I am consistently seeing/feeling a pressure drop just before the pump kicks in to refill the Pressure tank. I am on a well with a diaphragm pressure tank.

I have drained the system and verified the air pressure 40psi. The cut in pressure is 42psi and the cut out pressure is about 72psi. When I open the faucet the pressure goes down smoothly until it reaches about 52 psi, then there is a fast dip down to 42 then immediately returns to 52+psi as the pump activates.

I have video'd this and can see the gauge and the "plate" on the pressure switch dip at the same time so it isn't a bad gauge...I can also feel this dip while in the shower.

Everything else seems to be working fine. Just want to make sure that this isn't killing my pump or pressure tank.

If there is a fix, I am all ears.

  • I don’t think there is a fix with a diaphragm you have reached its limits. This is why bladder tanks are more popular they use almost 100% of the water in the tank the diaphragm just can not.
    – Ed Beal
    Commented Dec 29, 2020 at 20:49

1 Answer 1


Reduce the differential - raise the cut in pressure to 52 or 53. Or lower the cut-out to 62 and play with the air pressure in the tank, perhaps - I'm familiar with how bladder tanks behave, and got most of any answer written before noticing that you mentioned a diaphragm tank, specifically.

30PSI is an unusually large differential pressure (20PSI is what most tank charts assume - 20/40, 30/50, 40/60 and most pressure switches come pre-adjusted for that - but most are also adjustable. Read the directions for yours, and remember to turn off the breaker supplying power to the pump circuit before removing the pump control's cover)

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