What is a Vacuum Breaker?

Mary McMahon

In plumbing, a vacuum breaker is a safety device to prevent accidental siphoning of hazardous material into a plumbing system when there is a loss of pressure. Plumbers can install these devices at various points in a plumbing system and the building code may require people to fit their plumbing with vacuum breakers. It is important to note that vacuum breakers cannot be used in areas with airborne contaminants, as these contaminants could enter the system through the device.


The classic situation where a vacuum breaker becomes useful is when pressure is lost due to a power outage or other problem. If the lines drain out, as may happen when people run taps without realizing no water is available, this creates a vacuum in the plumbing. This can turn into a siphon, pulling non potable fluids into the plumbing and causing contamination. The vacuum breaker has a small valve that opens when the pressure drops, allowing air to bleed into the system. This prevents the formation of a vacuum and keeps contaminants out of the water supply.

Hose bibs and faucets can have a vacuum breaker, and these devices may also be used on other supply lines. They are part of a series of safety systems people use to keep drinking water safe. These include separating out drainage and sewage lines, installing emergency shutoff valves, and so forth. The vacuum breaker is usually cheap and people can install it quickly, with minimal fuss, to improve the safety of a plumbing system.

A plumber can determine if a vacuum breaker is necessary and where to install the device. There may be settings where people should not use these devices, or where they are simply not necessary because other safety features are present and the vacuum breaker would be redundant. In the case of a new plumbing installation, the plumber will take some time to plan out the system and determine the placement of safety features so it will be up to code and safe to use from the very start. In retrofits, the plumber may need to thoroughly inspect the system and its documentation to make decisions about how to proceed.

Hardware supply stores stock vacuum breakers in various styles and sizes to meet plumbing needs. If people are replacing an existing fitting, it can be helpful to bring it into the store to make sure the match is correct. Most hardware stores have very forgiving return policies, but people usually want to avoid a wasted trip.

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