Vacuum Breakers

Vacuum breakers are devices which prevent back-siphon of contaminated water to a potable water supply due to sudden vacuum conditions on the supply (inlet/feed) side. They also protect burners and heating elements inside the equipment from running dry, preventing damages and dangerous conditions. Vacuum breakers and relief valves are commonly used with water heaters (both floor standing and table-top - with bottom cold water inlet connections), unit heaters (especially with bottom and side connections), lab equipment and others.

Frequently Asked Questions:

Q: What is a vacuum breaker/relief valve?
A: Vacuum breakers and vacuum relief valves are intended to allow the air into the system in the event of back-siphon (inlet/supply water pressure suddenly drops below the atmospheric pressure level). They are installed on the supply line before the equipment and act as 1-way air valves which only allow the air in whenever there’s negative pressure in the system.
A supply line connected to a storage tank type water heater bursts, or is shut down and drained for repairs. A negative pressure is created on the supply side, causing the water inside the water heater (and possibly an in-line filter) to drain back into the fresh water supply, contaminating it and draining the tank. If a vacuum breaker is installed before the water heater, it will open once negative pressure occurs, allowing the supply line to siphon air instead of water.

Q: What is the difference a between vacuum breaker and a vacuum relief valve?
A: Anti-siphon vacuum breakers (ASVB’s) are 2-in-1 backflow preventer (check valve) and vacuum relief valve. A standard vacuum relief valve (VRV) does not provide the backflow protection feature. In other words, a VRV would only work where there’s a sudden negative pressure on the water supply side AND no pressure on the equipment side. ASVBs, on the other hand, will close off the line whether there’s a pressure on (from) the equipment side or not. Note: ASVB’s are not designed or intended for continuous backflow prevention - only short-term pressure changes (up to 12 hours per ASSE 1001).

Q: How to size a vacuum breaker?
A: For standard size residential applications (up to 2-story home w/ basement, water heater volume less than 50 gallons), models such as LFN36M1 would work with no sizing needed. For all others, vacuum breaker sizing is best left to professionals. The main factor in selecting a particular model is generally it’s air flow allowance (how much air it can admit into the system), measured in CFM (cubic feet per minute).

Q: What is the difference between a vacuum breaker and a pressure relief valve?
A: While somewhat similar in appearance, these are entirely different. First is designed to allow the air into the system, the other is designed to open when pressure inside a vessel/tank exceeds valve’s setting.

Q: What is the difference between a vacuum breaker and an air admittance valve?
A: The only major difference is that air admittance valves are designed for use in drainage applications while vacuum breakers are for supply applications. They utilize different types and quality of materials due to different operating conditions - otherwise, they function in the same manner.