What Are Globe Valves?
Globe valves, also known as shutoff valves, belongs to forced sealing valves, so when the valves are closed, pressure must be exerted on the disc to force the sealing surface not to leak. When the medium enters the valve from below the disc, the resistance to be overcome by the operating force is the friction between the stem and packing and the thrust generated by the pressure of the medium. The force to close the valve is greater than the force to open the valve, so the diameter of the valve stem is larger, otherwise the failure of the top bending of the valve stem will occur. There are three kinds of connection modes: flange connection, thread connection and welding connection. After the appearance of self-sealing valve, the medium flow direction of globe valve changes from above the disc to enter the valve chamber. Under the action of medium pressure, the force of closing the valve is small, while the force of opening the valve is large, and the diameter of the stem can be reduced accordingly. At the same time, under the action of medium, this form of valve is also more tight. Our country’s valve “three-way feed” once stipulated that the flow direction of globe valve should be from top to bottom. When the globe valve is opened, the opening height of the disc is 25%-30% of the nominal diameter. The flow rate has reached the maximum, indicating that the valve has reached the full open position. Therefore, the full open position of the globe valve should be determined by the stroke of the disc.
The opening and closing parts of stop valve (globe valve) are plug-shaped discs with a flat or sea cone on the top of the seal, and the disc moves in a straight line along the center line of the seat. The movement form of the valve stem (common name: concealed rod) can also be used to control the flow of air, water, steam, various corrosive media, mud, oil, liquid metal and radioactive media. Therefore, this type of cut-off globe valve is very suitable for cutting off or regulating and throttling. Because the stem opening or closing stroke of this kind of valve is relatively short, and has a very reliable cut-off function, and because the change of the seat opening is proportional to the disc travel, it is very suitable for flow regulation.
Valves play an important role in cutting off and throttling the medium in the pipeline where they are located. Globe valve is a very important kind of cut-off valve. Its seal is to exert torque on the stem, and the stem exerts pressure on the valve disc in the axial direction, so that the sealing surface of the valve disc and the seat is closely adhered to prevent the leakage of the medium along the gap between the sealing surface.
The sealing pair of globe valve is composed of valve disc sealing surface and seat sealing surface. The stem drives the disc to move vertically along the center line of the valve seat. In the opening and closing process of globe valve, the opening height is small, the flow rate is easy to adjust, the manufacture and maintenance are convenient, and the pressure is applicable in a wide range.
Compared with another commonly used cut-off type valve in industrial production – alarm valve, globe valve is simpler in structure and easier to manufacture and repair than the former. In terms of service life, the sealing surface of the globe valve is not easy to wear and scratch, and there is no relative sliding between the disc and the sealing surface of the seat during the opening and closing process of the valve. Therefore, the wear and scratch of the sealing surface is relatively small, so the service life of the globe valve improves the service life of the sealing pair during the whole closing process, and the disc stroke is smaller than that of the alarm valve. The disadvantage of globe valve is that the opening and closing moment is large and it is difficult to achieve rapid opening and closing. Because the flow passage inside the valve body is tortuous and the fluid flow resistance is large, the loss of hydrodynamic force in the pipeline is large.
- Nominal pressure or pressure level: PN1.0-16.0 MPa, ANSICLASS150-900, JIS10-20K
- Nominal diameter or caliber: DN10-500, NPS1/2-36“
- Connection mode: Flange, butt welding, thread and other applicable temperatures: – 196 ~700 C
- Driving mode: manual, bevel gear transmission, pneumatic, electric, hydraulic, pneumatic-hydraulic, electro-hydraulic linkage
- Valve body materials: WCB, ZG1Cr18Ni9Ti, ZG1Cr18Ni12Mo2Ti, CF8 (304), CF3 (304L), CF8M (316), CF3M (316L), Ti. Different materials can be used in water, steam, oil, nitric acid, acetic acid, oxidizing media, urea and other media.
- Cut-off valves are suitable for pipes or devices with high temperature and high pressure media. Such as thermal power plants, nuclear power plants, high temperature and high pressure pipelines of petrochemical systems.
