How to select the correct valve
The correct choice of valves: understand the characteristics of the valve and the steps and basis for selecting the valve
In the fluid piping system, the valve is a control element, which is mainly used to change the end of the pipeline and the direction of media flow, control the pressure, flow, temperature of the transported media a device. It is mainly used to change the end of the pipeline and the direction of media flow, control the pressure, flow, temperature of the transport medium of a device, so want to know how to choose the right valve? When selecting valves what factors are to be considered? Understanding the characteristics of the valve and the steps and basis for selecting the valve is essential.
01. Characteristics of the valve
The use characteristics of the valve
It determines the main use of the valve performance and use of the scope, belonging to the valve use characteristics are:
Category of the valves
Valves are classified according to the use of functional classification and drive mode classification.
A. The valve according to the use of functional classification
- 1. Cut-off class: also known as closed-circuit valves, mainly used to cut off the fluid path, including globe valves, gate valves, plug valves, ball valves, butterfly valves, diaphragm valves, pinch valves, etc.;
- 2. Regulating valves: mainly used to adjust the fluid pressure, flow, including regulating valves, throttle valves, pressure reducing valves and float regulating valves, etc;
- 3. Check valve: also known as a one-way valve or check valve, check valve belongs to a kind of automatic valve, used to stop the reverse flow of fluid, pump suction off the bottom valve also belongs to the check valve category;
- 4. Diverter valve: used to distribute the fluid pathway to go, or the two-phase fluid separation, including slide valves, multi-way valves, traps and air venting valves, etc.;
- 5. Safety valves: mainly used for safety protection, to prevent damage to the boiler, pressure vessel or pipeline due to overpressure;
- 6. Multi-purpose valve: is a valve with more than one function, such as cut-off check valve can play both the role of cutting off the flow and can play the role of check.
B. The valve is classified according to the driving mode
- 1. Automatic valves are valves that do not require external drive, but rely on the medium’s own energy to make the valve action. Such as safety valves, pressure reducing valves, traps, check valves, automatic control valves, etc..
- 2. Power-driven valves: power-driven valves can use a variety of power sources to drive. Divided into electric valves, pneumatic valves, hydraulic valves, etc.. Electric valve: the valve driven by electricity. Pneumatic valve: the valve driven by compressed air. Liquid-operated valves: Valves driven by liquid pressure such as oil. In addition, there are several combinations of the above driving methods, such as gas-electric valves, etc.
- 3. Manual valves: manual valves with the help of handwheels, handles, levers, chain wheels, by human to manipulate the valve action. When the valve opening and closing torque is large, a gear or worm gear reducer can be set between the handwheel and the valve stem. If necessary, it can also be operated from a distance by using universal joints and drive shafts.
Type of valve
The function determines the design of the standard valve type.
There are many ways to classify valves depending on the role of the opening and closing valve, and the following are introduced here.
Some of the most common types of valves: gate valves, globe valves, butterfly valves, ball valves, needle valves, metering valves, toggle valves, plug valves, safety valves, pinch valves, etc.
1. Classification by role and use
- (1) Cut-off valve: cut-off valve, also known as closed-circuit valve, its role is to connect or cut off the medium in the pipeline. Cut-off valves include gate valves, globe valves, rotary
- plug valve, ball valve, butterfly valve and diaphragm, etc.
- (2) Check valve: check valve is also known as a one-way valve or check valve, its role is to prevent the backflow of media in the pipeline. Water pump suction off the bottom valve also belongs to
- Check valve class.
- (3) Safety valve: the role of safety valves is to prevent the pipeline or device in the medium pressure exceeds the specified value, so as to achieve the purpose of safety protection.
- (4) Regulating valves: regulating valves include regulating valves, throttling valves and pressure reducing valves, whose role is to adjust the pressure of the medium, flow and other parameters.
- (5) Diverter valves: diverter valves include a variety of distribution valves and traps, etc., whose role is to distribute, separate or mix the media in the pipeline.
2. According to the nominal pressure classification
- (1) Vacuum valve: refers to the valve whose working pressure is lower than the standard atmospheric pressure.
- (2) Low pressure valve: the valve with nominal pressure PN≤1.6Mpa.
- (3) Medium pressure valve: refers to the valve with nominal pressure PN 2.5, 4.0, 6.4Mpa.
- (4) High pressure valve: refers to the nominal pressure PN for 10-80Mpa valve. This article is from the dream
- (5) Ultra-high pressure valve: refers to the nominal pressure PN ≥ 100Mpa valve.
3. According to the working temperature classification
- (1) Ultra-low temperature valve: the valve for the medium working temperature t < -100 ℃.
- (2) Low-temperature valve: for the medium working temperature -100 ℃ ≤ t ≤ -40 ℃ valve.
- (3) Room temperature valve: for the medium working temperature -40 ℃ ≤ t ≤ 120 ℃ valve.
- (4) Medium temperature valve: for the medium working temperature 120 ℃.
- (5) High temperature valve: for the medium working temperature t>450 ℃ valve.
