There are many types of valves used in water treatment, such as: gate valves, globe valves, butterfly valves, check valves, plug valves, valves, safety valves, and pressure reducing valves.
1. Gate Valve
Usages:
This is the most commonly used on-off valve, which uses a gate (i.e., the opening and closing member, referred to as a or door in a gate valve, and the valve seat is referred to as a gate seat or door seat) to connect (fully open) and shut off ( closed) the medium in the pipeline. It is not allowed to be used as a throttle, and during use, it should avoid partially opening the gate because the of high-speed flowing media can accelerate the damage to the sealing surface. The gate moves up and down in a plane perpendicular to the centerline of the gate seat, like a door, to shut off the medium in the pipeline, hence it is called a gate valve.
Features:
- Low fluid resistance. The internal medium passage of the valve body is straight, the medium flows in a straight line, and fluid resistance is small.
- Less force required for opening and closing. Compared with globe valves, gate valves require less force to open and close because the gate perpendicular to the direction of the medium flow, whether opening or closing.
- High height and long opening and closing time. The gate has a large travel distance and the lifting is done through a screw.
- Water hammer is unlikely to occur. This is due to the long closing time.
- The medium can in any direction on both sides, making it easy to install. The passages on both sides of the gate valve are symmetrical.
- Short structural length (the between the two connection ends of the shell).
- The sealing surface is prone to wear, affecting the service life. During opening and closing, the gate and valve seat's two sealing surfaces rub against each other, and under the action of medium pressure, they are prone to wear, affecting the sealing performance and shortening service life.
- High price. There are many contact sealing surfaces, the processing is complex, especially the sealing surface on the gate seat is difficult to process and there are many parts.
2. Globe Valve
Usages:
The globe valve is a type of closed circuit valve that controls the opening and closing of pipelines by moving the valve disc (the closing element the globe valve) along the centerline of the valve seat passage. The globe valve is generally suitable for various pressures and temperatures within the specified standard range, for liquid and gas media, but it is not suitable for conveying liquids containing solid precipitates or crystalline substances. In low-pressure pipelines, globe valves can also be to regulate the flow of media in the pipeline. Due to structural limitations, the nominal diameter of globe valves is below 250mm. In pipelines with media pressure and higher flow velocity, the sealing surface will wear out quickly. Therefore, when flow regulation is required, a throttle valve must be used.
Features:
- The wear and scratch of the sealing surface are not serious, so the work is more reliable and the service life is long.
- The sealing surface area is small, the structure is simple, the working hours required to manufacture the sealing surface and the expensive materials required for the sealing ring are than those of the gate valve.
- The valve disc travel is small when opening and closing, so the height of the globe valve is small. It is to operate.
- The valve disc is moved by the screw thread, so there is no sudden opening and closing phenomenon, and it is not easy to cause "water hammer" phenomenon.
- The opening and closing torque is large and it is laborious to open and close. When closing, the movement direction of valve disc is opposite to the direction of the medium movement pressure, so it is necessary to overcome the action force of the medium, thus the opening and closing torque large, which affects the application of large diameter globe valves.
- The flow resistance is large. Among various shut-off valves, the flow resistance of the globe is the largest (the medium passage is more tortuous).
- The structure is more complex.
- The medium flow direction is unidirectional. It ensure that the medium flows from bottom to top.
Usages:
A butterfly valve is a rotary valve that uses a disc-shaped (also known as a butterfly plate) closure member to open and close the passage rotating it 90° or approximately 90°. The movement of the butterfly valve's closure member has a wiping action, making most butterfly valves suitable media with suspended solid particles. There are two common types of butterfly valves: wafer type and flanged type. Wafer type butterfly valves are connected between two flanges using double-headed bolts, while flanged type butterfly valves have flanges on the valve itself, and are connected to the pipeline flanges using bolts.
Features:
- Compact size, short length, simple structure, and light weight.
- Easy operation, quick opening and closing, only need rotate the valve flap 90°.
