This Valterra 310-20 corrosion-resistant check valve is made of Black CPVC with a glass-filled injection molded shaft for resistance to corrosive chemicals, and has a service lid for easy cleaning and maintenance. It has a silicone gasket and a high-performance metal alloy spring for resistance to corrosive chemicals. The swing/spring construction of this valve makes it possible to install it in any position. This corrosion-resistant check valve has a maximum pressure rating of 150 pounds per square inch (psi) and comes with 2" slip connections, which must be fastened with glue. It is suitable for pool, spa, and other applications where corrosive chemicals are used. 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.