Spring Check Valves The spring style check valve has a seal on a piston.  The spring keeps the valve closed until sufficient pressure pushes the piston open.  The piston has a rubber seal on the end that gives a positive seal against backflow. When water goes forward through the valve, the spring is compressed and the piston pushes back and allows the water through the valve. When water attempts to go backwards through the valve the spring and the water pressure hold the valve closed.   Return to filter shopping