Low pressure cutoff switch is a nuisance!

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Old 06-02-18, 01:54 PM
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Low pressure cutoff switch is a nuisance!

The story:
We moved here from a house with city water about four years ago. The house loses water pressure often enough that it's really annoying (middle of a shower, using the bathroom in the night, on vacation with friends watching the house, etc). Nearly every time it's because the low pressure cutoff switch got tripped. Over the years I've read everything I can find and done lots of adjustments, some of which help a little. Now I have an idea for how to make it "just work" and need your input.

The setup:
We have a 70-foot well in a 6 inch bore, it was tested at around 2gpm just before we moved in. The well pump (3/4HP, 10GPM submersible) fills a 1,000 gallon cistern (black poly above ground, right next to the well house). The well pump is controlled by a no-load sensor and a normally-closed float switch inside the cistern at the top. The cistern supplies the jet pump (1-1/2HP), which pressurizes the house plumbing. The pressure tank is 33.4 gallon (about 9 gallon drawdown @30-50psi), and the jet pump is controlled by a standard Pumptrol 30-50psi pressure switch with low pressure cutoff to prevent running dry if the cistern runs out of water.

The problem:
A few times a month, or occasionally several times a week, the low pressure cutoff switch gets tripped, so we have no water pressure. All we have to do is run out to the well house and switch it back on, and the jet pump runs normally again. Aside from a few times when the cistern was actually out of water (watering the lawn too long, or once when the well pump failed and was replaced) the jet pump just starts working again for another week or three. It seems like something causes the pressure to drop momentarily to trip the switch, but I can't figure out why, as the cistern has plenty of water. I've replaced the pressure switch a few times when the contacts fused, and several times I spent a few hours measuring and adjusting the pressure in the switch and the pressure tank to get them tuned for each other. Getting the pressure tank precisely between 2-4psi below the switch cut-on pressure seems to lessen the frequency of the low pressure switch getting tripped, but it still happens too often.

The idea:
If I install a normally-open float switch at the bottom of the cistern and wire it to the jet pump, it would shut off the jet pump when the cistern is almost empty. Then I could replace the low pressure cutoff switch with a regular pressure switch. The jet pump would provide water pressure anytime there's water in the cistern, and be protected from running dry by the float switch at the bottom of the cistern. As a bonus, in the rare event that the cistern runs out of water, then the float switch would automatically turn the jet pump back on when there's water in the cistern again - without us having to flip the switch back on.

The questions:
Is there any reason why using a float switch in the cistern wouldn't be an effective safety cutoff for the pump, or wouldn't be reliable? Aside from the increased cost and installation work, why wouldn't our system have been originally set up with a float switch instead of low pressure cutoff switch, given that the jet pump is pulling from the cistern and not directly from a well? Is there anything else I need to be aware of before making this change?

Thanks!
Alex
(Cross-posted to Terry Love forums)
 
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Old 06-02-18, 02:22 PM
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Welcome to the forums.

Why is anything done the way it was ?? Just because that's how it was done.

I don't see a problem with your idea. I would use a float switch and a relay or contactor.
 
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Old 06-02-18, 09:55 PM
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Yeah, I wondered about that but I've seen float switches as the only control on things like sump pumps and sewage pumps that seem to work fine for years. The relay would just be there to take the electrical pressure (and possible arcing contacts) off the float switch, right? In my case, the float switch would be always on except for the rare times the cistern actually runs out of water, so I would guess the contacts inside would last a long time. Or is there another reason you'd use a relay on the float switch?
 
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Old 06-03-18, 06:05 AM
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I would try removing a couple more psi of air out of the pressure tank. You need to understand that there are few air pressure gauges that are overly accurate and a 30/50 pressure switch is also a close approximation. Also understand that as your water warms up it also heats up the air in the pressure tank, which also increases that air pressure and you can get to the point where the air in the pressure tank pushes ALL the water out of the pressure tank because its pressure is now slightly higher then the cut in pressure of the pressure switch.

Since a pressure tank cannot exert pressure on water when it is not in its tank you can get a quick drop off to zero psi as the last of the water is pushed out the tank. People with switches without that safety shut off just experience a drop off in water pressure and then a quick recovery as the pump turns on but with the safety shut off you don't get that recovery.

