Check valve

A check valve cannot be regarded as a safe substitute for a backflow preventer, especially when safeguarding drinking water.

Backwater valve

While having similar functions, backflow preventers and check valves are distinctly different devices by application. A backflow preventer is necessary to prevent contaminated water from flowing into potable or municipal water sources. Check valves are also one way valves, but cannot offer the high level of protection that backflow preventers do. This article overviews the primary differences between backflow preventers and check valves and describes different types of backflow preventers.

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A backflow preventer’s function (Figure 2) is to stop water from flowing in the opposite direction. The only purpose of a backflow preventer is to stop contaminated water from flowing into a source of potable water. Backflow preventers are installed at cross-connection points, such as where municipal drinking water enters a residential or commercial building or where the water supply attaches to appliances like a washing machine or dishwasher. Check with the local regulations to understand exactly where backflow preventers are necessary in a plumbing system.

There are different types of backflow preventers with varying mechanisms. The best backflow preventer for an application may depend on local regulations or specifics of the plumbing system.

A backwater valve is used to prevent sewage from flowing back into a building. A check valve stops media from flowing through it in the reverse direction. These two valves differ in their application.

Backflow is the reversal of a fluid's flow due to back pressure or back siphoning. If backflow occurs, it can cause issues for certain applications. For example, if contaminated water backflows into a clean water supply.

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Like a backflow preventer, a check valve stops media from flowing through it in the reverse direction. Check valves, however, do not offer the degree of protection that backflow preventers do and therefore are not suitable for protecting drinking water sources. If foreign material enters the check valve, it may block it open. In this case, there is no failsafe; the check valve will leak. Also, when check valves close too quickly, they become vulnerable to water hammer, which will damage the valve. Despite this, check valves are applicable for many applications. Read our water check valve and hydraulic check valve articles to learn more about specific applications. To learn about these valves in general, read our check valve overview article.

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Backflow preventers offer protection through their multiple failsafe features in case of backflow. One example is the double check valve assembly (DCVA) which has two check valves and an atmospheric vent for protection, with a backup valve in case of failure. The vent creates an air gap to prevent backflow from backpressure. If the vent becomes blocked, a relief valve opens to release pressure and prevent contaminated water from flowing back into the main supply. The DCVA's combination of check valves, vent, and relief valve provides a failsafe design to protect the main water supply. Other types of backflow preventers similarly offer multiple failsafe features.

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Check valves and backflow preventers are two different devices. Backflow preventers are specifically designed to prevent contaminated water from mixing with potable or municipal water sources.

A backwater valve stops sewage from flowing back into a building whereas a backflow preventer valve prevents contaminated water from mixing with drinking water.