Water tank air valve test (C) Daniel Friedman S PriorWater Tank Pressure Increases On Its Own
What causes creeping pressure increases in an internal-bladder water tank?

  • WATER TANK PRESSURE SELF-INCREASE - CONTENTS: what causes the water pressure in a bladder-type water tank to slowly creep up? Do we care? You betcha. Here we explain how a pinhole leak in the tank bladder can lead to weird water system, pump, and tank operation and we conclude that you want to replace the internal bladder or the whole tank itself.
  • POST a QUESTION or READ FAQs about diagnosing & fixing unexplained pressure increases in an internal-bladder type water pressure tank
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Water tank pressure creep-up:

This article describes the causes, effects, diagnosis & repair of slowly-increasing pressure in an internal-bladder type water pressure tank. It can seem very odd for tank pressure to increase above it's pre-charge or pump cut-off pressure but believe it or not it can happen.

The usual cause of un-planned water tank bladder pressure increase is a small leak that lets water into the tank's air space. Ultimately you'll need to repair this problem to stop pump short cycling or other weird water pressure behaviors in the building.

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Diagnose & Fix Mysterious Increases in Bladder Type Water Tank Pressure

Reader Question: water tank pressure creeps up and water pump short cycling: pinhole tank bladder leak symptoms?

Water pressure tank bladder leak test (C) InspectApedia(Oct 18, 2014) Rick said:

I have a 20 gallon diaphragm tank the air pressure goes from 28 to 40 psi in about 24 hours after I drain the water and reset the air pressure and starts short cycling.

Sounds like a pin hole in the bladder after reading your articles right.

8/10/2013 D.S. said:

First off, great site with tons of information! I don't have a question so much but wanted to submit an issue I had and the resolution as it was a bit different than anything you have listed. IF you choose to use this information on your site, feel free to edit as you wish.

[At your general page on water pressure tanks found at WATER TANK: USES, TROUBLESHOOTING, I was reading about tank pressure problems and short cycling water pumps.]

We have a Amtrol Well X Trol WX-250 (44 Gallon Pressure Tank) which is about 14 years old. 40/60 Pressure Switch on our well. We noticed the well was cycling too fast. We should have a drawdown of about 11 gallons. We were getting a drawdown of 2-3 gallons.

Followed the procedure assuming I would find a waterlogged pressure tank. Cut power to pump, open valves to drain water from system. Air gauge on the tank. I should get 38 if all is tuned right maybe less if the bladder is shot. The reading however was 52 PSI. That is odd. This reading was with a dial tire gauge. Try a digital one that I have 53 PSI.

After talking with a friend who is a plumber with 40 years experience he was stumped. The only thing I could figure out is that there is a small hole in the diaphragm allowing water to leak past to equalize the air chamber with the pressure of the water (60PSI). Never have noticed air coming out of any fixtures.

So I bled off the pressure to bring it down to 38 PSI expecting to get water out of the valve in the process. No water found and tank was set to 38. Turned everything back on and things were better but I still didn't think I was getting 11 gallons of drawdown but noticeably better. Ran the system 48hrs and repeated test.

Again, cut power, drain the system and pressure test. This time I got 45PSI. How could it rise 7 PSI in 2 days?

Call the plumber but he was busy with another customer so while waiting to hear from him I call Amtrol tech support. Explain what I am seeing, what I have done as described above. The tech stated that I have a small hole in the diaphragm just like I had thought was the only plausible explanation.

I asked what options I have and he said tank replacement. He commented that this issue is one they have seen before but is one that they had a hard time figuring out for a while as the symptoms are not what is normally expected. Pressure high not low, no water from pressure valve when venting air. He stated that the tank was getting water logged but basically we caught it early in the failure process. So it had not totally failed yet.

So new tank installed and everything is back to normal. Once the old tank was removed it was quite heavy as it was getting water logged. I used a tool to remove the core of the valve to fully vent all pressure from the air chamber.

Never got any water out. Finally I tipped the tank over to see what happens and at that point I started getting water out of the tank. So it was getting water logged as the tech mentioned it was just early in the failure process.

The main reason I wanted to write you is because everywhere I looked (this site and many others) described the normal failure symptoms. Low pressure and possible water from the air valve. Another possible symptom is high pressure though. It makes sense. The air chamber should be sealed. As long as the pump is off and water drained it should be 38 or 2 lbs below cut in as your site mentioned. If it is anything different (high or more commonly low), either it was set wrong during installation or the diaphragm has a hole or is ruptured. If it is different, adjust pressure to where it should be and run it for a couple days and check again. If the pressure changes again, odds are the tank is bad.

