The role of the outlet valve is to prevent the flow of liquid in the outlet pipe to form a water hammer caused by pump impeller damage.
     Check valve installation and the number of the pump has nothing to do, check valve is mainly in order to stop the operation of the pump, to prevent the liquid return, so that the pump back, causing damage to the accident, and in order to prevent backflow of liquid
     Damage to other storage tanks (from the top of the tank can cause the tank to fill up).
     If you can ensure that the first close the exit valve before the pump, and the outlet valve leakage or damage.
1 type selection of the pump outlet check valve
     General pumping station project, the selection of the pump outlet check valve, should follow the following principles;
     The pipeline of the pump outlet pipe smaller diameter, DN is less than or equal to 50mm, should use the lift check valve.
     On the pump outlet pipe diameter DN 50mm pipe line, should be used to swing check valve swing check valve can be horizontal or vertical installation. Swing type check valve to rotate the rotating shaft of the rotating shaft, and the fluid
     Resistance is generally less than the lift check valve, which applies to the larger diameter of the occasion, the installation location is not restricted, usually installed in horizontal pipe, it is suitable for large caliber occasions. According to the number of valve flap can be divided
     For single swing, double disc swing and multi disc swing three. Single swing check valve in general use and medium caliber occasions. Large diameter pipeline with single swing check valve, in order to reduce the water hammer pressure
     Force, the best use can reduce the water hammer pressure relief valve. Double valve swing check valve suitable for large and medium diameter pipe. On the double valve swing check valve structure is small, light weight, is a quick check valve
; multi valve swing check valve is suitable for large diameter pipeline.
2 installation of pump outlet check valve
     The swing check valve is generally installed on the horizontal pipe: the check valve for the diameter of DN~80mm can also be installed in vertical or upward inclined pipe.
     The straight through lift check valve should be installed in horizontal pipe; vertical lift check valve must be installed in the vertical pipe, medium is from the bottom up.
As the check valve is easy to damage, therefore, should be close to the pump outlet to install check valve, in the upper part of the check valve (usually with ball valve or gate valve), convenient maintenance.
     (4) are easy to check back valve before the demolition relief, in check valve itself, without a net valve, check valve and shut-off valve installed between the pressure relief with a net release valve in.
3 protection measures against the sealing cover of the check valve by preventing hydraulic impact
     The setting of the check valve has the function of preventing the backflow of the material and avoiding the fluid hammer of the pump impeller. But on the check valve itself, set up properly, will cause water hammer generated by the valve seat of the valve
Impact, damage and check valve cover. Therefore, we should take some protective measures.
     1, for the pump set >80mm of the swing check valve, should be used to install the way, in order to reduce the valve flap back seat and impact.
     2, for the pump outlet check valve diameter >=150mm pipeline, should be in the check valve before and after the bypass valve to prevent the valve before the pressure rise is too high, the valve sealing surface damage caused by.
     3, the starting point and the end point of the pump discharge pipe line, do not allow to set the bypass, can take the following measures.
     Set the safety valve to replace the bypass valve. Its role is similar to the bypass valve. It is set near the exit of the check valve, when the water hammer pressure increases, a portion of the water can be released to prevent the pressure to continue to increase.
Into damage
     Air or inert gas buffer tank. Put it near the exit of the check valve, when the water hammer is generated, the pressure gas is compressed through the buffer tank to ease the pressure rise caused by the water hammer.

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