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Conditions of Using Gate Valves and Operation

A gate valve is a valve whose closing member moves vertically along the centerline of the channel. The gate valve can only be used for the full opening and full closing of the pipeline, and cannot be used for regulation and throttling. Gate valve is a widely used valve. It is generally used for cutting devices with a diameter of DN50mm, and sometimes it is also used for cutting devices with small diameters.


1. Conditions of use of gate valve


The gate has two sealing surfaces. The two sealing surfaces of the commonly used mode gate valve form a wedge shape. When the medium temperature is not high, the wedge angle changes with the valve parameters. 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 pressure head that can produce slight deformation to improve its manufacturability and make up for the deviation of the angle of the sealing surface during processing. This indenter is called an elastic indenter.


When the gate valve is closed, the sealing surface can only be sealed by medium pressure, that is, the sealing surface of the gate valve is pressed to the valve seat on the other side by the medium pressure to ensure the sealing of the sealing surface, which is self-sealing. Most gate valves are forced to seal, that is, when the valve is closed, the gate must be pressed against the valve seat by external force to ensure the sealing of the sealing surface. A gate valve whose gate moves linearly with the valve stem is called a lifting stem gate valve (also known as an open stem gate valve). Usually, there are trapezoidal threads on the lift rod, and through the nut on the top of the valve and the guide groove on the valve body, the rotary motion is changed into a linear motion, that is, the operating torque becomes the operating thrust.


When the valve is open, the fluid passage is completely clear, but this position cannot be monitored during operation. In practice, the apex of the valve stem is used as a symbol, that is, the position where it cannot be opened is used as its fully open position. To account for locking due to temperature changes, it is usually at the top position and then back to 1/2-1 turn as the fully open valve position. Therefore, the fully open position of the valve is determined according to the position of the head (ie, the stroke).


2. Precautions for operation of gate valve


(1) Gate valves are usually used for opening and closing occasions, but not for throttling applications.


(2) Gate valves are usually installed on horizontal pipelines with the valve stem vertically upward. Installation in horizontal piping is also possible, but depending on valve size, application environment and specific material conditions, special construction may be required. If the valve is purchased to be installed in a special way, the orientation of the valve should be indicated when ordering.


(3) For the application environment where the temperature exceeds 260 degrees, it is recommended to use a flexible or split wedge gate to avoid the wedge gate being stuck due to thermal expansion. This can happen when the valve is closed cold and then opened hot.


(4) To avoid loosening when used in high velocity fluid (turbulent flow) or thermal cycling applications, the threaded seat ring should be locked and welded to the valve body.


(5) After closing the gate valve, the valve stem should be rotated slightly to release the valve stem load. This allows the valve stem to expand slightly without clogging or damaging the valve and without affecting the closing effect.


(6) The valves used in the pump station are not restricted by the site, there are many sundries in the water, and the important positions are easy to be blocked. Flashlight dual-purpose gate valve can be used; on the contrary, butterfly valve can be used, especially in the pump room renovation project, on the premise of not changing the original pump room area, the space of the original pump room can be effectively used to increase the water supply (drainage) water volume.

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