Case
Case
The gate valve is the most commonly used opening and closing valve, which uses the gate plate (i.e. the opening and closing part, in the gate valve the opening and closing part is called the gate plate or gate, and the valve seat is called the gate plate seat or gate seat) to connect (fully open) ) and cut off (fully close) the medium in the pipeline.
It is not allowed to be used as a throttling device. During use, you should avoid opening the gate a small amount, because the erosion of the high-speed flowing medium will accelerate the damage of the sealing surface. The gate moves up and down in a plane perpendicular to the center line of the gate seat channel, cutting off the medium in the pipeline like a gate, so it is called a gate valve.
1. Small flow resistance. The internal medium channel of the valve body is straight, the medium flows in a straight line, and the flow resistance is small.
2. It saves effort when opening and closing. It is compared with the stop valve, because whether it is open or closed, the movement direction of the gate is perpendicular to the direction of medium flow.
3. Large height, long opening and closing time. The opening and closing stroke of the gate is relatively large, and a screw performs the descent.
4. Water hammer is not easy to occur. The reason is the long shutdown time.
5. The medium can flow in any direction on both sides, making installation easy. The gate valve passage is symmetrical on both sides.
6. The structural length (the distance between the two connecting end faces of the shell) is small.
7. The sealing surface is easy to wear and affects the service life. When opening and closing, the two sealing surfaces of the gate and the valve seat rub and slide against each other. Under the action of medium pressure, scratches and wear are easy to occur, which affects the sealing performance and shortens the service life.
8. The price is more expensive. There are many contact sealing surfaces and the processing is more complicated. In particular, the sealing surface on the gate seat is difficult to process and has many parts.
The stop valve is a closed-circuit valve that uses the disc (the closing part of the stop valve is called the disc) to move along the center line of the disc seat (valve seat) channel to control the opening and closing of the pipeline.
Globe valves are generally suitable for transporting liquid and gaseous media under various pressure and temperature conditions within the specified standard range, but are not suitable for transporting liquids containing solid precipitation or precipitated crystals.
In low-pressure pipelines, stop valves can also be used to regulate the flow of media in the pipeline. Due to structural limitations, the nominal diameter of the stop valve is below 250mm. If it is on a pipeline with high medium pressure and high flow rate, its sealing surface will wear out quickly. Therefore, when the flow needs to be adjusted, a throttle valve must be used.
1. The wear and scratches on the sealing surface are not serious, so the operation is more reliable and the service life is long.
2. The sealing surface area is smaller and the structure is simpler. The man-hours required to manufacture the sealing surface and the precious materials required for the sealing ring are less than those of the gate valve.
3. When opening and closing, the valve disc stroke is small, so the height of the stop valve is small. Easy to operate.
4. By using the thread to move the valve disc, there will be no sudden opening and closing, and the "water hammer" phenomenon will not easily occur.
5. It is more laborious to open and close due to the large opening and closing torque. When closing, the movement direction of the valve disc is opposite to the direction of the medium movement pressure, and the force of the medium must be overcome, so the opening and closing torque is large, thus affecting the application of large diameter stop valves.
6. The flow resistance is large. The stop valve has the greatest flow resistance among all types of stop valves. (The medium channel is relatively tortuous)
7. The structure is complex.
8. The medium flow direction is unidirectional. It should be ensured that the medium flows from bottom to top, so the medium must flow in one direction.
Butterfly valve is a rotary valve that uses a disk-type (also called butterfly plate) opening and closing part to rotate 90° or about 90° to open and close the channel. The movement of the butterfly valve disc is wiping, so most butterfly valves can be used in media with suspended solid particles.
Commonly used butterfly valves include wafer butterfly valves and flange butterfly valves. Wafer-type butterfly valves use studs to connect the valve between two pipe flanges. Flange-type butterfly valves have flanges on the valve, and bolts are used to connect the flanges at both ends of the valve to the pipe flanges.