Anyway, remove a few psi of air and see how it works and if it does not work just put the air back in. Yes, you will get a reduced drawdown of water per cycle but a little less continuous water is probably preferred to 9 gallons and then you are done.
 
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Old 06-03-18, 06:24 AM
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In addition it is possible that you are drawing down the water level with a pump that exceeds the capacity of the well in which case your cut off switch is doing it's job.
The pump being too large could very well be your problem.
Hopefully removing the safety feature of the manual cut-off would not cause your pump to overheat when it looses it's prime.
 
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Old 06-03-18, 10:55 AM
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In this application.... the switch in question is on the booster pump from the cistern/storage tank to the house so it's technically not dependent on the actual well.
 
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Old 06-03-18, 01:53 PM
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Originally Posted by OptsyEagle View Post
I would try removing a couple more psi of air out of the pressure tank. You need to understand that there are few air pressure gauges that are overly accurate and a 30/50 pressure switch is also a close approximation. Also understand that as your water warms up it also heats up the air in the pressure tank, which also increases that air pressure and you can get to the point where the air in the pressure tank pushes ALL the water out of the pressure tank because its pressure is now slightly higher then the cut in pressure of the pressure switch.

Since a pressure tank cannot exert pressure on water when it is not in its tank you can get a quick drop off to zero psi as the last of the water is pushed out the tank. People with switches without that safety shut off just experience a drop off in water pressure and then a quick recovery as the pump turns on but with the safety shut off you don't get that recovery.

Anyway, remove a few psi of air and see how it works and if it does not work just put the air back in. Yes, you will get a reduced drawdown of water per cycle but a little less continuous water is probably preferred to 9 gallons and then you are done.
OptsyEagle, that's a helpful explanation. I hadn't considered the effects of heat; the well house is small and in full sun so it heats up in the summer. As I remember, the first summer we lived here it was the worst, but I was watering the lawn too much (effectively testing the limits of the well recharge) and I hadn't figured out the system or made any adjustments, just kept flipping the pressure switch back on. Also, as I've tested the system and adjusted pressures, I noticed a few times when I was watching the pressure drop as water was draining, and right at that last sudden pressure drop, the pump didn't cut on. I didn't understand why, but was in the middle of adjusting things anyway and just kept going to get the pressures correct. Now it makes sense - at those times the tank pressure was too high, so water pressure dropped too fast, right past the pump cut-in and into the low pressure cut-off before the pump could come on.

I have two digital tire pressure gauges which always read less than 1psi apart, and two analog water pressure gauges (one on the tank tee, one on the pump output) which agree with each other and the tire pressure gauges, at least to the few psi I can reliably read them. They might all be off by the same amount, but as I've played with adjusting the tank pressures and switch cut-on and cut-off pressures, everything seemed to agree and make sense. BTW I do this by draining all the water out with pump off, turning pump on and measuring both air and water pressure as it rises and recording the cut-off pressures, then draining water and watching pressures as the tank empties and recording the cut-on pressures. That seems to be the agreed method and makes sense to me why it would be the accurate way. Anyway, like you said the 30/50 is always an approximation, but it's measurable. Another thing is that while reading the documentation for the low pressure cutoff switch, it notes that it will cut off when pressure drops 10psi below cut-in pressure, no matter what that cut-in pressure is. So all it takes is a momentary drop to more than 10psi below cut-in, which obviously keeps happening randomly on my system. Actually, the first time I figured out how the pressure tank works and how to adjust it, almost a year after moving in here, I found it was about 15psi below the switch cut-in pressure. I thought that balancing that to a little under 5psi below cut-in would solve my problems, but it's kept happening. I've tried the recommended 2psi below but it seems too close (given the inaccuracy of gauges) and seems to cut off more. I tried 8-10psi below, and it seems more frequent than at a little under 5psi below, but since it's an occasional issue then even keeping records of every shutoff for a few months (which I've done) doesn't give me a large enough sample size.

Again, I feel like I've tried just about every combination of pressures at different times over the years, have replaced the switch a few times (simply due to fused contacts), and finally realized that I think I could get the same protection for the pump by using a float switch in the cistern instead. If a low pressure cutoff switch isn't necessary in my application, I'd love to get rid of it instead of continuing to adjust it, only to find it mysteriously cutting off in the middle of the night two weeks later.
 
