Approved Backflow Prevention Assemblies
Charleston Water System requires all backflow prevention assemblies to be approved by the University of Southern California’s Foundation for Cross-Connection Control and Hydraulic Research (USC-FCCCHR). Charleston Water System has required USC approval since 1989.
Although many manufacturers advertise that their backflow prevention assemblies are approved for a vertical orientation (through ASSE or IAPMO), unless the assembly has been approved by the USC Foundation for a vertical orientation, Charleston Water System will not approve the selection or installation of that assembly. Please call our office at (843) 727-7148 to verify the approval rating of a particular assembly before installing it. Please note that not all models or sizes of a particular backflow assembly are USC-approved.
In addition, manufacturers typically ship their product as a complete assembly, which consists of an inlet shutoff valve with the number one test cock on the up-stream side of the valve, an outlet shutoff valve, and the backflow prevention device with three test cocks. If any part of the complete assembly is removed, the USC Foundation approval is invalid. Contractors are encouraged to install the assembly as it was shipped, and not to change or alter the design characteristics or any part of the backflow prevention assembly.
Double Check Detector Assemblies
Charleston Water System does not approve Double Check Detector Assemblies (DCDA). The DCDA was designed as a means to monitor small volumes of water being drawn through a fire sprinkler system for purposes other than fire fighting. A DCDA has a bypass meter and a bypass Double Check Valve Assembly (DCVA). Additionally, the DCDA number one check valve is loaded higher than a DCVA, thereby increasing the overall head loss through the assembly. From an overall cost evaluation, the DCDA costs on average $400.00 more than a DCVA. Since it has a bypass meter and bypass backflow preventor, the annual testing and maintenance costs are doubled. The customer, not the contractor, pays these extra, unnecessary fees when a DCDA is used.
Pipe Materials
Only cement lined ductile iron pipe, copper pipe, stainless steel and bronze pipe may be used between Charleston Water System’s water meter and the inlet side of any backflow prevention assembly, as noted in Charleston Water System’s Water Rules and Regulations (a legal ordinance) and our Cross-Connection Control Manual on Backflow Prevention. Black steel or galvanized steel pipe ARE NOT ACCEPTABLE between our meter and any backflow assembly. Galvanized steel pipe tubercolates (inside pipe wall calcification) and the tuberculation can break off and damage the soft elastomer disc of the soft bronze seat of a backflow assembly. This may cause unnecessary repairs at a cost to our customer.
Differential Pressure Gauge Specifications
Differential Pressure Gauges are sensitive, mechanical instruments capable of obtaining very small pressure differentials between the high and low sides of valves. Since manufacturer’s specifications are very exact as to the parameters or values of check valves in backflow prevention assemblies, a gauge specification is necessary to ensure that gauge meets those calibration specifications. Click here to view the Gauge Calibration Specification document.
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