Swing Check Valve - 3 In Slip
Allows water to travel in one direction only
Submersible Pumps - prevents water from back flowing from the filter into the pond when the pump is turned off.
External Pumps - allows the pump to be primed by pouring water into the pump to fill the line.
A check valve is a PVC fitting that only allows water to travel one way through the fitting. If the water tries to travel the opposite direction, the valve will close and not allow water through. The idea with a check valve is to only allow water to flow from the pond to the pump, and not the other way around. If using with a submersible pump, the check valve prevents the filter from draining back into the pond when the pump is shut off.
If using with an external pump, before you turn on the pump, you can pour water into the pump to fill up the pump and pipe, and it won’t leak back into the pond because of the check valve. When you turn on the pump then, it will have water in the pump and pipes, ready to go.