Occasionally, a booster pump is used. The auxiliary system often is pressurized by a centrifugal pump, although backpressure may be caused by gas or steam pressure from a boiler. A reversal in differential pressure may occur when pressure in the potable system drops below that in the system to which the potable water is connected. The best method of preventing this type of backflow is the complete separation of the two systems and/ or an air gap. Other safety methods involve the installation of mechanical backflow prevention devices. All methods require regular scheduled inspection and maintenance to ensure on going effectiveness of installed devices.

Some areas that you should consider providing some form of protection from backflow and back siphonage include the following:

  • Water supply to pens for wash down or livestock watering.
  • Water supply to compressor cooling systems, cooling towers, and boiler rooms.
  • Water supply to cleanup systems, clean in place (CIP) systems, etc.
  • Water supply to hose connections.

Various mechanical anti-backflow devices are available to prevent backflow into a potable water supply system. Generally, the selection of the type and number of fail-safe devices should be based up on the degree of hazard from contamination. Additional considerations include piping size, location, and the need to test periodically the backflow devices to ensure proper operation.

There are six basic types of devices that can be used to correct cross-connections:

  • Air gap
  • Barometric loops
  • Vacuum breakers—both atmospheric and pressure type
  • Double check valves with intermediate atmosphere event
  • Double check valve assemblies
  • Reduced pressure principal backflow preventers
  • Specific requirements concerning backflow can be found in local building and board of health codes.
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