- Pipeline with lax convection resistance requirements. That is, the pressure loss is not taken into account.
- Needle valves, instrument valves, sampling valves and Pressure Gauge Valves are optional for small valves.
- There is flow regulation or pressure regulation, but the accuracy of regulation is not high, and the diameter of the pipeline is relatively small. If the nominal passage is less than 50 mm, the pipeline should be selected.
- High pressure angular globe valve or high pressure angular throttle valve with nominal pressure PN160 16 MPa or PN320 32 MPa should be selected for small and large chemical fertilizers in synthetic industrial production.
- In the desiliconization workshop and coke-prone pipeline of alumina Bayer process, it is easy to choose the direct-current globe valve or the direct-current throttle valve with separated valve body, removable valve seat and carbide sealing pair.
- In the water supply and heat supply projects in urban construction, nominal pipelines pass through smaller ones, and cut-off, balance or plunger valves can be selected, such as pipelines that nominal pipelines pass through less than 150 mm.
The application range of globe valves and gate valves is determined by their characteristics. In smaller channels, globe valves are often used when better shut-off sealing is required; in steam pipes and large diameter water supply pipes, gate valves are usually used because of less fluid resistance.
It can be used as shut-off valve for heat conducting oil, toxic, flammable, permeable, polluting environment, radioactive fluid medium pipeline, and can also be used for regulation. It is a high-quality product to create leak-free factory. All the valve castings are precision casting.
Globe valve is a valve whose closure (disc) moves along the center line of the seat. According to the movement of the disc, the change of the seat opening is proportional to the disc travel. Because the stem opening or closing stroke of this kind of valve is relatively short, and has a very reliable cut-off function, and because the change of the seat opening is proportional to the disc travel, it is very suitable for flow regulation. Therefore, this type of valve is very suitable for cutting or regulating and throttling.
Because the stem opening or closing stroke of globe valve is relatively short, and has a very reliable cut-off function, and because the change of seat opening is proportional to the stroke of disc, it is very suitable for flow regulation. Therefore, globe valves are very suitable for cutting off or regulating and throttling. Looking at the working principle, selection principle and use range of the above cut-off valves, we presumably now have a basic understanding of the cut-off valves.
Globe valves, also known as gate valves, are the most widely used type of valves, mainly composed of body, disc, cover and stem. The body and cover are pressure components, and the disc and stem are internal components. Globe valve is a valve in which the closure (valve) moves along the center line of the seat. According to the movement form of the flaps, the change of seat opening is proportional to the flaps travel.
Classification of Globe Valve:
According to the structure of the valve body, the globe valve can be divided into right angle type, straight type and direct current type.
- The right angle fluid only needs to change the main direction, so that the pressure drop through the valve is less than that of the traditional structure. Valve bodies are mostly forged and are suitable for small through high pressure globe valves.
- Straight-through is the most common structure. The inlet and outlet channels of medium are 180 degrees in the same direction, but the fluid resistance is the largest.
- In direct current or Y-shaped globe valves, the flow path of the valve body inclines with the main flow path, and the fluid resistance is small. It is mainly used for fluids containing solid particles or high viscosity.
Types of globe valves:
According to nominal pressure: vacuum, low pressure, medium pressure, high pressure, super high pressure valve, etc.
According to the working temperature: high temperature, medium temperature, normal temperature, low temperature, ultra-low temperature valves, etc.
According to the driving mode: manual valve, power driving valve (electromagnetic, pneumatic, hydraulic, electric and various linkage valves), automatic valve, etc.
According to the valve body material: cast iron, cast copper, cast steel, carbon steel, titanium, stainless steel valves, etc.
According to application departments: general valves, power station valves, marine valves, metallurgical valves, pipeline valves, water heating valves, etc.
According to the structure form: through, angle, DC, etc.
According to the connection form: internal thread, external thread, flange, welding, fixture, fixture, ring, etc.
Advantages and disadvantages of globe valves
- It is simple in structure and convenient in manufacture and maintenance.