Thank you for setting this site up and the work you do. - D.S. 8/10/2013


Thank you for the interesting water pressure tank water-logging and "high pressure" report - it helps us realize where we need to work on making our text more clear or more complete. A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone. And I suspect that in the case you describe, we could have missed something to complete an explanation of the system pressure readings you observed. But with what you've said I can offer a possible explanation that fits the facts as given.

If the pressure control switch on a water pump system is working properly, the system pressure will never exceed the pump pressure control switch cut-off pressure. Your pump cut-off pressure was 60 psi using a 40/60 pressure switch. The highest pressure you recorded at the tank was 52 psi - consistent with this rule. Amtrol posed that there was a small leak in the internal water tank bladder. This makes some sense to me and leads to speculation about what' was happening in your system.

Why would water tank pressure readings creep up in just a few days?

You asked how the apparent tank pressure could "creep up" above the cut-in pressure over several days.

I agree that the explanation probably lies in one of two areas:

  1. a faulty pressure control switch OR
  2. a leak in the pressure tank's internal bladder.

Debris clogging can cause a pressure control switch to properly sense lower pressures, failing to turn the pump on consistently, but debris clogging at the switch does not normally cause tank over-pressure. This does not sound like the situation you describe.

Other internal bladder type water pressure tank odd behavior can be caused when a bladder sticks to itself - often causing very small draw-down volumes as water cannot enter the tank. This too does not sound like the situation you describe.

An explanation for the unexpected increase in water pressure in the tank combined with shortening draw down cycle may be that water under pressure leaks out of the bladder into the space between tank and bladder through a small leak or opening.

Because the hole in the bladder is so small, it is quite possible to turn on water in the building and receive water at a lower pressure and quantity than normally delivered from the pressure tank because the rate at which water under higher pressure could leak back into the bladder interior would be very slow. In addition, water accumulating in the air space outside the bladder reduces the volume of that air space, thus reducing the draw-down water quantity and leading to short cycling.

Effects of a pinhole or small bladder leak in a water pressure tank

Re-stating what I think is going on, at the upper end of water tank pressure range that occurs during each pump-on cycle, some water is forced out of the water-containing bladder into the space between the steel tank and the bladder where it accumulates. The ability of water to return to the bladder interior may be less than its ability to leak out of the bladder due to the position of the particular pinhole or small leak. That is, leakage tends to be unidirectional, pushing out of the bladder into the air space only at the top of the pressure cycle.

The result of water accumulating out of the bladder and in the space normally occupied by air in the pressure tank is that the volume of air-space is gradually reduced, leading to short water pump on-cycles just as occurs in a bladderless water pressure tank that has become water-logged.

Why no water came out of the air valve at the pressure tank top

Water pressure tank bladder leak test (C) InspectApediaWhy, then might you have not been able to get water out of the leaky pressure tank through the air valve (as occurs in a water-logged bladderless tank)? Water has to be trapped within the tank's air space; the air valve is at the top of the tank. Water in an upright tank will be at the tank bottom.

Opening the air valve, even releasing all of the air pressure remaining in the tank will still leave water in the tank air space at the tank bottom. Upending the water tank might seem a course that would allow water to drain out of the air valve, but keep in mind that if there is no other way for air to enter the tank during this process, it will be difficult to drain any water out.

Here is a similar example; if we want to drain water out of a water heater tank, the tank drain, located at the bottom of the tank is opened. But unless we open a valve at the top of the water heater tank (often we use the relief valve for this purpose), because there is no path for air to enter the tank except through the same valve that is draining water out, the rate at which water leaves the water heater tank is very very slow.

Water drains out at a dribble until enough vacuum is created inside the tank to stop water leaving and instead draw a gulp of air into the tank. Then more water dribbles out. This is a very very slow process occurring through the 1/2" diameter tank drain valve opening. Now translate this situation back to an "upside down" water pressure tank trying to drain water out (and let air in) through the 3/16" diameter air valve opening. Little or no air can enter and little water will thus drain in out except at a very slow rate.

