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1. The fluid resistance is small, and its resistance coefficient is equal to that of pipe sections of the same length.
2. Simple structure, small size, and light weight. Electric stop valve
3. Tight and reliable, the sealing surface material of the gate valve is widely used in plastic, with good sealing performance, and has also been widely used in vacuum systems.
4. Convenient operation, quick opening and closing, with only 90 ° rotation from full opening to full closing, facilitating remote control.
5. Convenient maintenance, simple gate valve structure, generally movable sealing rings, and convenient disassembly and replacement.
6. When fully open or fully closed, the sealing surfaces of the ball and valve seat are isolated from the medium, and when the medium passes through, it will not cause erosion of the valve sealing surface.
7. Wide range of applications, ranging from small to a few millimeters in diameter to several meters in diameter, from high vacuum to high pressure applications.
Classification of electric stop valves
According to its channel position, it can be divided into straight through type and right angle type.
working principle
The working principle of the electric stop valve is to rotate the valve to make the valve unblocked or blocked. Gate valves are lightweight, small in size, and can be made into large diameters. They are reliable in sealing, simple in structure, and convenient in maintenance. The sealing surface and spherical surface are often in a closed state, and are not easily eroded by media. They are widely used in various industries.
A. Opening process
In the closed position, the valve body is mechanically pressed against the valve seat by the valve stem.
When the handwheel is rotated counterclockwise, the valve stem moves in the opposite direction, and its bottom angular plane disengages the ball from the valve seat.
The valve rod continues to lift and interacts with the guide pin in the spiral groove of the valve rod, causing the ball to begin to rotate frictionlessly.
4. Until the fully open position is reached, the valve rod is lifted to the limit position, and the ball rotates to the fully open position.
B. Closing process
When the valve is closed, rotate the handwheel clockwise, and the valve rod begins to lower and rotate as the ball moves away from the valve seat.
Continue to rotate the handwheel, and the valve rod is subjected to the action of the guide pin embedded in the spiral groove on it, causing the valve rod and gate plate to rotate simultaneously by 90 °.
The gate body had rotated 90 ° without contact with the valve seat when it was about to close.
During the last few turns of the handwheel rotation, the angular plane at the bottom of the valve rod mechanically wedges against the ball to tightly press it against the valve seat, achieving a complete seal.
Structural features of electric stop valve:
1. No friction during opening and closing. This function completely solves the problem that the sealing surfaces of traditional valves affect their sealing due to mutual friction.
2. Top-mounted structure. The valves installed on the pipeline can be directly inspected and repaired online, effectively reducing device downtime and reducing costs.
3. Single seat design. Eliminates the problem of abnormal pressure rise in the cavity medium of the valve that affects the safety of use.
4. Low torque design. The valve stem with a special structural design can be easily opened and closed with only a small handle.
5. Wedge shaped sealing structure. The valve is sealed by pressing the ball wedge onto the valve seat using the mechanical force provided by the valve stem, which prevents the sealing performance of the valve from being affected by changes in pipeline pressure differential. The sealing performance is reliably guaranteed under various working conditions.
6. Self cleaning structure of sealing surface. When the ball is tilted away from the valve seat, the fluid in the pipeline passes evenly along the sealing surface of the ball at a 360 ° angle, not only eliminating the local scouring of the valve seat by high-speed fluid, but also flushing away the accumulation on the sealing surface, achieving the purpose of self-cleaning.
7. Valve bodies and bonnets with valve diameters below DN50 are die forgings, while valve bodies and bonnets with valve diameters above DN65 are steel castings.
8. The connection forms of valve body and bonnet vary, including clamp pin type connection, flange gasket connection, and self sealing screw connection.
9. The sealing surfaces of the valve seat and flap are all made of plasma spray welding or surfacing cobalt chromium tungsten carbide, with high hardness, wear resistance, scratch resistance, and long service life.
10. The valve rod material is nitrided steel. The surface hardness of the nitrided valve rod is high, wear-resistant, scratch resistant, and corrosion resistant, with a long service life.
Installation precautions for electric stop valve
1. When installing the valve, pay attention to the flow direction of the medium and strictly follow the direction indicated by the valve flow arrow.
2. Valves can be installed at any position in the pipeline, and carbon steel or alloy steel valves can be selected based on the temperature of the medium and the medium.
3. The electric stop valve should be installed vertically as much as possible, with the valve stem upward.
Advantages and disadvantages
characteristic
(1) The structure of the stop valve is simpler than that of the gate valve, making it easier to manufacture and maintain.
(2) The sealing surface is not easy to wear and scratch, and has good sealing performance. During opening and closing, there is no relative sliding between the valve flap and the valve body sealing surface, resulting in no serious wear and scratch, good sealing performance, and long service life.
(3) When opening and closing, the valve disc stroke is small, so the height of the stop valve is smaller than that of the gate valve, but the structural length is longer than that of the gate valve.
(4) The opening and closing torque is large, the opening and closing is relatively laborious, and the opening and closing time is high.
(5) The fluid resistance is large, due to the tortuous medium channel in the valve body, the fluid resistance is large, and the power consumption is large.
