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chach 12-02-2008 04:32 PM

New Pressure Switch -- low water pressure

I recently replaced a gummed up pressure switch (plugged with sediment). I replaced the switch with the standard switch off the shelf at the hardware store which was a 30/50 psi switch (this was the only type they had stocked). I didn't realize it until afterwards that the switch I removed was an older 20/40 psi switch.

After replacing the switch, I'm finding the water pressure to be a bit weaker than when the previous switch was running. The pressure guage seems to be reading correctly - cuts in at about 28 psi and cuts out at just below 60 psi. If anything this should be providing greater pressure than before.

My question is whether I need to do anything with the pressure tank to match the new pressure switch. I thought I read somewhere that the pressure tank needs to be pressurized to 2 psi below the cut-in pressure. Should I add air to bring it up to 28 psi (or 26 psi in the case of my switch)?

Are there any other thoughts on what could be causing low pressure when the actual guage seems to be reflecting reasonable pressure?


Mike Swearingen 12-03-2008 10:29 PM

If the new pressure switch is factory pre-set for 30-50, then you need to check the air pressure in the bladder tank.
With the pump off and all water pressure drained down, check the tank air pressure with a tire gauge. It should be 28 psi.
If it is too low, air it up with a bicycle pump or portable air tank or compressor to 28 psi.
You can have a number of things that could be causing the drop in pressure.

micromind 12-04-2008 09:15 PM

Just because 20/40 was stamped on the original pressure switch doesn't mean the actual cut-in pressure was 20 PSI and cut-out was 40.

Almost all pressure switches can be easily adjusted, a 20/40 model could be adjusted to as high as 60/80, some of them even higher.

If the house and the pressure tank are at about the same elevation, 30 PSI is pretty low pressure. 40 or so would be about the minimum. Try adjusting it up a bit.

If this new switch has an adjustable differential, back it off as far as possible. 10 or 15 PSI of difference is much better, but if you have a small pressure tank, you'll short-cycle the pump, and it won't last very long.

If all this talk about pressure is just a bunch of gibberish, write back. Several of us can explain the actual hows and whys of a water system, and help you dial it in just right.


chach 12-05-2008 04:20 PM

I'll play around with the adjustments and the pressure tank taking these things into account. Thanks for the advice from both of you.

lilh2o3 01-18-2009 09:50 PM

late help
If you havent figured out your problem already i have some suggestions.
Im a licensed water well installer.

set Preasure switch to turn on at 40 and off at 60, that is a normal setting for a single home.

then air up your preasue tank to 38 psi that will give you all the water from the tank just before the pump turns on.

good luck

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