Backflow Preventers

Marine backflow prevention valves are installed where reverse flow must be prevented and cross-contamination risk must be controlled, particularly in potable water lines, seawater separation systems, and auxiliary shipboard piping. Selection should be based on flow direction, line pressure, allowable pressure loss, drainage of the relief zone, and system test requirements.

This category includes the Cla-Val RP2M, a reduced pressure principle backflow preventer. The assembly consists of two independent spring-loaded poppet check valves with an automatic differential pressure relief valve located between them. Under normal forward flow, both check valves remain open and the relief valve stays closed. If flow stops or a backflow condition develops, the intermediate zone discharges to atmosphere, limiting return of contaminated fluid to the supply side.

The RP2M is specified for potable water and seawater isolation service, with union-end versions in accordance with MIL-F1183 and flanged versions to MIL-F20042 Class 150. Published data indicate ANSI B16.15 threaded connections, sizes 3/4", 1", 1 1/4", and 1 1/2", maximum working pressure 150 psi, hydrostatic test pressure 300 psi, and maximum operating temperature 110 °F. Materials of construction include ASTM B-61 bronze body and cover, Monel/Delrin trim, Buna-N seals, and a nylon-reinforced Buna-N diaphragm.

Installation requires horizontal orientation, with the differential relief valve venting vertically downward. The installation should include suitable drainage and an air gap at the relief discharge. Maintenance checks should cover both check valves, the relief valve, test cocks, elastomeric sealing elements, and the actual pressure drop at operating flow. Media compatibility, seat leakage, and relief discharge behavior should be verified during inspection and functional testing.