(6) When the nominal pressure in the medium flow direction PN ≤ 16MPa, downstream flow is generally adopted, and the medium flows upward from the lower direction of the valve flap; When the nominal pressure PN ≥ 20MPa, countercurrent flow is generally used, and the medium flows downward from the upper direction of the valve flap to increase the seal energy. When in use, the medium of the stop valve can only flow in one direction, and the flow direction cannot be changed.
(7) When fully open, the valve flap is often eroded.
The stem axis of the stop valve is perpendicular to the sealing surface of the valve seat. The valve stem has a relatively short opening or closing stroke and a very reliable cutoff action, making this valve suitable for medium cutoff, adjustment, and throttling.
shortcoming
1. Fluid resistance bellows stop valve
Bellows valves
Large force, large force required for opening and closing.
2. Not suitable for media with particles, high viscosity, and easy to coke.
3. Poor regulation performance.
4. The bellows sealed globe valve adopts a bellows sealed design, completely eliminating the shortcomings of aging and easy leakage of ordinary valve stem packing seals. It not only improves the energy efficiency of use, increases the safety of production equipment, reduces maintenance costs and frequent maintenance, but also provides a clean and safe working environment.
advantage
1. Dual sealing design (bellows+packing) If the bellows fails, the valve stem packing will also be avoided;
2. External leakage and compliance with international sealing standards;
3. No fluid loss, reduce energy loss, and improve plant equipment safety;
4. Long service life, reduced maintenance times, and reduced operating costs;
5. Robust and durable bellows seal design ensures zero leakage of the valve stem, providing maintenance free conditions.
Installation method
The installation and maintenance of stop valves should pay attention to the following:
1. Handwheel and handle operated stop valves can be installed at any position in the pipeline.
2. Handwheels, handles, and micro mechanisms are not allowed for lifting purposes.
3. The flow direction of the medium should be consistent with the arrow direction shown on the valve body.
Main standards
1. GB/T 12233-2006 General Purpose Valves - Iron Globe Valves and Lift Check Valves
2. GB/T 12235-2007 Steel Globe and Lift Check Valves with Flange Connection for General Purpose Valves
3. JB/T53174-94 Quality Classification of Globe Valves
4. JB/T53165-92 High Pressure Balanced Stop Valves
5. GB/T 587-2008 "Marine Blue Bronze Stop Valves"
6. GB/T 590-2008 Marine Flanged Cast Iron Stop Valves
7. GB/T 8464-2008 Iron and Copper Threaded Valves
8. GB8465.2-87 "Basic Dimensions of Internally Threaded Gate Valves, Globe Valves, Ball Valves, and Check Valves - Iron Globe Valves"
Relevant knowledge
A globe valve is a valve in which the closing member (disc) moves along the centerline of the valve seat. According to this form of movement of the valve disc, the change in the valve seat opening is in direct proportion to the valve disc stroke. Due to the relatively short opening or closing stroke of the valve stem, as well as the very reliable cutoff function, and because the change in the valve seat opening is proportional to the stroke of the valve disc, this type of valve is very suitable for regulating flow. Therefore, this type of valve is very suitable for use as a shut-off or regulating and throttling valve.
Selection principles
1. Stop valves should be selected for pipelines or devices with high-temperature and high-pressure media. High temperature and high pressure pipelines in thermal power plants, nuclear power plants, and petrochemical systems.
2. On pipelines where the flow resistance requirements are not strict. That is, places where pressure loss is not considered much.
3. Small valves can be selected from needle valves, instrument valves, sampling valves, pressure gauge valves, etc.
4. There is flow regulation or pressure regulation, but the requirements for regulation accuracy are not high, and the pipeline diameter is relatively small. For example, on pipelines with a nominal diameter of ≤ 50mm, it should be selected.
5. For small and large fertilizers in the production of synthetic industry, high-pressure angle type globe valves or high-pressure angle type throttle valves with a nominal pressure of PN160, nominal pressure of 16MPa, or PN320, nominal pressure of 32MPa should be selected.
6. In the desilication workshop and pipeline prone to coking in the production of alumina Bayer process, it is easy to choose a direct flow stop valve or throttle valve with a separate valve body, removable valve seats, and a cemented carbide sealing pair.
7. For water supply and heating projects in urban construction, cut-off, balance, or plunger valves can be selected for pipelines with a smaller nominal diameter, such as pipelines with a nominal diameter less than 150mm.
During opening and closing, the friction between the valve flap and the sealing surface of the valve body is smaller than that of the gate valve, so it is wear-resistant. The opening height is generally only 1/4 of the diameter of the valve seat passage, so it is much smaller than the gate valve. Generally, there is only one sealing surface on the valve body and valve flap, so the manufacturing process is relatively good and convenient for maintenance.