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Old 06-03-18, 05:40 PM
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Have you observed any erratic behavior of the house (post cistern) pump cut in/cut out pump switch assembly? Have you replaced that switch and its connecting tube to the water line recently?

Have you noticed pressure fluctuations during the first 9 gallons of water usage? This could suggest a clogged connection to the pressure tank that in turn could cause random moments of abnormally low pressure.

Have you sometimes noticed the low cutoff happened without the cistern becoming empty and with nobody using water at thatt moment?

I would consider a cistern water level float switch to be a good alternative to a pressure switch to operate a no-water safety cutoff for the post-cistern pump.

Both float switches and pressure switches should snap on and snap off. Switches that gently make and break contact as the water level or pressure reaches or passes the magic number will arc more and are more likely to suffer from fused contacts sooner.
 

Last edited by AllanJ; 06-03-18 at 06:05 PM.
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Old 06-04-18, 06:19 AM
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BTW I do this by draining all the water out with pump off, turning pump on and measuring both air and water pressure as it rises and recording the cut-off pressures, then draining water and watching pressures as the tank empties and recording the cut-on pressures. That seems to be the agreed method and makes sense to me why it would be the accurate way
The way to measure the "air" pressure is to turn off the pump and drain the tank. Leave a tap in the house open to ensure no water is flowing out and then measure the air pressure. If you measure the air pressure when water is in the tank under any pressure you are actually measuring the water pressure. Basically the water pressure and the air pressure will be the same when in use.

I would think that if I am right, 8-10 psi below cut in pressure should have solved the problem completely. When I mentioned that heat affects the air pressure I should indicate that it affects it in a fairly small way. Gases (air) exert more pressure when heated up but they do so under the kelvin temperature scale. Also known as the absolute temperature scale. Just to give you an idea of what that means. If you set up the air pressure when the water was around 60F and then spring and a hot sun heated that water up to 75F, it would only increase the air pressure by around 1.5psi. That is why they suggest 2-3 psi below cut in pressure. The objective is any pressure below cut in but since the air pressure is not completely constant and to account for some measurement discrepancies, they suggest a few psi below cut in pressure, to ensure your system works well for all 12 months of the year. Your temperature range is probably higher then most peoples but I would still think that 5psi below the cut in pressure would account for all of it, including measurement discrepancies. 8-10 psi below cut in would resolve it for sure, although you would not be getting 9 gallons of water per cycle.

As you know, the air, that now exerts pressure because it is compressed, is what provides the water pressure when your pump is not running. But more correctly, it is the air, BEHIND the diaphragm that pushes on your water. When the air pressure is set or becomes higher then the cut in pressure, the air will push ALL the water out of your pressure tank before your pump turns on. Since the diaphragm bottoms out on the tank's bottom, the air could be set at 100psi but it will stop exerting any pressure on your household water the moment the tank becomes empty. This would create a quick and considerable pressure drop in your house and is why there must always be some water in the pressure tank when the pump is asked to refill it again.

That was what I was thinking was happening but if you are saying it still happened when everything was set 8-10psi below cut in then I would say that my theory may not be correct...provided you were measuring your air pressure the correct way I suggested above. If not, then measure it correctly and ensure that it is at least 5 psi below cut in and see how everything works out after that.
 
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Old 06-04-18, 06:49 AM
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What about increasing the submersible to 1 HP? is that a possibility. A 70' well might be a do it yourself project as long as the pump discharge pipe is poly. You can rent a three wheeled pipe puller, or pull by hand with a friend or two, or a couple of healthy kids.
Sid
 
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Old 06-04-18, 06:50 AM
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I had the same question. It sounds like you are not checking the air pressure properly. You have to have the tank empty and water gauge(s) reading zero- and the pump off. You can read "Pump cycling, or Water logged and other Well Info" at the top of this forum to see the exact procedure.

(You can check cut in/out running water as you did - but not the air pressure.)
 
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Old 06-04-18, 06:53 AM
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I did not read every word, but......posts #4 and #5 seem to be good suggestions. Also consider a Constant Supply Valve, about $30.... which will keep your well pump from cycling on and off while using a constant supply of water. Easier on your well pump, also.
 
