Irrigation System With a Dual Check and a Chemical Injection Point
A cemetery irrigation system is supplied by a 2-inch dedicated meter off a municipal main. The original installer used a dual check valve assembly (DCVA) at the meter and a pressure vacuum breaker (PVB) at the highest point of the irrigation loop, 4 feet above the lowest sprinkler head. A fertilizer injection pump was later added downstream of the PVB. During a site survey, the inspector notes the PVB is installed 4 feet above grade but the lowest sprinkler head is at grade, the injection point is 12 inches downstream of the PVB, and the DCVA has no test cocks. The irrigation operates on a timer at 4 a.m. The site also has a pond used for makeup water.
1. Evaluate each assembly against its intended application and identify the deficiencies.
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DCVA at the meter: A dual check is a non-testable device appropriate only for low-hazard, non-health applications. With a fertilizer injection pump downstream, the hazard is now health-hazard (chemical). A DCVA is not adequate, and it cannot be field tested because it lacks test cocks. It should be replaced with a testable RPZ or, at minimum, a testable double check if the hazard were non-health - but here it is not.
PVB at the loop high point: A PVB must be installed at least 12 inches above the highest downstream outlet, and it must be above all downstream piping. The lowest head at grade means the PVB is 4 feet above it, which satisfies elevation. However, the PVB is not approved for health hazards, and a fertilizer injection point downstream makes this a health hazard. The PVB is the wrong device type.
Injection point location: The injection point should be downstream of the backflow assembly with a sufficient distance and, ideally, a check valve at the injector. Twelve inches is minimal but the real problem is device type.
2. Recommend a compliant redesign and explain the reasoning for each change.
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Replace the DCVA with a testable RPZ at the meter, since the fertilizer injection creates a health hazard. An RPZ provides protection against both backpressure and backsiphonage and is testable.
Replace the PVB with an RPZ or a testable double check plus an air gap at the loop, or eliminate the PVB if the RPZ at the meter covers the entire system. If a second assembly is retained at the loop, it must be a device approved for the hazard and installed with proper elevation and drainage.
Install a check valve at the injection point and locate the injector downstream of the backflow assembly with adequate separation. Verify the injector cannot pressurize the assembly.
Provide drainage for the RPZ relief port and freeze protection for the vault.
Address the pond makeup line with an air gap or RPZ, since a pond is a health hazard and cannot be protected by a non-testable device.
3. What testing and recordkeeping obligations follow from this redesign?
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The RPZ must be field tested at installation and annually thereafter by a certified tester, with results submitted to the purveyor on the required form. The test includes check valve differential, relief valve opening point, and air-in-water. The tester must record the assembly make, model, size, serial number, location, test results, and tester certification number. The purveyor maintains the record and may require notification before installation and inspection after. The property owner is responsible for scheduling annual tests and for keeping the assembly accessible. The inspector should document the original deficiencies and the corrective actions in the site survey report, and confirm the injection system is included in the hazard assessment.