Function and selection of centrifugal pump outlet check valve

centrifugal chemical pump

The function of the centrifugal pump outlet check valve is to prevent the liquid in the outlet pipeline from flowing back to form water hammer and damage the impeller in the pump.

The installation of the check valve has nothing to do with the number of pumps. The check valve is mainly used to prevent the liquid from flowing back and causing the pump to reverse after the pump stops running, thereby causing an accident that damages the pump, and to prevent the liquid from flowing back to damage other storage tanks (backflow from the high-level tank will cause the tank to be damaged). Therefore, it is better to add a check valve. If you can ensure that the outlet valve is closed before stopping the pump, and the outlet valve does not leak or damage, you can also not install a check valve.

  1. Pump outlet check valve “Selection of check valve

In general pump station engineering situations, the following principles should be followed for the selection of pump outlet check valves;

For pipelines with smaller diameters of pump outlet pipelines, that is, DN When the diameter is less than 50mm, a lift check valve should be used.

For the pump outlet pipeline with a diameter of DN>50mm, a swing check valve should be used. The swing check valve can be installed horizontally or vertically. The valve disc of Sunpace Pumps Industry’s swing check valve rotates around the rotating shaft, and its fluid resistance is generally smaller than that of the lift check valve. It is suitable for occasions with larger diameters. The installation position is not restricted. It is usually installed in horizontal pipelines. It is suitable for occasions with larger diameters. According to the number of valve discs, it can be divided into single-disc swing type , double-flap swing check valve and multi-flap swing check valve. Single-flap swing check valve is generally used in medium-caliber occasions. When single-flap swing check valve is used for large-diameter pipelines, in order to reduce water hammer pressure, it is better to use a slow-closing check valve that can reduce water hammer pressure. Double-flap swing check valve is suitable for large and medium-diameter pipelines. Wafer double-flap swing check valve has a small structure and light weight, and is a faster check valve; multi-flap swing check valve is suitable for large-diameter pipelines.

  1. Installation of pump outlet check valve

① Swing check valves are generally installed on horizontal pipes: for check valves with a diameter of DN~80mm, they can also be installed on vertical or upward inclined pipes.

② Straight-through lift check valves should be installed on horizontal pipes; vertical lift check valves must be installed on vertical pipes, and the medium flows from bottom to top.

③ Since the check valve is easy to damage, the check valve should be installed close to the pump outlet, and a cut-off valve (generally a ball valve or a gate valve) is provided on the upper part of the check valve for easy maintenance.

④ In order to facilitate pressure relief before disassembly of the check valve, if the check valve itself does not have a drain valve, a drain valve for pressure relief should be installed between the check valve and the cut-off valve.

  1. Protective measures to prevent damage to the sealing surface of the check valve by hydraulic impact

The setting of the check valve plays a role in preventing material backflow and preventing the pump impeller from being subjected to liquid hammer. Sunpace Pumps Industry However, as far as the check valve itself is concerned, improper setting will cause the valve disc generated by water hammer to suddenly hit the valve seat, damaging the sealing surface of the check valve. Therefore, several protective measures should be taken.

1) For swing check valves with a pump outlet setting of >80mm, horizontal installation should be adopted to reduce the valve disc returning to the seat and the impact caused.

2) For pipelines with a check valve diameter of >=150mm at the pump outlet, a bypass should be set before and after the check valve to prevent the pressure before the valve from rising too high and causing damage to the sealing surface of the check valve.

3)For pipelines with high pressure at the starting and end points of the pump discharge pipeline, if bypass is not allowed, the following measures can be taken.

A safety valve is set up to replace the bypass valve. Its function is similar to that of a bypass valve. It is set up near the outlet of the check valve. When water hammer causes the pressure to rise, some water can be released to prevent damage caused by continued pressure increase.

An air or inert gas buffer tank is set up. It is set up near the outlet of the check valve. When water hammer occurs, the pressurized gas in the buffer tank is compressed to alleviate the pressure increase caused by water hammer.

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