(a) RPs may be utilized at premises where a substance is handled that would be hazardous to the public health if introduced into the potable water system. An RP is normally used in locations where an air gap is impractical. An RP is effective against both backsiphonage and backpressure.
(b) RPs shall be sized to provide an adequate supply of water and pressure for the premises being served. Flow characteristics are not standard. Consult manufacturer’s specifications for specific performance data.
(c) Premises where interruption of water supply is critical shall be provided with two assemblies installed in parallel. They shall be sized in such a manner that either assembly will provide the minimum water requirements while the two together will provide the maximum flow required.
(d) Bypass lines are prohibited. Pipe fittings which could be used for connecting a bypass line shall not be installed.
(e) (1) The assembly shall be readily accessible for testing and maintenance and shall be located in an area where water damage to buildings or furnishings will not occur from relief valve discharge. An approved air gap funnel assembly may be used to direct minor discharges away from the assembly; this assembly will not control flow in a continuous relief situation. Drain lines to accommodate full relief valve discharge flow should be considered.
(2) RPs are typically installed above grade in well drained areas, but may be installed below grade if an adequate drain to daylight is provided.
(3) Enclosures shall be designed for ready access and sized to allow for the minimum clearances established below. Removable protective enclosures are typically installed on the smaller assemblies. Daylight drain ports shall be provided to accommodate full pressure discharge from the assembly.
(4) All assemblies larger than two inches shall have a minimum of 12 inches on the back side, 24 inches on the test cock side, and the relief valve opening shall be at least 12 inches plus nominal size of assembly above the floor or highest possible water level. Headroom of six feet is required in vaults without a fully removable top. A minimum access opening of 24 inches square is required on all vault lids.
(5) Assemblies installed more than five feet above floor level must have a suitable platform for use by testing or maintenance personnel.
(f) The assembly must be protected from freezing and other severe weather conditions.
(g) Vertical installation is prohibited.
(h) Lines shall be thoroughly flushed prior to installation. A strainer with blowout tapping may be required ahead of the assembly.
(i) The property owner assumes all responsibility for leaks and damage. The owner shall also see that the vault is kept reasonably free of silt and debris.
(j) All RP assemblies shall be tested in accordance with this division. Any premises that have RP assemblies that are point-of-use protection without high hazard premises isolation protection shall be tested every six months. Any premises that have an RP assembly as premises isolation without high hazard point-of-use protection assembly shall be tested every six months. Tests are the responsibility of the assembly owner. The owner shall notify the director upon installation of any backflow prevention assembly.
(k) Variances from these specifications will be evaluated on a case-by-case basis. Any deviations shall be prohibited without prior written approval of the director.
Reduced Pressures Principle Large Assembly
Notes:
(1) Large assemblies are those that are 2-1/2 inches and larger.
(2) Assembly shall not be subject to flooding.
(3) Drain lines shall be sized to accommodate full relief valve discharge flow. See flow chart 12.5-555.2.
(4) Reduced pressure backflow assemblies are typically installed above grade in well draining areas, but may be installed below grade if an adequate drain to daylight is provided.
(5) The installation on the supply line (ahead of assembly) of a strainer with tapping blowout may be required. See standard detail 12.5-555.3.
Relief Valve Discharge for Reduced Pressure Backflow Assemblies
Strainers
One of the most common causes of backflow prevention assembly failure is the accumulation of sand, scale or debris trapped in the assembly. This debris can cause the assembly to fail its required testing and can contribute to a shorter working life span of the assembly.
Reduced Pressure Principle Small Assembly
Notes:
(1) Assembly must be protected from freezing.
(2) Removable insulated covers can be used.
(3) Enclosures shall be in an area not subject to flooding.
(4) The installation on the supply line (ahead of assembly) of a strainer with tapping blowout may be required. See standard detail no. 12.5-555.3.
(Ord. 12274, § 1, passed 11-28-1995)