The function of the check valve of centrifugal pump outlet is to prevent the flow of liquid in the outlet pipeline to form a water hammer which causes impeller damage in the pump.
Check valve installation has nothing to do with how much pump, pump the check valve is mainly in order to stop after the operation, prevent the reverse flow of liquid, invert the pump, causing damage to the pump of the accident, and in order to prevent the liquid flow back damage to other tanks (from high fill reversals will cause the pot smoking bad).
So it's best to add check valves.
If you can ensure that the exit valve is closed before the pump is stopped, and the outlet valve is not leaking or damaged, the check valve can also be disturbed.
1. Pump outlet check valve "check valve type selection.
The general pump station engineering situation, for the pump outlet check valve selection, should follow the following principles;
The lift check valve should be used when the pipe with smaller diameter of the pump outlet pipe is less than 50mm.
For pipe line with diameter DN > 50mm, swing check valve swing check valve can be installed horizontally or vertically. Swing check valve disc around the axis of rotation, the fluid resistance is generally less than lift check valve, it is suitable for large caliber, installation position is not restricted, are normally installed in horizontal pipe, which applies with the occasion of the large diameter. According to the number of disc can be divided into single swing, double swing and multi - flaps. Single swing check valves are generally used with medium - caliber occasions. To reduce water hammer pressure, it is better to use a slow closed check valve that can reduce the pressure of water hammer. Double swing check valves for large and medium caliber pipeline. It is a quick check valve with small structure and light weight. Multi - valve swing check valve for large diameter pipeline.
2. Installation of pump outlet check valve.
The swing check valves are normally installed on horizontal pipes: the check valves for the caliber DN~80mm can also be installed on vertical or upward sloping pipes.
The straight-through type lift check valve shall be installed on the horizontal pipe; Vertical lift check valve must be installed on vertical pipe, medium is upward flow.
Because the check valve is easy to be damaged, it should be close to the pump outlet to install the check valve. There is a cut-off valve (usually with ball valve or gate valve) on the top of the check valve for easy maintenance.
In order to facilitate the disassembly of the check valve, the relief valve should be installed between the check valve and the cut-off valve for the check valve itself.
3. Protection measures to prevent damage to the sealing surface of the check valve by hydraulic impact.
The check valve is set up to prevent the backflow of the material and prevent the pump impeller from being hit by the liquid. However, in the case of the check valve itself, improper setting will result in the sudden impact of the disc on the seat and the sealing surface of the check valve. Therefore, several protection measures should be taken.
1. The swing check valve with >80mm for the pump outlet shall be installed horizontally to reduce the disc return and the impact.
2. For the pipe with the pump outlet check valve diameter >=150mm, the bypass should be set before and after the check valve to prevent the pressure from rising too high and damage the sealing surface of the check valve.
3. The following measures can be taken to pump out the starting point and terminal pressure of the pump and not allow the bypass to be set.
Set the relief valve to replace the bypass valve. The function is similar to the bypass valve. It is located near the check valve outlet. When the water hammer increases the pressure, a part of the water can be released to prevent the damage caused by the increase in pressure.
Set air or inert gas buffer tank. Set it close to the check valve outlet. When the water hammer is produced, the pressure in the buffer tank is compressed to reduce the pressure caused by the water hammer.