What is a Check Valve?

Mary McMahon
Mary McMahon

A check valve is a type of valve which only permits flow in one direction. These valves are often designed for safety reasons, to prevent backflow and to ensure that someone operating a system knows which direction fluids and gases are flowing in. Check valves can also be used for tasks like creating leak tight seals, which can be an important safety or convenience future. They are also used for the routine task of directing fluids or gases efficiently through a system.

A ball valve may be used as a check valve.
A ball valve may be used as a check valve.

Also known as a one way valve or a nonreturn valve, a check valve can work in a number of ways. One of the most common styles is the ball valve, made by mounting a ball over a disc with a small hole in it. Liquid or gas can flow through the hole and around the ball, but when it tries to push the other way, it shoes the ball up against the disc, creating a seal. Other styles include clapper, swing, and diaphragm check valves, each designed for varying applications.

In some regions of the world, check valves may be required by law with certain types of systems, for safety. For example, a water heater and associated plumbing use check valves to control pressure and reduce the risk of explosion. Check valves are also important components in many types of medical equipment, such as non-rebreather masks used to provide supplementary oxygen. Most plumbing systems have at least one check valve, and complicated arrangements of such valves are used for safety in chemical plants, on tankers, and in a variety of other facilities.

Check valves come in a range of diameters for different kinds of piping. They are also tested to determine their load rating, determining how much pressure is required to break the valve. As a general rule, experts recommend purchasing check valves with pressure ratings which exceed the potential pressure which can be generated by a system, ensuring that the check valve will hold up even if the system reaches a critical point of pressure.

The check valve can even be found inside the body. The heart, for example, has what are essentially check valves which permit the one way flow of blood through the heart. These valves prevent oxygenated blood from flowing back into the heart, and force deoxygenated blood through the heart, and they are designed to deal with a high level of pressure and to withstand years of use; nature can be an excellent engineer, apparently.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


@NathanG - Yeah, I know what you mean. I also have a drip irrigation system to water my plants, and it uses check valves as well. I like it because during the summer it gets really hot, and if I just dose my plants with water I can really waste a lot of water.

The drip irrigation uses a gradual drip method directed at the base of the plants. I also use a liquid fertilizer that gets applied to the base of the plants at the same time, using the same method.

I conserve water and the plants are getting targeted nutrition and irrigation. They’ve grown much better than they did when I just splashed water on the surface, like I used to do.


I have an irrigation sprinkler that uses a flow check valve in the system. It lets the water flow out in one direction to irrigate my lawn, but will not water drain back in the opposite direction.

The benefit of this is that it keeps the contaminated water on the lawn from draining back into the hoses and stuff. You don’t want that back flow to happen, because it can pick up fertilizer, waste by-products and other junk, and you definitely don’t need that in the water pipes or in your hose.

So it makes sense that the irrigation water flow is only in one direction.

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