4. According to the driving mode classification
(1) Automatic valve refers to the valve that does not require external drive, but relies on the medium’s own energy to make the valve action. Such as safety valves, pressure reducing valves, traps, check valves, electric control valves, etc.
(2) Power-driven valves: power-driven valves can be driven by various power sources.
- Electric valve: the valve driven by electricity.
- Pneumatic valve: the valve driven by compressed air.
- Hydraulic valves: valves driven with the help of oil and other liquid pressure.
In addition there are combinations of the above driving methods, such as gas – electric valves, etc.
(3) Manual valves: manual valves with the help of handwheels, handles, levers, sprockets, by human to manipulate the valve action. When the valve opening and closing torque is large, the
This wheel or worm gear reducer can be set between the hand wheel and the valve stem. If necessary, it can also use universal joint and drive shaft to operate from a distance.
5. According to the nominal diameter classification.
- (1) Small diameter valve: nominal diameter DN ≤ 40mm valve.
- (2) Medium diameter valves: valves with nominal diameter DN 50-300mm.
- (3) Large diameter valves: valves with nominal DN of 350-1200mm.
- (4) Extra large diameter valve: nominal diameter DN ≥ 1400mm valve.
6. Classification by structural features
- (1) Cut-off valve: opening and closing member (valve flap) driven by the stem along the centerline of the valve seat for lifting movement.
- (2) Plug valve: the opening and closing member (gate valve) is driven by the stem along the center line perpendicular to the valve seat for lifting movement.
- (3) Plug valve: the opening and closing member (cone plug or ball) rotates around its own centerline.
- (4) Swing valve: the opening and closing member (valve flap) rotates around the axis outside the seat.
- (5) Butterfly valve: the opening and closing member (disc) rotates around a fixed axis inside the valve seat.
- (6) Slide valve: the opening and closing member slides in the direction perpendicular to the channel.
7. Classification by valve connection method
- (1) Threaded connection valve: the valve body with internal or external threads, and pipeline threaded connection.
- (2) Flange connection valve: valve body with flange, flange connection with the pipeline.
- (3) Welded connection valve: the valve body with welding bevel, and pipeline welding connection.
- (4) Clamp connection valve: The valve body has a clamp port and is connected to the pipe clamp.
- (5) Ferrule connection valve: with pipe with ferrule connection.
- (6) Clamp connection valve: bolts directly to the valve and the two ends of the pipeline wear clamped together in the form of connection.
8. Control valves by valve body material classification
- (1) Metal material valve: its valve body and other parts made of metal materials. Such as cast iron valve, carbon steel valve, alloy steel valve, copper alloy valve, aluminum alloy valve, lead alloy valve, titanium alloy valve, monel alloy valve, etc.
- (2) Non-metallic material valve: its valve body and other parts made of non-metallic materials. Such as plastic valves, ceramic valves, enamel valves, glass steel valves, etc.
- (3) Metal body lined valves: valve body shape for metal, internal where the main surface in contact with the media are lined, such as rubber-lined valves, plastic-lined valves, ceramic-lined valves, etc.
Material selection of valve parts
There are many materials for manufacturing valve parts, including all kinds of ferrous and non-ferrous metals and their alloys, and all kinds of non-metallic materials. The materials for manufacturing valve parts should be selected according to the following factors:
- (1) Pressure, temperature and characteristics of the working medium.
- (2) The force of the part and its role in the valve structure.
- (3) Good manufacturability.
- (4) When the above conditions are met, the cost should be lower.
Material for body, cover and plate (disc)
- Gray cast iron: Gray cast iron is suitable for water, steam, air, gas, oil and other media with nominal pressure PN≤1.0MPa and temperature -10℃ ~ 200℃. Gray cast iron commonly used grade: HT200, HT250, HT300, HT350.
- Malleable iron: Suitable for water, steam, air and oil medium with nominal pressure PN≤2.5MPa and temperature -30 ~ 300℃. Commonly used brands are: KTH300-06, KTH330-08, KTH350-10.
- Nodular cast iron: suitable for water, steam, air, oil and other media with PN≤4.0MPa and temperature of -30 ~ 350℃. Commonly used brands are: QT400-15, QT450-10, QT500-7.
- Carbon steel (WCA, WCB, WCC) : suitable for nominal pressure PN≤32.0MPa, suitable for the working temperature between -29~+425℃ medium and high pressure valves, 16Mn, 30Mn working temperature of -29~ 595℃, commonly used in place of ASTM A105. Commonly used grades are WC1, WCB, ZG25 and high quality steel 20, 25, 30 and low alloy structural steel 16Mn.
- Low temperature carbon steel (LCB) : Suitable for nominal pressure PN≤6.4Mpa, temperature ≥-196℃ ethylene, propylene, liquid natural gas, liquid nitrogen and other media, commonly used brands are ZG1Cr18Ni9, 0Cr18Ni9, 1Cr18Ni9Ti, ZG0Cr18Ni9.
