2 pressure tanks - different PSI?

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bhf21279

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A couple of questions. I'm not sure I understand the setup...

I have 2 x 20 gal. steel pressure tanks. Assuming the water flow is from left to right (from the well pump to the pressure switch), one pressure tank is on the left side of the pressure switch, the other tank is on the right side (after) the pressure switch.

Question: is this an acceptable setup for pressure tanks? I'm assuming the pressure tanks would both be on one side of the pressure switch... either before or after the switch.


My other issue:
We have had a combination of very low and very high water pressure (cyclical) during water usage (i.e. shower). I am aware the maximum water tank PSI for a 40/60 well would be about 2 PSI less than the low-pressure setting on the switch. Therefore, with the tanks FILLED with water, I checked their air pressure (assuming a minimum of ~38 PSI would be observed). The pressure tank to the left of the pressure switch showed just below 20 PSI, the tank to the right of the switch showed about 30 PSI. The pressure switch gauge (on the well line) shows a consistent 60 PSI.

Question: Should the air PSI have been higher with water in the tanks?

I added more air to the left tank to bring it up to 30 PSI (with water in the tank). After adding the air, I noticed a positive difference with the water pressure (much better and consistent pressure than before).

Question: Is there a PSI range that pressure tanks should be at when they contain water? I would assume the tank PSI should be the same (if not more) than what a pressure tank would be set at when the tank is empty (i.e. ~2 PSI less than the low pressure setting).

Thanks!
-confused&not_sure
 

Reach4

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Where is your pump-- down the well, or above ground?

How much pipe is between the two tanks-- length and pipe size.

Your air pressure gauge is suspect. When a tank has water in it, the air pressure is about the same as the water pressure.

Air precharge is always measured and set with the water pressure zero.
 

Bannerman

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Question: is this an acceptable setup for pressure tanks?
Acceptable, yes in the situation you describe, assuming there is no check valve or other flow limiting device to isolate or reduce the flow from one tank to the other, or isolating the tanks from the pressure switch.

With both tanks combined together in the manner you describe, they will both function equal to one 40 gallon tank.

I am aware the maximum water tank PSI for a 40/60 well would be about 2 PSI less than the low-pressure setting on the switch.
To check and adjust each tank(s) 38 psi air pre-charge pressure, the pump first must be deactivated (de-energized) and both tank(s) must be completely drained of water.

Therefore, with the tanks FILLED with water, I checked their air pressure (assuming a minimum of ~38 PSI would be observed).
When the pressure switch shuts down the pump at 60 psi, each tank's air pressure should then also be 60 psi, equal to the water pressure measured at the combined outlet for both tanks.

20 gallons is the total volume of space occupied by each pressure tank. Each tank will contain only about 5 gallons water when filled to 60 psi when the pressure switch shuts down the pump, with the remaining 15 gallons of space containing 60 psi compressed air.

Since the compressed air will push the water out from the tanks whenever water is consumed while the pump is not running, the air will then expand into the tank space that had been occupied by the water, but since the same volume of air is expanded into a larger space, the air pressure will become lower. Once the air is expanded so the pressure is only 40 psi which will activate the pump, there will be only a minimal amount of water remaining and so the 40 psi compressed air will occupy almost all of the tank space. "Almost all" due to the 38 psi pre-charge, which will cause a small quantity of water to remain in each tank when the pressure switch activates the pump at 40-psi.

Because water will be pushed back into each tank while the pump is running, the air within the tank will be again further compressed into a smaller space, in proportion to the amount of water that enters. Once the air is compressed to 60 psi, the pressure switch will shut down the pump. This cycle will be repeated numerous times per day, each time more than 10-gallons water is consumed.
 
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bhf21279

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Reach4 / Bannerman -
Thank you very much for the replies! Very informative.

Where is your pump-- down the well, or above ground?

How much pipe is between the two tanks-- length and pipe size.

Your air pressure gauge is suspect. When a tank has water in it, the air pressure is about the same as the water pressure.

Air precharge is always measured and set with the water pressure zero.
- Pump is down in the well
- Maybe no more than 4ft of pipe between the tanks. From what I recall, the pipe size (outside diameter) is probably 1 1/2"
- The air gauge is one of those small ones typically used on tires. It's accurate within 2lbs as compared to the other gauges I use. Thanks - this is what I thought about when first reading the low PSI of the tanks.

Acceptable, yes in the situation you describe, assuming there is no check valve or other flow limiting device to isolate or reduce the flow from one tank to the other, or isolating the tanks from the pressure switch.

With both tanks combined together in the manner you describe, they will both function equally as one larger tank


To check and adjust each tank(s) air pre-charge pressure, the pump must be deactivated (de-energized) and both tank(s) must be completely drained of water.


