Backflow glossary.

ABPA

The American Backflow Prevention Association, which runs a national tester certification some states accept.

Air gap

A physical vertical gap between the end of a supply pipe and the flood level of whatever it fills. The most reliable backflow protection, since nothing connects the two.

Air inlet

On a PVB or SVB, the spring-loaded valve that opens to let air into the body when pressure drops, breaking a siphon. It must open at 1.0 psid or more.

Apparent differential

On an RPZ, the #1 check reading taken early in the test while water may still be moving. The actual differential is read later with the assembly in a no-flow condition.

Approved assembly

An assembly on the USC Foundation's list, approved for a specific model, size and orientation. Most water systems accept nothing else.

ASSE 5110

A national standard for backflow prevention assembly tester certification, from ASSE International. Several states accept it in place of their own exam.

Backflow

Water flowing the wrong way in a pipe, from a customer's plumbing back into the public water supply. It happens by backpressure or backsiphonage.

Backflow assembly tester (BAT)

A person certified to field test backflow prevention assemblies. Who certifies testers depends on the state and the water system.

Backflow prevention assembly

A testable device, with shut-off valves and test cocks, installed to stop backflow at a cross-connection. RPZs, double checks, PVBs and SVBs are all assemblies.

Backpressure

Backflow caused when pressure downstream rises above the supply pressure, for example from a pump, a boiler or piping higher than the assembly.

Backsiphonage

Backflow caused when the supply pressure drops below atmospheric, for example during a main break or heavy firefighting draw, and pulls water back from the customer's side.

Bleed needle valve

Valves on the test kit that purge air from the gauge and its hoses, so the reading is true.

Bleed-off valve arrangement

A tee and valve fitted between a test cock and the gauge hose, used to divert a shut-off valve's leak so the check can still be read.

Bypass hose

The test kit's third hose, used on an RPZ to put pressure on the downstream side of the #2 check, or to carry water around a leaking #2 shut-off.

Canopy

The cover over a PVB's or SVB's air inlet. It comes off for the test and goes back on afterwards.

Check valve

A spring-loaded valve that lets water through in one direction and closes against flow the other way. Tested by the pressure drop it holds, in psid.

Containment

Protecting the public water system with one assembly at the service connection, so whatever is on the premises stays there. The water system's responsibility.

Control needle valve

Valves on the test kit that move water between its high side, low side and bypass hose, used to open an RPZ's relief valve and backpressure its #2 check.

Cross-connection

Any actual or possible connection between the drinking water system and something that could contaminate it, such as irrigation, a boiler or process equipment.

Cross-connection control program

A water system's rules for finding cross-connections, requiring assemblies, tracking annual tests and accepting test reports.

Cross-connection control specialist (CCS)

The certified person who runs a water system's cross-connection control program and decides what protection each connection needs.

Differential pressure

The pressure on one side of a valve less the pressure on the other. A check valve passes when it holds at least its minimum differential.

Disc compression

A check disc pressing further into its seat under backpressure. It can let a reading settle rather than fall, and still counts as a tight check.

Double check (double check valve assembly)

Two independent check valves in series between two shut-off valves, with four test cocks. Protects against backpressure and backsiphonage on low-hazard connections only.

Health hazard

A cross-connection where backflow could make people sick, such as chemicals, sewage or medical equipment. Needs an RPZ or an air gap.

Isolation

Protecting the people inside a building with an assembly at each hazard, such as a boiler feed or irrigation line. Usually the plumbing code's job.

Low hazard

A cross-connection where backflow would spoil the water's taste, color or smell without making anyone sick. A double check is enough.

N.I.I.O.

Notify, Identify, Inspect and Observe: what a tester does before every test, before a hose goes on.

psid

Pounds per square inch, differential: the difference in pressure between two points, which is what a backflow test kit reads.

PVB (pressure vacuum breaker assembly)

A spring-loaded check valve and a spring-loaded air inlet that opens when pressure drops. Protects against backsiphonage only, and must sit above every downstream outlet.

Relief valve

On an RPZ, the valve that opens to dump water from the zone between the two checks before the #1 check's differential falls below 2 psid.

RPZ (reduced-pressure principle assembly)

Two independent check valves with a relief valve between them that vents to air. Protects against backpressure and backsiphonage on high-hazard connections.

Shut-off valve (SOV)

The valves at each end of an assembly: #1 upstream, #2 downstream. Closing them isolates the assembly for testing, and a leaking one changes how the test is run.

Sight tube

A clear tube on a test cock that does not rise above its check valve, so the gauge can be held at the true water level during a static test.

SVB (spill-resistant vacuum breaker assembly)

A vacuum breaker built not to spill water from its air inlet at rest, so it can go indoors. Protects against backsiphonage only. Tested through one test cock and a vent valve.

Test cock (TC)

A small valve on the assembly where the test kit's hoses attach. Numbered from upstream: #1 before the #1 shut-off, #2 before the #1 check, #3 between the checks and #4 between the #2 check and the #2 shut-off.

Test kit

The differential pressure gauge, with high and low hoses, bleed needle valves and control needle valves, used to test an assembly. Water systems require it calibrated, usually every 12 months.

Test report

The form a tester completes after each test, with the assembly's details and readings, and sends to the water system by its deadline.

Thermal expansion

Water swelling as it heats. On a closed system, such as one behind a closed shut-off, a water heater can raise the pressure sharply.

USC Manual

The Manual of Cross-Connection Control from the USC Foundation for Cross-Connection Control and Hydraulic Research. Its field test procedures are the ones most states name.

Vent valve

On an SVB, the screw-closed port used during the test to drop the body to atmospheric pressure and to watch for the air inlet opening.

Water system

The utility that supplies the water: a city, a district or a private company. Its cross-connection control program decides which assemblies are tested and where reports go.

Zone of reduced pressure

The space between an RPZ's two check valves. It is held at a lower pressure than the supply, so any leak goes out the relief valve rather than upstream.

The software

• Bookings from a booking page, your own website, and an AI receptionist on your phone.
• Schedule board and route for each tester.
• Field app that scores every test, even with no signal.
• Test reports sent to the water system that serves each address.
• Card payments to your own Stripe account, and yearly renewals that charge after the test.
• Client portal for HOAs, property managers and contractors.
• $50/month flat: no per-test fee, no cut of payments.

• Every feature →What the app does, part by part.
• Compare →Next to other backflow and field-service software.
• Start free →No card. $50/month or $500/year once you go live, 45 days free.
• Free exam prep →Study questions, practice exams, device tests, a VR wet lab.

Contact

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