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Backflow preventer rattle

August 18, 2014

Hello everyone,

I have a RainBird irrigation system watering my lanw and one zone is a drip line for my plant beds. I have recently tapped into the drip line and extended it to water additional beds that I just put in. And now whenever the drip zone runs there is a loud rattle sound coming from the backflow preventer. The entire system is only about 1 years old and the backflow preventer is about 2 years old, with the house that is the same age. I don't think it is pipes rattling. I have checked that and the sound is coming from the backflow preventer.

Does anyone know what could cause this? Is there some backflow pressure that I introduced into the system by extending the drip line? I extended it maybe 75 feet. Any ideas on how to fix this or what I may need to add to the system?

Thank you.

Comments (3)
  • lehua49


    You didn't introduce added pressure but with the added flow demand through the BFP you are probably hearing the noise cause by higher velocity than the fixture is designed for. Increase the size to a larger BFP and the noise should go away.
    The Flow is equal to area of BFP opening times velocity through that opening. If flow rate(demand) increases the opening stays the same then the velocity has to increase. This also causes water hammer when in your system when auto valves close suddenly. WH can cause damage to valves and can cause cracks in the pipeline. Just a thought. JMHO Aloha

  • remenakb

    That surprises me that the increase flow would be more than the BFP could handle. I would think I have more flow from my regular rotary heads watering the lawn than I do on the drip line, even with it extended. Maybe the drip line uses more water than I thought it did.

  • HU-343397127

    The increased water demand is making the valves open and shut because you don't have enough water to maintain pressure on the inlet side of the valve. There are inherent pressure drops built in to these devices. Hopefully this advice helps 4 years late!

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