The opening and closing member of the gate valve is a gate. The direction of movement of the gate is perpendicular to the direction of the fluid. The gate valve can only be fully open and fully closed, and cannot be adjusted and throttled. The gate has two sealing faces. The two sealing faces of the most common mode gate valves form a wedge shape. The wedge angle varies with the valve parameters, usually 50, and is 2°52' when the medium temperature is not high.
The gate of the wedge gate valve can be made into a whole, called a rigid gate; it can also be made into a gate that can produce a small amount of deformation to improve its processability and make up for the deviation of the sealing surface angle during the machining process. The board is called a resilient shutter. When the gate valve is closed, the sealing surface can be sealed only by the medium pressure, that is, the sealing surface of the ram 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 of the gate valves are forced to seal, that is, when the valve is closed, the external force is forced to press the gate to the valve seat to ensure the sealing of the sealing surface. The gate of the gate valve moves linearly with the valve stem. The liftgate gate valve is also called the open gate valve. Usually there is a trapezoidal thread on the lifting rod, and the rotary motion is changed into a linear motion by the nut at the top end of the valve and the guide groove on the valve body, that is, the operating torque is changed to the operating thrust. When the valve is opened, when the lifting height of the gate is equal to 1:1 times the diameter of the valve, the passage of the fluid is completely unblocked, but this position cannot be monitored during operation. In actual use, the apex of the valve stem is used as a mark, that is, the position where the valve is opened, as its fully open position. In order to consider the temperature change, the lock phenomenon occurs, usually at the position of the opening to the apex, and then back to 1/2-1 circle as the position of the fully open valve. Therefore, the fully open position of the valve is determined by the position of the shutter, that is, the stroke. In some gate valves, the stem nut is arranged on the gate plate, and the rotation of the hand wheel drives the valve stem to rotate, and the shutter is lifted. This valve is called a rotary lever gate valve or a dark rod gate valve.
The disadvantages of the gate valve are as follows:
1. It is easy to cause erosion and abrasion between the sealing surfaces of the gate valve, and maintenance is difficult.
2. The gate valve has a large outer shape, requires a certain space for opening, and has a long opening and closing time.
3. The structure of the gate valve is more complicated.
The gate valve has the following advantages:
1. The gate valve has small fluid resistance, and the sealing surface is less brushed and eroded by the medium.
2. The gate valve is easier to open and close.
3. The flow direction of the gate valve medium is not restricted, no disturbance, no pressure reduction.
4. The gate valve has a simple shape, short structure length, good manufacturing process and wide application range.
The types of gate valves can be divided into wedge gate gate valves and parallel gate gate valves according to the sealing surface configuration. The wedge gate gate valves can be further divided into: single gate type, double gate type and elastic gate type; parallel gate type gate valves can be Divided into single gate type and double gate type. According to the thread position of the valve stem, it can be divided into two types: open gate valve and dark gate valve.
The following matters should be noted for the installation and maintenance of the gate valve:
1. The gate valve handwheel, handle and transmission mechanism are not allowed to be used for lifting, and collision is strictly prohibited.
2. The gate valve double gate should be installed vertically, that is, the valve stem is in the vertical position, and the hand wheel is at the top.
3. The gate valve with the bypass valve should open the bypass valve before opening to balance the pressure difference between the inlet and outlet and reduce the opening force.
4. For the gate valve with transmission mechanism, install according to the product manual.
5. If the gate valve is used frequently, it should be lubricated at least once a month.