How to Install a Pressure Vacuum Breaker on an Irrigation Supply

Why this matters

An irrigation system is a cross-connection by design: hundreds of feet of pipe with open heads sitting in soil, fertilizer, pet waste and puddles, tied to the house's drinking water. When the street main loses pressure, from a main break or a fire hydrant opened down the block, that water can be pulled back into the house. A pressure vacuum breaker (PVB) stops it by letting air into the line before a siphon can form, but only when it sits high enough above everything downstream of it. A PVB mounted at grade in a yard that slopes uphill is a device that passes its annual test and protects nobody.

This card covers tapping the supply, setting a PVB at the right height, supporting it, and getting it into service with its first test. Testing procedure is in How to Test a Backflow Preventer; the fall shut-down and spring start-up are in Irrigation Backflow Winterization and Startup.

What a PVB is, and what it cannot do

A PVB listed to ASSE 1020 has an inlet shutoff, a spring-loaded check valve, an air inlet valve on the downstream side of the check, two test cocks and an outlet shutoff. In normal flow the check is open and the air inlet is held shut by line pressure. When supply pressure drops, the check closes and the air inlet opens, so the downstream piping fills with air instead of pulling water back.

            air inlet under canopy
                    |
  supply   inlet  +-+--------+   outlet
  from --->[V1]---|  check   |---[V2]---> to zone
  tap      shut   | valve    |    shut      valves
           off    +----------+    off
              TC1 upstream     TC2 downstream
              of the check     of the check
  ---------- critical level line on body ----------
   at least 12 in above the highest downstream
   outlet and the highest downstream pipe

Three limits decide whether a PVB is allowed at all:

• Elevation. It works only by gravity and air. The adopted code requires it to be installed at least 12 in above the highest downstream outlet and the highest point of downstream piping (IPC Section 608 and UPC Section 603 in the 2021 editions, as adopted). The 12 in is measured from the device's critical level, which the maker marks on the body; where it is not marked, the maker's instructions say what point to use.
• No backpressure. A PVB protects against backsiphonage only. A booster pump downstream, a connection to another water source, or a fertilizer or chemical injector creates backpressure or a high hazard, and needs a reduced pressure principle assembly (RPZ) listed to ASSE 1013.
• It spills. The air inlet discharges water when it opens, especially at startup. A PVB does not go indoors or anywhere a spill does damage. Where a vacuum breaker must sit indoors, a spill-resistant type (ASSE 1056) exists for that purpose.

The water purveyor's program can override all of this. Many utilities run a cross-connection program that names the device for irrigation (some accept a PVB, some require an RPZ, some accept a double check assembly), requires a permit, and requires a test report on file. Call before you buy the device.

Steps

1. Locate buried utilities before you dig. Call the one-call center (811) and wait for the marks before trenching from the tap to the device location. Hand-dig inside the marked tolerance zone. If you strike a gas line, everyone leaves the area, nobody starts an engine or uses a phone near it, and you call the gas utility and 911 from a safe distance; a struck electrical line means stay clear of the trench and the tools in it and call the utility. Do not try to plug or bury either.

2. Tap the supply with its own isolation valve. Tee off the service where the adopted code and the purveyor allow, and put a full-port shutoff at the tap so the irrigation can be isolated without shutting off the house. Why: the next repair to the PVB, and every winterization, needs it. Joining method per The Joining Method Standard SOP. The house main is off and the service drained while the tee goes in; reopen the main with the new tap valve closed, and check the tee dry before you go on.

3. Find the highest point downstream, then set the height. Walk the whole zone layout: the highest sprinkler head, the highest drip emitter, and any pipe that climbs a wall, a planter or a slope. Measure each against the grade where the PVB will stand. The device's critical level goes at least 12 in above the highest of them. What breaks if skipped: the yard's highest head is often far from the house and uphill, and a PVB set by habit at the usual height beside the foundation sits below it.

