Question about Pentair Fns Plus 48 sqft De Pool Filter (In Ground Pool)

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Our fns plus pool filter works, but it gets air into the system through the outlet spout when the filter goes off. This causes a 30 second routine of air leaving the system each morning when the timer turns the system back on. Should I replace the unit at the top of the dome?

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A check valve is a good idea, as back up! Not to fix a symptom due to a problem, that will go unsolved or unprepared. Replace the assembly at the top of the filter.
If you do decide to install a check valve, I presume what Adam is referring to is to put one in front of the pump onto your suction line. If you do do this, ensure you are NOT installing a disc style spring check. These will, especially when installed on a suction side, because of vacuuming debris like leaves, will get clogged and you will end up cutting them out due to very restricted water flow. The disc style spring check can be used on a pressure side, immediately after the pump. Instead, use a Swing Check on the suction side. Now, he swing flap even has a spring assist to keep them closed, when no flow.
When I feel the need to install a check valve on the suction side to eliminate back flow, I use this one...
Valterra 200 CU20 PVC Swing Spring Combination Check Valve Clear 2 Union

  • swing - to eliminate clogging
  • Spring - to assist keeping it closed when no flow
  • 2" - because bigger diameter, more room for debris to pass
  • Unions - if it does clog, unions make easy clean out.

Posted on Apr 12, 2015

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You may either replace the air relief valve, or plumb in a check valve so that the water cant backflow

Posted on Apr 05, 2011

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