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Non rising stem gate valve is also called rotary stem gate valve (also called non rising stem wedge gate valve). The valve stem nut is set on the gate, and the handwheel rotation drives the valve stem to rotate, so as to lift the gate. Generally, there are trapezoidal threads at the bottom end of the valve stem. Through the thread at the bottom end of the valve and the guide groove on the valve disc, the rotary motion is changed into linear motion, that is, the operating torque is changed into the operating thrust. When the non rising stem gate valve is opened, when the lifting height of the ram is equal to 1:1 of the valve diameter, the fluid channel is completely unblocked, but in operation, this position cannot be monitored. In actual use, the apex of the valve stem is used as the mark, that is, the position that can not be opened is used as its full open position. In order to consider the lock phenomenon of temperature change, usually in the open to the top position, and then back 1 / 2 ~ 1 turn, as the full open valve position. Therefore, the full open position of the valve is determined by the position of the RAM (i.e. stroke).
As one of the most professional non-rising stem gate valve manufacturers in China, Mstnland provides different kinds of non-rising stem gate valves for customers to choose from.
1. The stem of the rising stem gate valve is exposed and can be seen, while the stem of the non rising stem gate valve is not seen in the valve body;
2. The rising stem gate valve drives the gate up and down through the thread transmission between the stem and the steering wheel; the non rising stem gate valve drives the gate up and down through the rotation of the stem at a fixed point. When switching, the steering wheel and the stem are connected and relatively fixed.
3. The transmission thread of the non rising stem gate valve is located inside the valve body. During the opening and closing process of the valve, the valve stem only rotates in place, so the opening and closing state of the valve can not be judged by naked eyes. However, the transmission thread on the rising stem gate valve stem is exposed outside the valve body, which can directly judge the opening and closing position of the gate;
4. The height of non rising stem gate valve is small, and the installation space is relatively small; the height of rising stem gate valve is large when it is fully opened, which requires large installation space;
5. Standard China steam gate valve: the stem of the rising stem gate valve is outside the valve body, which is conducive to maintenance and lubrication; the stem thread of the non rising stem gate valve is inside the valve body, which is difficult to maintain and lubricate, and the stem is easy to be directly eroded by the medium, so the valve is easy to be damaged. In the scope of use, rising stem gate valve is more widely used.
The advantages of non rising stem gate valves: the height of the gate valve always remains unchanged, so the installation space is small. It is suitable for gate valves with large diameter or limited installation space. This kind of structure should be equipped with opening and closing indicator to indicate the opening and closing degree.
The disadvantage of non rising stem gate valves: the stem thread is not only unable to be lubricated, but also directly subject to medium erosion, easy to damage.
Non rising stem gate valves can use wedge-shaped plugs or parallel plates. Plugs usually seal both the up and downstream sides of the valve while plates usually only seal on the upstream face. Wedges can take on a variety of design alternatives that reduce or accommodate wear of the sealing surfaces. Although the advantage of gate valves is their reduced head loss when open compared to globe valves, they are not useful for throttling and may not produce the positive shut-off that globe valves provide. Non rising stem gate valves are used in wastewater plants, power plants, and process plants for shut-off and for isolating service.
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