This Valterra 200-20W check valve is made of white schedule 40 PVC (polyvinyl chloride) for strength and resistance to corrosion and mild chemicals. Its EPDM (ethylene propylene diene monomer) seal resists degradation caused by water and oils, and its full flow construction allows for insignificant flow loss at the swing check, so no spring is needed. It has 2" slip connections at both ends, which must be fastened with glue, and a maximum pressure rating of 150 pounds per square inch (psi). This check valve is suitable for use with landscape and irrigation, pool and spa, aquaculture, and general purpose applications.Check valves have two ports and restrict the flow of fluids and other loose materials through a pipe or passageway to one direction. Flow enters through one port and exits through the other, closing when flow reverses or stops. Two common types of check valves are ball cone valves and swing check valves. A ball cone valve utilizes a spring-loaded ball seated against a cone-shaped interior surface to stop the flow of fluid in a forward direction, and a swing check valve has a movable disc on a hinge to block reverse flow. Check valves are rated by their cracking pressure (the minimum upstream pressure required for the valve to operate), and they are used in various water, gas, air, and steam lines.Valterra Products manufactures and distributes valves, hoses, sewer systems, and pool and spa products. The company, founded in 1981, is headquartered in Mission Hills, CA.