Description
The opening and closing part of the fire gate valve is the gate, and 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 has two sealing surfaces. The two sealing surfaces of the most commonly used pattern gate valve form a wedge shape. The wedge angle varies with the valve parameters, usually 50, and 2°52' when the medium temperature is not high. The gate of the wedge gate valve can be made into a whole, which is called a rigid gate; it can also be made into a gate that can produce a small amount of deformation to improve its manufacturability and compensate for the deviation of the sealing surface angle during processing. The plate is called the elastic gate.
The types of fire gate valves can be divided into wedge gate valves and parallel gate valves according to the sealing surface configuration. Wedge gate valves can be further divided into: single gate type, double gate type and elastic gate type; parallel gate valves It can be divided into single ram type and double ram type. According to the thread position of the valve stem, it can be divided into two types: rising stem gate valve and dark stem gate valve.
Working Principle
When the fire gate valve is closed, the sealing surface can be sealed only by the medium pressure, that is, relying on the medium pressure to press the sealing surface of the gate plate to the valve seat on the other side to ensure the sealing of the sealing surface, which is self-sealing. Most of the gate valve is forced seal, that is to say, when the valve is closed, the gate should be pressed to the valve seat by external force, so as to ensure the sealing surface sealing.
The gate valve of the fire gate valve moves in a straight line with the valve stem, which is called a lifting stem gate valve (also called a rising stem gate valve). Usually there is a trapezoidal thread on the lifter, and through the nut at the top of the valve and the guide groove on the valve body, the rotating motion is changed into a straight line motion, that is to say, the operating torque is changed into the operation thrust.
When the valve is opened, when the lift height of the gate plate 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 sign, that is, the position where the valve stem does not move is taken as its fully open position. In order to consider the locking phenomenon of temperature changes, it is usually opened to the top position, and then reversed 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 (that is, the stroke).
In some gate valves, the stem nut is set on the gate plate, and the rotation of the hand wheel drives the valve stem to rotate, and the gate plate is lifted. This kind of valve is called a rotary stem gate valve or a hidden stem gate valve.
