Spill-resistant vacuum breaker (SVB)
A spill-resistant vacuum breaker (SVB) is a testable backsiphonage assembly, listed to ASSE 1056, that works like a pressure vacuum breaker but does not discharge water when the line pressurizes. That makes it the vacuum breaker of choice indoors. Like a PVB it protects against backsiphonage only, not backpressure, and must sit above the highest downstream outlet.
Updated 2026 · Researched from published standards, not professional or legal advice.
SVB vs PVB vs AVB
| Device | Standard | Testable | Spills on startup | Continuous pressure | Backpressure |
|---|---|---|---|---|---|
| SVB | ASSE 1056 | Yes | No | Yes | No |
| PVB | ASSE 1020 | Yes | Yes | Yes | No |
| AVB | ASSE 1001 | No | Can | No | No |
A spill-resistant vacuum breaker is a backsiphonage prevention assembly that works on the same principle as a pressure vacuum breaker: a spring-loaded check valve backed by an air inlet that opens when supply pressure is lost. The difference is in its internal design, which closes the air inlet before water reaches it during startup and pressurization. That refinement means the SVB does not spit or spill water in normal operation the way a standard PVB can.
The spill-resistant design matters most indoors. Laboratories, mechanical rooms, and commercial interiors often need vacuum breaker protection on equipment connections, but a device that discharges water onto a floor or bench during every pressurization cycle is unacceptable in those settings. The SVB fills that niche, providing testable backsiphonage protection under continuous pressure without the housekeeping problems. Like all vacuum breakers, however, it provides no protection against backpressure and must not be used where downstream pressure sources exist.
Testers and property owners should treat the SVB's siting rules like those of a PVB: it must be installed above the highest downstream outlet, remain accessible for testing and service, and be protected from freezing. Because it is a testable assembly with test cocks, it falls under the same periodic testing expectations as other assemblies, typically annual where required, set by the water authority. Confirm the application is strictly backsiphonage before accepting the installation.
Common questions
What is an SVB in backflow?
SVB stands for spill-resistant vacuum breaker (also called a spill-resistant pressure vacuum breaker). It is a testable assembly with a check valve and an air inlet, built so it does not spit water when the system pressurizes.
SVB vs PVB: which one do I need?
Both protect against backsiphonage only. Choose an SVB where water discharge would cause damage, such as indoors or in a lab; a PVB is common outdoors on irrigation. Your water authority or plumbing inspector has the final say.
Sources
- ASSE International product standards (1001, 1013, 1015, 1020, 1056)
- USC Foundation for Cross-Connection Control and Hydraulic Research, Manual of Cross-Connection Control
- U.S. EPA, Cross-Connection Control Manual (EPA 816-R-03-002)
Related terms
| Pressure vacuum breaker (PVB) | A testable backflow prevention assembly with a spring-loaded check valve and an air inlet valve that protects against backsiphonage only. |
| Atmospheric vacuum breaker (AVB) | A simple, non-testable backsiphonage prevention device that uses a float or disc to seal against flow and admit air when pressure is lost. |
| Backsiphonage | Backflow caused by a drop or loss of pressure in the supply piping that siphons water backward through a cross-connection. |
The three-year clock sheet, free
Both clocks of the testing trade, your credential and your customers, counted backward on one printable page. Enter your email and we will send you straight to it.
No spam. One useful sheet and occasional notes.