Glossary · 24 terms
The vocabulary of the trade
The words the authority, the course and the test all assume you know.
Cross-connection
Any actual or potential physical link between a potable water system and a source of contamination or pollution.
Backflow
The undesirable reversal of water flow in a piping system that can carry non-potable water or other substances back into the potable supply.
Backsiphonage
Backflow caused by a drop or loss of pressure in the supply piping that siphons water backward through a cross-connection.
Backpressure
Backflow caused when pressure downstream of the potable connection becomes greater than the pressure of the supply itself.
Potable water
Water that is safe for drinking, cooking, and other human consumption, free from harmful levels of contaminants.
Degree of hazard
The classification of a cross-connection by the severity of harm its contaminant could cause, typically as a health hazard or a non-health hazard.
Containment vs. isolation
Two complementary protection strategies: containment protects the public main at the service connection, while isolation protects users inside the building at each hazard.
Reduced pressure principle assembly (RP)
A testable backflow prevention assembly using two independently acting check valves with a pressure differential relief valve between them, suitable for high hazard applications.
Double check valve assembly (DC)
A testable backflow prevention assembly consisting of two independently acting spring-loaded check valves, used for non-health hazard applications.
Pressure vacuum breaker (PVB)
A testable backflow prevention assembly with a spring-loaded check valve and an air inlet valve that protects against backsiphonage only.
Spill-resistant vacuum breaker (SVB)
A testable vacuum breaker that functions like a pressure vacuum breaker but is designed to avoid spilling water during pressurization, making it suitable for indoor use.
Atmospheric vacuum breaker (AVB)
A simple, non-testable backsiphonage prevention device that uses a float or disc to seal against flow and admit air when pressure is lost.
Air gap
A physical, unobstructed vertical separation between a water outlet and the flood level rim of the vessel it feeds, providing the most reliable form of backflow protection.
Check valve
A valve that allows water to flow in one direction and closes to prevent flow in the reverse direction.
Relief valve
The hydraulically operated valve between the checks of a reduced pressure principle assembly that discharges water to atmosphere when internal pressure conditions become unsafe.
Differential pressure gauge
The calibrated field test instrument that measures pressure differences across the components of a backflow prevention assembly to verify they are holding.
Test cocks
Small valved ports on a backflow prevention assembly that give a tester gauge access to the pressure zones inside the assembly.
Shutoff valves
The isolation valves at the inlet and outlet of a backflow prevention assembly that allow it to be tested, serviced, and replaced.
Detector assembly
A backflow prevention assembly for fire service lines that includes a metered bypass to detect low flows such as leaks or unauthorized water use.
Thermal expansion
The pressure increase that occurs when heated water expands inside a plumbing system that has been closed off from the supply by a backflow preventer or check valve.
Water purveyor
The utility or organization that owns, operates, and supplies a public drinking water system and is responsible for the quality of water it delivers.
Cross-connection control program
The organized system of surveys, device requirements, testing, and recordkeeping through which a water purveyor or authority manages backflow risks.
Backflow incident
An event in which contaminated or non-potable water actually enters a potable water system through a cross-connection.
Annual testing
The periodic field testing of backflow prevention assemblies, typically annual where required, set by the water authority, that verifies each assembly still works.