Rising Stem Gate Valve Vs. Non-rising Stem Gate Valve

Rising stem gate valve VS concealed stem gate valve

Gate Valve is a gate valve of the opening and closing part. The movement direction of the gate valve 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.

Rising stem valve

Turn the handwheel, and lift or lower the valve plate connected to the valve stem through the advance and retreat of the thread of the handwheel and the valve stem to achieve the function of opening and closing.

Advantages of rising stem gate valve:

Small fluid resistance, and the sealing surface is less eroded and corroded by the medium.

Opening and closing is more labor-saving.

The flow direction of the medium is not restricted, and there is no disturbance or pressure reduction.

Simple shape, short structural length, good manufacturing processability, and wide range of applications.

Disadvantages of rising stem gate valve:

Erosion and scratches are easily caused between the sealing surfaces, and maintenance is relatively difficult.

Large external dimensions, a certain space is required for opening, and the opening and closing time is long.

The structure is more complex.

The concealed stem gate valve is also called the rotary stem gate valve (also called the concealed stem wedge gate valve). The valve stem nut is set on the gate plate. The handwheel rotates to drive the valve stem to rotate, and the gate plate is lifted. Usually, there is a trapezoidal thread at the bottom of the valve stem. Through the thread at the bottom of the valve and the guide groove on the valve disc, the rotary motion is converted into linear motion, that is, the operating torque is converted into operating thrust.

When the valve is opened, when the gate plate lifting height is equal to 1:1 times the valve diameter, the fluid channel is completely unblocked, but this position cannot be monitored during operation. In actual use, the top of the valve stem is used as a mark, that is, the position where it cannot be opened, as its fully open position. In order to consider the locking phenomenon caused by temperature changes, it is usually opened to the top position, and then retracted 1/2~1 turn as the position of the fully open valve. Therefore, the fully open position of the valve is determined by the position of the gate plate (i.e., the stroke).

The advantages of this structure are: 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 disadvantages of this structure are: the valve stem thread is not only unable to be lubricated, but also directly corroded by the medium and easily damaged.

1 The screw cannot be seen in the concealed stem valve, while the screw can be seen in the exposed stem valve.

2 The lifting screw of the concealed stem flange gate valve only rotates without moving up and down. Only a rod is exposed. Its nut is fixed on the gate plate. The gate plate is lifted by rotating the screw. There is no visible door frame; the lifting screw of the exposed stem flange gate valve is exposed, and the nut is close to the handwheel and is fixed (no rotation or axial movement). The gate plate is lifted by rotating the screw. The screw and the gate plate only have relative rotational movement without relative axial displacement. The appearance is a door-shaped bracket.

3 When the concealed stem valve is switched, the steering wheel and the valve stem are connected together and relatively immobile. It is opened and closed by rotating the valve stem at a fixed point to drive the valve disc to lift up and down. The rising stem valve raises or lowers the valve disc through the threaded transmission between the valve stem and the steering wheel. To put it simply, the rising stem valve is a valve disc that moves up and down together with the valve stem, and the steering wheel is always at a fixed point.