b'LT ENGINEERINGCATALOGthat are objectionable but non-toxic. Double Checks mayMAINTENANCEbe installed under continuous pressure service and may be subject to back pressure. Double checks can be used inBackflow preventers must be inspected annually with the sprinkler irrigation systems, fire protection without chemicalresults recorded on an official Water Backflow PreventerDomestic & Fire Wateradditives, protection of industrial plants, and other systemsInspection Report to be submitted to the local AHJ. If requiring protection. See ParkUSA Model BP. any essential part of the unit fails inspection, it must be repaired or replaced then pass a subsequent inspection.Operation: In a non-flow condition, the check valves hold a one PSI minimum in the direction of flow. In aSIZINGflow condition, the check valves are open proportionalFor the complete design of a backflow prevention system, to the flow demand. In a backflow condition, the checkthere are three basic topics that must be addressed.valves will close until the resumption of normal flow. The degree of hazard, the type of application, and the type Double Detector Check Backflow Assembly of installation.Used in a Class I, II, III, or IV application (low hazard)The degree of hazard is the primary factor when Detector Check Backflows are the same as the Doubledetermining the proper model. Checks previously described except for the addition of a By-Pass Detector Meter installed across the check valves.Low hazard application: potential backflow can pollute This detector meter is used to detect unauthorized waterthe drinking water. usage or system leakage. See ParkUSA Model DDBP.Pollution is defined as materials that can cause Operation: In a non-flow condition, check valves in undesirable effects to the water, such as discoloration, the by-pass and mainline units are closed. Flows fromsmell or taste, but will not cause sickness or death. 0 to 5 GPM will flow through the bypass. This operationHigh hazard application: potential backflow can at low flow rates is accomplished by designing thecontaminate the water supply.differential pressure drop across the by-pass line toContamination is defined as any impairment to the water be slightly less than the mainline check valves. Flows quality such that contact with this water can result in in excess of 5 GPM will open the mainline check valvesillness or death. for normal flow. A lethal hazard involves radioactive material or raw sewage. An air gap is the only effective means of protectingReduced Pressure Backflow Preventer against lethal hazards. Under no circumstance wouldUsed in a Class IV, V or VI (high hazard) applications,a mechanical backflow preventer be used to protect Reduced Pressure Assemblies are used to protect againstagainst a lethal hazard.toxic fluids in water services to industrial plants, hospitals, morgues, mortuaries, and chemical plants, and otherThe type of application and industry, such as fire applications requiring maximum protection. See ParkUSAprotection, irrigation, waterworks, and plumbing, each Model RPBP. have particular requirements. Fire sprinkler systems may require detector assemblies, and irrigation systems may Operation: In a flow condition, the check valves are openrequire products that are not used universally in plumbing with the pressure between the checks, called the zone,systems. Each application is also unique in regards to being maintained at least five PSI lower than the inletflow requirements. Plumbing and waterworks require pressure, with the relief valve maintained closed. consistent flow of water. Irrigation requires flow perhaps Should abnormal conditions arise under no flow ortwo percent of the time and the remaining 98 percent of reversal of flow, the differential relief valve will open the time is in a static condition. Fire protection must stand and discharge to maintain the zone at least three PSIready for action with 100 percent static water pressure. lower than the supply. In resumption of normal flow, Each application can present a unique situation, which will the zones differential pressure will resume and theaffect a backflow preventer differently.relief valve will close.Installation types include outdoor, indoor, below gradeDESIGN CONSIDERATIONS (pit installations), horizontal, and vertical installations. Codes and jurisdictions require a backflow preventerFacilities that require uninterrupted supply of water, such device when certain types of hazards exist, includingas hospitals, resort hotels, or industrial applications, will contamination of public water supply from a water user,require multiple connections or manifold assemblies. this issue is known as cross-connection. Cross-connection Outdoor installations face the potential vandalism, hazards are found in potable, fire-protection, irrigation,theft, soil erosion, and freezing temperatures. Protective and industrial water lines. The design professional shouldenclosures can help to mitigate some of these issues. consult local building codes and consider potential cross-Indoor installations might need to address the issue of connection hazards within. water discharge. Of the five standard types of backflow preventers, three spill water, two at start-up and oneas a normal function. INFO@PARKUSA.COM|888-611-7275|WWW.PARKUSA.COM 27'