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Old 06-05-18, 01:17 AM
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The way to measure the "air" pressure is to turn off the pump and drain the tank. Leave a tap in the house open to ensure no water is flowing out and then measure the air pressure. If you measure the air pressure when water is in the tank under any pressure you are actually measuring the water pressure. Basically the water pressure and the air pressure will be the same when in use.
Yeah, I didn't mention that I was first measuring static air pressure with the pump off and all water drained out of the system (I just hook a hose to the bib on the tank tee so I don't have to run back and forth) and record that, then measure both air and water pressure as the pump is dynamically changing the pressure up and down, to get a solid read on the actual cut-in and cut-out pressures. Like you said while the system is pressurized, the air and water pressures are always the same since the diaphragm effectively transfers one to the other. I take notes on it as I go and adjust pressures (adding or removing air from the tank only when there's no water in the system), and then do the whole read sequence again to make sure it's correct.

That was what I was thinking was happening but if you are saying it still happened when everything was set 8-10psi below cut in then I would say that my theory may not be correct...provided you were measuring your air pressure the correct way I suggested above. If not, then measure it correctly and ensure that it is at least 5 psi below cut in and see how everything works out after that.
That's what's weird about it; I've experimented with tank pressures kind of all over the place. The first time I figured out the tank pressure thing and did all the measurements, it was about 15psi below cut-in pressure, and had been working "fine" for a year or so with the normal occasional times it would trip the low-pressure switch. At that time I set it at 2psi below cut-in, but it seemed to trip a few times a week - more than before. I went back to about 8-10psi below, and it was back to the usual where the low pressure would trip a few times a month. I tried even lower pressure than what I'd initially found - about 20psi below, but then it was tripping more than once a week again. So I went to 3-5psi below and that's seemed to have the fewest cut-offs, sometimes we get a whole month between them. Again, I used to check the cistern water every time but it was always full unless I'd been running the sprinklers too much - I don't count those among the mystery low-pressure cut-offs since those were obvious why.
 
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Old 06-05-18, 01:32 AM
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Have you observed any erratic behavior of the house (post cistern) pump cut in/cut out pump switch assembly? Have you replaced that switch and its connecting tube to the water line recently?

Have you noticed pressure fluctuations during the first 9 gallons of water usage? This could suggest a clogged connection to the pressure tank that in turn could cause random moments of abnormally low pressure.
Yeah, as I mentioned I've replaced that switch a few times due to fused contacts. It's mounted on a 6" riser on the tank tee, and the one thing I haven't done is take the riser off or take pipes off the pump tee to inspect it for crud and blockage. But I wicked out the water from the riser and shone a light in and it was pretty clean looking, plus the switch diaphragm was clean. And I often use sprinklers in the summer and watch them to be sure they're set up right (sometimes while close to the well house so I can hear the pump cycle on and off), so I'd notice pressure fluctuations if they were happening. So the switch is not at fault, and I don't suspect the riser or nearby plumbing but it's possible.

Have you sometimes noticed the low cutoff happened without the cistern becoming empty and with nobody using water at thatt moment?
Having the low cutoff happen in the middle of the night or while we're away from home is actually about as common as while we're home and using water regularly during the day. And I used to check the cistern every time but it was always full so I don't check it every time anymore.

I would consider a cistern water level float switch to be a good alternative to a pressure switch to operate a no-water safety cutoff for the post-cistern pump.

Both float switches and pressure switches should snap on and snap off. Switches that gently make and break contact as the water level or pressure reaches or passes the magic number will arc more and are more likely to suffer from fused contacts sooner.
Thanks, I've had several people say something similar and nobody has raised a warning about the float switch instead of the low-pressure cutoff as a safety. The float switch I had in mind is the normal tethered kind with a ball, not the reed switch kind. I had to replace one with a cracked housing in our sewage pump last year, and watching it work, it seems to have a sort of spot where the ball inside suddenly snaps over to the other side. Is that what you're talking about?
 
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Old 06-05-18, 09:50 AM
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Having the low cutoff happen in the middle of the night or while we're away from home is actually about as common as while we're home and using water regularly during the day.
That does seem strange. It seems to me that would indicate a leak but then you would think that would just cause the switch to hit the low limit and turn on the pump, and wouldnt cause the low pressure shutoff to activate. Why would the pressure switch do anything if no water is being used?

