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Photograph of a water pressure tank air valveWater Pressure Falls, then Stops Falling
After the pump stops

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After the pump stops the water pressure falls a few psi, then stabilizes:

Questions & answers on the causes of a brief water pressure drop each time the water pump cycles off.

This article series describes how to diagnose slow water pressure loss and erratic well pump behavior.



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Diagnose slow water pressure drop then stabilizes after water pump stops

Photo of a water pressure gauge showing pressure below pump cut-inThese questions about diagnosing the cause of a slow but brief or "fixed quantity" fall-off in building water pressure when no water is being run (we think) were posted originally at WATER PRESSURE FALLS SLOWLY, ERRATIC PUMP

If when the water pump shuts off the water pressure falls quickly to a lower level then stops falling, this article explains the possible causes of that aggravation.

On 2017-07-08 by Chun - pressure drops 5psi then it stays there everytime pump reaches cut off

Mac, same exact thing is happening to me, it drops about 5psi then it stays there everytime it reaches cut off, let me know if you have figured it out

On 2017-04-28 1 by Mac

The water pressure drops 5 psi every time it stops either at 50 or 60. If I set to 30/50, it stops at 50, then comes down to 45..at 40/60, it stops at 60, but comes down to 55... every time.

At first I thought there was a leak somewhere, but then I noticed the pressure will not keep going down.. i've left it for over 2 hrs and it will not continue to drop once it drops the 5 psi..so maybe there is no leak.

I have replaced the pressure switch and the gauge a couple of times with new ones and different models - same thing.

This have driven me crazy for a very long time and I can't figure it out.

Six explanations for small, consistent pressure drop after the water pump stops running

Chun and Mac

Diagnostic question: How much does pressure fall? Could there be a toilet tank filling? Could there be a debris clogged, slow-to-respond pressure gauge?

0. Rule out water leaks or running toilets. I've seen this pressure drop at the end of a pump-on cycle too. When pressure remains steady afterwards we know it's not an actual water leak - no running toilet, no leaky foot valve. Or we think so

So what might be causing this brief pressure drop that occurs at every pump on-off cycle?

1. Air cushion in the system? I previously thought this was an artifact of the particular pump, piping arrangement, controls - and not something that I think needs fixing. It's probably nothing to do with the switch - more likely the tank and piping and an air cushion somewhere.

2. Pressure cushion in the system? A less-likely possible explanation is that pressure during pumping is, after the pump stops, converted to an expansion of plastic parts or a tank bladder component that absorbs a bit more of the system pressure.

3. Pinhole leak in water tank bladder? There is another possibility: a very small pinhole leak in the flexible rubber bladder in the pressure tank may open enough to pass a few psi worth of water at your cutoff pressure - say 50 psi - then as pressure drops even a little - to say 45 psi - the hole closes enough that any remaining leakage is so slow that you don't notice it.

You'll eventually find this problem - if a pinhole tank bladder leak is what's happening in your case - when over time the water pressure tank becomes waterlogged even though with an internal bladder that should not occur. It will show up as

4. Leaky check valve or foot valve? usually a leaky check valve or foot valve will cause pressure to fall continuously even if slowly after the pump turns off. But on occasion debris on a valve seat might leak water mostly at higher pressure, falling off to very slight or even zero leakage after pressure in the system has dropped.

See WATER PRESSURE FALLS SLOWLY, ERRATIC PUMP and also see CHECK VALVE

A bad internal pump seal might water leak-back into the well piping system and into the well itself (depending on check valve locations) and it will almost always cause a reduced ability of the pump to reach cut-off pressure.

Favorite - 5. Debris-clogged pressure gauge or pump pressure switch? I think the most-common cause of this phenomenon is simply a lack of precision in the pump pressure control switch (or an effect of its location on the plumbing system) combined with the location of a pressure gauge (perhaps right on the pump housing).

Both pump pressure control switches and pressure gauges accept water pressure through a small opening in the body or base of those instruments.

