Pressure switch cutting off with low pressure?

[Anthony W]

I recently had to replace our pressure tank, so I replaced the tank tee, gauge, and pressure switch at the same time. I installed a Square D 30/50 switch with a low pressure cutoff, just like the one I installed 30 years ago. I set the air in the pressure tank to 28 psi.

Everything seems to work fine, except multiple times now the pressure switch has kicked off due to low pressure. For example, it shut off yesterday when filling our 40 gallon bath tub. When I went out to restart the pump I saw there was still 20 psi on the gauge before I restarted the pump.

We have had a very dry summer which could have lowered our water table, but in 30+ years we've never had an issue unless we were using lots of water at once (i.e. running lawn sprinklers and clothes washer at the same time). It certainly never shut off filling our bath tub. I used to routinely fill a 150 gallon stock tank without issues.

Is there any way to adjust the low pressure cutoff separately, or is it always 10 psi lower than the cut-in setting? I know our old switch would get down to 15 psi or less before it would cutoff.

Our well is 98 feet deep, with a static water level of 35 feet when it was drilled in 1987. My pump is placed around 60 feet (all measured from the top of the well).

I haven't noticed any sputtering or change in water quality when the pump kicks off.

Is there some adjustment I can make to the pressure switch, or is our well going dry? It seems too coincidental that the problem would start right after changing the pressure switch.

 

[Valveman]

No there is no adjustment on that switch. But no matter the setting it will trip out on low pressure at the same pressure as the air charge in the tank. Reduce the air charge in the tank from 28 PSI to about 20. That will usually keep the low pressure kill from opening.

 

[Sponsor]

 

[Reach4]

Is there any way to adjust the low pressure cutoff separately, or is it always 10 psi lower than the cut-in setting? I know our old switch would get down to 15 psi or less before it would cutoff.

Always nominal 10 psi.

The good news is that you can usually cure this by decreasing air precharge. Usually air precharge 2 psi below the cut-in pressure is enough. So most probably letting another 1 or 2 psi of air out of the tank will solve this.

It is also possible that your start capacitor in your control box is failing. So the motor sometimes delays starting. Those capacitors are not expensive if you are not in a big hurry.

Most people don't use low-pressure-cutoff switches.

When your water pressure is zero, does your water pressure gauge read zero?

Also note that when your water pressure is over 40, the air pressure will be very close to the water pressure. The usual time you use that air pressure measurement is to compare the calibration on your water pressure gauge and air pressure gauge.

 

[Anthony W]

Reduce the air charge in the tank from 28 PSI to about 20. That will usually keep the low pressure kill from opening.

you can usually cure this by decreasing air precharge.

Thanks guys, I'll give it a try!

Most people don't use low-pressure-cutoff switches.

The guy who sold us the well parts 30 years ago recommended the low pressure cutoff type switch to "save the pump" if the water level got too low in the well. We never had an issue with the old switch, so I just replaced it with the same type switch when I replaced the pressure tank.

When your water pressure is zero, does your water pressure gauge read zero?

Normally, yes.

However, when the water shut off in the house, I went out to restart the pump and the gauge showed 20psi. If there was still 20psi, why didn't water still flow to the house? Restarting the pump returned everything to normal.

 

[Reach4]

However, when the water shut off in the house, I went out to restart the pump and the gauge showed 20psi. If there was still 20psi, why didn't water still flow to the house?

I totally agree with your logic. That is why I suspected the water pressure gauge was not good. Probably either the gauge was bad, or you had not actually opened a faucet. I can see one additional possibility: You opened a faucet, noticed bad flow, and then closed the faucet. By the time you got to the gauge, some water got heated up, such as the water heater turned on. The water expanded. It would not take much expansion to raise the pressure to 20 psi if the air precharge on the tank was higher than that.

The guy who sold us the well parts 30 years ago recommended the low pressure cutoff type switch to "save the pump" if the water level got too low in the well. We never had an issue with the old switch, so I just replaced it with the same type switch when I replaced the pressure tank.

That is the purpose. I think that could work, but I don't remember anybody posting how such as switch saved them. That is not the kind of thing people tend to post about, however.

I think there are cases where the low pressure cut-off would not save the pump. Yet the difference is cheap enough that if it saved you in 1/2 of the possible situations, it would be worthwhile. One such positive case would be that if the start capacitor was getting weak, the pump could delay starting a random amount of time. This could serve as an early indication, where a 1-second stutter in the water pressure might not be noticed. Start capacitors can be cheap if you are not in a hurry.

