Gate valve introduction-The opening and closing part of the gate valve is the gate. The movement direction of the gate valve is perpendicular to the fluid direction. The gate valve can only be fully opened and fully closed, and cannot be adjusted and throttled. The ram has two sealing surfaces. The most commonly used mode is that the two sealing surfaces of the ram valve form a wedge. The wedge angle varies with the valve parameters, usually 50. When the medium temperature is not high, it is 2 ° 52 ‘. The gate of wedge gate valve can be made into a whole, which is called rigid gate; It can also be made into a ram that can produce slight deformation to improve its processability and make up for the deviation of sealing surface angle during processing. This ram is called elastic ram.
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 valve is pressed against the valve seat on the other side by the medium pressure to ensure the sealing of the sealing surface, which is self sealing. Most gate valves are forced sealed, that is, when the valve is closed, the gate must be forced to the valve seat by external force to ensure the tightness of the sealing surface.
The gate valve whose gate moves linearly with the valve stem is called the lifting rod gate valve (also called the rising rod gate valve). Generally, the lifting rod is provided with trapezoidal thread. Through the nut at the top of the valve and the guide groove on the valve body, the rotary motion is changed into linear motion, that is, the operating torque is changed into operating thrust.
When the valve is opened, when the lifting height of the ram is equal to 1:1 times of the valve diameter, the fluid channel is completely unblocked, but this position cannot be monitored during operation. In actual use, the apex of the valve stem is taken as the mark, that is, the position where the valve stem cannot be opened is taken as its full open position. In order to consider the locking phenomenon caused by temperature change, it is usually turned back 1 / 2-1 circle at the position of the top as the position of fully opening the valve. Therefore, the fully open position of the valve shall be determined according to the position of the RAM (i.e. stroke >.
For some gate valves, the valve stem nut is set on the gate, and the rotation of the hand wheel drives the valve stem to rotate and lift the gate. This valve is called a rotating stem gate valve or a non rising stem gate valve.
Advantages of gate valve:
- The fluid resistance is small, and the sealing surface is subject to medium brushing and erosion.
- Opening and closing is labor-saving.
- The flow direction of the medium is not restricted, and the flow is not disturbed and the pressure is not reduced.
- Simple shape, short structure length, good manufacturing process and wide application range.
Disadvantages of gate valve
- It is easy to cause erosion and scratch between the sealing surfaces, and it is difficult to maintain.
- The overall size is large, and the opening and closing time is long.
- The structure is complicated.
The types of gate width can be divided into wedge gate valve and parallel gate valve according to the sealing surface configuration. Wedge gate valve can be divided into single gate type, double gate plate type and elastic gate type; Parallel gate valve can be divided into single gate plate and double gate plate. According to the thread position of the valve stem, it can be divided into two types: rising stem gate valve and Non rising stem gate valve.
Precautions for gate valves
- Handwheel, handle and transmission mechanism are not allowed to be used for lifting, and collision is prohibited.
- Double gate valves shall be installed vertically (i.e. the valve stem is in the vertical position and the handwheel is on the top).
- The gate valve with bypass valve shall be opened before opening (to balance the pressure difference between the inlet and outlet and reduce the opening force).
- The gate valve with drive mechanism shall be installed according to the product instruction manual.
- If the valve is used frequently, lubricate it at least once a month.