1. Small appearance, short length, simple structure and light weight.
2. Easy to operate, quick to open and close, just rotate the valve disc 90° to open and close
3. The sealing and adjustment performance are good. Since the rubber is used as the sealing ring, the compression and resilience are good (that is, it will not harden), so the sealing is good. The valve disc can perform sensitive flow control when it is opened between 15° and 70°.
4. Small operating torque and fluid resistance. According to measurements, the fluid resistance of butterfly valves is smaller than other types of valves except ball valves.
5. Due to the limitation of sealing material, the operating pressure and operating temperature range of butterfly valves are small.
The check valve is a valve used to prevent the medium in the pipeline from flowing back. It opens when the medium flows forward and automatically closes when the medium flows backward. It is generally used in pipelines that do not allow the medium to flow in the opposite direction to prevent the reverse flow of medium from damaging equipment and components.
Do not cause the rotary pump to reverse when the pump is stopped. In pipelines, check valves and closing valves are often used in series. This is due to the poor sealing of the check valve. When the medium pressure is small, a small part of the medium will leak, and a closing valve is required to ensure the closure of the pipeline.
The bottom valve is also a kind of check valve. It must be submerged in the water and is specially installed at the front end of the suction pipe of a water pump that cannot self-prime or does not have vacuum pumping and water diversion.
Transmission failure often manifests as valve stem jamming, inflexible operation, or valve inoperability.
Reason:
① The valve rusts after being closed for a long time;
② Improper installation operation damages the valve stem thread or valve stem nut;
③ The gate is stuck in the valve body by foreign matter;
④ The gate is often in a half-open and half-closed state, and the valve stem screw and the valve stem nut wire are misaligned, loosened.
⑤ Seized due to hydraulic or other impact forces;
⑥ The packing is pressed too tightly and the valve stem is locked;
⑦ The valve stem is pushed or stuck by the closing member.
Solution:
① Lubricate the transmission parts during maintenance.
② With the help of a wrench and tapping gently, the jamming and jamming can be eliminated;
③ Stop the water supply to repair or replace the valve.
Reasons for valve body damage and rupture:
① The corrosion resistance of the valve material decreases;
② Pipeline foundation settlement;
③ The pressure or temperature difference of the pipe network changes greatly;
④Water hammer;
⑤ Improper operation of the closing valve, etc.
Solve:
External causes should be eliminated promptly and valves or valves of the same model should be replaced.
The symptoms of valve leakage are:
① The valve stem core is leaking;
② The gland is leaking;
③ The flange rubber gasket is leaking.
④ Common reasons include:
⑤ The valve stem (valve shaft) is worn, corroded and peeled off, and the sealing surface appears pitted and peeled off;
⑥ Seal aging and leakage;
⑦ The gland bolts and flange connecting bolts are loose.
Solve:
① Add and replace sealing media during maintenance;
② Replace the new nut and readjust the position of the fastening bolt.
The symptoms of poor valve opening and closing include the valve not opening or closing, and the valve not operating normally.
The reasons are:
① The valve stem is corroded;
② The gate is stuck or the gate is rusted when it is closed for a long time;
③ The gate falls off;
④ Foreign matter is stuck in the sealing surface or sealing groove;
⑤ The transmission parts are worn and jammed.
Solve:
① Repair and lubricate transmission parts;
② Repeatedly open and close the valve and impact foreign objects with water;
③ Replace the valve.
The surface of the valve, the trapezoidal thread on the valve stem and valve stem nut, the sliding part of the valve stem nut and bracket, as well as gears, worm gears and other components are easily contaminated with dust, oil, media residue and other dirt, which will cause wear and corrosion to the valve. Therefore, it is necessary to keep the outside and moving parts of the valve clean; protect the integrity of the valve paint.
The trapezoidal thread of the valve, the sliding parts of the valve stem nut and bracket, the bearing parts, the meshing parts of gears and worm gears, worms, and other cooperating parts all require good lubrication conditions to reduce mutual friction and avoid mutual wear. Lubricated parts should be refueled regularly according to specific conditions.
