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What is a backflow preventer?

Posted on: June 22, 2012

If you have a lawn irrigation system in your home or a fire sprinkler in your building, you may have heard of the dangers of backflow and the need for a backflow preventer. Backflow is the reversal of dirty water or other substances through a cross-connection between the public water system or your own potable water system and any system containing used water. Backflow can occur by either backpressure or backsiphonage. For the uninitiated:

  • Backpressure backflow is caused by an increase in downstream (used water) pressure until it’s greater than upstream (clean water) pressure, which can be caused by any kinds of pumps, temperature increases, etc. The pressure increase causes water downstream to be forced upstream, where it can potentially get into your potable water system.
  • Backsiphonage is backflow created by negative pressure in the public water supply. You can think of this like sipping water through a straw – when you suck in, the water moves up the straw quickly. Backsiphonage can occur when there is a sudden, severe drop in the water supply, such as when the fire sprinklers go off, when the water main breaks, etc.
  • A backflow preventer is exactly what it sounds like – a device that prevents backflow. The most basic way to do this is with an air gap, which does one of two things: either eliminates a cross-connection or provides a barrier to prevent backflow. An air gap is an actual vertical separation between the end of the water supply outlet and the flood level rim of the receiving vessel where the two are not connected by any means. Backflow preventers can also be mechanical, using either a reduced-pressure principle assembly, a pressure vacuum breaker assembly, or a double check valve assembly.


    Backflow Preventer Testing in MD & DC

    If you have a backflow preventer in your home or building, it’s important that you have it tested from time to time. Mechanical backflow preventers have internal seals, springs, and other moving parts that are subject to fouling, wear and tear, and fatigue. Both mechanical and air gap backflow preventers can also be bypasses, so it’s important to make sure yours are working properly by checking it every now and then. You can click here to learn more about backflow preventer testing in Maryland.

    At Wheat & Sons, we offer backflow preventer testing for homes and small businesses throughout the Montgomery County, MD and NW Washington, DC area. If you need backflow preventer testing, call us today!