- Small working journey and short start-up and shut-down time.
- Good sealing, small friction between sealing surfaces and long service life.
- The structure of globe valve body is straight through, direct current and right angle. Straight-through structure is the most common structure, but its fluid resistance is the largest. DC fluid has less resistance and is mostly used for fluids with solid particles or high viscosity. The right angle valve body is usually forged, which is suitable for globe valves with smaller pass and higher pressure.
- Double sealing design (bellows + packing) If bellows fail, stem packing will also be avoided.
- Leakage and conform to international sealing standards;
- No fluid loss, reduce energy loss and improve plant equipment safety;
- Long service life, less maintenance times and lower operating costs;
- Strong and durable bellows seal design ensures zero leakage of valve stem and provides maintenance-free conditions.
The types of globe valves can be divided into external threaded and internal threaded according to the position of stem threads. According to the flow direction of the medium, there are direct, direct and angular. Globe valves can be divided into packing sealing globe valves and bellows sealing globe valves.
- Fluid resistance is high and the force required for opening and closing is large.
- It is not suitable for medium with granules, high viscosity and easy coking.
- The regulation performance is poor.
- The types of globe valves can be divided into external threaded and internal threaded according to the position of stem threads. According to the flow direction of the medium, there are direct, direct and angular. Globe valves can be divided into packing sealing globe valves and bellows sealing globe valves.
- The bellows sealing globe valve is designed with bellows sealing, which completely eliminates the shortcomings of the common valve stem packing seal which is aging fast and easy to leak. It not only improves the energy efficiency, increases the safety of production equipment, reduces the maintenance cost and frequent maintenance, but also provides a clean and safe working environment.
- Fluid resistance is small and its coefficient of resistance is equal to that of the same length of pipe.
- It has simple structure, small volume and light weight. Electric globe valve
- It is compact and reliable. The sealing surface material of gate valve is widely used in plastics and has good sealing property. It has also been widely used in vacuum system.
- Easy to operate, quick to open and close, from full to full switching as long as the rotation of 90 degrees, easy to control over long distances.
- Maintenance is convenient, gate valve structure is simple, sealing ring is generally mobile, disassembly and replacement are more convenient.
- When fully open or fully closed, the sealing surface of the sphere and seat is isolated from the medium. When the medium passes through, it will not cause the erosion of the sealing surface of the valve.
- It can be used in a wide range of applications, ranging from small to several millimeters in diameter and from high vacuum to high pressure.
Classification of Electric Globe Valves
According to its channel position, it can be divided into straight-through type and right-angle type.
Working Principle of Electric Globe Valve
The working principle of electric globe valve is to make the valve unblocked or blocked by the love of rotary valve. Gate valve switch is light, small, can be made into a large caliber, reliable seal, simple structure, easy maintenance, sealing surface and spherical surface are often in closed state, not easy to be eroded by media, widely used in various industries.
A. Opening process
- In the closed position, the valve body is pressed on the seat by the mechanical pressure of the stem.
- When the handwheel is rotated counter-clockwise, the stem moves in reverse, and the bottom corner plane of the stem causes the ball to detach from the seat.
- The valve stem continues to lift and interact with the guide pin in the spiral groove of the valve stem to start the ball to rotate without friction.
- Up to the full open position, the stem is raised to the limit position and the sphere rotates to the full open position.
B. Closing process
When closed, turn the handwheel clockwise, the stem begins to drop and the ball starts to rotate away from the seat.
Continue to rotate the handwheel, and the stem is acted by the guide pin embedded in the upper spiral groove, so that the stem and the gate rotate 90 degrees at the same time.
The gate has rotated 90 degrees without contact with the seat when it is about to close.
In the last few turns of the handwheel rotation, the angular plane at the bottom of the stem mechanically wedges the sphere so that it is pressed tightly on the seat to achieve complete sealing.
Structural characteristics of electric globe valve:
- Opening and closing without friction. This function completely solves the problem that traditional valves are affected by friction between sealing surfaces.
