The function of the check valve at the outlet of pumps is to prevent the impeller damage caused by the backflow of liquid in the outlet pipe from forming a water hammer.
The installation of check valve has nothing to do with the amount of pump. The check valve is mainly used to prevent the backflow of liquid and reverse the pump after the pump stops running, thus causing damage to the pump.
Pump outlet “check valve” selection
The following principles should be followed in selecting centrifugal pumps outlet check valves
1. For pipelines with small diameter at the pump outlet, i.e., when DN is less than or equal to 50mm, the lifting check valve shall be adopted.
2. For DN>50mm pipe line at pump outlet, swing check valve can be installed horizontally or vertically.
The swing check valve disc rotates around the rotating shaft, and its fluid resistance is generally smaller than that of the lift check valve. It is suitable for large bore, unrestricted installation position, and is usually installed in horizontal pipeline, which is suitable for large bore.
Installation of pump outlet check valve
1. Swing check valves are generally installed on horizontal pipes: for check valves with DN<80mm diameter, they can also be installed on vertical or upward sloping pipes.
2. The straight-through lifting check valve shall be installed on the horizontal pipe;
The vertical lift check valve must be installed on the vertical pipe and the medium should flow from bottom to bottom.
3. As the check valve is easy to be damaged, the check valve should be installed close to the pump outlet. The upper part of the check valve is provided with a cut-off valve (usually ball valve or gate valve) for convenient maintenance.
4. In order to facilitate the pressure relief before the check valve is disassembled, if the check valve itself is not equipped with a purge valve, the pressure relief valve for the check valve and the cut-off valve shall be installed between the check valve and the cut-off valve.
Protection against hydraulic shock damage to sealing surface of check valve
The setting of check valve prevents the material from flowing backwards and prevents the impeller from being hit by liquid.
However, in the case of the check valve itself, improper installation will result in a sudden impact of the disc to the seat caused by water impact, and damage to the sealing surface of the check valve.
Therefore, several protective measures should be taken.
1. For the swing check valve with >80mm at the pump outlet, the horizontal installation method shall be adopted to reduce disc seat and impact.
2. For pipeline whose pump outlet check valve diameter is more than 150mm, bypass should be set before and after the check valve to prevent excessive pressure rise in front of the valve and damage to the sealing cover of the check valve.
3. For pipelines with high starting and ending pressure of pump discharge pipeline, it is not allowed to set bypass, the following measures can be taken: setting safety valve to replace bypass valve.
It ACTS like a bypass valve.
It is located near the check valve outlet, and when the pressure is increased by a water blow, some of the water can be released to prevent damage caused by the increased pressure.