The following methods and devices for prevention of backflow or back-siphonage shall be provided for the conditions indicated.
(A) Dry chemical feeders. Dry chemical feeders submerged water inlets shall have a non-pressure type vacuum breaker installed on the atmospheric side of the last control valve.
(B) Fluoride chemical feeders.
(1) Sodium fluoride saturation tank makeup water lines shall have air gaps between the overflow rim of the tank and the water supply pipe of at least four inches.
(2) When using the positive displacement fluoride chemical solution feed pumps, if the point of application to the water supply is at atmospheric pressure and is below the maximum elevation of the solution in the fluoride discharge line at a point above the liquid level in the tank. If the point of application is a pressure line, then a pressure type vacuum breaker shall be used.
(C) Filter surface wash agitators. Either a non-pressure type vacuum breaker shall be installed on the atmospheric side of the last control valve of each agitator, or pressure type vacuum breaker, or an approved backflow preventer shall be installed on the pipe line supplying only the agitators.
(Prior Code, § E-V-7)