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2022

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08

The uses and characteristics of various water treatment valves

Author:


It 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. Gate valve    

  

use:

It 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.    

 

Features:

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 the lowering is carried out through the screw.

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 it easy to install. 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 the 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 complicated. Especially the sealing surface on the gate seat is difficult to process and has many parts.

 

2. Stop valve

use:

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.    

 

Features:

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. The large opening and closing torque requires more effort to open and close. When closing, the movement direction of the valve disc is opposite to the direction of the pressure of the medium movement, and the force of the medium must be overcome, so the opening and closing torque is large. Therefore, it affects the application of large diameter stop valves.

6. The flow resistance is large. The flow resistance of stop valves is greater among various types of stop valves. (The medium channel is relatively tortuous)

7. The structure is complex.

8. The medium flow direction is one-way. It should be ensured that the medium flows from bottom to top, so the medium must flow in one direction.

 

3. Butterfly valve

use:

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.

 

Features:

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 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 .

 

 

4. Check valve

 

Purpose and features:

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 also has a check valve, which must be submerged in the water and 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.

 

5. Plug valve

use:

Plug valve refers to a valve in which the closing member (plug with channel) rotates around the center line of the valve body itself to open or close. It used to be called cock, also known as cock. It is widely used in pipelines transporting media with temperature ≤120℃. Since the plug and shell expand due to heat, jamming may occur, so they are rarely used at high temperatures. The plug valve can be used to cut off the flow of the medium, and can also be used as a regulating valve, a three-way valve, a four-way valve, a distribution valve or to change the flow direction of the medium.    

 

Features:

1. The resistance is small when the medium passes through, especially the straight-through type.

2. Simple structure, light weight, small size, convenient and quick operation.

3. When there is considerable pressure in the medium in the pipeline, "water hammer" may occur due to rapid closing.

4. It is laborious to turn the plug (the sealing surface is large).

5. Can be installed horizontally or vertically.

6. The cone surface in contact between the valve body and the plug is large, which is easy to wear during use and affects the sealing. If an unsealed structure is used, injecting grease on the sealing surface to create an oil film can improve the sealing performance.

 

6. Throttle valve

Purpose and features:

The throttle valve adjusts the flow and pressure of the pipeline medium by changing the cross-sectional area of ​​the valve channel. The smaller the cross-sectional area, the greater the resistance to the passing medium and the smaller the flow rate. In fact, all kinds of cut-off valves can adjust the flow, but because the connection between the opening and closing parts and the valve stem is movable, there is a gap at the connection. Therefore, during the change process, the lifting and lowering of the opening and closing parts and the change of the channel area are not easy to cause. The proportion and adjustment performance are not good, so a special throttle valve is used for adjustment. The throttle valve cannot be used as a cut-off valve and generally does not have a sealing surface. Even if it does have a sealing surface, the sealing surface will be quickly eroded under the action of high-speed media and lose its sealing properties. Therefore, the throttle valve on the pipeline cannot replace the function of the closed-circuit valve.   

 

7. Safety valve

Purpose and features:

The safety valve is a protective valve. It is installed on pressure equipment, vessels and pipelines. The safety valve is in a normally closed state due to external force. When the pressure of the protected pipeline medium exceeds the specified value, the valve flap automatically opens, discharges the excess medium, and causes the pressure to drop; and when the medium pressure returns to within the specified value, it automatically closes again. Safety valves play a role in ensuring the safe operation of systems and equipment on pipelines. Safety valves are widely used in equipment such as boilers, compressor gas tanks, high-pressure vessels and pipelines where the working pressure of the medium may exceed the allowable value, causing the risk of explosion.

 

8. Pressure reducing valve

Purpose and features:

The pressure reducing valve reduces the medium pressure in the equipment container or pipeline to a specified pressure, and can still maintain the outlet pressure within a certain range when the inlet pressure changes and the flow outlet changes. The pressure reducing valve uses flow control to reduce pressure, making it suitable for the needs of various production processes.