Should a check valve be installed before or after the outlet valve?

Thread Content

A check valve, also known as a non-return valve, is an automatic valve that relies on the pressure of the fluid flowing within the pipeline to push the valve disc open or closed. When the flow of fluid stops, the valve disc closes, thereby preventing the fluid from flowing in reverse. This plays a crucial role in ensuring the safety of the pipeline. Check valves are installed to ensure the flow direction of water inside the pump, thereby ensuring its proper operation. So, regarding the installation location of the check valve – whether it should be installed in front of or behind the water pump – there are two possibilities: one is to install it at the end of the vertical suction pipe in front of the water pump, which is also known as a foot valve. The purpose is to avoid having to fill the water pump with water each time it needs to be used; since the pump cannot draw water when there is no water inside it or in the suction tube ahead of it, the pump must be filled with water in order to be able to draw water out. The installation of this type of water pump involves placing it above the liquid level, and this method is also known as the negative pressure method. Another option is to install it behind the water pump. This installation method allows the water level to be above the water pump, which facilitates starting and stopping the pump without the need to close the pump’s outlet valve; it is especially useful in master pipe water pump systems to prevent backflow. So, should the check valve be installed in front of or behind the outlet valve? The answer is that the check valve must be installed at the pump’s outlet, before the outlet control valve, in order to allow for its maintenance. The outlet of a regular pump is equipped with a flexible connection (shock absorber); after that comes a check valve, and further on there are isolation valves (such as butterfly valves, gate valves, globe valves, etc.). Installing the check valve first and then the gate valve or butterfly valve can protect the check valve; this is especially important in parallel pump systems, where when one pump stops operating and its outlet valve closes, the impact force is absorbed by the gate valve or butterfly valve when the other pump starts operating. If a check valve fails, the inlet and outlet valves can be closed to isolate the system for repair. Installing the gate valve or butterfly valve first and then the check valve can protect the butterfly valve or gate valve, with the impact force being absorbed by the check valve. However, a check valve operates based on pressure differences: it closes when the pressure in the main pipe is high, and it opens when the pressure from the pump is high. If the flow rate used is unstable, the check valve will open and close repeatedly, which can affect its lifespan. Moreover, the check valves are broken, especially in the main piping system; repairs can only be carried out after shutting down the system.