4. Set the assembly on a rigid riser and support it. Rise out of the ground in copper, brass or galvanized, not exposed PVC, which breaks when kicked and degrades in sunlight. Mount the assembly level with the test cocks reachable and the canopy clear. Strap the riser to a wall or a driven support so the weight of the assembly and the torque of a tester's fittings do not bend the riser at grade. Leave room around the device for a tester's hoses and for the canopy to vent.

5. Flush the line before the internals go in. Most PVBs let you remove the bonnet, the air inlet poppet and the check. With the internals out, open the supply and flush the new piping through the body until it runs clean, then reassemble. Why: pipe chips, solder and dirt from the trench are exactly what lodges on a check seat, and a check held open by a chip fails its first test. Flushing through a finished assembly puts the debris where it does the most harm.

6. Restore slowly and pressurize. Open the tap's isolation valve slowly with the PVB's outlet shutoff closed, then open the inlet shutoff, then the outlet. Expect a brief spurt from the canopy as the air inlet seats; a steady discharge means the poppet is not seating and the device is not ready. Stand to the side of the canopy, not over it, while it seats.

7. Have it tested by a certified tester before it goes into service. The initial test is required by most programs at installation and then at the interval the purveyor sets, commonly annually, by a tester certified where your state or locality certifies them. If you hold that certification, test per How to Test a Backflow Preventer and file the report; if not, the tester does, and the job is not closed until the report is on file.

The install record, filled in for one job

A ranch house on a lot that slopes up toward the back fence. Five irrigation zones, plus a drip line feeding a raised planter on the deck. UPC jurisdiction; the purveyor accepts a PVB for residential irrigation with no injector, with a permit and an initial test report.

Why the drip line governed. The back-fence head at 30 in looked like the high point and would have called for a critical level at 42 in. The planter line, which climbs the deck, sits 22 in higher than that, and it is downstream piping like any other. Measured against the head alone, the PVB would have been installed 22 in too low, 10 in below the drip line it is meant to protect against.

The options weighed. The device could have gone uphill near zone 4, but the planter line at the house would still have governed, at 52 in above house-side grade. Feeding the planter from a separate small device was possible, at the cost of a second annual test. An RPZ would not need the elevation, but it discharges water when it relieves, needs a spot where that water can drain, and still needs a certified test each year. The customer chose the single PVB on the wall, and the 2 in of margin was kept rather than trimmed, because the height is a minimum and any rounding has to run upward.

Finish test

• Height, measured last. With everything assembled, measure from the critical level mark to house-side grade (66 in here) and compare to the highest downstream point plus 12 in (64 in). Re-measure after the brackets are tightened; a riser that settled an inch is the most common way an installed PVB loses its margin.
• Each zone runs from the controller without the canopy discharging.
• Static test after shutoff. Close the tap valve with a zone running: the canopy opens and vents as the pressure drops, which is the device doing its job. Reopen the tap valve slowly and confirm the canopy reseats dry.
• Test report passed and filed, and the date written on the work order.

What changes the device

A fertilizer or chemical injector, now or planned. That is a high hazard with possible backpressure, and the model codes, as adopted, call for an RPZ or an air gap, not a PVB. Ask whether the customer intends to add one before choosing the device.

A booster pump or a second source. A pump downstream or a connection to a well or a rainwater tank creates backpressure; an RPZ, and possibly a purveyor-mandated air gap, replaces the PVB.

A flat yard. With nothing climbing, the usual 12 in above the highest head is often easy to meet beside the foundation, and the measurement still has to be made and written down.

References

• IPC 2021 Section 608 and UPC 2021 Section 603, as adopted, for backflow protection of irrigation systems; check the current edition and the purveyor's cross-connection program.
• ASSE 1020 (pressure vacuum breakers), ASSE 1013 (reduced pressure principle assemblies), ASSE 1056 (spill-resistant vacuum breakers); the device maker's installation instructions.
• See related: How to Test a Backflow Preventer
• See related: Irrigation Backflow Winterization and Startup