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　　Check valve, also known as check valve, is a fully automatic valve. It uses the working pressure of the flowing medium in the pipeline to promote the piston valve and complete the closing and opening of the gate valve. When the medium stops flowing and the check valve piston valve is closed, the reverse flow of the medium in the pipeline can be reasonably avoided, which has a great effect on ensuring the safety of the pipeline.

　　The check valve can be divided into regulating check valve, swing check valve and stack check valve according to the structural division. The regulating check valve can be divided into vertical check valve and immediate check valve. The rotary check valve is divided into single, double and multiple discs. The stack check valve is divided into butterfly double valve and stack single valve. The above check valves can be divided into flange connection, flange connection, electric welding and clamping connection.

　　The check valve is installed to ensure the direction of water flow in the pump and thus ensure the normal operation of the pump. Therefore, the installation position of check valve can be divided into two conditions:

　　One is the top of the vertical plastic suction pipe installed in front of the pump, also known as the pump bottom valve. The purpose is not to pump water once. When the pump and the plastic suction pipe in front of the pump have no water, the pump can only pump at high speed, so the pump must be full of water before pumping. This kind of pump is installed in a way that is higher than the level gauge, also known as the negative pressure method.

　　The other is installed behind the pump. This kind of installation method is that when the liquid level meter is higher than the pump, it is convenient to start and stop the pump without closing the pump outlet and inlet valve, especially for the main centrifugal pump system software to avoid flow back.

　　The check valve must be installed before the pump outlet and outlet pressure regulating valve to maintain the check valve. Generally speaking, the * * outlets of the pump are electrically conductive soft connections (shock absorbers), followed by check valves, and then by decoration isolation valves (such as butterfly valves, stop valves, stop valves, etc.)