Anyway, see if lowering your air precharge helps, but also compare the calibration of your water pressure gauge with your air pressure gauge. If I ever replace my water pressure gauge, I am considering a liquid-filled one. https://www.supplyhouse.com/sh/control/search/~SEARCH_STRING=liquid pressure gauge

These are anti-low-pressure-cutoff switches:
https://terrylove.com/forums/index.php?threads/low-pressure-cutoff-switch-is-a-nuisance.75858/
https://terrylove.com/forums/index....d-well-pressure-is-at-zero.88864/#post-637381
https://terrylove.com/forums/index.php?threads/frugality-at-its-finest.82903/#post-597659 says

I looked at the Square D I had with low cut-off and figured out that I could lobotomize it. I removed the little metal piece that trips it and so now it is a standard pressure switch.
A dollar saved is a dollar earned and I just earned 40 bucks in less time than it would take to drive to the store.​

 

[LLigetfa]

However, when the water shut off in the house, I went out to restart the pump and the gauge showed 20psi. If there was still 20psi, why didn't water still flow to the house? Restarting the pump returned everything to normal.

Your gauge is faulty unless the location of the gauge is 46 feet lower. Replace it if not. Calibrate the new water pressure gauge to the air pressure gauge used to measure the air precharge to be sure the precharge is set correctly.

 

[Anthony W]

Probably either the gauge was bad, or you had not actually opened a faucet.

It is a brand new liquid filled gauge. It seems to be accurate at the 30psi cut-in and 50psi cut-off settings, so I have no reason to believe it is faulty.

As for the faucet, I was soaking in the bathtub while it filled when the water just stopped flowing. I didn't turn the faucet off until water had already stopped coming out. I had just hopped in the tub and covered with bubbles, I was in no hurry to go restart the pump.

I probably won't be able to adjust the tank pressure till Monday. Even then, the low pressure shut off is rare so I might not know for a while if it was successful or not. I suppose I could test it by filling the bathtub again while the sprinklers are running?

 

[CenterTree]

..

The guy who sold us the well parts 30 years ago recommended the low pressure cutoff type switch to "save the pump" if the water level got too low in the well. We never had an issue with the old switch, so I just replaced it with the same type switch when I replaced the pressure tank.

Yes, keep your low pressure switch.

That is the purpose. I think that could work, but I don't remember anybody posting how such as switch saved them. That is not the kind of thing people tend to post about, however.

I think there are cases where the low pressure cut-off would not save the pump. Yet the difference is cheap enough that if it saved you in 1/2 of the possible situations, it would be worthwhile.

I will jump in to mention that just this past Summer while taking a shower the water flow stopped. Went down stairs, saw the Ptank gauge very low. Held the little lever on the low pressure switch until JET pump ran steady. Turned to walk back up stairs, pump stopped again. .
Tried switch again, now pump would not stay running if I let go of the lever.

Dried off, got dressed, went outside, pulled lid on rain cistern (our only H2O source out here). EMPTY!

Firm believer in low pressure switches.

 

[Djc11369]

I'll throw in my 2 cents here as I experienced the very exact symptom when I replaced my tank/switch a couple of years ago. In my case the switch would trip when my water softener or iron filter would backwash. Is it possible that your pump is no longer putting out enough volume to fill the tub and keep the pressure above the 20 psi threshold? That's what I chalked it up to on mine which the pump at that time was 21 years old. I just switched to a regular switch to bypass the problem (aka stick my head in the sand) but looking to replace the pump now.

 

[LLigetfa]

Is it possible that your pump is no longer putting out enough volume to fill the tub and keep the pressure above the 20 psi threshold?

Since you mention an iron filter, before you write off the pump as bad, consider that the line could be constricted with iron buildup. I have to rod out my line periodically.

The exact pressure that trips a low-pressure cutoff switch is not precise. A replacement switch might not trip at the exact same pressure as the one it replaced.

 

[Djc11369]

Since you mention an iron filter, before you write off the pump as bad, consider that the line could be constricted with iron buildup. I have to rod out my line periodically.

I don't want to hijack the OP's thread with my own woes but I ran my pump into a 5 gal bucket and timed it at 1 minute and I had a little over 3.5 gallons so it's outputting 3.5 gpm. This is from the spigot at the tank which is before the filter/softener. It takes 1 min and 45 seconds to fill the 20 gal tank which has a 6.2 gal drawdown. It used to fill the tank in about 30-40 seconds. I don't know what the pump is actually supposed to be able to output since I have no info on what's in the well but I'd guess about double what it's doing now.