Check valves are usually installed in pipelines to prevent backflow. A check valve is basically a one-way valve in which the flow can move freely in one direction, but if the flow returns, the valve closes to protect pipelines, other valves, pumps, etc. If the flow returns and the check valve is not installed, a water hammer may occur. Hydraulic shock often occurs with extreme force and easily damages the pipeline or components.
Check valves are used in many applications. For example, they are often placed on the pump outlet side to protect the pump from backflow. Centrifugal pumps, the most common type of water pump, are not self-priming, so check valves are necessary to keep water in the pipes. Also, check valves are very often used in HVAC systems (heating, ventilation and air conditioning systems). HVAC systems, for example, are used in large buildings where coolant is pumped over many floors. These check valves are installed to prevent the coolant from being flushed back out.