- Uploading structure. Valves installed in pipelines can be directly inspected and maintained online, which can effectively reduce the device parking and cost.
- Single seat design. It eliminates the problem that the medium in the valve chamber will affect the safety of operation due to abnormal boosting.
- Low Torque Design. The valve stem with special structure design can be opened and closed easily with a small handle.
- Wedge sealing structure. The valve is sealed by the mechanical force provided by the stem, which presses the ball wedge onto the valve seat, so that the sealing of the valve is not affected by the variation of pipeline pressure difference, and the sealing performance can be guaranteed reliably under various working conditions.
- Self-cleaning structure of sealing surface. When the sphere tilts away from the valve seat, the fluid in the pipeline passes uniformly along the sealing surface of the sphere to 360 degrees, which not only eliminates the local scour of the high-speed fluid on the valve seat, but also washes away the accumulation on the sealing surface, so as to achieve the purpose of self-cleaning.
- Valve body and cover with diameters below DN50 are die forgings, valve body and cover with diameters above DN65 are steel castings.
- There are different connection forms between valve body and valve cover, pin-pin pin connection, flange gasket connection and self-sealing thread connection.
- The seats and discs are welded by plasma spraying or surfacing with Co-Cr-W cemented carbide. The seals have high hardness, wear resistance, abrasion resistance and long service life.
Stem material is nitrided steel. The surface of nitrided valve stem is high hardness, wear resistance, abrasion resistance, corrosion resistance and long service life.
Attention to Installation of Electric Globe Valve
- When installing the valve, pay attention to the flow direction of the medium and install it strictly in the direction indicated by the arrow of the flow direction of the valve.
- Valves can be installed in any position of the pipeline, and at the same time according to the medium and medium temperature to select carbon steel or alloy steel valves.
- Electric globe valve should be installed vertically as far as possible with stem up.
Comparisons between Bellows Globe Valve and Ordinary Globe Valve
- Dual sealing design (bellows + packing) If bellows fail, stem packing will also avoid leakage and meet international sealing standards.
- No fluid loss, reduce energy loss and improve plant equipment safety.
- Long service life, less maintenance times and lower operating costs.
- Strong and durable bellows seal design ensures zero leakage of valve stem and provides maintenance-free conditions.
- PTFE soft sealing material is used in gas medium seat to improve the sealing performance of the valve.
- Conical hard seals are used for seats with high temperature resistance less than 425 C. It achieves zero leakage of air tightness.
With the rising labor costs, more and more enterprises hope to reduce the labor force. With such BELLOWS GLOBE valves, workers can switch more easily, products with longer service life and better sealing performance can be used. It is reasonable to believe that its prospects will be more and more broad.
The Difference and Advantages of Globe Valve and Ball Valve
Gate valves and globe valves are shutoff valves, and are the two most common types of valves. They are different in many ways. For example, the globe valve is a rising stem, and the handwheel rotates and rises with the stem. Gate valves are hand wheels rotating and stem rising. Now let’s take a look at the difference between globe valve and gate valve. What are the advantages and selection principles of globe valves?
What is the difference between globe valve and gate valve?
1. Different sealing surfaces
When the valve is opened and closed, the sealing surfaces of the valve core and the valve seat are always in contact and friction with each other, so the sealing surface is easy to wear, especially when the valve is close to the closed state, the pressure difference between the front and back of the valve core is large, and the wear of the sealing surface is more serious; and once the valve disc of the globe valve is open, the sealing surface between the valve seat and the valve disc will no longer contact, so its sealing surface machine. Mechanical wear is small, but if the medium contains solid particles, it is easy to damage the sealing surface. The sealing surface of gate valve has certain self-sealing ability. Its valve core contacts with the sealing surface of valve seat tightly depending on medium pressure, so as to achieve tightness and leakproof.
The inclination of the spool of wedge gate valve is generally 3-6 degrees, and it is easy to jam when excessive closure or large temperature change is forced. Therefore, high temperature and high pressure wedge gate valves have taken some measures to prevent the valve core from being stuck.