- Alloy steel (WC6, WC9), suitable for high temperature and high pressure valves with non-corrosive media operating temperature between -29 and 595℃; WC5 and WC9 are suitable for high temperature and high pressure valves with corrosive media between -29 and 650℃.
- Austenitic stainless steel, suitable for the valve of corrosive media operating temperature between -196 ~ +600℃.
- Monel alloy: mainly suitable for valves with hydrogen and fluorine medium.
- Cast copper alloy: mainly suitable for oxygen pipeline valves with working temperature between -29 and 595℃.
Table. Common materials of valve housing
|Material of shell||Standard||Applicable temperature /℃||Applicable pressure /MPa||Suitable medium|
|Gray cast iron||-15 to 200||1.6 or less||Water and gas|
|Black heart malleable cast iron||-15 to 300||2.5 or less||Water, sea water, gas, ammonia|
|Nodular cast iron||-30 to 350||4.0 or less||Water, sea water, gas, air, steam|
|Carbon steel (WCA, WCB, WCC)||ASTM A216||-29 to 425||32.0 or less||Non corrosive applications including water, oil and gas|
|Low temperature carbon steel (LCB, LCC)||ASTM A352||-46 to 345||32.0 or less||Low temperature application|
|Alloy steel (WC6, WC9)||ASTM A217||-29 to 595||High pressure||Non corrosive medium|
|(C5, C12)||-29 to 650||Corrosive medium|
|Austenitic stainless steel||ASTM A351||-196 to 600||Corrosive medium|
|Monel alloy||ASTM A494||400||Media containing hydrofluoric acid|
|Hastelloy alloy||ASTM A494||649||Dilute sulfuric acid and other strong corrosive media|
|Titanium alloy||A variety of highly corrosive media|
|Cast copper alloy||-273 ~ 200||Oxygen, sea water|
|Plastic, ceramic||~ 60||1.6 or less||Corrosive medium|
|Code||The material||Standard||Conditions of Application||Range of temperature|
|WCB||Carbon steel||ASTM A216||Non corrosive applications including water, oil and gas||-29℃ ~ +425℃|
|LCB||Low temperature carbon steel||ASTM A352||Low temperature application||-46℃ ~ +345℃|
|LC3||3.5% nickel steel||ASTM A352||Low temperature application||-101 ° C to +340 ° C|
|WC6||1.25% chromium 0.5% molybdenum steel||ASTM A217||Non corrosive applications including water, oil and gas||-30℃ ~ +593℃|
|C5||5% chromium 0.5% molybdenum||ASTM A217||Mildly corrosive or erosive applications and non-corrosive applications||-30℃ ~ +649℃|
|C12||9% chromium and 1% molybdenum|
|CA15(4)||12% chrome steel||ASTM A217||Corrosive application||+ 704 ℃|
|CA6NM(4)||12% chrome steel||ASTM A487||Corrosive application||-30℃ ~ +482℃|
|CF8M||316 stainless steel||ASTM A351||Corrosive or ultra-low temperature or high temperature non-corrosive application||-268℃ to +649℃, 425℃ above the specified carbon content of 0.04% and above|
|CF8C||347 stainless steel||ASTM A351||Mainly used for high temperature, corrosive applications||-268℃ to +649℃, 540℃ above the specified carbon content of 0.04% or above|
|CF8||304 stainless steel||ASTM A351||Corrosive or ultra-low temperature or high temperature non-corrosive application||-268℃ to +649℃, 425℃ above the specified carbon content of 0.04% and above|
|CF3||304L stainless steel||ASTM A351||Corrosive or non-corrosive applications||+ 425 ℃|
|CF3M||316L stainless steel||ASTM A351||Corrosive or non-corrosive applications||+ 454 ℃|
|CN7M||Alloy steel||ASTM A351||It has good corrosion resistance to hot sulfuric acid||+ 425 ℃|
|M35-1||Monel||ASTM A494||Weldable grade. Excellent resistance to all common organic acids and salt water corrosion. It also has high corrosion resistance to most alkaline solutions||+ 400 ℃|
|N7M||Haast nickel alloy B||ASTM A494||Especially suitable for processing hydrofluoric acid of various concentrations and temperatures. It has good corrosion resistance to sulfuric acid and phosphoric acid||+ 649 ℃|
|CW6M||Haast nickel alloy C||ASTM A494||It has good corrosion resistance to strong oxidation environment. It has excellent properties at high temperatures and has very high corrosion resistance to formic acid (formic acid), phosphoric acid, sulfite and sulfuric acid||+ 649 ℃|
|CY40||Inke nickel alloy||ASTM A494||Performs well in high temperature applications. It has good corrosion resistance to strong corrosive fluid media|
Sealing surface material
The sealing surface is the most critical working face of the valve. The quality of the sealing surface is related to the service life of the valve. Usually, the sealing surface material should consider corrosion resistance, abrasion resistance, erosion resistance, oxidation resistance and other factors. There are usually two broad categories:
- (1) Rubber (including butadiene rubber, fluorine rubber, etc.)
