Table 2-16 diaphragm valve parameters
Less than / C
|Nominal diameter DN/mm|
|Diaphragm valve||G41W-6||Zero point six||Acids and alkaloids||Sixty-five||15~200|
|Rubber lined diaphragm valve||G41J-6||25~300|
|Pneumatic rubber diaphragm valve||G641J-6||25~200|
|Pneumatic constant open diaphragm valve||G6K41J-6||25~200|
|Pneumatic normally closed rubber lined diaphragm valve||G6B41J-6||25~200|
|Electric rubber lined diaphragm valve||G941J-6||50~200|
|Enamel diaphragm valve||G41C-6||One hundred||25~200|
Table 2-17 stopcock parameters
Less than / C
|Nominal diameter DN/mm|
|Plug valve||X43W-6||Zero point six||Oils||One hundred||One hundred million one hundred and twenty-five thousand one hundred and fifty|
|T shape three way plug valve||X44W-6||25~100|
|Internal thread cock valve||X13W-10T||One||water||15~50|
|Internal thread cock valve||X13W-10||Oils||15~50|
|Internal thread cock valve||X13T-10||water||15~50|
|Oil seal T shape three way plug valve||X46W-10||Oils||25 ~ 100|
|Oil seal cock valve||X47W-16||One point six||25~150|
|Plug valve||X43W-16I||Sand containing oil||Five hundred and eighty||50~125|
Table 2-18 check valve parameters
Less than / C
|Nominal diameter DN/mm|
|Internal thread lifter bottom valve||H12X-2.5||Zero point two five||water||Fifty||50, 65, 80|
|Lift bottom valve||H42X-2.5||50~300|
|Rotary double valve bottom valve||H46X-2.5||350~500|
|Swing multi valve check valve||H45X-2.5||Sixteen million one thousand and eight hundred|
|Swing multi valve check valve||H45X-6||Zero point six||Twelve million one thousand and four hundred|
|Swing multi valve check valve||H45X-10||One||700~1000|
|Swing check valve||H44X-10||50~600|
|Swing check valve||H44T-10||Steam and water||Two hundred||50~600|
|Swing check valve||H44W-10||Oils||One hundred||50~450|
|Internal thread lift check valve||H11T-16||One point six||Steam and water||Two hundred||15~50|
|Internal thread lift check valve||H11W-16||Oils||One hundred||15~50|
|Lift check valve||H41T-16||Steam and water||Two hundred||25~200|
|Lift check valve||H41W-16||Oils||One hundred||25~200|
|Lift check valve||H41W-16P||Nitric acid||80~150|
|Lift check valve||H41W-16R||Acetic acid||80~150|
|External thread lift check valve||H21B-25K||Two point five||Ammonia and ammonia solution||-40 ~ 150||15, 20, 25|
|Lift check valve||H41B-25Z||32, 40, 50|
|Swing check valve||H44H-25||Three hundred and fifty||200~500|
|Lift check valve||H41H-40||Four||Oil, steam and water||Four hundred and twenty-five||10~150|
|Lift check valve||H41H-40Q||Three hundred and fifty||32~150|
|Swing check valve||H44H-40||Four hundred and twenty-five||50~400|
|Swing check valve||H44Y-40I||Oils||Five hundred and fifty||50~250|
|Swing check valve||H44W-40P||Nitric acid||One hundred||200~400|
|External thread lift check valve||H21W-40P||15, 20, 25|
|Lift check valve||H41W-40P||32~150|
|Lift check valve||H41W-40R||Acetic acid||32~150|
|Lift check valve||H41H-64||Six point four||Oil, steam and water||Four hundred and twenty-five||50~100|
|Swing check valve||H44H-64||50~500|
|Swing check valve||H44Y-64I||Oils||Five hundred and fifty||50~500|
|Lift check valve||H41H-100||Ten||Oil, steam and water||Four hundred and fifty||10~100|
|Swing check valve||H44H-100||50~200|
|Swing check valve||H44H-160||Sixteen||Oil and water||50~300|
|Swing check valve||H44Y-160I||Oils||Five hundred and fifty||50~200|
|Lift check valve||H41H-160||Four hundred and fifty||15~40|
|Socket welding lift check valve||H61Y-160||15~40|
Table 2-19 pressure reducing valve parameters
Outlet pressure /
|Nominal diameter DN/mm|
|Direct acting bellows type pressure reducing valve||Y41T-10||One||Steam and air||One hundred and eighty||0.05 to 0.4||20~50|
|Direct acting membrane pressure reducing valve||Y12N-40||Four||atmosphere||-40 ~ 70||0.05 to 2.5||25~80|
|Direct acting membrane pressure reducing valve||Y42X-40||Four||Water and air||Seventy||1 to 2.5||25~80|
|Direct acting membrane pressure reducing valve||Y42X-64||Six point four||Water and air||Seventy||1 to 2.5||25~50|
|Pilot piston type pressure reducing valve||Y43H-16||One point six||steam||Two hundred||0.05 to 1||20~300|
|Pilot piston type pressure reducing valve||Y43H-16Q||steam||Three hundred||0.05 to 1||200~300|
