Reduced pressure backflow assembly

Plumbing · Distribution Piping In the House · printed page 268 (PDF page 269)

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Book index entries

Reduced Pressure Principle Device Reduced Pressure Principle Device – Plumbing Supply Plumbing – In-house

Text in the illustration

Reduced pressure backflow assembly water flow also called reduced pressure zone (RPZ)
also called reduced pressure zone (RPZ)
normal operation
primary check (open)
secondary check (open)
water
water flow
upstream valve
downstream valve
atmospheric vent (closed)
backflow condition
primary check (closed)
secondary check (closed)
atmospheric vent (open)
any residual water is discharged through vent port
note: mechanism simplified for clarity

Generated explanation

Two simplified cutaway diagrams show a reduced pressure backflow assembly between upstream and downstream shutoff valves. During normal operation, water flows from left to right through open primary and secondary check valves, while the atmospheric vent remains closed. In the backflow condition, the flow arrow points toward the assembly from the downstream side and both check valves are closed. The atmospheric vent opens, allowing residual water to discharge through the vent port. The diagrams compare operating states rather than proper and improper installations.

Components

reduced pressure backflow assembly upstream shutoff valve downstream shutoff valve primary check valve secondary check valve atmospheric vent vent port water supply piping