Test cocks
Small valved ports on a backflow prevention assembly that give a tester gauge access to the pressure zones inside the assembly.
Test cocks are the small ball valves threaded into the body of a testable backflow prevention assembly at specific points: upstream of the first check, in the zones between components, and downstream. They exist so a tester can attach the hoses of a differential pressure gauge and read what is happening inside the assembly without disassembling it. Their presence is part of what distinguishes a testable assembly from a simple non-testable device.
In the field, test cocks are both essential and vulnerable. They are small, they protrude, and they live outdoors or in mechanical rooms where they collect debris, corrosion, and accidental knocks. A seized or broken test cock can make an otherwise healthy assembly untestable until it is repaired. Testers routinely flush each test cock briefly before attaching hoses, because sediment blown into a gauge can damage the instrument and distort readings.
Testers and property owners should keep test cocks protected and functional. They should remain closed and ideally fitted with plugs or caps between tests to keep out insects and grit, and they must never be used as convenient outlets to draw water for other purposes, since that invites contamination and wear. During any service call it is worth confirming that each test cock opens, closes, and seals properly, because the next scheduled test depends on all of them working.
Related terms
| 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. |
| Shutoff valves | The isolation valves at the inlet and outlet of a backflow prevention assembly that allow it to be tested, serviced, and replaced. |
| 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. |
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