When the pressure switch shuts down the pump at 60 psi, each tank's air pressure should then also be 60 psi, equal to the water pressure observed at the combined outlet for both tanks.

20 gallons is the total volume of space occupied by each pressure tank. Each tank will contain only about 5 gallons water when filled to 60 psi when the pressure switch shuts down the pump, with the remaining 15 gallons of space containing 60 psi compressed air.

Since the compressed air will push the water out from the tank when water is consumed while the pump is not running, the air will then expand into the tank space where the water was located, but since the same volume of air is expanded into a larger space, the air pressure will become lower. Once the air is expanded so the pressure is only 40 psi which will activate the pump, there will be only a minimal amount of water remaining and so the compressed air will occupy almost all of the tank spce.

Since water will be pushed into each tank while the pump is running, the air trapped within the tank will be again compressed into a smaller space, in proportion to the amount of water that enters. Once the air is again compressed to 60 psi, the pressure switch will shut down the pump. This cycle will be repeated numerous times per day, each time more than 10-gallons water is consumed.
- Great information! You are correct, there is no check valve or other limiting devices between the tanks.

Question: With the lower air PSI in the tanks, does this mean the tanks are filling with more water (more than the 5-gallons)? And then when there is a water demand, it is subsequently expelled at a lower PSI? If this is potentially the case, could this mean the tank bladders has been stretched to accommodate the water inflow?

I'm trying to determine if I need (or should get) new tanks.

Thanks again for the assistance.
 

Bannerman

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The pressure switch gauge (on the well line) shows a consistent 60 PSI.
I suspect your pressure gauge is defective and is 'stuck' showing 60 psi regardless of the actual water pressure within the system.

If your pressure switch is properly calibrated for a 40 psi ON and 60 psi OFF pressure range, then the gauge should be indicating 40 psi whenever the pump is first activated by the pressure switch, and showing 60 psi when the pump is first shut off by the PS.
 
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bhf21279

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Good point. I'll check the pressure gauge. So far, all my checking/research has been focuses on the pressure tanks.
Thank you.
 

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Bladders/Diaphragms in tanks fail because the pump is cycling on and off too much. Fix the cycling problem and you have way more tanks than needed.

 

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hmmm.. as a follow up, I tested the water pressure on an indoor and outdoor faucet. Both show about 62 lbs. ...same as what the water pressure gauge switch shows near the water tanks.

I'm not sure how/why the water tanks can show less PSI than the water line.
 

bhf21279

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Thank you very much guys for your knowledge on this!! I drained the tanks and both of them (with little to no water in them) were each about 12 PSI. I added air to both tanks ensure PSI was just below the low-water mark for the pump.

All is good! Hopefully, no other issues!

Thanks again!
 

Valveman

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hmmm.. as a follow up, I tested the water pressure on an indoor and outdoor faucet. Both show about 62 lbs. ...same as what the water pressure gauge switch shows near the water tanks.

I'm not sure how/why the water tanks can show less PSI than the water line.
Testing the pressure when everything is off only gives you the static pressure, which should all be the same. The dynamic pressure will be different when using water and when the tanks are filling. There will be more pressure at the pump and before the tanks because of the friction loss in the lines going to the tanks. With a little adjusting you can make two tanks work. But two tanks or a room full of tanks still won't stop the cycling or deliver strong constant pressure to the house like a Cycle Stop Valve will do.
 

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Thanks again! Everything started coming together with the pressure tank and line PSI... after a few small "taps" on the pressure gauge for the water line, it started showing proper pressure; I'm sure if the gauge was working properly when I first started looking at this, I probably would have made better progress.

Thanks for the input!
 

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Just remember, almost every problem with a pump system including sticking pressure gauges, torn tank diaphragms, burned pressure switches, leaking check valves, sediment in the water, and most importantly a shorter life of the pump and motor are all caused by the pump cycling on and off too much.
 

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could this mean the tank bladders has been stretched to accommodate the water inflow?
Some tanks are equipped with a guard to prevent the diaphragm from stretching too much when the air pre-charge pressure is too low. Perhaps your tanks are equipped with such a guard. If so, that would be a reason for the tank air pressure to remain less than the water pressure (while the pump is running) since the guard would prevent the air from being compressed to the full 40-60 psi range, particularly when the air pre-charge pressure is substantially less than it should be.

Because the tanks are a captive design, the pre-charge air pressure should not significantly change over time. This leads to the question, was the pre-charge pressure too low from the start (seems most likely with both tank's pre-charge being identical), or is there a defect with both tanks?
 
