FAQ

Types of Backflow Preventers

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Reduced Pressure Principle Detector Assembly (RPDA)

A specifically designed assembly composed of a line-sized approved reduced pressure principle backflow assembly, with a specific by-pass water meter, and a meter-sized approved reduced pressure principle backflow prevention assembly. The meter shall register accurately for all flows up to three (3) GPM. The meter shall show a registration for all flows above three (3) GPM, This assembly is intended for use in continuous and non-continuous pressure installations, in back-siphonage and backpressure conditions. The Reduced Pressure Principle Detector Assembly is intended to provide protection in low and high hazard situations.

Testing:
1) The pressure differential relief valve must operate to maintain the "zone" between the two check valves at least 2 psi less than the supply pressure.
2) The No. 2 check valve shall be tight against reverse flow under all pressure differentials.
3) The static pressure drop across check valve No. 1 should be at least 3.0 psi greater than the relief valve opening point (test no. 1). This 3.0 psi "buffer" will prevent the relief valve from discharging during small fluctuations in upstream line pressure. A "buffer" of less than 3.0 psi does not imply a leaking check valve No. 1 (i.e. allowing backflow), but rather is an indication of how well the check valve No. 1 is holding.

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Text courtesy of Wilkins a Zurn company.