A valve that ensures water in your pipes only flows one direction — preventing contaminated water from getting back into the clean water supply.
A mechanical device installed in a plumbing system to prevent contaminated water from flowing backward into the potable water supply. Backflow can occur when pressure drops in the supply line, creating a siphon effect. Types include reduced pressure zone (RPZ) assemblies, double check valves, and pressure vacuum breakers, each suited to different hazard levels.
Backflow preventers are code-mandated on most commercial and many residential projects, so missing them in a plumbing takeoff creates a scope gap that surfaces during inspection rather than bid review. The device type drives cost significantly, since an RPZ assembly with its required annual testing and clearance space costs far more to furnish and install than a simple double check valve. Estimators who pin down the correct hazard level early avoid both under-bidding the assembly and absorbing change orders for the testing and tamper-sensitive installation requirements.
Reviewing the plumbing spec for a medical office bid, the estimator sees the irrigation and boiler feeds are classified as high-hazard, so she prices RPZ assemblies plus a line item for the initial certified test rather than the cheaper double-check valves shown on an earlier addendum.
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