PVC Check ValvesA PVC check valve (or non return valve) is a simple device that lets water flow in one direction but automatically stops it from flowing backward, protecting your equipment and preventing tanks from draining. Swing Check Valve This valve has a flap inside that swings open to let water pass through with very little resistance. When the water stops, the flap swings shut. PVC Spring Check Valve This valve uses a spring to hold a seal closed. Water