(A) Water outlets. A potable water system shall be protected against backflow and back-siphonage by providing and maintaining at each outlet:
(1) An air gap, as specified in division (B) below, 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) An approved device or means to prevent backflow.
(B) Minimum required air gap.
(1) Measuring method. 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 a 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 as specified hereinafter in § 50.40(A).
(C) Installation of devices.
(1) Nonpressure type vacuum breakers.
(a) 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.
(b) 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 type 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.
(D) 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 diameter of overflow not less than that given in the table set out in § 50.40(B), the overflow pipe shall be provided with an air gap as close to the tank as possible.
(2) (a) The potable water outlet to the tank or vat shall terminate a distance not less than one and one-half times the height to which water can rise in the tank above the top of the overflow.
(b) This level shall be established at the maximum flow rate of the supply to the tank or vat and with all outlets except the air gap overflow outlet closed.
(c) The distance from the outlet to the high water level shall be measured from the critical point of the potable water supply out.
(E) 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 a 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 backpressure. Where a water connection is not subject to backpressure, a vacuum breaker shall be installed on the discharge side of the last valve on the line serving the fixture or equipment.
(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 backpressure, and an air gap cannot be installed, the Manager will require adequate protection, which may include the use of an approved reduced pressure principle backflow preventer.
(F) Low pressure cutoff required on booster pumps. When a booster pump is used 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.
(Prior Code, § 8-4-4) (Ord. 428, passed 7-1-1982) Penalty, see § 50.99