Check valve /s are used when there is a change in elevation in a swimming pool. For instance if you have a raised spa or fountain it is used so that 1) air will not enter into the plumbing/pump and 2) so the raised hot tub/spa for instance will not drain down to the current water level in the swimming pool. Water will balance itself, so if you have a raised hot tub/spa and there is no check valve the water in the raised spa will drain down to the current water level in the swimming pool. Also if your equipment is located at a drastically higher elevation than your pool Crystal Pools and Spas Inc. will install check valves so that when the homeowner empties the pump basket it will not require a long time to prime the pump or also prevents loss of prime to the pump. If you have a raised spa or fountain/wall and you have a check valve and after time the spa starts going do, before panicking thinking your spa is leaking you should check the check valve. There are a wide range of check valves on the market and some cheaper pool builders will put inexpensive in-line check valves, ones that can’t be checked easily and will have to be cut free from the plumbing to be checked or changed. Jandy makes a great check valve that has a clear lid that allows you, the homeowner to visibly look into to see if the flap is closed. The Jandy check valve is held on by a series of screws and you can have just the internal flap changed out. The ones Crystal Pools likes to install is one that has unions and can be changed without re plumbing. This check valve requires no tools to check/take apart. Sometimes a check valve problem can be as simple as some debris like a leaf get caught up so that the check valve can’t close. A check valve in easy terms is a valve that allows water to only go one way/direction. So if you have a raised spa water can only go TO the spa and when the pump turns off the valve shuts not allowing the water to go backwards inside your plumbing allowing the water level in the spa stay put. If for any reason so debris or a spring goes out in the check valve the valve will not be allowed to work properly. If you have any questions about a swimming pool feel free to email us at Crystal Pools and Spas Inc. at email@example.com. And if you live in Southeast Louisiana or Southern Mississippi please give us a shot at your swimming pool or renovations. Thanks!