A double check valve or double check assembly (DCA) is a backflow prevention assembly designed to protect water supplies from contamination. It consists of two check valves assembled in series usually with a ball valve or gate valve installed at each end for isolation and testing. Often, test cocks (very small ball valves) are in place to attach test equipment for evaluating whether the double check assembly is still functional.
The double check valve assembly is suitable for prevention of back pressure and back siphonage, but is not suitable for high hazard applications. It is commonly used on lawn irrigation, fire sprinkler and combi-boiler systems.
A reduced pressure (RP) backflow prevention assembly is a assembly used to protect the potable water supply from contaminated water. An RP valve consists of an automatic pressure relief valve in between two check valves. The pressure relief valve opens to the atmosphere in the event of a reduction in the pressure differential between the first two chambers of the assembly.
The assembly is considered to provide redundant means of protection because: (1) check valves keep water flowing in one direction only, and; (2) the relief valve will operate in the event the supply pressure drops below atmospheric pressure.
Reduced pressure backflow preventers can be abbreviated RP, RPP (Reduced Pressure Principle) and RPZ (Reduced Pressure Zone). RP assemblies protect against backsiphonage and backpressure, and may be used where a potential hazard exists. RP valves can be found in commercial buildings, hospitals, and industrial applications.
A Pressure Vacuum Breaker (PVB) is a type of backflow prevention assembly, used to keep non-potable (or contaminated) water from entering the water supply. A PVB is similar to an atmospheric vacuum breaker (AVB), except that the PVB contains a spring-loaded poppet. This makes it acceptable for applications that are high hazard or where valves are downstream. Pressure vacuum breakers must be protected from freezing when installed outdoors. PVBs usually have test cocks, to which specially-calibrated gauges are attached, in order to ensure that they are functioning properly.
PVBs are manufactured by Watts, Febco, Zurn and other manufacturers. Backflow prevention devices such as PVBs are regulated by the International Plumbing Code, but may also be required by government regulations.
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