I've found that when a switch or pressure gauge is partly-clogged with debris but before it fails entirely it will begin to respond slowly, or to show a delayed response to pressure changes. That's because it takes extra time for pressurized water to enter OR to leave the body of the gauge or switch.

That can cause a switch or gauge to be "behind" the actual pressure in the system

See our pressure control switch repair discussion wherein we discuss

Also see more discussion of this question at WATER PRESSURE FALLS SLOWLY, ERRATIC PUMP

6. Pressure control or jet pump too distant from water pressure tank: water pressure control manufacturers and water pressure tank manufacturers generally instruct that the pressure control switch and pressure tank should be as close to one another as possible.

Gould Pumps suggests that the jet pump should be no more than 5 ft. from the pressure tank.

Here is what Amtrol™ says about tank & pressure control switch location:

The Well-X-Trol should be installed as close as possible to the pressure switch. This will reduce the adverse effects of added friction loss and pressure switch bouncing, and the difference in elevation between WELL-X-TROL and switch.

Question: why does water tank pressure slowly fall down from 40 psi when the pump stops to a stable 35-36 psi?

(Oct 9, 2015) Bill said:

I have a question. My tank pumps up to 40 psi, but then it slowly "relaxes" to 35 or 36 psi and then stabilizes there. Why could this be?

There is little or no air or water leaking. I know this because the cycle time of the pump is very stable. This happens even when I have the output of the tank closed off, so it's not an effect of anything inside the house.

My first tank arrangement had the input at the top of the tank, pumping the water through the air and splashing into the water and creating bubbles in the water (I'm fairly sure) which might cause a slow air loss into the pipes in the house. I didn't see this relaxing effect then. The output was a few inches above the bottom of the tank.

I had to change the tank and since I was concerned about the air loss, I did it differently. Now the output is still a few inches above the bottom but the input is from the side about six inches above the output. This should be under water all the time I think so there should be no more bubbles to cause air loss.

What could be causing this pressure relaxing? Could the check valve be leaking backwards until the pressure reduces a bit?

Could there be cavitation causing water vapor bubbles that slowly reabsorb into the water and give the air room to expand? Any other ideas?

This question and reply were posted originally at BOYLE's LAW where we explain water tank pressures and volumes controlled by this law: P1V1 = P2V2 at constant temperature

Reply:

Thanks for the interesting question. I've seen this discussed before without an authoritative scientific explanation.

At WATER PRESSURE FALLS SLOWLY, ERRATIC PUMP I commented that I've originally figured this problem was an artifact of the particular pump, piping arrangement, controls - and not something that I think needs fixing. It's probably nothing to do with the switch - more likely the tank and piping and an air cushion somewhere.

There I give other possible explanations for the phenomenon you describe.

How to rule out running water or a leaky check valve or foot valve

If there were a bad check valve or a running toilet, water pressure measured at the tank would

For cases in which the water pump pressure falls after the pump stops, but on every pump cycle the pressure drop stops at about the same point and after the same time interval, something else is going on.

More explanations of possible causes of this pressure drop are given in the top of this article.

Question: Gauge at well shows about 62 when pump stops, then settles down to 59.

(Nov 14, 2014) Tim2014 said:

Drilled Well 16yrs old. Previous owner said 400+ ft. I had a short cycle issue that was resolved by re-pressurizing the tank. Pump now works 40-60 as expected and tank is holding the expected air pressure.

I then noticed a slow leak of water pressure while I was correcting the short cycle. Symptom: Gauge at well shows about 62 when pump stops.

Then settles down to 59. I assume that much play in gauge is ok given it is a $6 part.

Water pressure then slowly drops at a slightly variable rate over hours. 15 lbs-9 hrs, 5 lbs-6 hrs, 7 lbs-6.5 hrs, etc... I can turn off the flow to the house at the well and the well and tank holds water pressure constant at 59 lbs for 6 hours.

That leaves me to believe that the drilled well itself (foot valve, piping, etc..) is ok. I don't see any signs of leakage in my home (no visible water, no toilet leak,etc..), but to make sure, I turn off the water as it enters the house and have similar drop rates in pressure as listed above.

