There are many types of valves used in water treatment, such as: gate valves, globe valves, butterfly valves, check valves, plug valves, throttle valves, safety valves, and pressure reducing valves, etc.

I. Gate Valve

Purpose:

It is a commonly used shut-off valve that uses a gate (the closing member; in a gate valve, the closing member is called a gate or gate valve, and the valve seat is called the gate seat or gate seat) to connect (fully open) and shut off (fully closed) the medium in the pipeline. It is not allowed to be used for throttling, and during use, avoid slightly opening the gate, as 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 centerline of the gate seat channel, like a gate, cutting off the medium in the pipeline, hence the name gate valve.

Features:

1. Small flow resistance. The medium channel inside the valve body is straight through, and the medium flows in a straight line, with small flow resistance.

2. Less effort required for opening and closing. Compared with globe valves, because whether it is open or closed, the direction of the gate movement is perpendicular to the direction of the medium flow.

3. Large height, long opening and closing time. The opening and closing stroke of the gate is large, and the lifting is done through the screw rod.

4. Water hammer phenomenon is not easy to occur. Due to the long closing time.

5. The medium can flow in any direction on both sides, easy to install. The two sides of the gate valve channel are symmetrical.

6. Small structural length (the distance between the two connecting end faces of the shell).

7. The sealing surface is easily worn, affecting the service life. When opening and closing, the two sealing surfaces of the gate and valve seat rub and slide against each other. Under the action of medium pressure, scratches and wear are easily generated, affecting the sealing performance and shortening the service life.

8. Relatively expensive. There are many contact sealing surfaces, the processing is more complex, especially the sealing surface on the gate seat is not easy to process, and there are more parts.

II. Globe Valve

Purpose:

A globe valve is a type of shut-off valve that controls the opening and closing of the pipeline by moving the valve disc (the closing member of the globe valve) along the centerline of the valve seat (valve seat) channel. Globe valves are generally suitable for various pressures and temperatures, within the specified standard range, for transporting liquid and gaseous media, but not for transporting liquids containing solid sediments or precipitated crystals. In low-pressure pipelines, globe valves can also be used to regulate the flow rate of the medium in the pipeline. Due to structural limitations, the nominal diameter of globe valves 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 adjusting the flow rate, a throttle valve must be used.

Features:

1. The wear and tear of the sealing surface is not serious, so the work is more reliable and the service life is long.

2. The sealing surface area is small, the structure is simple, and the man-hours required for manufacturing the sealing surface and the precious materials required for the sealing ring are less than those of gate valves.

3. When opening and closing, the valve disc stroke is small, so the globe valve height is small. Easy to operate.

4. Using threads to move the valve disc will not cause sudden opening and closing, and it is not easy to cause a "water hammer" phenomenon.

5. The opening and closing torque is large, and the opening and closing is more laborious. When closing, the direction of movement of the valve disc is opposite to the direction of the medium pressure, and the force of the medium must be overcome, so the opening and closing torque is large, which affects the application of large-diameter globe valves.

6. The flow resistance is relatively large. Among various shut-off valves, the flow resistance of globe valves is the largest (the medium channel is more tortuous).

7. The structure is more complex.

8. The flow direction of the medium is unidirectional. The medium should be ensured to flow from bottom to top.

III. Butterfly Valve

Purpose:

A butterfly valve is a rotary valve that uses a disc-type (also known as a butterfly plate) closing member to rotate 90° or about 90° to open and close the channel. The movement of the butterfly valve valve disc has a wiping property, so most butterfly valves can be used for media with suspended solid particles.

Commonly used butterfly valves include wafer-type butterfly valves and flanged butterfly valves. Wafer-type butterfly valves use double-headed bolts to connect the valve between two pipeline flanges, and flanged butterfly valves have flanges on the valve, and the two end flanges of the valve are connected to the pipeline flanges with bolts.