- (2) Plastic (PTFE, nylon, etc.)
Hard sealing materials
- Copper alloy (for low pressure valves)
- Chromium stainless Steel (for ordinary high pressure valves)
- Sitari alloy (for high temperature and high pressure valves and strong corrosion valves)
- Nickel-based alloy (for corrosive media)
Valve stem in the valve opening and closing process, under tension, pressure and torsion forces, and direct contact with the medium, at the same time and packing between the relative friction movement, so the valve stem material must ensure that under the specified temperature has enough strength and impact toughness, a certain corrosion resistance and abrasion resistance, as well as good technology. Commonly used stem materials are as follows.
For low pressure and medium temperature does not exceed 300℃ water, steam medium, generally choose A5 ordinary carbon steel (now Q275, A3 Q235).
For medium pressure and medium temperature does not exceed 450℃ water, steam medium, generally choose 35 high quality carbon steel.
For medium pressure and high pressure, medium temperature does not exceed 450℃ water, steam, petroleum and other media, generally choose 40Cr (chromium steel).
For high pressure, medium temperature does not exceed 540℃ water, steam and other media, can choose 38CrMoALA nitriding steel.
When it is used for steam medium with high pressure and medium temperature not exceeding 570℃, 25Cr2MoVA chromium molybdenum-vanadium steel is generally selected.
Stainless and acid-resistant steel
For medium pressure and high pressure, medium temperature does not exceed 450℃ non-corrosive medium and weak corrosive medium, can choose 1Cr13, 2Cr13, 3Cr13 chrome stainless steel.
For corrosive media, Cr17Ni2, 1Cr18Ni9Ti, Cr18Ni12Mo2Ti, Cr18Ni12Mo3Ti and other stainless acid-resistant steel and PH15-7Mo precipitation hardened steel can be selected.
Heat resistant steel
4Cr10Si2Mo Martensitic heat-resistant steel and 4Cr14Ni14W2Mo Austenitic heat-resistant steel can be selected for high temperature valve whose medium temperature does not exceed 600℃.
Stem nut material
Stem nuts bear stem axial forces directly during valve opening and closing, and therefore must have a certain strength. At the same time, it and the valve stem is threaded drive, requiring small friction coefficient, no rust and avoid the phenomenon of bite.
Copper alloy is one of the most widely used materials with low friction coefficient and no rust. For Pg<1.6Mpa low pressure valve can use ZHMn58-2-2 cast brass. For Pg16-6.4Mpa medium pressure valve can be used ZQAL9-4 bronze. For high pressure valves can use ZHAL66-6-3-2 cast brass.
When working conditions do not allow the use of copper alloy, can choose 35, 40 and other high-quality carbon steel, 2Cr13, 1Cr18Ni9, Cr17Ni2 stainless acid resistant steel. Working conditions do not allow the following conditions.
- (1) Stem nuts with melon clutches for electric valves requiring heat treatment to obtain high hardness or surface hardness.
- (2) The working medium or the surrounding environment is not suitable for the selection of copper alloy, such as copper corrosion of ammonia medium.
When using steel stem nuts, pay special attention to thread bite phenomenon.
Fasteners, packing and gasket materials
Fasteners mainly include bolts, stud bolts and nuts. Fasteners bear pressure directly on the valve and play an important role in preventing the outflow of the medium. Therefore, the materials selected must ensure sufficient strength and impact toughness at the service temperature.
According to the medium pressure and temperature selection fastener material can be selected according to the table.
|The name of the||Nominal pressure Pg(Mpa)||Medium temperature (℃)|
|Bolt and double end bolt||1.6-2.5||Q235 (A3)||35||30CrMoA||–|
The selection of alloy steel materials must undergo heat treatment. When fasteners have special corrosion resistance requirements, Cr17Ni2, 2Cr13, 1Cr18Ni9 and other stainless acid resistant steels can be selected.
On valves, packing is used to fill the space in the cover packing chamber to prevent media leakage through the stem and cover packing chamber space.
Requirements for fillers
- (1) Good corrosion resistance, packing and medium contact, must be able to resist the corrosion of the medium.
- (2) Good sealing, packing does not leak under the action of medium and working temperature.
- (3) The friction coefficient is small to reduce the friction torque between the stem and packing.
Types of packing
Packing can be divided into soft packing and hard packing two kinds:
(1) Soft packing: it consists of planting materials, such as hemp, flax, cotton, jute, etc., or mineral materials, such as asbestos fiber, or wire woven by asbestos fiber with metal wire inside and graphite powder outside, as well as pressed molding packing materials, and newly developed flexible graphite packing materials in recent years.
Plant material packing is often used for low pressure valves below 100℃; Mineral packing can be used for valves at 450-500℃.
In recent years, the temperature of structural medium with rubber O-ring as filler is generally limited to below 60℃.
The packing on the high temperature and high pressure valve is also made of pure asbestos and flake graphite powder.
(2) Hard packing: that is, the packing made of metal or metal mixed with asbestos and graphite and the packing formed by pressing and sintering of PTFE. The metal packing is used less.
