Check valve, also called a non-return valve, is an automatic valve that relies on the pressure of the flowing medium in the pipeline to push the valve disc, thus closing and opening the valve. When the medium stops flowing, the check valve disc closes, effectively preventing backflow of the medium in the pipeline, which plays a significant role in ensuring pipeline safety.
Check valves can be classified into three types according to their structure: lift check valves, swing check valves, and butterfly check valves. Lift check valves are further divided into vertical and straight-through types. Swing check valves are divided into single-disc, double-disc, and multi-disc types. Butterfly check valves are divided into double-disc and single-disc butterfly types. These check valves can be connected in four ways: threaded connection, flange connection, welded connection, and wafer connection.
Check valves are installed to ensure the direction of water flow inside the water pump, thereby ensuring the normal operation of the pump. Therefore, regarding the installation location of the check valve, whether it is installed before or after the water pump, there are two scenarios:
One is installed at the end of the vertical suction pipe before the water pump, also called a foot valve. The purpose is to avoid refilling the water pump every time it pumps water. Since the pump will only run dry and won't draw water if there's no water inside or in the suction pipe before it, it must be filled with water to pump any water. This method of installing the pump above the liquid level is also called the negative pressure method.
Another method is to install it after the pump. This method is used when the liquid level is higher than the pump, allowing for easy start-up and shutdown without closing the pump's outlet valve, especially important for mainline pump systems to prevent backflow.
The check valve must be installed at the pump outlet, before the outlet control valve, for easy maintenance. Generally, the first connection at the pump outlet is a flexible joint (shock absorber), followed by the check valve, and then an isolation valve (such as a butterfly valve, gate valve, or globe valve).
1. Install the check valve first, then the gate valve or butterfly valve.
Advantages: It protects the check valve, especially in parallel pumps. When one pump is not running and its outlet valve is closed, the gate valve or butterfly valve bears the impact force when the other pump starts. 1. If a check valve malfunctions, the inlet and outlet valves can be shut down to isolate the system for repair.
Disadvantage: Who will protect the gate valve or butterfly valve? There was a case where the butterfly valve's disc was damaged.
2. Install the gate valve or butterfly valve first, then the check valve.
Advantage: It can protect the butterfly valve or gate valve; the impact force is absorbed by the check valve.
Disadvantage: Who will protect the check valve? Check valves open and close based on pressure differentials. If the main pipe pressure is high, it closes; if the pump pressure is high, it opens. If the flow rate is unstable, the check valve will repeatedly open and close, affecting its lifespan. Furthermore, if the check valve fails, especially in a main pipe system, the entire system must be shut down for repair.