- Rising stem valve
Turn the handwheel and advance or retreat the thread between the handwheel and the valve stem to lift or lower the valve plate connected to the valve stem to open and close.
- Advantages of rising stem gate valve:
The fluid resistance is small, and the sealing surface is less eroded and eroded by the medium.
Opening and closing requires less effort.
The flow direction of the medium is not restricted, and there is no flow disturbance or pressure reduction.
It has a simple shape, short structural length, good manufacturing process, and wide application range.
- Disadvantages of rising stem gate valve:
Erosion and scratches can easily occur between the sealing surfaces, making maintenance difficult.
The overall size is large, it requires a certain amount of space to open, and it takes a long time to open and close.
The structure is more complex.
- Concealed stem valve
Concealed stem gate valve is also called rotating stem gate valve (also called concealed stem wedge gate valve). The valve stem nut is set on the gate plate. The rotation of the handwheel drives the valve stem to rotate, which lifts the gate plate. There is usually a trapezoidal thread at the bottom of the valve stem. The rotating movement is carried out through the thread at the bottom of the valve and the guide groove on the valve disc. It changes into linear motion, that is, the operating torque is changed into 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 caused by temperature changes, the valve is usually opened to the top position and then retracted 1/2 to 1 turn as the fully open valve position. Therefore, the fully open position of the valve is determined by the position of the gate (i.e. stroke).
The advantage of this structure is that the height of the gate valve always remains unchanged, so the installation space is small, and it is suitable for gate valves with large diameters or limited installation space. This structure should be equipped with an opening and closing indicator to indicate the degree of opening and closing.
The disadvantage of this structure is that the valve stem thread is not only unable to be lubricated, but also directly eroded by the medium and easily damaged.
- Exposed pole VS concealed pole
1. The lead screw cannot be seen in concealed stem valves, while the lead screw can be seen in open stem valves.
2. The lifting screw of the concealed stem flange gate valve only rotates without moving up and down. Only a rod is exposed, and its nut is fixed on the gate plate. The gate plate is lifted by the rotation of the screw, and there is no visible door frame. ; The lifting screw of the rising stem flange gate valve is exposed, and the nut is close to the handwheel and is fixed (does not rotate or move axially). The gate is lifted by rotating the screw. The screw and the gate only have relative rotational movement. There is no relative axial displacement, and the appearance is a door-shaped bracket.
3. The steering wheel and the valve stem of the concealed stem valve are connected together and are relatively immobile when opening and closing. It opens and closes by rotating the valve stem at a fixed point to drive the valve disc upward and lower the gate. The rising stem valve uses threaded transmission between the valve stem and the steering wheel to lift or lower the valve disc. To put it simply, in a rising stem valve, the valve disc moves up and down together with the valve stem, and the steering wheel is always at a fixed point.