Selection of filler
Choose the filler according to the medium, temperature and pressure to choose, commonly used materials are the following:
(1) Oil-immersed asbestos rope, which can be selected according to Table 5-2.
(2) Rubber asbestos rope: can be selected according to Table 5-3.
(3) Graphite asbestos rope: asbestos rope coated with graphite powder, available temperature above 450℃, pressure can reach 16Mpa, generally suitable for high pressure steam. Recently and gradually adopted the pressure of adult font packing, single ring placement, good sealing.
(4) Polytetrafluoroethylene (PTFE) : This is a widely used filler at present. Especially suitable for corrosive media, but the temperature shall not exceed 200℃. It is usually made of pressed or bar material.
|The name of the||Brand||The shape of||Specifications||Applicable limit pressure kgf/cm2||Applicable limit temperature (℃)||Use|
|Asbestos rope dipped in oil||YS450||F||22.214.171.124.8.10||60||450||Used for water vapor, air, petroleum products|
|YS350||F, Y, N||126.96.36.199.10.13||45||350|
|YS250||F, Y, N||188.8.131.52.10.13.||45||250|
Note: Shape code F stands for square, through the heart or one to multi-layer braid; Y means round, in the middle is a twisted core, outside is one to multiple layers of braid; N for twisted.
|The name of the||Brand||Specification (straight formula or square side length)||Applicable limit pressure kgf/cm2||Applicable limit temperature (℃)||Use|
|Rubber||XS450||184.108.40.206.8||60||450||Used for steam and petroleum products|
Gaskets are used to fill all the bumps between two joint surfaces (such as the sealing surface between the valve body and the valve cover) to prevent medium leakage from the joint surface.
Requirements for gaskets
The gasket material has certain elasticity and plasticity and sufficient strength at working temperature to ensure the sealing. At the same time, it should have good corrosion resistance.
Type and selection of gasket materials
Gaskets can be divided into soft and hard two kinds, soft is generally non-metallic materials, such as cardboard, rubber, asbestos rubber board, PTFE and so on. Hardness is generally metal materials or metal coated asbestos, metal and asbestos wound, etc.
There are many shapes of spacers, such as flat, round, oval, toothed, lenticular and other special shapes.
The material of metal gasket is generally 08, 10, 20 high-quality carbon steel and 1Cr13, 1Cr18Ni9 stainless steel. The processing accuracy and surface finish are high, and it is suitable for high temperature and high pressure valves.
Non-metallic gasket material is generally plastic, with little pressure can achieve seal, suitable for low temperature and low pressure valves.
Gasket materials can be selected according to Table.
|Gasket material||Medium||Scope of application|
|Pressure (Mpa)||Temperature (° C)|
|Heavy board board||Water, oil||10 or less||40|
|Oil impregnated board||Water, oil||10 or less||40|
|Rubber rubber sheet||Water, air||6 or less||50|
|Sheet of asbestos||Steam and gas||6 or less||450|
|Polytetrafluoroethylene||Corrosive medium||25 or less||200|
|Rubber asbestos board XB450||Water steam, air, gas||60 or less||450|
|XB350||Water steam, air, gas||40 or less||350|
|XB200||Water steam, air, gas||15 or less||200|
|Oil resistant rubber asbestos sheet||Oil||160||30|
|08 steel is filled with XB450||Steam||100||450|
|08 steel is filled with XB350||Steam||40||350|
|1Cr13, 0Cr13 asbestos filling||Steam||100||600|
|08 steel filled with oil-resistant rubber asbestos board||Oil||100||350|
|Copper||Water vapor, air||100||250|
|Aluminum||Water vapor, air||64||350|
|10 steel, 20 steel||Water vapor, oil||200||450|
Common materials of valve inner parts
|Inner part material||Applicable temperature /℃||Inner part material||Applicable temperature /℃|
|304||-268 to 316||440 stainless steel 60RC||-29 to 427|
|316||-268 to 316||17-4PH||-40 to 427|
|bronze||-273 to 232||Alloy steel No. 6 (Co-Cr)||-273 ~ 816|
|Incor nickel alloy||-240 to 649||Electroless nickel plating||-268 to 427|
|K Monel alloy||-240 to 482||Chrome plated||-273 to 316|
|Monel alloy||-240 to 482||Nitrile butadiene rubber||-40 to 93|
|Hastroy alloy B||-198 to 371||Fluorine rubber||-23 to 204|
|Hastroy alloy C||-198 to 538||Polytetrafluoroethylene||200|
|Titanium alloy||-29 to 316||nylon||-73 to 93|
|Nickel base alloy||-198 to 316||polyethylene||-73 to 93|
|Alloy no. 20||-46 to 316||Chloroprene rubber||-40 to 82|
|Model 416 stainless steel 40RC||-29 to 427|
Common materials and applicable temperature of valve sealing surface
