An RP assembly discharges steadily from its relief valve with no water being used downstream. What is the most common cause?
- A spring on the second check that is too strong
- A supply pressure that is steady and too high
- An outlet shutoff valve that is fully closed
- Debris holding the first check valve off its seat
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D. Debris holding the first check valve off its seat
A fouled first check lets supply pressure leak into the zone, and the relief valve opens to hold the zone below supply. A closed outlet shutoff by itself does not cause discharge on a sound assembly.
Reference: USC FCCCHR Manual of Cross-Connection Control, 10th ed., field test procedures; troubleshooting
An RP assembly spits briefly from the relief valve several times a day during periods of no flow, but passes its field test. What is the likely cause?
- A ruptured relief diaphragm
- Fluctuating supply pressure
- A missing first check spring
- A closed inlet shutoff valve
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B. Fluctuating supply pressure
When supply pressure dips, the trapped zone pressure is momentarily too close to supply and the relief valve opens for an instant. The effect is worst when the first check's buffer over the relief opening point is small. A ruptured diaphragm would fail the test.
Reference: USC FCCCHR Manual of Cross-Connection Control, 10th ed., field test procedures; troubleshooting
During an RP test, the differential is lowered all the way to zero and the relief valve never opens. What should be suspected?
- A relief valve stuck closed or a plugged sensing passage
- A first check valve held open by pipe debris
- A second check valve with a weak spring
- A test gauge that is reading 0.2 psi low
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A. A relief valve stuck closed or a plugged sensing passage
The relief valve should open at 2.0 psi or more; staying shut at zero differential means it is seized by scale or corrosion, or the passage feeding its diaphragm is blocked. This is a failed test and a dangerous condition.
Reference: USC FCCCHR Manual of Cross-Connection Control, 10th ed., field test procedures; troubleshooting