Nominal pressure or pressure class: PN1.0-16.0MPa, ANSI CLASS 150-900, JIS10-20K Nominal diameter or diameter: DN10-500 NPS 1/2 to 36 "connection method: flange, butt welding, thread, etc. Applicable temperature: - 196 ℃ to 700 ℃ Drive method: pneumatic, electric, hydraulic, pneumatic-hydraulic, valve body material: WCB, ZG1Cr18Ni9Ti, ZG1Cr18Ni12Mo2Ti, CF8 (304), CF3 (304L), CF8M (316), CF3M (316L), Ti. Different materials are selected, and can be applied to various media such as water, steam, oil, nitric acid, acetic acid, oxidizing media, urea, and so on.
operation
For globe valves, it is necessary to not only be able to install and maintain them, but also be able to operate them.
When opening and closing the stop valve, the force should be stable and not impact. Some components of high-pressure stop valves that are opened and closed by impact have considered that this impact force cannot be equal to that of ordinary stop valves.
After the stop valve is fully opened, the handwheel should be turned back a little to tighten the threads tightly to avoid looseness and damage.
When the pipeline is initially used, there is a lot of dirt inside. You can slightly open the shutoff valve, use the high-speed flow of media to flush it away, then gently close it (not quickly or violently, to prevent residual impurities from pinching the sealing surface), and then open it again. Repeat this process for many times to flush the dirt before putting it into normal operation.
Normally open globe valves may have dirt stuck to their sealing surfaces. When closing, it is also necessary to flush them clean using the above methods, and then officially close them tightly.
If the handwheel and handle are damaged or lost, they should be immediately equipped and cannot be replaced by a flexible wrench to prevent damage to the valve stem square and poor opening and closing, leading to accidents in production.
"Some media cool down after the shutoff valve is closed, causing the valve to contract. The operator should close it again at an appropriate time to ensure that there are no fine seams on the sealing surface. Otherwise, the media flows through the fine seams at a high speed, which can easily erode the sealing surface.".
During operation, if it is found that the operation is too laborious, the reason should be analyzed. If the packing is too tight, it can be loosened appropriately. If the valve rod is skewed, personnel should be notified for repair. Some shutoff valves, when in the closed state, expand due to heat on the closing part, causing difficulty in opening; If it is necessary to open at this time, loosen the bonnet thread by half a turn to one turn to relieve the stress on the valve stem, and then press the handwheel.
Moment analysis
At the stage when the stop valve starts to close from the fully open position, as the valve disc descends, the fluid creates a pressure difference before and after the valve disc to prevent the valve disc from falling, and this resistance increases rapidly as the valve disc descends. When the stop valve is fully closed, the pressure difference between the front and rear of the valve flap is equal to the working pressure of the medium, and the resistance is high. The forced sealing force is applied to quickly increase the operating force at the moment of closing the stop valve. During the valve opening process, the thrust caused by the medium pressure or the pressure difference between the front and rear of the valve flap is helpful in opening the valve. It should be pointed out that the torque at the moment of opening the valve may exceed the torque at the moment of closing the valve, as it is necessary to overcome the large static friction force at this time.
When the stop valve is opened, when the opening height of the valve flap reaches 25% to 30% of the nominal diameter of the stop valve, the flow rate has reached a high level, indicating that the stop valve has reached the fully open position. Therefore, the fully open position of the stop valve should be determined by the valve flap stroke. The closing and reopening conditions of the stop valve are similar to those of a forced seal gate valve. Therefore, the closing position of the stop valve should be determined by increasing the operating torque to the specified value.
Working principle and selection principle
The stop valve only allows one-way flow of media, and has directionality during installation. The structural length of the stop valve is larger than that of the gate valve, and the fluid resistance is large. During long-term operation, the sealing reliability is not strong.
Stop valves are divided into three categories: straight through stop valves, right angle stop valves, and direct flow inclined stop valves.
The obvious advantage is that during the opening and closing process, the friction between the valve flap and the sealing surface of the valve body is smaller than that of the gate valve, so it is wear-resistant. The opening height is generally only 1/4 of the diameter of the valve seat passage, so it is much smaller than the gate valve. Generally, there is only one sealing surface on the valve body and valve flap, so the manufacturing process is relatively good and convenient for maintenance.
Stop valve nominal pressure or pressure class: PN1.0-16.0MPa, ANSICLASS150-900, JIS10-20K, nominal diameter or diameter: DN10-500 NPS 1/2 to 36 ", connection mode of stop valve: flange, butt welding, thread, etc., applicable temperature: - 196 ℃ to 700 ℃, drive mode of stop valve: manual, bevel gear transmission, pneumatic, electric, hydraulic, pneumatic-hydraulic, electro-hydraulic linkage, valve body material: WCB, ZG1Cr18Ni9Ti, ZG1Cr18Ni12Mo2Ti, CF8 (304), CF3 (304L), CF8M (316), CF3M (316L), Ti. Stop valves are made of different materials.
The selection principles of stop valves are:
Stop valves should be selected for pipelines or devices with high-temperature and high-pressure media. High temperature and high pressure pipelines in thermal power plants, nuclear power plants, and petrochemical systems.
2. On pipelines where the flow resistance requirements are not strict. That is, places where pressure loss is not considered much.
Small valves can be needle valves, instrument valves, sampling valves, pressure gauge valves, etc.
4. There is flow regulation or pressure regulation, but the regulation
