The gate valve is a gate that opens and closes. The movement direction of the gate is perpendicular to the direction of the fluid. The gate valve can only be fully opened and fully closed, and cannot be adjusted or throttled. The gate valve is sealed through the contact between the valve seat and the gate plate. Usually the sealing surface is surfacing with metal materials to increase wear resistance, such as 1Cr13, STL6, stainless steel, etc. Gates include rigid gates and elastic gates. According to the different gates, gate valves are divided into rigid gate valves and elastic gate valves.
Gate valve movement mode:
When the gate valve is closed, the sealing surface can be sealed only by the medium pressure, that is, the sealing surface of the gate plate is pressed to the valve seat on the other side by the medium pressure only to ensure the sealing of the sealing surface. This is self-sealing. Most gate valves adopt forced sealing, that is, when the valve is closed, external force must be relied on to force the gate plate to the valve seat to ensure the sealing performance of the sealing surface.
The gate plate of the gate valve moves linearly with the valve stem. It is a rising stem gate valve.
Usually there is a trapezoidal thread on the lift rod. Through the nut on the top of the valve and the guide groove on the valve body, the rotating motion is changed into linear motion, that is, the operating torque is changed into the operating thrust. When the valve is opened, when the lift height of the gate plate is equal to 1:1 times of the valve diameter, the fluid channel is completely unobstructed, but during operation, this position cannot be monitored.
In actual use, the top of the valve stem is used as a mark, that is, the position that does not open, as its fully open position. In order to consider the locking phenomenon due to temperature changes, the valve is usually opened to the top position and then retracted 1/2-1 turn as the fully open valve position.
Therefore, the fully open position of the valve is determined by the position of the gate plate (i.e. stroke). Some gate valve stem nuts are set on the gate plate, and the rotation of the handwheel drives the valve stem to rotate, thereby lifting the gate plate. This kind of valve is called Rotating rod gate valve or hidden rod gate valve.
Advantages of gate valves:
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 requires less 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 lifting and lowering is performed by a 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. Simple shape, short structural length, good manufacturing process and wide application range.
8. The structure is compact, the valve has good rigidity, the channel is smooth, and the flow resistance is small. The sealing surface is made of stainless steel and carbide, which has a long service life. It uses PTFE packing to ensure reliable sealing and light and flexible operation.
Disadvantages of gate valves:
1. Generally, gate valves have two sealing surfaces, and the processing and manufacturing are more complicated than globe valves.
2. There is relative friction between the sealing surfaces, resulting in greater wear and tear. It is inconvenient to repair the sealing surfaces after wear.
3. The structural size of the middle cavity of the valve is large, resulting in a long structural length, large external dimensions, and large installation space. Large-diameter gate valves are especially bulky.
4. The valve takes a long time to open and close.
5. It can form a closed valve cavity, so if necessary, a pressure relief structure should be installed to prevent abnormal pressure increase in the middle cavity.
Gate valve features:
The body is made of high-grade ductile iron, which is about 20% to 30% lighter than traditional gate valves and is easy to install and maintain.
Flat bottom gate seat:
Traditional gate valves often have foreign objects such as stones, wood blocks, cement, iron filings, debris, etc. accumulated in the groove at the bottom of the valve after the pipe is washed with water, which can easily cause leakage due to inability to close tightly. The elastic seat seals the bottom of the gate valve. It adopts the same flat bottom design as the water pipe machine, which is not easy to cause debris accumulation and allows the fluid to flow smoothly.
Overall rubber coating:
The gate is made of high-quality rubber for the entire inner and outer cover. European rubber vulcanization technology enables the vulcanized gate to ensure precise geometric dimensions, and the rubber and ductile cast gate are firmly connected, not easy to fall off, and have good elastic memory.
Precision cast valve body:
The valve body is precision cast, and its precise geometric dimensions ensure the sealing of the valve without any finishing work inside.
Precautions for gate valves:
1. The handwheel, handle and transmission mechanism are not allowed to be used for lifting, and collision is strictly prohibited.
2. Double-gate gate valves should be installed vertically (that is, the valve stem is in a vertical position and the handwheel is at the top).
3. Before opening the gate valve with a bypass valve, the bypass valve should be opened first (to balance the pressure difference between the inlet and outlet and reduce the opening force).
4. Gate valves with transmission mechanisms should be installed according to the product instruction manual.
5. If the valve is frequently used on and off, lubricate it at least once a month.
6. The gate valve is only used to fully open or fully close the medium running on various pipelines or equipment, and is not allowed to be used for throttling.
7. For gate valves with handwheels or handles, no additional auxiliary levers are allowed during operation (if the seal is not tight, the sealing surface or other parts should be inspected and repaired). Turn the handwheel and handle clockwise to turn off, and vice versa to turn on. Gate valves with transmission mechanisms should be used according to the product instructions.
1. The installation position, height, and entrance and exit directions must meet the design requirements, and the connections should be firm and tight.
2. The handles of various manual valves installed on insulated pipes must not be downwards.
3. Appearance inspection must be carried out before the valve is installed. The nameplate of the valve should comply with the current national standard “General Valve Marking” GB 12220. For valves with a working pressure greater than 1.0 MPa and which function as a cut-off on main pipes, strength and tight performance tests should be conducted before installation, and they can only be used after passing the test.
During the strength test, the test pressure is 1.5 times the nominal pressure and the duration is no less than 5 minutes. The valve shell and packing should be free of leakage to be qualified. During the tightness test, the test pressure is 1.1 times the nominal pressure; the test pressure should comply with the requirements of the GB 50243 standard for the duration of the test, and the sealing surface of the valve disc is deemed to be qualified if there is no leakage.
4. The handwheel, handle and transmission mechanism are not allowed to be used for lifting, and collision is strictly prohibited.