Check Valves A check valve (also called non-return valve) is a valve which allows water to flow in one direction and prevents unwanted backflow of water in the opposite direction. Without a check valve, used or polluted water in plumbing systems could contaminate the potable water supply. Neoperl® check valves are primarily designed for the plumbing industry for use on the clear water side, drinking water in particular. Applications include faucets, showers, valves and heating systems for residential or commercial installations, as well as pumps, water filters and appliances. Check valves can also be used in other applications such as air. Most standard models are 100% factory-tested during production for drip tight operation. Maximum temperature and pressure rating is for most models 200F/230psi. The average cracking (opening) pressure of most valves is between 1/4 and 1/3 of a psi.