This assembly consists of two internally loaded independently operating check valves and a relief valve located between the check valves. This relief valve is designed to maintain a zone of reduced pressure between the two check valves at all times. The RP also contains tightly closing, resilient seated gate valves upstream and downstream of the check valves along with test cocks. This assembly is used for the protection of the potable water supply from either pollutants or contaminants and may be used to protect against either back siphonage or backpressure.

Pressure reducing valveadjustment

Since back pressure can cause the float to stick open, there can be no irrigation heads above the vacuum breaker.  In the image below, sprinkler heads are located on a slope.  If an atmospheric vacuum breaker is used, it would have to be placed at the top of the slope and 12" above the highest head.

Pressure Reducing ValvePrice

Waterpressure Reducing Valve

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The PVB includes a check valve which is designed to close with the aid of a spring when flow stops. It also has an air inlet valve which is designed to open when the internal pressure is one psi above atmospheric pressure so that no non-potable liquid may be siphoned back into the potable water system. Being spring loaded it does not rely upon gravity as does the atmospheric vacuum breaker. This assembly includes resilient seated shut-off valves and test cocks. The PVB must be installed at least twelve (12) inches above all downstream piping and outlets. The PVB may be used to protect against a pollutant or contaminant, however, it may only be used to protect against back siphonage. It is not acceptable protection against backpressure.

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15mmPressure Reducing Valve

Howpressure reducing valveworks

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What does apressure reducing valvedo

This is a cut-away of the atmospheric vacuum breaker, available in brass or plastic.  Look at the image and note that inside the brass casing is a plastic float with a seal.  Water under pressure pushes the float up and flows out the side fitting to the irrigation system.  If water is back siphoned water pressure closes the float seal and the water is discharged through the bell and onto the ground.  Therefore, this device must be located 12" above ground and on the downstream side of each remote control valve.

The reduced pressure backflow preventer is placed on the mainline, 12" above ground.  It is located regardless of the elevation of the heads on the project.  Since it is a large device it is best to screen it with vegetation.  The cost of a 1" device is about $225.

This device is appropriate for residential use but is not effective enough to be used in high hazard situations, such as when fertilizer is injected into the irrigation water.  A 1" size atmospheric vacuum breaker costs about $25.

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It is to be placed on the mainline and below ground in a box.  One device per project is sufficient.  The double check backflow preventer may be placed without regard to the elevation of the heads on the project.  Cost for a 1" device is about $125.

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