New Installation: Air Gap Versus Reduced-Pressure Assembly on a Boiler Feed Line
A mechanical contractor is installing a new boiler feed line in a 12-story office building. The boiler uses chemical treatment, and the feed line is connected to the potable water system. The contractor proposes a reduced-pressure principle backflow prevention assembly inside the mechanical room, but the room is tight and the assembly would be installed at ceiling height with no drain nearby. The local authority requires the highest level of protection for boiler feed connections. The building owner wants to minimize floor space and avoid a floor drain. The contractor asks the tester, as the backflow expert, whether an air gap would be acceptable and what the installation requirements would be.
1. Is an air gap an acceptable choice for this boiler feed connection, and what does it require that the reduced-pressure assembly does not?
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Yes. An air gap provides the highest degree of protection against backflow, and it is acceptable, and often preferred, for a boiler feed connection where chemical treatment is present. However, an air gap requires a physical separation between the potable water outlet and the flood-level rim of the receiving vessel. That separation must be at least twice the diameter of the effective opening of the outlet, with a minimum of 1 inch, and it must be maintained at all times. The air gap also requires a receiving vessel or a drain that can handle the discharge, and it must be located where the gap can be inspected. Unlike a reduced-pressure assembly, an air gap has no testable mechanical components, so it is not subject to annual testing, but it must be inspected and kept free of obstructions. The contractor must confirm the receiving vessel's flood-level rim and provide a drain or receptor sized for the discharge.
2. The contractor decides to keep the reduced-pressure assembly instead. What installation conditions must be met for that choice to be code-compliant, and how should the tester document the decision?
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A reduced-pressure assembly must be installed where it can be tested and maintained. That means adequate clearance around the assembly, a suitable drain to receive relief valve discharge, and protection from freezing and flooding. The assembly must be installed in a horizontal position unless the manufacturer approves otherwise, and it must be accessible for testing and repair. The relief valve discharge must terminate at a point that does not create a hazard, and the assembly must not be installed at ceiling height where it cannot be safely reached. If the mechanical room cannot meet these conditions, the contractor must relocate the assembly or choose another approved method. The tester should document the installation conditions, the clearance, the drain, and the assembly's location, and should note in the report that the assembly was installed in accordance with the manufacturer's instructions and the local code.