[It is also worth noting a condition that probably was not occurring on your system: in some situations we are measuring or sensing tank pressures differently at the pump control than at a tire gauge used at the air valve. The air valve location senses air-pressure in the air space around the bladder, while the pressure gauge senses water pressure in the piping system - under normal circumstances that includes water pressure inside the bladder. In a normally-operating system these pressures (air and water) should be the same; but if a bladder is damaged and sticking over the water outlet, that pressure consistency might be lost.]

Reader follow-up:

Based on the water pressure gauge I feel that my 40/60 pressure switch was operating properly. When replacing the pressure tank I also replaced the pressure switch, connecting pipe for it and pressure gauge. These items are pretty in expensive to they were done as preventative maintenance as I don't want to go back and address these other items in a few months or so. The pressure gauge was showing signs of sticking as it was dropping once it got to about 50 PSI. Of course the pressure gauge had nothing to do with the operation of the pressure switch other than provide feed back as to what pressure the water is at in the system.

One symptom that may be worth mentioning is that when I shut off the power to the well and opened a drain valve next to the pressure switch to drain the system I also opened a faucet in the laundry room 10' away from the pressure tank as well as a bathroom faucet upstairs. This was done to try and drain the water from the house pipes the one upstairs opened to allow air in to speed things up. Like you mentioned in draining a water heater. So what I saw that may be worth noting.

While that valve was open, I did still see a trickle of water coming out of the valve at the pressure switch. I attributed it to water draining back from the house. However in my case it may have been water leaking from the small hole in the waterlogged pressure tank. When I disconnected the tank it was quite heavy (compared to the new one) and it continued to drain water very slowly from the tank even though the core of the air valve was removed. Also when I tipped it over it did drain water from the air valve. This is shown in the photo that is attached. Of course one would have to be certain that any trickle from that valve is not coming from the house plumbing as it is draining to the low point in the system.

I suspect that I didn't get any water from the air valve when venting air from 52 back down to the proper level of 38 because as you mentioned the air valve is at the top of the tank and it appears that no air never left the tank (via plumbing) other than what I vented explaining the high pressure. Because of this head space the water never reached the air valve when venting while it was hooked up. Once I could tip it on its side then I could get water to exit from the air valve. - D.S. 08/11/2013


I think you've got it just right. As long as water in the pressure tank bladder was pressurized and unable to exit at a tank drain, when the water tank is removed and placed upside down or on its side with the air valve facing down, pressurized water in the bladder might indeed slowly leak back out of the (stretched) bladder, into the air space of the tank and out of the air space slowly through the schrader valve.

And I agree it's much cheaper to replace old plumbing parts during a water tank replacement than to have to re-visit the the topic later.

Thanks for the photo of your water tank. - DF

Reader Question: how does water leak into the air space of a bladder type water tank?

AUTHOR:Anonymous or Jim: (no email)

You say water leaks into the tank air space to cause increasing tank pressure. How is that possible without water coming out of the tank top air valve?

COMMENT:If, as you say early on that "air pressure and water pressure inside the tank will be at the same psi", how does the pressure rising at the air valve indicate a pinhole leak in the bladder? Thanks Jim


Anon/ Jim:

it's not what I say, it's basic laws of physics. But I agree with you that the article above needs clarification.

IF air is outside the bladder and water leaks into that air space, it can only enter hat air space when the water pressure is above the initial air charge pressure of the tank when installed. That initial or pre charge pressure, if measured with no water in the tank, will be set at 2 psi below the pump cut in pressure. As water leaks into the air space it reduces the available space for the air. Thus if pressure is measured just at the point of pump cut-in, the pressure *at that time* will read above the original tank Pre charge pressure. You'd only see that if you measured at pump cut in. Later the tank air and water pressure will be higher - up to the pump cut off pressure.

Eventually enough water leaks into the air space that the pump short cycles.

What this case might let us distinguish is a pinhole bladder leak from a ruptured bladder. The latter can show up as a period of air at faucets, then short cycling pump, and then water squirting out of the air valve if it is opened.

More generally, Higher pressure at the air valve means higher pressure in the tank and at the air valve. So we should have made clear the point in the pump cycle when you can see air pressure as elevated is at or close to pump cut in time. And the higher pressure is only in relation to the original Pre charge air pressure.

Measured later in the pumping cycle or at pump cutoff, air and water pressure will of course be one and the same.

I suspect this effect can't be detected so easily later in the life of the bladder leak.

If water is leaking out of the bladder, the effects include pump short cycling and ultimately water squirting out of the air valve if it's pin is depressed.

Thanks for asking, let me know if this is still unclear.


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