A. Water Outlets. A potable water system shall be protected against backflow and back-siphonage by providing and maintaining at each outlet:

1. Air Gap. An air gap, as specified in subsection B of this section, between the potable water outlet and the flood-level rim of the fixture it supplies or between the outlet and any other source of contamination; or

2. Backflow Preventer. An approved device or means to prevent backflow.

B. Minimum Required Air Gap.

1. How Measured. The minimum required air gap shall be measured vertically from the lowest end of a potable water outlet to the flood rim or line of the fixture or receptacle into which it discharges.

2. Size. The minimum required air gap shall be twice the effective opening of the potable water outlet unless the outlet is a distance less than three times the effective opening away from a wall or similar vertical surface, in which cases the minimum required air gap shall be three times the effective opening of the outlet. In no case shall the minimum required air gap be less than shown in Table 13.72.370(1), codified at the end of this chapter.

C. Approval of Devices. 1. Before any device for the prevention of backflow or siphonage is installed, it shall have first been certified by a recognized testing laboratory acceptable to the agency director. Devices installed in a building’s potable water supply distribution system for protection against backflow shall be maintained in good working condition by the person or persons responsible for the maintenance of the system.

2. The agency director or his designee shall inspect routinely such devices and if they are found to be defective or inoperative, shall require the replacement thereof.

D. Installation of Devices.

1. Nonpressure Type Vacuum Breakers. Atmospheric vacuum breakers shall be installed with the critical level at least six inches above the flood-level rim of the fixture they serve, and on the discharge side of the last control valve to the fixture. No shutoff valve or faucet shall be installed beyond the vacuum breaker. For closed equipment or vessels such as pressure sterilizers the top of the vessel shall be treated as the flood-level rim but a check valve shall be installed on the discharge side of the vacuum breaker.

2. Reduced Pressure Principle Backflow Preventer. A reduced pressure principle backflow preventer may be installed subject to full static pressure.

3. Devices of All Types. Backflow and back-siphonage preventing devices shall be accessibly located, preferably in the same room with the fixture they serve. Installation in utility or service spaces, provided they are readily accessible, is also permitted.

E. Tanks and Vats--Below Rim Supply.

1. Where a potable water outlet terminates below the rim of a tank or vat and the tank or vat has an overflow of a diameter not less than that given in Table 13.12.070(2), codified at the end of this chapter, the overflow pipe shall be provided with an air gap as close to the tank as possible.

2. The potable water outlet to the tank or vat shall terminate a distance of not less than one and one-half times the height to which water can rise in the tank above the top of the overflow. This level shall be established at the maximum flow rate of the supply to the tank or vat with all outlets except the air gap overflow outlet closed. The distance from the outlet to the high water level shall be measured from the critical point of the potable water supply outlet. The following diagram illustrates this principle:

Figure 3.85 Properly protected tank with below rim supply.

F. Protective Devices Required. Approved devices to protect against backflow and back-siphonage shall be installed at all fixtures and equipment where backflow and/or back-siphonage may occur and where minimum air gap cannot be provided between the water outlet to the fixture or equipment and its flood level rim.

1. Connections Not Subject to Back Pressure. Where a water connection is not subject to back pressure, a vacuum breaker shall be installed on the discharge side of the last valve on the line serving the fixture or equipment. A list of some conditions requiring protective devices of this kind is given in Table 13.12.070(3), codified at the end of this chapter.

2. Connections Subject to Backpressure. Where a potable water connection is made to a line, fixture, tank, vat, pump or other equipment with a hazard of backflow or back-siphonage where the water connection is subject to back pressure, and an air gap cannot be installed, the public works administrator will require adequate protection which may include the use of an approved reduced pressure principle backflow preventer. A partial list of such connections is shown in Table 13.12.070(4).

G. Low Pressure Cutoff Required on Booster Pumps. When a booster pump is required on a water pressure booster system and the possibility exists that a positive pressure of less than 20 psi may occur on the suction side of the pump, there shall be installed a low pressure cutoff on the booster pump to prevent the creation of a vacuum or negative pressure on the suction side of the pump, thus cutting off water to other outlets. (Ord. 1987-9 § 3.8, 1987)