|Pilot piston type pressure reducing valve||Y43F-16Q||water||0~70||0.1 to 1||20~300|
|Pilot piston type pressure reducing valve||Y43X-16Q||atmosphere||-40 ~ 70||0.05 to 1||20~300|
|Pilot piston type pressure reducing valve||Y43H-25||Two point five||steam||Three hundred and fifty||0.1 to 1.6||25~300|
|Pilot piston type pressure reducing valve||Y43F-25||Two point five||water||0~70||0.1 to 1.6||25~100|
|Pilot piston type pressure reducing valve||Y43X-40||Four||atmosphere||-40 ~ 70||0.1 to 1.6||25~200|
|Pilot piston type pressure reducing valve||Y43H-40||steam||Four hundred||0.1 to 2.5||25~200|
|Pilot piston type pressure reducing valve||Y43F-40||water||0~70||0.1 to 2.5||25~80|
|Pilot piston type pressure reducing valve||Y43X-40||atmosphere||-40 ~ 70||0.1 to 2.5||25~100|
|Pilot piston type pressure reducing valve||Y43H-64||Six point four||steam||Four hundred and fifty||0.5 to 3.5||25~100|
|Pilot piston type pressure reducing valve||Y43F-64||water||0~70||0.5 to 3.5||25~50|
|Pilot piston type pressure reducing valve||Y43X-64||atmosphere||-40 ~ 70||0.5 to 3.5||25~50|
|Pilot bellows type pressure reducing valve||Y44H-16||One point six||Steam and air||Two hundred||0.1 to 1.4||20~50|
|Pilot diaphragm pressure reducing valve||Y45X-16C||water||Fifty||0.05 to 10||25~300|
|Pilot diaphragm pressure reducing valve||Y45H-16||Steam and air||Two hundred and fifty||0.02 to 1.5||25~300|
Table 2-20 safety valve parameters
Less than / C
|Nominal diameter DN/mm|
|External thread spring safety valve||A27W-10T||One||0.4 to 1||atmosphere||One hundred and twenty||15~20|
|External thread spring type safety valve with wrench||A27H-10K||0.1 to 1||Air, steam, water||Two hundred||10~40|
|Spring type safety valve with wrench||A47H-16||One point six||0.1 to 1.6||40~100|
|External thread spring closed safety valve||A21H-16C||Air, ammonia, water and ammonia||10~25|
|External thread spring closed safety valve||A21W-16P||Nitric acid, etc.||10~25|
|Spring closed safety valve||A41H-16C||Air, ammonia, water, ammonia and oil.||Three hundred||32~80|
|Spring closed safety valve||A41W-16P||Nitric acid, etc.||Two hundred||32~80|
|Spring type safety valve with wrench||A47H-16C||Air, steam, water||Three hundred and fifty||40~80|
|Duplex spring closed safety valve||A43H-16C||Air and steam||80~100|
|Spring fully open safety valve||A40H-16C||Oil and air||Four hundred and fifty||50~150|
|Spring fully open safety valve||A40Y-16I||Five hundred and fifty||50~150|
|Spring closed full start safety valve||A42H-16C||0.06 to 1.6||Three hundred||40~200|
|Spring closed full start safety valve||A42W-16P||Nitric acid, etc.||Two hundred||40~200|
|Spring closed wrench full start safety valve||A44H-16C||0.1 to 1.6||Oil and air||Three hundred||50~150|
|Spring fully open safety valve||A48H-16C||Air and steam||Three hundred and fifty||50~150|
|External thread spring closed safety valve||A21H-40||Four||1.6 to 4||Air, ammonia, water and ammonia||Two hundred||15~25|
|External thread spring closed safety valve||A21W-40P||Nitric acid, etc.||15~25|
|Spring closed safety valve||A41H-40||1.3 to 4||Air, ammonia, water, ammonia and oil.||Three hundred||32~80|
|Spring closed safety valve||A41W-40P||1.6 to 4||Nitric acid, etc.||Two hundred||32~80|
|Spring type safety valve with wrench||A47H-40||1.3 to 4||Air and steam||Three hundred and fifty||40~80|
|Duplex spring closed safety valve||A43H-40||80~100|
|Spring fully open safety valve||A40H-40||0.6 to 4||Oil and air||Four hundred and fifty||50~150|
|Spring fully open safety valve||A40Y-40I||Five hundred and fifty||50~150|
|Spring closed full start safety valve||A42H-40||1.3 to 4||Three hundred||40~150|
|Spring closed full start safety valve||A42W-40P||1.6 to 4||Nitric acid, etc.||Two hundred||40~150|
|Spring closed wrench full start safety valve||A44H-40||1.3 to 4||Oil products.atmosphere||Three hundred||50~150|
|Spring fully open safety valve||A48H-40||Air. steam||Three hundred and fifty||50~150|
|Spring closed safety valve||A41H-100||Ten||3.2 to 10||Air, water and oil||Three hundred||32~50|
|Spring fully open safety valve||A40H-100||1.6 to 8||Oil and air||Four hundred and fifty||50~100|
