High-Hazard Tenant Connections in a Strip-Mall Restaurant
A 4,000-square-foot restaurant in a strip mall is served by a 1.5-inch water service at 80 psi. The tenant has a carbonator for fountain drinks, an espresso machine with a direct water connection, a mop sink with a 10-foot hose that is often left submerged in a bucket of sanitizer, and an irrigation system with a fertilizer injection pump. The building also has a wet fire-sprinkler system supplied from the same service. The water purveyor requires containment backflow protection at the service and annual testing. The tenant currently has a pressure vacuum breaker on the irrigation line and a hose-bibb vacuum breaker on the mop sink. The building owner wants to avoid an RPZ because it would reduce pressure and require a drain. The local health department has also asked about protection for the carbonator and espresso machine.
1. Classify the hazards and select the containment assembly. Can a double check or pressure vacuum breaker be used at the service?
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The fertilizer injection makes the irrigation a high-hazard cross-connection because a toxic chemical can be siphoned or pushed back into the potable line. A pressure vacuum breaker is not adequate downstream of an injector, and a double-check assembly is not adequate for a high hazard. The containment assembly at the service should be a reduced-pressure-principle backflow assembly (RPZ), with no bypass, installed in an accessible location with a drain and freeze protection. The carbonator and espresso machine also need point-of-use protection, and the mop sink with a submerged hose is another high-hazard connection. The RPZ protects the public main from all of these, but it does not replace fixture-level protection. The fire-sprinkler branch also needs the protection required by the local code and the purveyor; a wet system without antifreeze may use a double check, but the containment RPZ is still required for the high-hazard tenant connections.
2. What protection is needed at the mop sink and the beverage equipment? Explain why the existing hose-bibb vacuum breaker is not enough.
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The mop sink is the clearest problem. A hose-bibb vacuum breaker is not adequate when a hose can be left submerged in a bucket; the vacuum breaker can be defeated by backpressure or a continuously attached hose. Provide a fixed air gap at the mop sink, or a reduced-pressure-principle assembly on that branch, and keep the hose end above the flood level. For the carbonator, use an air gap or a listed dual-check/backflow device as required by the local code; carbonated water must not be able to back up into the potable line. The espresso machine’s direct connection needs the backflow protection specified for its boiler, often an air gap or a listed RP assembly. Label each device and keep it accessible.
3. What are the installation, testing, and thermal-expansion implications of the service RPZ?
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Install the RPZ at the service downstream of the meter and upstream of all fixtures, with a full-size drain, accessible test cocks, and no bypass. It must be tested by a certified tester at installation and annually, and the test report must go to the purveyor. Because the RPZ creates a closed system, add a thermal-expansion tank on the water heater; otherwise the T&P valve may discharge. The RPZ will drop pressure, so check the residual pressure at the topmost fixture and add a booster pump if needed. Do not remove the device to solve a pressure complaint. Keep the irrigation PVB only if there is no injection; with injection, replace it with an RPZ at the irrigation connection.