Features:

1. Small overall dimensions, short length, simple structure, and light weight.

2. Easy to operate, quick opening and closing, only 90° rotation of the valve disc is required for opening and closing.

3. Good sealing and regulating performance. Because rubber is used as the sealing ring, the compression and rebound are good (i.e., it will not harden), so the sealing performance is good. The valve disc can perform sensitive flow control when opened by 15°～70°.

4. Small operating torque and fluid resistance. According to measurements, the fluid resistance of butterfly valves is smaller than that of other types of valves except ball valves.

5. Due to the limitations of the sealing material, the operating pressure and temperature range of butterfly valves are relatively small.

IV. Check Valve

Purpose and Features:

A check valve is a valve used to prevent the backflow of the medium in the pipeline. It opens when the medium flows in the forward direction and automatically closes when the medium flows in the reverse direction. It is generally used in pipelines where the medium is not allowed to flow in the reverse direction to prevent the reverse flow medium from damaging equipment and parts. When the pump stops running, it prevents the rotary pump from reversing. In the pipeline, the check valve and the shut-off valve are often used together. This is because the check valve has poor sealing performance. When the medium pressure is low, a small part of the medium will leak, and a shut-off valve is needed to ensure the closure of the pipeline. The foot valve is also a type of check valve, which must be submerged in water and is specifically installed at the front end of the suction pipe of a water pump that cannot self-prime or does not have vacuum degassing water intake.

V. Plug Valve

Purpose:

A plug valve is a valve in which a closing member (a plug with a passage) rotates around the centerline of the valve body to achieve opening or closing. It used to be called a plug valve, also known as a cock. It is widely used in pipelines conveying media with a temperature ≤120℃. Due to thermal expansion of the plug and shell, jamming may occur, so it is less used at high temperatures. Plug valves can be used to shut off the flow of media, and can also be used as regulating valves, three-way valves, four-way valves, and distribution valves or to change the flow direction of the media.

Features:

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

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

3. When there is considerable pressure of the medium in the pipeline, the rapid closure may cause a "water hammer" phenomenon.

4. It takes more effort to rotate the plug (large sealing surface).

5. It can be installed horizontally or vertically.

6. The conical surface where the valve body and plug contact is relatively large, and it is easy to wear during use, affecting the sealing. If a non-sealed structure is used and grease is injected into the sealing surface to create an oil film, the sealing performance can be improved.

VI. Throttle Valve

Purpose and Features:

A throttle valve regulates the flow and pressure of the medium in the pipeline by changing the cross-sectional area of the valve passage. The smaller the cross-sectional area, the greater the resistance experienced by the medium passing through, and the smaller the flow rate. In fact, all kinds of shut-off valves can regulate the flow rate, but because the connection between the closing member and the valve stem is movable, there is a gap at the connection, so during the change process, the rise and fall of the closing member and the change of the passage area are not easily proportional, and the regulation performance is not good, so a special throttle valve is used for regulation. Throttle valves cannot be used as shut-off valves, generally do not have sealing surfaces, even if they have sealing surfaces, the sealing surfaces are quickly eroded under the action of high-speed media, losing their sealing properties. Therefore, throttle valves in pipelines cannot replace the function of shut-off valves.

VII. Safety Valve

Purpose and Features:

A safety valve is a protective valve. It is installed on pressure vessels, containers, and pipelines. The safety valve is normally closed under external force. When the pressure of the medium in the protected pipeline exceeds the specified value, the valve disc automatically opens, discharging excess medium to reduce the pressure; when the medium pressure returns to within the specified value, it automatically closes. The safety valve plays a role in ensuring the safe operation of the system and equipment in the pipeline. Safety valves are widely used in boilers, compressor air storage cylinders, high-pressure containers, and pipelines, etc., on equipment where the working pressure of the medium may exceed the allowable value, causing a risk of explosion.

VIII. Pressure Reducing Valve

Purpose and Features:

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