Every backflow term, explained

A

Air gap (AG)

A physical, unobstructed vertical space between a water outlet and the flood-level rim of the receiving tank or fixture. It is the most reliable form of backflow protection because there’s no mechanical part to fail. Air gaps are inspected rather than tested.

Approved assembly

A backflow assembly model that has passed laboratory and field evaluation and appears on the list Washington purveyors accept. Only approved assemblies count for compliance.

Atmospheric vacuum breaker (AVB)

A simple, non-testable device that protects against back-siphonage only. It can’t be under continuous pressure, so it’s generally not accepted where a testable assembly is required.

B

Backflow

Any unwanted reversal of flow, where water (and whatever is in it) moves from a customer’s plumbing back toward the public water supply.

Backpressure

Backflow caused when pressure on the customer side exceeds the supply pressure, for example from a boiler, pump or elevated tank.

Back-siphonage

Backflow caused by negative or reduced pressure in the supply, such as during a water-main break or heavy hydrant use, which can pull water backward out of a property.

BAT (Backflow Assembly Tester)

A person certified by the Washington State Department of Health to test backflow assemblies. Purveyors only accept test reports from certified BATs.

Bypass meter

The small meter on a detector assembly that registers low flows, used to reveal leaks or unauthorized water use on fire lines.

C

CCS (Cross-Connection Control Specialist)

A DOH-certified specialist who develops and runs a water system’s cross-connection control program, including hazard surveys and deciding what protection each connection needs.

Check valve

A spring-loaded valve that lets water flow in one direction and closes against reverse flow. Most testable assemblies contain two, in series.

Cross-connection

Any actual or potential connection between drinking-water plumbing and a source of contamination: an irrigation system, boiler, pond fill, chemical dispenser, hose submerged in a bucket and so on.

Cross-connection control program

The program every Group A public water system in Washington must run to find cross-connections and make sure they’re protected and tested.

D

DCVA (Double check valve assembly)

Two independent check valves between two shut-off valves, with four test cocks. It protects against backpressure and back-siphonage for low-hazard connections, like many irrigation and fire-sprinkler systems.

DCDA (Double check detector assembly)

A DCVA with a metered bypass, typically installed on fire-sprinkler lines.

Differential pressure (psid)

The difference in pressure across a check valve or relief valve, measured in pounds per square inch differential. Test results are recorded in psid.

F

Failed test

A test where a check valve doesn’t hold, a relief valve doesn’t open at the right differential, or a shut-off won’t close tight enough to test. The assembly must be repaired or replaced, then retested.

H

High health hazard

A cross-connection involving substances that could cause illness or death, such as chemicals, sewage or medical waste. It requires an air gap or reduced-pressure assembly.

I

In-premises protection

Backflow protection at individual fixtures or equipment inside a building, governed by the plumbing code and your local plumbing official.

P

Premises isolation

A backflow assembly at or near the service connection that protects the public water system from the entire property. Purveyors decide when this is required.

Purveyor

Your water utility: the city, water district or PUD that supplies your water, sends your test notice and receives your test report.

PVBA (Pressure vacuum breaker assembly)

A testable assembly with a spring-loaded check and an air-inlet valve that protects against back-siphonage only. Common on residential irrigation, and it must be installed above the highest downstream outlet.

R

Relief valve

The valve between the two checks on a reduced-pressure assembly. If either check leaks, it opens and discharges water to the atmosphere rather than letting it flow backward.

RPBA (Reduced pressure backflow assembly)

Two independent checks with a relief valve between them. It protects against backpressure and back-siphonage for high-hazard connections. Also called an RP or RPZ.

RPDA (Reduced pressure detector assembly)

An RPBA with a metered bypass, used on high-hazard fire-sprinkler systems (for example, those with antifreeze or chemical additives).

S

Shut-off valves

The two valves at each end of an assembly, numbered #1 (upstream) and #2 (downstream). They isolate the assembly for testing and repair.

SVBA (Spill-resistant vacuum breaker assembly)

Similar to a PVBA but designed not to spit water when it pressurizes, which makes it suitable for indoor locations.

T

Test cocks

Small valves on an assembly where the tester connects the gauge hoses.

Test kit (differential pressure gauge)

The calibrated gauge a BAT uses to measure pressure across each valve. It must be accuracy-verified regularly for results to be valid.

Test report

The official record of the test: assembly details, readings, pass or fail, and the tester’s certification. It’s submitted to the purveyor.

Test tag

A durable tag attached to the assembly showing the date of the last test and who performed it.