What is the function of the relief valve on an RPZ backflow preventer?

• A. To discharge water and relieve pressure when backflow or relief conditions occur.
• B. To regulate irrigation pressure entering the head.
• C. To measure backflow rate.
• D. To shut off the water supply during maintenance.

Answer: (A)

The main idea is that the relief valve on an RPZ backflow preventer is a safety vent that dumps water to a drain to prevent reverse flow when pressure conditions could cause contamination. Inside an RPZ there are two checks with a relief valve between them. Under normal operation the checks hold water in and nothing vents. If backflow or a relief condition could occur—for example a pressure drop on the downstream side or a backpressure situation—the relief valve opens and discharges water to the drain. That venting prevents any contaminated water from being pushed backward through the checks into the potable supply. It’s not used to regulate irrigation pressure, measure flow, or shut off water during maintenance; its purpose is to relieve pressure and discharge to protect the system.