I have a 3/4HP well for my lawn sprinkler system. I recently changed the pressure gauge, the pressure switch (set to 20/40) and a new pressure tank (18PSI from the factory). When I turn on the power, the pressure goes to just above 20 and then shuts off. When I run the sprinklers, it drops below 20, then turns on to above 20, and then just short cycles above and below 20. I let this continue and blew out the first new pressure switch. I then installed a second brand new pressure switch and the same thing is happening. What's going on?
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How fast is the short cycle and what is the tank size– Ed BealCommented Jun 13, 2020 at 5:06
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The tank size is 2 gallons and the cycling is constant on and off above and below 20psi.– Tom TCommented Jun 13, 2020 at 5:24
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Sounds like either the rate of demand is too large for the tank so reduce that rate or the tank is too small so increase the tank volume.– Solar MikeCommented Jun 13, 2020 at 7:21
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1That tank is very small some 3/4 hp pumps have a rate of close to 20 gallons per minute Depending on depth but 10 gpm would be easy at that low a pressure so to prevent short cycling increase the tank size or bump the pressure much higher. I have only used tiny tanks like that to prevent problems with expansion and hot water tanks.– Ed BealCommented Jun 13, 2020 at 15:09
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Sounds like there's not enough air in the tank (or it is simply too small).– Hot LicksCommented Aug 23, 2022 at 12:35
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2 Answers
Guess us country folks are dumb, but this is 100% too small a tank for the application.
Is the pressure gauge close to the pressure switch or some distance away. Maybe the pressure switch is seeing a different pressure than the gauge. Too small piping could also contribute as well as any blockages. Either that or the pressure switch isn't adjusted properly.
With that small a tank the usage by the sprinkler system and the production rate of the pump would need to be very closely matched or you'd short cycling as you describe. It sounds more like an expansion tank.
Short cycling is also very hard on the pump motor too.
You mentioned you recently replaced some items, was it working before? What is the reason for the changes?
I'd put in a much larger storage/pressure tank. That would minimize the short cycling. A diagram of your plumbing would help us sort this this out as well.
Sorry for posting this as an "answer", but it was too long for the comment section.
answered Jun 13, 2020 at 14:11
