FAQ

Types of Backflow Preventers

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Atmospheric Vacuum Breakers (AVB)

A device containing a float-check, a check seat and an air inlet port. The flow of water into the body causes the float to rise and close the air inlet port. When the flow of water stops, the float falls and forms a check valve against back-siphonage and, at the same time, opens the air inlet port to allow air to enter and satisfy the vacuum. A shut-off valve immediately upstream may be an integral component of the assembly. This valve is intended for use in a non-continuous pressure application (no more than 12 hours of pressure per 24 hour period), in a back-siphonage condition only. An Atmospheric Vacuum Breaker is intended to provide protection in low and high hazard situations.

Testing:
This device is not testable once installed.


Pressure Vacuum Breakers (PVB)

An assembly containing an independently acting, internally loaded check valve with an independently acting loaded air inlet valve, located on the discharge side of the check valve. Additionally, this assembly shall have two (2) resilient-seated isolation valves attached at each eand of the assembly and two (2) properly located resilient seated test cocks, This assembly is intended for use in both continuous and non-continuous pressure applications, in a back-siphonage condition only. A Pressure Vacuum Breaker is intended to provide protection in low hazard and high hazard situations.

Testing:
1) The air inlet valve shall open when the pressure in the body is no less than 1.0 psi above atmospheric pressure. And, the air-opening valve shall be fully open when the water drains from the body.

2) The check valve shall be drip-tight in the normal direction of flow when the inlet pressure is 1 psi and the outlet pressure is atmospheric.

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Text courtesy of Wilkins a Zurn company.