Measuring air pressure in a bladder type water pressure tank (C) Daniel FriedmanSet Air Pressure in Water Pressure Tank
Bladder type pressure tank air pressure adjustment

  • WATER TANK BLADDER PRESSURE ADJUSTMENT - CONTENTS: How to check and adjust air pressure in an internal bladder well water tank. Where to measure air pressure or water pressure on a water tank. Typical water tank actual draw-down volume vs. tank rated size. Questions & Answers on internal-bladder water pressure tanks. Well pump & water tank diagnosis & repair procedures
  • POST a QUESTION or READ FAQs about setting the air precharge pressure in internal-bladder type water pressure tanks

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How to set the air pressure in a water tank using an internal bladder:

this article describes how to determine the proper air pressure setting in a bladder-type well tank, when, and how to actually change the air pressure in the water tank.

We explain how to determine the proper air charge for water pressure tank and how to adjust the actual tank air pressure to that number. We detail how to fine tune the water pressure tank air charge to match the pump pressure control switch settings.

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How to Select the Proper Air Pressure Charge for a Bladder-Type Well Tank

Bladder type Well X Trol Water Tank (C) Daniel FriedmanReaders of this document should also see WATER PUMP REPAIR GUIDE an specific case which offers an example of diagnosis of loss of water pressure, loss of water, and analyzes the actual repair cost. The page top photo shows the author testing the air pressure in a Well-X-Trol bladder type well tank.

[Click to enlarge any image]

Factory air pressure settings in the water pressure bladder tank

According to Well-X-Trol bladder type well tank air precharge: typical factory set air pressure on a bladder-type residential well water tank is 18 psi. Some models may come with different pressure settings however. WELL-X-TROL™ water pressure tanks are shipped from the factory with a standard precharge of

Before discussing doing anything to a bladder-type water pressure tank, read this safety warning from WELL-X-TROL, a leading well tank manufacturer:


Factory warnings about changing the bladder tank pressure setting

When the Well-X-Trol has been in service and a change to a higher pre-charge pressure is necessary due to a required change in the pressure switch setting, failure to follow instructions below can cause a rupture or explosion, possibly causing serious or fatal personal injury, and/or property damage.

How to Read Water Tank Pressure or any Pressure Gauge Accurately

If you are fine-tuning water tank bladder or air pressure be sure that you are using an accurate pressure gauge and that you know how to obtain an accurate pressure reading.


Well Tank Air Pressure Setting at Time of Tank Installation

Photo of a water tank air valve for adding air to a water pressure tank

Set the well tank air pressure to 2 psi below the well pump control switch cut-in pressure.

We detail this procedure just below.

Remember to use your separate air pressure (tire) gauge to check the actual water tank pressure when your well pump turns on and off - that's because the dial gauge installed on your water tank may be inaccurate.

Well Tank Air Pressure Adjustment Procedure

Water tank air pressure (C) Daniel Friedman

If you need to tune your bladder-type water tank to work exactly properly with your pump pressure control switch, or if you know that someone has already modified the pressure in your water tank and you want to restore it to factory specifications, a reasonable procedure is the following recommended by the manufacturer:

Water tank air valve (C) Daniel Friedman

Leaky or Burst Water Tank Bladder Warnings When Adjusting Water Tank Air or Water Pressure

Watch out: these WATER TANK PRESSURE ADJUSTMENT instructions are for an un-damaged water pressure tank that uses an internal bladder. Reader Robert Ford pointed out by comment (17 Sept 2015) that if the internal bladder in the pressure tank has a leak or has burst you will probably have difficulty getting the water to drain out of the pressure tank. However his suggestion of using air pressure to force water out of the tank was not correct and could be dangerous.

Watch out: do not attempt to use high air pressure at the water tank's air adjustment valve to force water out of a water pressure tank that uses an internal bladder. Doing so can rupture and destroy the bladder and worse, it can burst the water tank injuring or even killing a bystander.

If the water tank bladder has developed a leak or has burst water will have left the bladder and entered the air space in the tank making it difficult or even impossible to drain the tank completely.

That's because water that leaks into the tank's air chamber from a small hole in the tank bladder will not readily return to the bladder (water space) as you are draining the tank.

Further, if the water tank bladder has burst completely it can collapse, blocking all or most water from leaving the tank at all. If the internal bladder in a water tank is leaky or burst you'll need to replace either the bladder or the tank and bladder assembly. Adding air pressure will simply press the collapsed bladder more tightly against the water tank's drain opening.

If the water tank bladder is un-damaged, air pressure in the bladder will push water out of the tank completely leaving some air charge inside the bladder (unless you inadvertenly let air out of the bladder through the air valve). In a bladder type water tank with proper pressure adjustment, when all water has left the tank you'll see air pressure at 2 psi below the pressure switch cut-in setting. Even if the tank air pressure is too low, you should still see some air pressure at the tank air valve when all water has left the tank.

See WATER TANK BLADDERS for an explanation of the difference between a bladderless and an internal-bladder water tank as well as for a description of what goes wrong with the internal bladder in water pressure and storage tanks.

Watch out: high pressures can burst the water tank bladder. Exposing the water pressure tank to excessive water pressures can also burst the water tank's internal bladder. Sometimes a water tank bladder sticks to itself, preventing water from entering the water tank and causing well pump short cycling.

We might un-stick the bladder by slightly and just temporarily over-pressurizing the tank by say 15 psi but we should never exceed or really even approach actual pressures close to the water tank's rated or safe operating pressure. Typical maximum operating residential water pressures run between 20 psi and 70-80 psi. Higher pressures cause leaks and can burst the water tank or water piping.

How to Fine Tune the Pump Pressure Control Switch to the Water Tank

Well-X-Trol offers excellent advice on adjusting the water pressure control switch which we paraphrase, edit, and expand below:

Because well pump pressure control switches are not precise, "lab grade" instruments, the actual pressures at which a pump control switch turn the pump on or off will sometimes be above or below the stated pressure setting on the package of the control switch or above or below the pressure range shown on the switch itself (if your switch has such markings, most do not).

A difference between the marked pressure settings on a control switch and its actual performance can cause a delay between the time that a water pressure tank becomes completely empty and the time that the pump turns on.

Usually this delay is brief, though some readers have reported that their pump simply did not turn on at all under these conditions.

We want to adjust the water pump pressure switch to be"tuned to the Well-X-Trol (or other brand) bladder-type water tank air pressure that was set at the factory (or is presently the actual pressure in the tank). Here is the procedure:

  1. Close off all plumbing fixtures that are using water in the building.
  2. Turn on the water pump and let the system run until the water pump cuts off.
  3. Open one or more plumbing fixtures to drain the water pressure tank; during this draining, watch and listen to the water tank and pump.
  4. If there is a momentary pause in the water flow from the time the well water pressure tank is emptied and the time that the water pump starts, adjust pump cut-in setting clockwise slightly to increase the pump cut-in (turn on) setting.

    If your water pump is in your well rather than on or next to your water tank, you can't hear the pump run. But you can listen for the "click" of the pump switch cutting in or out. For more photos and description of exactly which nut or screw to turn to adjust the well pump switch cut-in,
  5. Close the plumbing fixtures and let the water pump continue to fill the water tank until the water pump cuts off.
  6. Check time it took to fill the water tank.
  7. Open the same plumbing fixtures again, follow the steps above, this time to see if pause in water delivery has been is eliminated. If not, continue adjusting pressure switch.


Continue reading at WATER TANK PRESSURE RELIEF VALVE or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.




Or see WATER TANK AIR PRESSURE SETTING FAQs - companion to the article above on this page




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