RPZ – Reduced Pressure Zone
An assembly consisting of two independently operating approved check valves together with a hydraulically operating, mechanically independent, pressure differential relief valve located between the check valves and at the same time below the first check valve. The assembly shall include properly located test cocks for the testing of the check and relief valves and tightly closing resilient seated shut-off valves at each end of the assembly.
DDC – Double Detector Check
An assembly of two independently operating approved check valves with tightly closing resilient seated shutoff valves at each end of the assembly and properly located test cocks.
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