Gate valve
A gate valve is a gate plate of an opening and closing part. The movement direction of the gate plate is perpendicular to the direction of the fluid. The gate valve can only be fully opened and closed, and cannot be adjusted or throttled.
Turn the handwheel to advance or retreat through the thread of the handwheel and the stem to raise or lower the valve plate connected to the stem to achieve opening and closing.
Advantages of rising stem gate valve
The fluid resistance is small, and the sealing surface is less eroded and eroded by the medium.
Less effort to open and close.
The flow direction of the medium is not restricted, without disturbing the flow or reducing the pressure.
The shape is simple, the structure length is short, the manufacturing process is good, and the application range is wide.
Disadvantages of rising stem gate valve
Erosion and scratches are easily caused between the sealing surfaces, and maintenance is difficult.
The external dimensions are large, and a certain space is required for opening, and the opening and closing time is long.
The structure is more complicated.
The non rising stem gate valve is also called the rotating rod gate valve (also called the hidden rod wedge gate valve). The stem nut is set on the gate, and the rotation of the hand wheel drives the stem to rotate, and the gate is lifted. Usually, the bottom end of the stem has a trapezoidal thread. The thread at the bottom of the valve and the guide groove on the valve flap will rotate. It becomes linear motion, that is, it changes the operating torque to the operating thrust.
When the valve is opened, when the lifting height of the gate is equal to 1:1 of the valve diameter, the fluid channel is completely clear, but during operation, this position cannot be monitored. In actual use, the apex of the valve stem is used as a mark, that is, the position where it cannot be moved, as its fully open position. In order to consider the phenomenon of temperature lock-up, it is usually opened to the apex position, and then rewinded 1/2 to 1 circle as the position of the fully open valve. Therefore, the fully open position of the valve is determined according to the position of the gate (ie, stroke).
Advantage
The height of the gate valve always remains the same, so the installation space is small, suitable for gate valves with large diameter or limited installation space.
This structure should be equipped with an opening and closing indicator to indicate the degree of opening and closing.
Disadvantages
The stem thread is not only unable to lubricate, but also directly damaged by medium erosion.
