Dropping Water Pressure FAQs

Every time our water pump reaches cut off pressure the water pressure drops about 5psi, then stays there: Why?

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. On 2017-04-28 by Mac

by (mod)

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

by Chun

Mac, same exact thing is happening to me, it drops about 5psi then it stays there every time it reaches cut off, let me know if you have figured it out On 2017-07-08

Explanation by (mod) re: common reason for small pressure drop after the pump stops running

Chun and Mac:

I've seen this pressure drop at the end of a pump-on cycle and have corresponded with quite a few readers about it. Possible explanations for a fixed pressure drop at the end of a pump cycle are at WATER PRESSURE FALLS BRIEFLY THEN STOPS

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. Or we think so.

I've always figured it 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.

But 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 it 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

- pump cycles on and off increasingly frequently even though the water usage rate remains unchanged (in a test case)
- the water pressure tank becomes heavier when tested "empty" - with pump off and all pressure drained from the system via nearby taps the pressure tank has more weight than when new

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.

Also see BOYLE's LAW where we explain P₁V₁ = P₂V₂ at constant temperature

Water Pressure Keeps Falling Slowly After Pump Stops

We have a 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? (Nov 14, 2014) Tim2014

Reply: look for a slow leak or water usage in the building such as a running toilet

Tim

A slow leak of water out of the piping anywhere between well bottom and building water equipment including leaks or water running in the house 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. But if you shut of water going into the house and pressure in the rest of the water system holds steady, that tells me that the leak is in the house, not in the well piping nor foot valve.

So you should look first for a slow-running toilet. That can be tricky to spot as if the toilet flush valve leak is small, you may not notice it by simply taking a quick look in the toilet bowl or tank.

See our detailed diagnostic procedure at TOILET RUNS CONTINUOUSLY 

More clues and sources of hard-to-find water line leaks or check valve leaks are at WATER PUMP INTERMITTENT CYCLING

 

Water pump shuts off, then pressure drops, 20 minutes later pump comes on

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? (Mar 28, 2013) janet

Reply:

Janet,

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 perfect, 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 more causes and solutions of this problem at WATER PUMP INTERMITTENT CYCLING