Do you have any water treatment equipment that is on an automatic timer backwash? Like a water softener or something like that? Im not sure that would matter but I installed an Acid Neutralizer Filter and I might be wrong about this but I think when the backwash valve opens I seem to remember seeing on my gauges a real fast but large momentary drop in pressure when the valve opens just before the pump kicks in.

Not 100% sure however.

Or maybe some other kind of valves that are opening automatically? Just a thought.
 
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Old 06-05-18, 01:11 PM
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I suspect that if no water was used no one would have known that the safety cutoff was activated. I suspect that what he was saying is that the lack of water was observed in the middle of the night, obviously when someone turned on a tap or flushed a toilet. Since it seems random I don't think that observation is overly material.

Even if he had a leak or some appliance was drawing water automatically, the pump should kick on correctly and refill his water system, but it is not. Other then my "too much air" theory, I got nothing.
 
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Old 06-05-18, 02:10 PM
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The
“while we are away from home”
made me think that the system was OK when they left home, but was already tripped when they returned home - with nobody in the house that could have used water. Thus the safety is sometimes tripping when there is no known water usage. But I guess Alex would have to clarify. It does seem mysterious.
 
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Old 06-05-18, 11:03 PM
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OptsyEagle and zoesdad, you guys pretty much nailed it down - it's a mystery. This thing has been knocking around in my head since we moved here, and at least twice a year it boils over into a new idea I want to try, or just a bunch more diving in forums, watching YouTube videos, reading manuals for pumps and switches, etc. Sometimes I think I've got something (like the first year I worked hard to track down plumbing leaks because why else would it shut off in the middle of the night) and other times I just flip the switch occasionally and move on with life.

The only automatic valves are during a few summer irrigation months, when I schedule the drip irrigation in the garden or lawn sprinklers mostly in the evening or overnight. The low pressure switch definitely gets tripped more often then, but anytime I know the irrigation was running overnight and find the switch got tripped, I don't record it as a mystery since maybe the cistern ran out of water and got partly refilled by the time I found the jet pump off.

You both mentioned what I think is happening whenever the system is tripped in the middle of the night or while we're away - it actually got tripped just before we went to bed or left home, but there was a few gallons still in the pressure tank. Then as soon as there's a decent amount of water used - bathroom visit in the middle of the night or coming home - we find there's no pressure. As OpstyEagle notes, the observation time doesn't necessarily have much to do with the event that triggered the cutoff. And since we have 20-40 of these events a year, and 10-15 of them are while I feel sure nobody was recently using water, it's hard to paint a picture. Essentially, the fact that I find it both when I know we're using lots of water in the middle of the day (I've had to reset the clothes washer and dishwasher numerous times) or with sprinklers running, but I also find it when there's no recent usage, means there's no pattern I can use to diagnose the problem.

That's why I started this thread, because I finally have an idea to get rid of that troublesome low pressure switch. I kept wondering if this is just what it's like to be on well water, or if there was some magic combination of pressures I could set and dances I could do that would make it work. Again, there have been some times when I know or suspect the cistern was out of water, and those aren't part of this - I'm just trying to prevent a low pressure cutoff when I know the cistern had water.

Between this thread and the one on Terry Love, I've had many votes of confidence in the safety of using a float switch instead of the low pressure switch, and nobody was concerned. So I'm going to do that; the small expense and hassle upfront to switch it over should mean that the only time the house loses water pressure is when the cistern (and therefore also the well) has actually been pumped dry (and it will reset itself when the cistern refills). I'm happy to live within the limits of my 2GPM well and 1000 gallon cistern, as long as I can reliably make use of those.
 
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Old 06-06-18, 05:59 AM
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If you want some redundancy against the pump running dry you could also install a separate low pressure cutoff that is set much lower than 10 psi less than the pump cut on. This way the mystery (probably still abnormal) pressure bounces in your system (comparable to momentary brownouts in an electrical system) would not be expected to trip the low pressure cutoff.

Or maybe your existing pressure switch setup does not have a full consistent 10 psi below pump turn on before the low pressure cutoff.

At one time I was taking care of at a house with a well. I shut off the pump for any period of several days I would be gone.
 
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