Backflow Base / Tester certification / Test procedures / Double check
Double check test procedure, step by step.
Double check valve assembly (DCVA). Each check holds 1.0 psid or more.
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Before you test: N.I.I.O.
Notify, Identify, Inspect and Observe, in that order, before a hose goes on.
Notify
- Tell the owner or whoever is on site that water past the assembly is about to go off, and for how long.
- Ask what is on the line before you close a valve: anything that cannot lose water or pressure, such as dialysis, boilers, medical or process equipment, livestock waterers or fire protection.
- Notify the water system too, if its program asks for notice before a test.
On a double check:
- Double checks are common on fire sprinkler lines. Call the alarm monitoring company before you close a shut-off, and tell the owner the system is out of service until you reopen it.
Identify
- Copy make, model, size and serial number off the assembly itself, not off last year's report. A swapped assembly is a new record.
- Record where it is on the premises.
- Confirm the assembly type matches the hazard the water system assigned to this connection.
- Confirm it is on the USC Foundation list of approved assemblies for the way it is installed.
On a double check:
- A double check is for low hazard only. If the connection carries a health hazard, it needs an RPZ: report it.
Inspect
- Inspect before you touch a valve. An assembly that is the wrong type, or installed wrong, fails no matter how it gauges.
- Both shut-off valves operate and hold.
- No visible leaks, cracks or freeze damage.
- Your test kit is in calibration. Most water systems want it calibrated within the last 12 months.
On a double check:
- Accessible for testing and protected from freezing.
- Not submerged. A double check in a flooded vault is not protecting anything.
- All four test cocks present, operable and not plugged.
Observe
- Watch the assembly at rest before you start: discharge, drips and noise all tell you something.
- Watch for thermal expansion on a closed system: a water heater downstream of a closed shut-off can spike the pressure.
On a double check:
- Check whether the #3 and #4 test cocks rise above the check valves. If one does not, you will need a sight tube on it.
- Note the flow direction and where you can hold the gauge level with each test cock.
TC is a test cock. SOV is a shut-off valve. psid is pounds per square inch, differential.
Pressurizing the gauge
- FLUSH TCs #1, #2, #3 and #4. Attach a sight tube to the #3 TC if it does not rise above the #1 check valve.
- ATTACH the bleed-off valve arrangement to the high hose, then attach it to the #2 TC.
- PRESSURIZE the gauge by opening the #2 TC. Open the high bleed needle valve to purge air from the gauge, then close the high bleed needle valve.
- FILL the sight tube (if attached) by opening the #3 TC, then close the #3 TC.
Check valve #1 test
The static pressure differential across check valve #1 must be at least 1 psid.
- CLOSE shut-off #2.
- POSITION the gauge at the appropriate level. With a sight tube, hold the gauge so the water level in the tube is at the centerline of the gauge. Without one, hold the gauge centerline at the same height as the #3 TC.
- CLOSE shut-off #1.
- OPEN the #3 TC and wait for the water to stop running. If it does not stop, see troubleshooting: this indicates a shut-off leak.
Record the static value as the pressure differential across check valve #1. - CLOSE the #2 TC.
- CLOSE the #3 TC.
- OPEN shut-off #1 to re-pressurize the assembly.
- ATTACH a sight tube to the #4 TC if it does not rise above the #2 check valve.
- ATTACH the high hose, with the bleed-off valve arrangement attached, to the #3 TC.
- PRESSURIZE the gauge by opening the #3 TC. Open the high bleed needle valve to purge air from the gauge, then close the high bleed needle valve.
- FILL the sight tube (if attached) by opening the #4 TC, then close the #4 TC.
Check valve #2 test
The static pressure differential across check valve #2 must be at least 1 psid.
- POSITION the gauge at the appropriate level. With a sight tube, hold the gauge so the water level in the tube is at the centerline of the gauge. Without one, hold the gauge centerline at the same height as the #4 TC.
- CLOSE shut-off #1.
- OPEN the #4 TC and wait for the water to stop running. If it does not stop, see troubleshooting: this indicates a shut-off leak.
Record the static value as the pressure drop across check valve #2. - CLOSE the TCs, detach the gauge, slowly restore customer service (open SOV #1 first, then slowly open SOV #2), and complete the test report.
Failure matrix
What can go wrong at each step, what it means, and what goes on the report.
| Step | You see | It means | Result | Next |
|---|---|---|---|---|
| 8 | Water keeps running from the #3 TC | Shut-off #1 is leaking, or #2 is leaking with backpressure | Check | Open the bleed-off valve at the #2 TC and adjust for a slight drip at the #3 TC. See troubleshooting. |
| 8 | Water recedes into the #3 TC | #2 check and shut-off #2 are leaking, with demand downstream | #2 check fails | Lower the gauge to the assembly centerline and record the #1 reading. Repair. |
| 8 | #1 check reads below 1.0 psid | #1 check is weak or fouled | #1 check fails | Repair before testing the #2 check. |
| 18 | Water keeps running from the #4 TC | Shut-off #1 is leaking | Check | Open the bleed-off valve at the #3 TC and adjust for a slight drip at the #4 TC. See troubleshooting. |
| 18 | Water recedes into the #4 TC | Shut-off #2 is leaking, with demand downstream | Record | Lower the gauge to the assembly centerline, record the #2 reading, note shut-off #2 leaks. |
| 18 | #2 check reads below 1.0 psid | #2 check is weak or fouled | #2 check fails | Record the reading; clean or repair and retest. |
Troubleshooting a DCVA
Many problems are corrected by cleaning the internal components. Carefully observe the condition of the components. Shut-off valves can be re-opened and closed for a better seal. Use lubricants only to help reassemble components, and only non-toxic ones.
| Problem | What to do |
|---|---|
| Water flows from the #3 TC (#1 check test) | Observe the gauge reading. Open the bleed-off valve arrangement at the #2 TC and watch it.
|
| Water recedes from the #3 TC (#1 check test) | The #2 check valve is leaking and SOV #2 is leaking with demand downstream. Move the gauge down to the centerline of the assembly and record the pressure differential across the #1 check valve. Repairs are needed. |
| Water flows from the #4 TC (#2 check test) | Observe the gauge reading. Open the bleed-off valve arrangement at the #3 TC and watch it.
|
| Water recedes from the #4 TC (#2 check test) | SOV #2 is leaking and there is demand downstream. Move the gauge down to the centerline of the assembly and record the pressure differential across the #2 check valve. Note that SOV #2 leaks. |
Other assemblies
- RPZ test procedure →Reduced-pressure principle backflow assembly (RPBA)
- PVB test procedure →Pressure vacuum breaker assembly (PVBA)
- SVB test procedure →Spill-resistant pressure vacuum breaker assembly (SVBA)
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