ASHRAE Terminology

A Comprehensive Glossary of Terms for the Built Environment
ashrae.org/ashraeterms

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back-siphonage preventer
backflow preventer

device designed to prevent reverse flow in a water system. Note: term normally used where back-pressure-type backflow is implied.

cross connection

(1) connection between supply and return line in a hydronic system. May be used to balance system pressure, maintain a minimum circulation flow rate or temperature, etc. (2) in a piping system, a connection in which a pipe carrying potable water is connected to a closed vessel (or system) that is above atmospheric pressure and that contains nonpotable fluid. This is typically the point where a backflow preventer is required.

cross-connection control backflow prevention

(first line of defense) installation of a backflow preventer or a vacuum breaker at each cross connection on a premise to protect both premise system and the main system.

double-check valve backflow preventer

a backflow prevention device 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. May also be referred to as double-check assembly (DCA).

double-detector check (DDC) backflow preventer

device designed to serve also as a detector check on fire-protection systems where pollutants are involved. Note: DDC includes a line size, approved double-check valve backflow preventer with a metered bypass, into which has been incorporated a three-quarter inch, approved, double-check valve backflow preventer.

intermediate atmospheric vent backflow preventer

small back-pressure- and back-siphonage-type backflow prevention device designed to operate under continuous pressure, for use where certain quasi contaminants are involved.

reduced pressure detector check (RPDC)

back-pressure and back-siphonage-type device designed to serve as a detector check on fire protection systems where contaminants are involved. Note: RPDC includes a line-size approved, reduced pressure zone backflow preventer with a metered bypass into which has been incorporated a three-quarter inch, approved, reduced pressure zone backflow preventer.

reduced pressure zone backflow preventer

back-pressure and back-siphonage-type device designed to operate under continuous pressure where contaminants are involved.