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Reach4

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Thanks again! Everything started coming together with the pressure tank and line PSI... after a few small "taps" on the pressure gauge for the water line, it started showing proper pressure; I'm sure if the gauge was working properly when I first started looking at this, I probably would have made better progress.
For temporary use, a garden hose thread pressure gauge can go onto the pressure tank drain valve.

I am wondering if a liquid-filled gauge might be better.
In the filters on the left, I suggest selecting 100 PSI. While 75 or 90 PSI sound good, they are something else. Do not pick one that has the blue circle non-potable symbol.

I have my eye on https://www.supplyhouse.com/Winters...auge-1-4-Back-NPT-w-Brass-Internals-0-100-PSI while https://www.supplyhouse.com/Winters...cale-Liquid-Filled-Gauge-1-4-Bottom-0-100-PSI would be more of a spurge.
 
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bhf21279

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Just remember, almost every problem with a pump system including sticking pressure gauges, torn tank diaphragms, burned pressure switches, leaking check valves, sediment in the water, and most importantly a shorter life of the pump and motor are all caused by the pump cycling on and off too much.
I'm beginning to see that...

Some tanks are equipped with a guard to prevent the diaphragm from stretching too much when the air pre-charge pressure is too low. Perhaps your tanks are equipped with such a guard. If so, that would be a reason for the tank air pressure to remain less than the water pressure (while the pump is running) since the guard would prevent the air from being compressed to the full 40-60 psi range, particularly when the air pre-charge pressure is substantially less than it should be.

Because the tanks are a captive design, the pre-charge air pressure should not significantly change over time. This leads to the question, was the pre-charge pressure too low from the start (seems most likely with both tank's pre-charge being identical), or is there a defect with both tanks?
Our tanks are the Well-x-Trol, WX-202. I think those have the diaphragm guards. Right, I seriously think the pre-charge pressure was too low. We've been in the house for 10 years and have always noticed a drop in water pressure for a period of a minute or two, and then it's back to "normal" for a few minutes, then back to low pressure. I added more air up to the low-pressure range and the water pressure now feels good... barely any drop in pressure.


For temporary use, a garden hose thread pressure gauge can go onto the pressure tank drain valve.

I am wondering if a liquid-filled gauge might be better.
In the filters on the left, I suggest selecting 100 PSI. While 75 or 90 PSI sound good, they are something else. Do not pick one that has the blue circle non-potable symbol.

I have my eye on https://www.supplyhouse.com/Winters...auge-1-4-Back-NPT-w-Brass-Internals-0-100-PSI while https://www.supplyhouse.com/Winters...cale-Liquid-Filled-Gauge-1-4-Bottom-0-100-PSI would be more of a spurge.
Thanks for the links! I'm going to be looking into upgrading the pressure switch, gauge, and a drain valve for the main line. My current setup has a drain plug, but it looks well rusted into place.

Thanks again for all the suggestions! A great help!
 

Bannerman

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always noticed a drop in water pressure for a period of a minute or two, and then it's back to "normal" for a few minutes, then back to low pressure.
Low pre-charge pressure in combination with a diaphragm guard, would explain the symptoms you describe.

Since the guard will restrict the amount of diaphragm travel, with a significantly low air pre-charge, the air within the tank's air chamber will not be fully compressed to 60 psi as it should be when the tank contains the appropriate quantity of water, but instead will max out at a lower pressure.

While the pump is running, since a single faucet such as a shower, will not consume all of the water being delivered from the pump, water pressure will increase, so once the pressure switch senses 60 psi, it will shut off the pump.

With less than 60 psi within the tank's air chamber, the water pressure will immediately drop to equal whatever air pressure is within the tank. This might be only 30 psi so you would immediately recognize a rapid flow and pressure decrease.

As 40 psi will initiate pump operation, the pump will be rapidly restarted but will now need to begin building pressure not from 40 psi, but instead, from the lower tank pressure. While this will somewhat extend the time for pressure to build, once 60 psi is achieved, the pump will again shut down and the cycle will be repeated for as long as water continues to be utilized.

Since the tanks are suspect, suggest rechecking each tank pre-charge pressure after about 1-week. If the pressure remains consistent, recheck 2-weeks later, then 1-month afterward then annually if the pre-charge pressure remains consistant each time.

If you find the pre-charge pressure has decreased in either tank, that will indicate an air link which will likely require tank replacement.

Better yet, to upgrade your system to prevent cycling and to achieve constant pressure for as long as water is being utilized, install Valveman's Cycle Stop Valve PK1A Pside-Kick kit. That kit includes not only a CSV, but also a new 4.4 gallon pressure tank, 40/60 pressure switch, pressure gauge, relief valve, wall brackets and various plumbing fittings.
 
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