- Good sealing and regulating performance, using rubber as the sealing ring, with good compression and resilience (i., will not harden), so the sealing performance is good. The valve flap can perform sensitive flow control when opened from 15° to 70.
- Small operating torque and fluid resistance. According to measurements, the fluid resistance of butterfly valves is less than that of other types of valves except ball.
- Due to the limitations of the sealing material, the operating pressure and working temperature range of butterfly valves are relatively small.
4. Check Valve
Usages and Features:
A check valve, also known as a non-return valve, is a type of valve that prevents the backflow of media in pipelines. opens when the media flows in the forward direction and automatically closes when the media flows in the reverse direction. It is typically used in pipelines where media is not allowed flow in the opposite direction, to prevent damage to equipment and machinery from reverse flow. When a pump stops running, it prevents the rotation of the pump in the direction. In pipelines, check valves are often used in series with shut-off valves. This is because the seal of a check valve is relatively poor, and when media pressure is low, a small amount of media may leak, so a shut-off valve is needed to ensure the pipeline is closed. A foot valve is also type of check valve that must be submerged in water and is specifically installed at the front end of the suction pipe of a pump that cannot self-prime or does have a vacuum suction to draw water.
5. Cock Valve
Usages:
The plug valve refers to a type of valve where the closure member (a plug with a passage) rotates around the centerline of the valve to achieve opening or closing. It is widely used in pipelines conveying media with temperatures ≤120℃. Due to the thermal expansion of the plug and the body, it may cause jamming, so it is less used at high temperatures. The plug valve can be used to cut off the flow of media, and can also be used as a control valve, three-way valve, four-way valve, or distribution valve, as well as to change the direction of the media flow.
Features:
- The resistance is relatively small when the medium passes through, especially for the straight-through type.
- Simple structure, light weight, size, convenient and fast operation.
- When there is considerable pressure of the medium in the pipeline, "water hammer" may occur due to rapid closure.
- Turning the plug is laborious (large sealing surface).
- Can be installed horizontally or vertically.
- The cone surface in contact between the valve body the plug is large, which is prone to wear during use and affects the seal. If a sealed structure is adopted, injecting grease into the sealing surface to form oil film can improve the sealing performance.
6. Throttle Valve
Usages and Features:
The throttle valve regulates the flow and pressure of the pipeline medium by changing the cross-sectional area of the valve passage. The smaller the cross area, the greater the resistance to the medium, and the smaller the flow. In fact, all kinds of shut-off valves can regulate flow, but because the between the closure member and the valve stem is movable, there is a gap at the connection, so during the process of change, the rise and fall of the member is not easily proportional to the change in passage area, resulting in poor regulation performance. Therefore, a special throttle valve is used for regulation. The throttle valve be used as a shut-off valve, generally it does not have a sealing surface, even if it has a sealing surface, the sealing surface is quickly eroded the action of high-speed medium, losing its sealing property. Therefore, the throttle valve on the pipeline cannot replace the function of a shut-off valve.
7. Safety Valve
Usages and Features:
A safety valve is a protective valve. It is installed on pressurized equipment, containers, and pipelines. The safety valve remains closed under conditions. When the pressure of the medium in the protected pipeline exceeds the specified value, the valve disc automatically opens to discharge the excess medium, thereby reducing the; and when the medium pressure returns to within the specified range, it automatically closes. The safety valve ensures the safe operation of the system and equipment on the pipeline Safety valves are widely used on boilers, compressor air receivers, high-pressure containers, and pipelines where the working pressure of the medium may exceed the allowed value and cause hazards.
8. Pressure Reducing Valve
Usages and Features:
The pressure reducing valve reduces the pressure of the medium in the equipment container or pipeline to the specified pressure, and maintains the outlet pressure within a range despite changes in inlet pressure or outlet flow. The pressure reducing valve achieves pressure reduction by regulating the flow, making it suitable for the needs of various production processes.