The sealing surface of globe valve must be closed by force to achieve sealing. Under the same caliber, working pressure and driving device, the driving torque of globe valve is 2.5-3.5 times of that of gate valve. Attention should be paid to this point when adjusting the torque control mechanism of electric valves. The sealing surface of globe valve contacts each other only when it is completely closed. The relative slip between the mandatory closing spool and the sealing surface is very small, so the wear of the sealing surface is also very small. The wear of sealing surface of globe valve is mostly caused by debris before the valve core and sealing surface, or by the high-speed erosion of medium caused by the inadequate closing state.
2. Different structures
Gate valves are more complex than globe valves in structure and high dimension. From the appearance, gate valves are shorter and higher than globe valves, especially open-rod gate valves need higher height space, which should be paid attention to in the case of limited installation space.
3. Flow resistance is different
Compared with globe valve, the main advantage of gate valve is that the fluid flow resistance is small. The flow resistance coefficient of common gate valve is about 0.08-0.12, while that of common globe valve is about 3.5-4.5. Small opening and closing force. Gate valves are generally applicable, do not need to be frequently opened and closed, and keep the gate fully open or closed, not suitable for regulation, throttling use. The flow resistance and unbalance force of the globe valve are very large during the whole stroke, and the driving force or moment required are also much larger. But it is very suitable for the regulation and throttling of fluids. For high-speed flow medium, the vibration of the valve can be caused by the partial opening of the gate, and the vibration may damage the sealing surface of the gate and the seat, while throttling will cause the gate to be eroded by the medium.
4. Different itineraries
The stroke of the gate valve is larger than that of the globe valve.
5. Flow direction is different
When the globe valve is installed, the medium can enter from the bottom of the spool and from the top. The advantage of medium entering from the bottom of the valve core is that when the valve closes, the packing root is not pressurized, and the service life of the packing root can be prolonged, and the work of replacing the packing root can be carried out under the pressure of the pipe in front of the valve. The disadvantage of medium entering from the lower part of the spool is that the driving torque of the valve is larger, about 1.05-1.08 times that of the upper part, the axial force on the valve stem is large, and the valve stem is easy to bend. For this reason, the way of medium entering from below is generally only suitable for small caliber globe valves (below DN50). The way of medium entering from above is chosen for globe valves above DN200. Electric globe valves generally use medium from the top into the way. The disadvantage of medium entering from the top is just opposite to that from the bottom. The flow direction of the gate valve, from both sides into the effect is the same. Compared with gate valves, globe valves have the advantages of simple structure, good sealing performance and convenient manufacture and maintenance, while the disadvantages are large liquid resistance and large opening and closing force.
6. Maintenance process is different
Gate valve repair is not suitable for on-site pipeline, and most of the globe valve seats and discs can be replaced online, without the need to remove the entire valve from the pipeline, which is very suitable for the occasion where the valve and pipeline are welded together. Of course, the difference between gate valve and globe valve is not only these kinds, but also their similarities and differences should be well distinguished in the selection and use so as to avoid mistakes. The application range of globe valves and gate valves is determined by their characteristics. In smaller channels, globe valves are often used when better shut-off sealing is required; in steam pipes and large diameter water supply pipes, gate valves are usually used because of less fluid resistance.
For globe valves, not only installation and maintenance, but also operation.
Open and close globe valve, force should be smooth, not impact. Some parts of high-pressure globe valves with impact opening and closing have considered that the impact force is not equal to that of general globe valves.
When the globe valve is fully open, the handwheel should be reversed a little to tighten the threads so as to avoid loosening damage.
When the pipeline is first used, there are many internal dirt, so it can open the globe valve slightly, flush it away by using the high-speed flow of medium, then close it gently (can not close quickly, close sharply, in order to prevent residual impurities from injuring the sealing surface), open it again, so many times, clean dirt, and put it into normal work.
Often open the shutoff valve, the sealing surface may stick dirt, when closed, also use the above method to wash it clean, and then formally closed.