|Sealing surface material||Applicable temperature /℃||Hardness||Suitable medium|
|Bronze||– 273 ~ 232||Water, sea water, air, oxygen, saturated steam, etc|
|316L||– 268 ~ 316||14HRC||Steam, water, oil, gas, liquefied gas, and other medium with slight corrosion and no erosion|
|17-4PH||-40 to 400||40 to 45HRC||A slightly corrosive but erosive medium|
|Cr13||– 101 ~ 400||37 to 42HRC||A slightly corrosive but erosive medium|
|Stellit alloy||– 268 ~ 650||
40 ~ 45HRC (room temperature)
|Erosive and corrosive media|
|Monel alloy KS||– 240 ~ 482||
27 to 35HRC
30 to 38HRC
|Alkali, salt, food, air – free acid solution, etc|
|Hastelloy CB||371||14HRC||Corrosive mineral acid, sulfuric acid, phosphoric acid, wet hydrochloric acid gas, chloric acid free solution, strong oxidizing medium|
|Alloy no. 20||45.6 ~ 316||– 253 ~ 427||Oxidizing medium and sulfuric acid of various concentrations|
Cast iron valve stem, sealing surface, gasket, packing, fastener material table
|The name of the||Standard||Grade of material||Note|
|The valve stem||ASTM A 182||F6a|
|ASTM A 276||410 、420|
|GB/T 1220||1Cr13, 2Cr13|
|Seal sealing surface||GB/T 1176||ZCuZn25Al6Fe3Mn3||Cast aluminum brass|
|ZCuZn38Mn2Pb2||Cast manganese brass|
|ZCuAl9Mn2, ZCuAl10Fe3||Cast aluminium bronze|
|GB/T 1220||1Cr13, 2Cr13, 1Cr18Ni9, 1Cr18Ni9Ti|
|Gasket||GB/T 3985||XB350, XB450||Rubber asbestos sheet|
|JB/T 6617||Flexible graphite ring|
|Screw screw firmware||GB/T 699||Bolt 35/ nut 25|
|GB/T 3077||Bolts 30CrMo, 35CrMo/ nuts 35, 45|
Valve transmission mode
The transmission modes of valves include manual, electric, pneumatic, hydraulic, hand hydraulic, electro-hydraulic, pneumatic, worm gear, bevel gear, etc. Which one is best depends on the actual situation, and the one that is suitable for the working condition is the best. However, the electric control is labor-saving and convenient. It can realize the integration of mechanical, electrical, hydraulic and instrument, on-site control, centralized monitoring or automatic control.
Structural characteristics of valves
It determines the methods of installation, maintenance and repair of valves. The structural characteristics include:
- The structural length and overall height of the valve, and the connection form with the pipeline (flange connection, threaded connection, clamp connection, external thread connection, welding end connection, etc.);
- Form of sealing surface (insert ring, threaded ring, surfacing, spray welding, valve body);
- Structural form of valve rod (rotary rod, lifting rod), etc.
02. Valve selection steps and selection basis
Valve selection steps
(1) Clear use, determine the working conditions
Define the use of the valve in the equipment or device, determine the working conditions of the valve: applicable media, working pressure, working temperature, etc.
(2) Determine the nominal diameter and connection
Determine the nominal diameter of the pipe connected to the valve and the connection: flange, thread, welding, etc.
(3) Determine the way to operate the valve
Manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electro-hydraulic linkage, etc.
(4) Determine the valve shell and inner parts of the material
According to the medium transported by the pipeline, working pressure, working temperature to determine the selected valve shell and internal parts of the material: gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, stainless acid-resistant steel, copper alloy, etc.
(5) Select the type of valve
Closed-circuit valves, regulating valves, safety valves, etc.
(6) Determine the type of valve
Gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap, etc.
(7) Determine the parameters of the valve
For automatic valves, according to different needs to determine the allowable flow resistance, discharge capacity, back pressure, etc., and then determine the nominal diameter of the pipeline and valve diameter.
(8) Determine the geometric parameters of the selected valve
Structure length, flange connection form and size, the size of the valve height direction after opening and closing, the size and number of connected bolt holes, the entire valve appearance size, etc.
(9) The use of existing information
Valve catalog, valve product samples, etc. to select the appropriate valve products.
Valve selection basis
In understanding the steps to master the selection of valves, should further understand the basis for the selection of valves.
(1) The use of the selected valve, the use of working conditions and manipulation control mode.