|Spring fully open safety valve||A40Y-100I||Five hundred and fifty||50~100|
|Spring fully open safety valve||A40H-100P||Six hundred||50~100|
|Spring closed full start safety valve||A42H-100||3.2 to 10||Nitrogen, hydrogen, oil and air||Three hundred||40~100|
|Spring closed but spanner full start safety valve||A44H-100||Oil and air||50~100|
|Spring fully open safety valve||A48H-100||Air and steam||Three hundred and fifty||50~100|
|Spring closed safety valve||A41H-160||Sixteen||10~16||Air, nitrogen, hydrogen, water and oil||Two hundred||15~32|
|Spring fully open safety valve||A40H-160||Oil and air||Four hundred and fifty||50~80|
|Spring fully open safety valve||A40Y-160I||Five hundred and fifty||50~80|
|Spring fully open safety valve||A40Y-160P||Six hundred||50~80|
|Spring closed full start safety valve||A42H-160||Nitrogen, hydrogen, oil and air||Three hundred||15, 32~80|
|Spring closed safety valve||A41H-320||Thirty-two||16~32||Air, nitrogen, hydrogen, water and oil||Two hundred||15~32|
|Spring closed full start safety valve||A42H-320||Nitrogen, hydrogen, oil and air||Three hundred||32~50|
Matters needing attention in selecting special valves
The selection of special valves should be noted that most of the fluid media used in the processing industry involve oil and gas flow of different corrosive grades. These flow conditions, including medium flow, are considered to be either clean, dirty or worn (in mud conditions). The main difference lies in the number and type of solid suspended particles that cause valve blockage or corrosion damage. In addition, the medium flow containing sulphur and other mixtures will contribute to the formation of corrosive environment when combined with high temperature. For such media flow, careful selection of materials is needed to maintain sufficient service life of the valve. Corrosion engineers continue to research and develop materials to solve these problems.
Special Valve for Refinery Hydrocracking and Coking Unit
Delayed coking unit is the process of producing gas, light fraction oil and coke from vacuum residue by deep thermal cracking. It is an important means of improving light oil yield and producing petroleum coke in refineries. The process is divided into two parts: coking and de-coking. Coking is continuous production and coke removal is intermittent production. The inlet and outlet of heating furnace and coke tower are connected by four-way valve. Four-way valve is an important channel for switching heating furnace into coke tower. It belongs to a special valve, which is used in high temperature situations. Its quality directly affects the production capacity of the device. In China, imported four-way cock valves are mostly used in both new and old devices, but the price is expensive. However, domestic four-way valves generally have problems of unreasonable structure, unstable quality and prone to failure.
Hydrocracking is one of the main crude oil refining processes in refineries. Because the hydrocracking unit operates at high temperature and pressure, the medium is flammable and explosive hydrogen and hydrocarbons, and the working condition is special, so the sealing must be reliable. Therefore, higher requirements are put forward for the design and structure of valves. At present, stainless steel tinsel gate valves and direct current globe valves are mostly used in China.
Special Valve for Oil and Gas
In order to control the flow of oil and gas, the special valve for oil and gas should have the following basic properties: sealing, compressive strength, safety, adjustability, fluid flow and switching flexibility. For high pressure, flammable and explosive oil and gas media, the sealing should be solved first, and the special working conditions of special oil and gas valves should be considered.
- In wet natural gas containing hydrogen sulfide and carbon dioxide, special requirements are put forward for valve body material.
- There are brine, residual acid and other corrosive media in wellhead devices and gathering and transportation systems, which require the selection of valve body materials and anti-corrosion requirements.
