A vacuum breaker is an attachment commonly placed on a bibcock valve or toilet

Flush toilet

A flush toilet is a toilet that disposes of human waste by using water to flush it through a drainpipe to another location. Flushing mechanisms are found more often on western toilets , but many squat toilets also are made for automated flushing...

 or urinal flush valve

Sloan Valve Company

Sloan Valve Company was founded in 1906 with the introduction of the Royal Flushometer, which is now widely used.The company was founded by William Elvis Sloan in Chicago, Illinois. When he initially sold his Royal flushometer in 1906, he only sold one at the time because customers were wary of...

, that prevents water from being siphon

Siphon

The word siphon is sometimes used to refer to a wide variety of devices that involve the flow of liquids through tubes. But in the English language today, the word siphon usually refers to a tube in an inverted U shape which causes a liquid to flow uphill, above the surface of the reservoir,...

ed backward into the public drinking water

Drinking water

Drinking water or potable water is water pure enough to be consumed or used with low risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually...

 system. This prevents contamination should the public drinking water system's pressure drop.

A vacuum breaker typically contains a plastic disc that is pressed forward by water supply pressure, and covers small vent holes. Should the supply pressure drop, the disc springs back opening the vent holes (which let in outside air), and preventing backflow of water.

A more complex valve that accomplishes much the same purpose is the backflow preventer

Backflow prevention device

A backflow prevention assembly is used to protect water supplies from contamination or pollution.In water supply systems, water is normally maintained at a significant pressure to enable water to flow from the tap, shower etc...

.

Vacuum relief valve

Relief valve

The relief valve is a type of valve used to control or limit the pressure in a system or vessel which can build up by a process upset, instrument or equipment failure, or fire....

s are sometimes known as vacuum breakers.

External links

• Vacuum Breakers Tutorial Vacuum breakers protect plant and process equipment against vacuum conditions, typically associated with cooling.