For example, the pump room pump outlet valve selection, the first need to meet the pump can close the valve to start and stop to reduce the start current and stop the impact on the pump; secondly, need to be equipped with a check valve, in the pump unit accidental shutdown can quickly close the valve to prevent the pump reversal for a long time; third, need to be equipped with a valve to eliminate water hammer to protect the safety of the pump unit operation. After understanding the use of the selected valve, it is also necessary to understand the installation site and use conditions in order to correctly select the valve. If you choose electric butterfly valve + micro-resistance slow-closing check valve, electric butterfly valve can meet the closed valve start and stop. The micro-resistance slow-closing check valve is used to prevent the pump from reversing and water hammer, and the failure rate is low due to the relatively simple structure, but the installation length is long and the water resistance is large, which is suitable for pumping stations with large installation space and low energy consumption requirements, such as small pumping stations; choose the liquid-controlled slow-closing check valve to meet the three necessary functions of the pump outlet valve at the same time, and the installation length can be very small, and the water resistance is relatively small, but the structure is complicated and requires A set of high-pressure hydraulic system, so the failure rate is high and difficult to maintain, so suitable for installation in large pumping stations and more standby units; pump export can also choose multifunctional pump control valve, its installation length is less than the electric butterfly valve + micro-resistance slow-closing check valve, without electric or hydraulic system vacant, the structure is simple, the failure rate is very low, and water hammer elimination effect is good, but high water resistance, suitable for water hammer is more serious or Unattended pumping station use.
(2) The nature of the working medium
Working pressure, working temperature, corrosive properties, whether it contains solid particles, whether the medium is toxic, whether it is flammable, explosive media, the viscosity of the medium and so on.
(3) The requirements of the valve fluid characteristics
Flow resistance, discharge capacity, flow characteristics, sealing grade, etc.
(4) Installation size and size requirements
How do I choose valve size? Nominal diameter, and pipeline connection and connection size, external dimensions or weight restrictions, etc. Control valves are an important component in successfully controlling the flow of fluids in process plants and systems. Control valves include many different types of valves, including rotary motion valves, such as ball valves, butterfly valves and gate valves. They can also be classified as flow regulating or open or closed depending on their function. To ensure optimum system performance, control valves must be properly sized.
The guideline for proper sizing is to select a valve that should operate between 20% and 80% at maximum flow and no less than 20% at minimum required flow. This allows the valve to be used over most of its operating range while maintaining a reasonable but not excessive safety factor.
Valve sizing usually begins with the calculation of the flow coefficient (Cv). The flow coefficient is defined as the number of U.S. gallons of water per minute at 60°F that flows through the valve at the specified opening with a pressure drop of 1 psi at both ends of the valve. The flow coefficient is used to calculate the valve size to pass the desired flow rate while maintaining consistent control of the process fluid.
Incorrectly sized valves can lead to unnecessarily rapid wear of internal components and can also cause valve chatter and, in some cases, catastrophic damage. At the very least, incorrect initial sizing may force the user to start from scratch to correct the problem. This can result in lost production time, increased labor, additional costs for shipping and related expenses, and, if the original product cannot be returned, the cost of the final product itself.
We have assisted our customers in properly sizing their valves so that our customers can optimize performance and service life. Therefore, we prefer that our customers send us all relevant information prior to ordering a valve so that we can assist you with sizing from the outset. We can provide advice within 24 hours of the request.
(5) Additional requirements
Additional requirements for the reliability of the valve product, service life and explosion-proof performance of the electric device.
In the selection of parameters should be noted: If the valve is to be used for control purposes, the following additional parameters must be determined: method of operation, maximum and minimum flow requirements, pressure drop for normal flow, pressure drop at closure, maximum and minimum inlet pressure of the valve.
Based on the above basis and steps for selecting valves, a reasonable and correct selection of valves must also be based on a detailed understanding of the internal structure of the various types of valves so that the right choice can be made for the preferred valve.
The final control of the pipeline is the valve. Valve opening and closing pieces control the way the medium flows in the pipeline, the shape of the valve flow channel so that the valve has certain flow characteristics, which must be taken into account when selecting the most suitable valve for installation in the pipeline system.
03. Valve selection should follow the principle
Valves for shutoff and open media
The flow path for the straight-through valve, its flow resistance is small, usually selected as a cut-off and open media with the valve.
Downward closing type valve (globe valve, plunger valve) because of its flow path zigzag, flow resistance than other valves, so less choice.
In the occasion of allowing a higher flow resistance, closed type valves can be selected.
Control the flow of valves
Usually choose easy to adjust the flow of the valve as a control flow. Downward closing type valve (such as shut-off valve) is suitable for this purpose, because its seat size is proportional to the stroke of the closing member.
Rotary valves (plug valves, butterfly valves, ball valves) and flexural body type valves (clamping valves, diaphragm valves) can also be used for throttling control, but usually only in a limited range of valve bore.
Gate valve is a disc-shaped gate to the circular seat mouth to do cross-cutting movement, it is only close to the closed position, to better control the flow, so usually not used for flow control.
Valves for reversing and shunting
Depending on the need for directional flow diversion, this valve can have three or more channels.
Plug and ball valves are more suitable for this purpose, therefore, most of the valves used for directional flow diversion are selected one of these types of valves.
But in some cases, other types of valves, as long as two or more valves are properly connected to each other, can also be used for directional flow diversion.
With suspended particles in the media with the valve
When the medium with suspended particles, the most suitable for the use of its closing member along the sealing surface of the sliding with wiping effect of the valve.
If the back and forth movement of the closing member to the valve seat is vertical, then it may trap particles, so this valve unless the sealing surface material can allow embedded particles, only for basic clean media.