That leaves me to believe I have a slow leak in the yard line between the well and the home. Does that sound right? Of course there is no visible evidence of a leak, and that line crosses the sewage, power, phone/internet and propane gas line before it enters the home as the builder was apparently not a good planner.

Question: My tank at the well is supposed to produce a 5 gal draw down at 40/60. So, if I let the well pump 60lbs then open the faucet at the well and let it run in a bucket until the pump kicks back on, I should expect to fill up a 5 gal bucket? So I did that after 6 hours and had about 2 gals in the bucket

So, I'm leaking 3 gals in 6 hours correct? I don't know much about this, but I assume if the water pressure drops that the water had to go somewhere even I can't find the leak.

I don't understand how air could leak into the system, but I've had several people and couple of articles on this site indicate that air might be leaking into the system. Any comments or suggestions?

Reply:

Tim

At the start of WATER PRESSURE FALLS BRIEFLY THEN STOPS we list possible explanations for why a water pump keeps losing pressure at the end of the pump-on cycle, for the case in which the pressure loss seems to stop after just a few psi.

At WATER PRESSURE FALLS SLOWLY, ERRATIC PUMP we describe a similar problem except that water pressure sometimes continues to drop until the pump turns on even though no water is being run in the building.

A slow leak of water out of the piping anywhere between well bottom and building water equipment can leak both water out and in some circumstances air in to the system. Usually we look first for a bad foot valve or check valve

At AIR DISCHARGE at FAUCETS, FIXTURES gives sources of air leaks into a water system: well piping leaks, snifter valves, etc. are discussed. One of those could cause the formation of unexpected "air cushions" or air bubbles in the water supply system.

On 2017-01-26 by Susan - Opened house water valve and lost 10 pounds of pressure.

Had a new well pump installed, now my pressure tank will lose pressure right after the pump turns off. I shut the water to the whole house off and kept the pump to tank valve open, Pressure maintained in tank.

Opened house water valve and lost 10 pounds of pressure. No house water running. Toilets are not running. Does this indicate we have some kind of leak in the house or could there be other reasons why we are losing pressure?

On 2017-01-26 by (mod) Reply: pressure tank will lose pressure right after the pump turns off.

If pressure continues to fall then look for a leaky check valve or foot valve in the well - see WATER PRESSURE FALLS SLOWLY, ERRATIC PUMP

and see

If pressure falls a fairly consistent few psi and then stops, see our speculations at WATER PRESSURE FALLS BRIEFLY THEN STOPS

Question: as soon as pump shuts off pressure drops for 20 minutes then pump turns back on

(Mar 28, 2013) janet said:

I have a double line jet pump system. The cut in is 30 and off is 50 on pressure switch.

The problem is as soon it shuts off, the pressure drops, takes about 20 minutes then cycles again. We installed a check flow valve at the pump, thinking water was flowing back down to well. That didn't solve it. What could be the problem?

(Apr 15, 2015) Anonymous said:

the pump pumps water but when shut off the pressure falls

Reply:

Janet & Anonymous

It should be pretty easy to determine if the leak is in the building, at the pump and water tank, or in the well piping. If you shut off all water entering the building and pressure drops, the problem is not a leak in the building.

If your check valve is absolutely pefect, or if you use a temporary shutoff valve between the pressure tank and pump and the well itself, and pressure drops, there is a leak on the pump and tank side of that valve.

See WATER PUMP INTERMITTENT CYCLING

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Continue reading at WATER PRESSURE FALLS SLOWLY, ERRATIC PUMP - topic home, or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see WATER PUMP INTERMITTENT CYCLING - pump runs at odd times for no apparent reason

Or see WATER PRESSURE FALLS SLOWLY FAQs

Or see WATER TANK PRESSURE GAUGE - troubleshooting guide for the gauge itself

Or see WATER PRESSURE INTERMITTENT LOSS - occasional loss of water pressure

Or see WATER PRESSURE COMES & GOES - water pressure is lost, then returns

Or see these common sources of slow dropping in water pressure and loss of well prime:

WELL PIPING CHECK VALVES

WELL PIPING FOOT VALVES

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