- Dust and solid particles accelerate the erosion and wear of valve closures. Make the sealing pair fail quickly.
- Outdoors in plateau, desert and alpine areas, low temperature embrittlement and bending deformation of valve materials, etc.
- Special valves for oil and gas in long-distance pipelines shall have the same service life as pipelines and shall not be replaced for decades.
All of these show that the special valve for oil and gas is different from the ordinary valve, and it should have high reliability, high strength and no leakage under harsh conditions.
Conditions with chlorine
The selection of valves under chlorine-containing conditions should refer to the Dry Chlorine Gas Pipeline System compiled by the American Chlorine Society. The working condition of chlorine gas or liquid chlorine is high corrosion condition, especially water in this condition. HCI (hydrochloric acid) formed by mixing chlorine with water will corrode the valve body and internals. Because chlorine has a high coefficient of thermal expansion, if liquid chlorine is stored in the valve chamber, the pressure in the valve chamber will increase rapidly. Valves used in this condition should have a reliable middle chamber pressure relief function.
Refrigeration (Low Temperature) Conditions
Although valves for cryogenic conditions are based on ASME_B16.34 and API standards, these valves also have other design functions to ensure reliable operation in cryogenic conditions. Such valves may also include a cover extension design that extends the distance between the filler and the operating mechanism and the cryogenic fluid, allowing stem packing to be operated at a higher temperature and ensuring that the valve operating device is not frozen in use. MISS SP-134 provides some details including the bonnet extension design.
Hydrofluoric acid working condition
Valves used in hydrofluoric acid conditions should be limited to the types of valves that have been demonstrated in use or that can be successfully handled in testing. Valves that do not normally provide opportunities for solid accumulation are preferred. Hydrofluoric acid treatment operations should be performed by qualified technicians who strictly control the valves on the market.
The design and material requirements of these (typical carbon steel valves with special or solid Monel internals) and the details of the internal geometry are very detailed. The valves should be designed to have a special structure resistant to hydrofluoric acid corrosion. In hydrofluoric acid-containing conditions, the inspection and test of valves should be higher than the standard used for typical process valves.
Hydrogen-containing working conditions
Valves used in oxygen-containing conditions should follow the American Compressed Gas Association Standard CGA_G4.4-2003 Oxygen Pipeline System when applicable. Valves for this condition should be completely degreased, clean and installed under clean conditions and properly packaged and sealed, as oil and grease are extremely flammable in the presence of oxygen. Relevant guidelines are given in the CGA G4.1 oxygen cleaning equipment. It is necessary to handle and store properly before installation.
Bronze or Monel body and interior materials for oxygen-containing conditions are often used to prevent sparks and ignition due to high-energy mechanical collisions. Silicon-based greases with special formulations are used in oxygen-containing conditions because standard hydrocarbon lubricants should not be used in the presence of oxygen.
Fluctuating or unstable flow
Check valves for pulsating or unstable flow should be selected with special consideration. For example, check valves for reciprocating compressors may be quickly opened and closed with the change of flow rate, which may lead to hammering and valve damage. There may be different opinions on the types of valves used in pulsating and unstable flow, but butterfly, swashplate and axial flow check valves are generally recommended for pulsating or unstable flow.
Acidic condition (wet H2S condition)
Valve materials used in acidic conditions should comply with NACEMR0103 standard. This standard for downstream hydrocarbon processing industry limits the hardness of all steels; requires austenitic steel to be melted and annealed; prohibits the use of certain materials for pressure-bearing parts (including valve stems); and puts forward special requirements for bolted connections and welded valves.
Attention should be paid to the user’s responsibility in NACE MR0103, which stipulates that the user should specify in detail whether the bolt is exposed to H2S environment. Unless specified by the user, bolts that are not inside the valve, such as bonnet connection bolts, are often subject to product standards, which are not included in sulphur-containing conditions. If the bolted material does not directly withstand the process fluid, the body-cover bolting does not need to meet NACE requirements. If any sulphur leakage from sulphur-containing oils cannot be eliminated or evaporated (e.g. partition valves), then bolted connections should comply with NACE standards.
If the material allowed by NACE is considered unnecessary, the bolted connection material should be of special concern. This imposed hardness requirement will result in a reduction in strength. The strength of bonnet connection bolts will be reduced and may not be suitable for the same design conditions as standard bolting materials.
Viscosity or curing conditions
Valves in viscous or solidified conditions, such as liquid sulphur or heavy oil, often require steam tracing or steam casing to maintain adequate operating temperature in order to make the valves operable. Because the hysteretic reaction of check valve can cause operation problems, special attention should be paid to it.
Source: China Valves Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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