Types of Backflow Preventers

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Dual Check Valve Assembly

Dual Checks are designed for use in low hazard applications where a fully approved, testable backflow preventer is not required. Check with the local authority having jurisdiction for acceptance.

Reduced Pressure Principle Assembly (RP)

An assembly containing two (2) independently acting, approved check valves together with a hydraulically operated, mechanically independent, differential pressure relief valve located between two check valves. This assembly is intended for use in continuous and non-continuous pressure applications, in back-siphonage and backpressure conditions. The Reduced Pressure Principle Assembly is intended to provide protection in low and high hazard situations.

1) The pressure differential relief valve must operate to maintain ther "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.