Ball valves and plug valves have a wiping effect on the sealing surface during the opening and closing process, so they are suitable for use in media with suspended particles.
At present, whether in the petroleum, chemical, or pipeline systems in other industries, valve applications, operating frequencies and services vary widely, to control or eliminate even the slightest leakage, the most important and critical equipment is still the number of valves. The ultimate control of pipelines is the valve, and valves are unique in their service and reliable performance in all areas.
04. Valve selection instructions
Selecting the gate valve
In general, the gate valve should be preferred. Gate valve is suitable for steam, oil and other media, but also for media containing granular solids and viscosity, and for venting and low vacuum system valves. For the media with solid particles, the gate valve body should have one or two blowing holes. For low-temperature media, a special low-temperature gate valve should be used.
Disconnecting valve selection instructions
Disconnecting valve is suitable for the fluid resistance requirements of the pipeline, that is, the pressure loss is not considered large, as well as high temperature, high pressure media pipeline or device, for DN <200mm steam and other media pipeline; small valves can be selected disconnecting valve, such as needle valve, instrumentation valve, sampling valve, pressure gauge valve, etc.; disconnecting valve has a flow adjustment or pressure adjustment, but the adjustment accuracy requirements are not high, and the pipeline diameter and For highly toxic media, it is appropriate to use the bellows-sealed globe valve; but the globe valve should not be used for viscous media and media containing particles that are easy to precipitate, but also not for venting valves and low vacuum system valves.
Ball valve selection instructions
Ball valves are suitable for low temperature, high pressure, viscous media. Most ball valves can be used in the media with suspended solid particles, according to the material requirements of the seal can also be used for powder and granular media; full-channel ball valves are not suitable for flow regulation, but suitable for the requirements of fast opening and closing occasions, to facilitate the realization of the accident emergency cut off; usually in the sealing performance is strict, wear, indented channel, opening and closing action quickly, high pressure cut-off (large differential pressure), low noise, the phenomenon of gasification, operation Small torque, small fluid resistance in the pipeline, the recommended use of ball valves; ball valves are suitable for light structure, low-pressure cut-off, corrosive media; ball valves are also the most ideal valve for low temperature, deep cold media, low-temperature media piping systems and devices, it is appropriate to use plus the cover of the low-temperature ball valves; the choice of floating ball ball valve seat material should take the load of the ball and the working medium, large-diameter ball valves require greater operating Force, DN ≥ 200mm ball valve should be selected in the form of worm gear drive; fixed ball valve for larger diameter and higher pressure occasions; in addition, for the process of highly toxic materials, combustible media pipeline ball valve, should have a fire, anti-static structure.
Throttle valve selection instructions
Throttle valve is suitable for low media temperature, high pressure occasions, suitable for the need to regulate the flow and pressure of the parts, not suitable for viscosity and solid particles containing the media, not suitable for isolation valve.
Cock valve selection instructions
Plug valve is suitable for the occasion requiring fast opening and closing, generally not suitable for steam and high temperature media, for lower temperature, viscosity media, also suitable for media with suspended particles.
Butterfly valve selection instructions
Butterfly valve is suitable for larger diameter (such as DN>600mm) and short structure length requirements, as well as the need for flow regulation and opening and closing requirements for fast occasions, generally used for temperature ≤ 80 ℃, pressure ≤ 1.0MPa water, oil and compressed air and other media; as butterfly valve compared to the gate valve, ball valve pressure loss is relatively large, so the butterfly valve is suitable for pressure loss requirements are not strict pipeline system.
Check valve selection instructions
Check valve is generally suitable for clean media, should not be used for media containing solid particles and large viscosity.
When DN ≤ 40mm, it is appropriate to use lift check valve (only allowed to be installed on the horizontal pipeline).
When DN = 50-400mm, it is advisable to use swinging lift check valve (can be installed on both horizontal and vertical pipelines, such as installed on vertical pipelines, the media flow direction should be from bottom to top).
When DN ≥ 450mm, it is appropriate to use buffer type check valve.
When DN = 100-400mm can also be used to choose the clamp-on check valve.
Swing check valve can be made into a very high working pressure, PN can reach 42MPa, according to the different materials of the shell and seals can be applied to any working medium and any working temperature range. The medium is water, steam, gas, corrosive media, oil, pharmaceuticals, etc. The medium working temperature range is between -196-800℃.
Diaphragm valve selection instructions
Diaphragm valve is suitable for working temperature less than 200 ℃, pressure less than 1.0MPa oil, water, acidic media and media containing suspended matter, not for organic solvents and strong oxidant media; abrasive granular media should be selected weir type diaphragm valve, select weir type diaphragm valve to refer to its flow characteristics table; viscous fluid, cement slurry and sedimentation media should be selected straight through diaphragm valve; in addition to specific requirements, diaphragm valve should not be used for vacuum pipeline and vacuum equipment.
Valve applications, operating frequencies and services vary widely, to control or eliminate even the slightest leakage, the most important and critical equipment is still the valve. Learning to select the correct valve is essential.
Source: China Valve Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)