Backflow Base / Tester certification / Test procedures / SVB
SVB test procedure, step by step.
Spill-resistant pressure vacuum breaker assembly (SVBA). Check holds 1.0 psid or more. Air inlet opens at 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 an SVB:
- SVBs are often indoors, on lab, kitchen or process lines. Find out what the line serves and agree when it can be off.
- The vent valve will spill water during the test. Protect what is underneath.
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 an SVB:
- An SVB protects against backsiphonage only, like a PVB, and is built not to spill at rest. Confirm it is an SVB and not a PVB before you choose the procedure.
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 an SVB:
- Installed vertically and upright.
- At least 12 in. above the highest downstream outlet or point of use.
- Air inlet and vent clear and unobstructed, vent valve screw present.
- Test cock 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 an SVB:
- Is the vent valve dripping at rest? That points to the check or the air inlet seat.
- Look downstream for anything that could push pressure back. An SVB is not approved for backpressure.
TC is a test cock. SOV is a shut-off valve. psid is pounds per square inch, differential.
Pressurizing the gauge
- REMOVE the canopy.
- FLUSH the test cock.
- FLUSH the vent valve by loosening the screw slightly, then re-tightening it.
- ATTACH the bleed-off valve arrangement to the high hose, then attach it to the TC.
- PRESSURIZE the gauge by opening the TC. Open the high bleed needle valve to purge air from the gauge, make a puddle of water on top of the air inlet to help judge the air inlet opening point, then close the high bleed needle valve.
Check valve test
The static pressure differential across the check valve must be at least 1 psid.
- CLOSE shut-off #2.
- POSITION the gauge with its centerline at the same height as the assembly's vent valve.
- CLOSE shut-off #1.
- OPEN the vent valve by slowly loosening and removing the screw completely, to lower the pressure in the body to atmospheric. Watch the gauge, and record the value if the air inlet opens at this point.
- READ the gauge when the flow from the vent valve stops or is no more than a slight drip. The reading is the differential pressure across the check valve. If the water does not stop, see troubleshooting: this indicates a shut-off leak.
Record the static value as the pressure differential across the check valve.
Air inlet opening
The air inlet must open before the pressure in the body is no less than 1 psi above atmospheric pressure. Keep the gauge at the height of the vent valve.
- OPEN the high bleed needle valve slowly, no more than ¼ turn, so the gauge reading doesn't drop too fast.
- OBSERVE the gauge reading when the air inlet valve opens: water begins to flow from the vent valve opening.
- CLOSE the high bleed needle valve and remove the high side hose from the bleed-off valve arrangement to drain water from the body. Observe that the air inlet has fully opened.
Record the air inlet opening point (must be 1 psid or greater). - CLOSE the TC and the vent valve.
- OPEN shut-off #1 first, then slowly open shut-off #2, replace the canopy, 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 |
|---|---|---|---|---|
| 9 | Air inlet opens while the vent valve is being opened | The air inlet opening point has been reached | Record | Record that reading as the air inlet opening point. |
| 10 | Water keeps running from the vent valve | Shut-off #1 is leaking | Check | Use the bleed-off valve arrangement to get a slight drip at the vent. See troubleshooting. |
| 10 | Check reads below 1.0 psid | Dirty or damaged check disc, damaged seat, or a leaking diaphragm or seal | Check fails | Record the reading; clean or repair and retest. |
| 11 | Gauge will not drop with the high bleed needle valve open | Shut-off #1 is leaking | Check | Use the bleed-off valve arrangement to divert the leak. |
| 12 | Air inlet opens below 1.0 psid | Dirty or damaged air inlet disc | Air inlet fails | Record the reading; clean or repair and retest. |
| 12 | Gauge falls to 0.0 psid and the air inlet never opens | Disc stuck to the seat, broken or missing spring, a leaky #2 shut-off on a parallel install, or it is a PVB | Air inlet fails | Record it. Confirm the assembly type. |
| 13 | Air inlet does not open fully when the hose is removed | Air inlet disc sticking | Air inlet fails | Record it; clean or repair and retest. |
Troubleshooting an SVBA
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 | Possible causes |
|---|---|
| Air inlet valve does not open, as the gauge drops to 0.0 psid | Air inlet disc stuck to seat Broken or missing air inlet spring Parallel installation with a leaky #2 shut-off valve It is a PVB, not an SVB |
| Air inlet valve does not open, and the gauge reading will not drop | Leaky #1 shut-off valve (use the bleed-off valve arrangement) |
| Air inlet opens below 1.0 psid | Dirty or damaged air inlet disc |
| Check valve reading below 1.0 psid | Dirty or damaged check disc Damaged seat Leaking diaphragm or seal |
| Water runs continuously from the vent valve (test #2) | Leaky #1 shut-off valve (use the bleed-off valve arrangement to get a slight drip at the vent opening) |
Other assemblies
- RPZ test procedure →Reduced-pressure principle backflow assembly (RPBA)
- Double check test procedure →Double check valve assembly (DCVA)
- PVB test procedure →Pressure vacuum breaker assembly (PVBA)
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