If the handwheel and handle are damaged or lost, they should be matched immediately, and can not be replaced by movable winding plate hand, so as to avoid damaging the four sides of the valve stem and failing to open and close, so as to cause accidents in production.
In some media, when the shutoff valve is cooled and the valve shrinks, the operator should close it again at an appropriate time so that no slits are left on the sealing surface. Otherwise, the medium will flow through the slits at high speed and easily erode the sealing surface.
When operating, if it is found that the operation is too arduous, the reasons should be analyzed. If the packing is too tight, it can be relaxed properly. If the valve stem is skewed, the repairman should be notified. In some globe valves, when in closed state, the closing parts are heated and expanded, which makes it difficult to open. If it must be opened at this time, the cover threads can be screwed half to one turn to eliminate the stem stress, and then the plate operates the handwheel.
In operation, all kinds of valves should be complete and intact. Bolts on flanges and brackets are indispensable. Threads should be intact and intact. No loosening is allowed. The fastening nuts on the handwheel should be tightened in time if loosening is found, so as not to wear the connection or lose the handwheel and nameplate. If the handwheel of globe valve is lost, it is not allowed to be replaced by a live wrench. It should be matched in time. Packing gland is not allowed to be skewed or without pre-tightening clearance. For globe valves in environments susceptible to rain, snow, dust, sand and other contaminants, the valve stem should be equipped with a protective cover. The gauge on the globe valve should be complete, accurate and clear. Lead seals, caps and pneumatic accessories of globe valves should be in good condition. It is not allowed to knock, stand or support heavy objects on globe valves in operation; especially non-metallic valves and cast iron valves, it is more important to prohibit the maintenance work during grease injection of valves before and after welding, which plays a vital role in the service of valves in production and operation. Correct and orderly and effective maintenance will protect valves and make valves safe. Function normally and prolong the service life of the valve. Valve maintenance seems simple, but it is not. There are often neglected aspects of work.
First, when globe valve is injected with grease, the problem of the amount of grease injected is often neglected. After oil filling, the operator chooses the valve and the connection mode for oil filling, and then carries on the oil filling operation. There are two situations: on the one hand, less grease injection and insufficient grease injection, and the sealing surface accelerates wear due to lack of lubricant. On the other hand, excessive fat injection causes waste. Because there is no accurate calculation of sealing capacity of different globe valves according to the type and type of valves. Sealing capacity can be calculated according to the size and type of globe valve, and a reasonable amount of grease can be injected.
Secondly, pressure is often neglected in grease injection of globe valves. During the operation of lipid injection, the pressure of lipid injection varies regularly from peak to valley. The pressure is too low, the seal leaks or fails, the pressure is too high, the grease injection mouth is blocked, the inner grease of the seal is hardened or the seal ring is locked with the valve ball and the valve plate. Usually when the pressure of grease injection is too low, the grease injected into the bottom of the valve chamber, usually occurs in small gate valves. The pressure of grease injection is too high, on the one hand, check the grease injection nozzle, such as the identification of the blockage of the grease hole for replacement; on the other hand, lipid hardening, to use cleaning fluid, repeatedly soften the failed sealing grease, and inject new grease replacement. In addition, sealing type and sealing material also affect the grease injection pressure. Different sealing forms have different grease injection pressure. Generally, the grease injection pressure of hard seal is higher than that of soft seal. Ball valve maintenance is generally in the open state, in special cases choose to close maintenance. Other valves cannot be treated as open valves. Gate valves must be closed during maintenance to ensure that grease is filled with sealing grooves along the sealing ring. If opened, the grease will fall directly into the flow channel or valve chamber, causing waste.
After installation, the globe valve shall be inspected regularly. Main inspection items are as follows:
- (1) Wear condition of sealing surface of globe valve.
- (2) Trapezoidal thread wear of stem and stem nut.
- (3) Whether the filler is out of date or not, and if it is damaged, it should be replaced in time.
- (4) After repair and assembly of globe valve, sealing performance test should be carried out.
Source: China Globe 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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