How to Set or Adjust the Air Pressure in Bladder Type Water Storage & Pressure Tanks InspectAPedia® -
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
Questions & answers about setting the air precharge pressure in internal-bladder type water pressure tanks
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.
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Readers of this document should also see Water pump and pressure tank repair diagnosis & cost 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.
How to Select the Proper Air Pressure Charge for a Bladder-Type Well 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
18 psig for models WX-101 and WX-102
30 psig for models WX-103 - WX-203
38 psig for models WX-205 through WX-350.
Before discussing doing anything to a bladder-type water pressure tank, read this safety warning from WELL-X-TROL, a leading well tank manufacturer:
DANGER! [Water Pressure Tank] EXPLOSION HAZARD
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.
DO NOT ADJUST OR ADD PRESSURE IF THERE HAS BEEN A LOSS OF AIR.
DO NOT ADJUST THE PRE-CHARGE PRESSURE IF THERE IS VISIBLE EXTERIOR CORROSION.
DO NOT ADJUST THE PRE-CHARGE PRESSURE IF THERE HAS BEEN A REDUCTION OF THE PUMP
CYCLE TIME OR THE PRE-CHARGE PRESSURE
COMPARED TO ITS INITIAL SETTING. THIS IS
BECAUSE REDUCTION IN PUMP CYCLE TIME
CAN RESULT FROM LOSS OF TANK AIR
PRESSURE WHICH IN TURN CAN MEAN THERE MAY BE INTERNAL CORROSION AND ANY REPRESSURIZATION OR ADDITIONAL PRESSURE
COULD RESULT IN RUPTURE OR EXPLOSION.
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. See WATER PRESSURE GAUGE ACCURACY for details.
Well Tank Air Pressure at Time of Tank Installation
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 during Water System Maintenance or Repair
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:
Remove all water from the water tank. This means turn off the water pump, open a nearby plumbing fixture, run water until the water stops entirely - your water tank should be empty or close to empty.
Check the air pressure in the water tank by using an accurate air pressure gauge (such as a dial type or digital tire pressure gauge) to measure the air pressure at the schrader valve on the water tank. The tank pressure should be within 10% of the original factory water tank pressure setting. Our photo (above left) shows the water tank air inlet valve on the top of our Well-X-Trol well tank. We removed the cap and label for the photo.
Our photo at above right shows our digital air pressure gauge measuring the air pressure in the water tank. The reading of 39 psi tells us that the dial pressure gauge that we illustrated at How to Read Water Tank Air Pressure Accurately (and located on this same water system) agrees with our pressure gauge within 1/2 psi.
Because water tank pressure controls normally use a pressure difference of 20 psi between the cut-in pressure and cut-off pressure at the water tank, a gauge error of one or two psi is not a concern. Thanks to Jeff Garmel for suggesting text clarification in this discussion of water pressure tank diagnosis.
Set the air pressure in the empty water tank to 2 psi below the well pump pressure switch cut-in pressure. Bleed air pressure out of the water tank, or add air pressure into the water tank, until the tank pressure. For example, if your well pump pressure control switch is set to "cut in" (start pumping water from the well) at 30 psi, then set the pressure tank to (30 - 2) = 28 psi.
Replace the air cap on the tank air pressure valve and be sure that any warning labels that you took off during cap removal are back in place.
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:
Close off all plumbing fixtures that are using water in the building.
Turn on the water pump and let the system run until the water pump cuts off.
Open one or more plumbing fixtures to drain the water pressure tank; during this draining, watch and listen to the water tank and pump.
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, see WATER PUMP PRESSURE CONTROL ADJUSTMENT.
Close the plumbing fixtures and let the water pump continue to fill the water tank until the water pump cuts off.
Check time it took to fill the water tank.
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.
Frequently-Asked Questions (FAQs) on internal-bladder water pressure tanks & draw-down water volume, pressure switch adjustment, and proper air pre-charge pressure
Question: what is the relationship of water tank rated size to actual water draw-down volume?
How much water should be in the water pressure tank intenral bladder? The water tanks are rated as 85 gallons. When the system cut-out water pressure is reached there is only about 5gal in tanks? - Stephen
Reply: Table of Water Tank Draw-Down vs Rated Size
Modern internal bladder type water pressure tanks give an "equivalent draw down" cycle to the actual "gallons" number on the equipment, but the actual physical volume of water may be significantly less.
5 Gallons does not sound reasonable. Typically on an "85 gallon" sized water tank, the actual water draw-down volume will be about 25 gallons. Below we include a table of rough estimates of actual water draw down volumes for different internal bladder water pressure tanks.
Table of Typical Water Tank Draw-Down vs Rated Size
Water Tank Rated-Size (approximate gallons)
Actual Volume of Water Draw Down (approximate gallons)
20
6
30
9
50
14
85
25
120
36
Notes to the water tank draw-down volume table above:
The "actual draw down" is the physical volume of water that is drawn from the water pressure tank before we expect the pressure drop in the water supply system to reach the well pump cut-in pressure.
The exact water tank size and expected draw-down water volume will vary by manufacturer and tank model, so our data above is only approximate.
The significance of the "draw-down" volume of water is that it determines the frequency with which the water pump has to cycle on and off which in turn affects equipment life.
Detailed Chart of Water Pressure Tank Sizing, Tank Volume, Water Drawdown Gallons
Well-Rite Tank Model
Total Tank Volume
Equivalent
Bladderless
Tank Size
Drawdown Water Volume
20/40 psi
30/50 psi
40/60 psi
Gals
Liters
Gallons
Gals
Liters
Gals
Liters
Gals
Liters
WR45
14
60
30 Gal
5.2
19.68
4.3
16.28
3.8
14.38
WR60
20
80
43 Gal
7.4
28
6.2
23.47
5.4
20.41
WR80
26
100
82 Gal
9.6
36.34
8.1
30.66
7
26.5
WR100
32
120
82 Gal
11.8
44.66
9.9
37.47
8.6
32.55
WR120
33
130
82 Gal
12.3
46.56
10.3
38.99
9
34.06
WR140
44
170
120 Gal
16.3
61.7
13.6
51.48
11.9
45.04
WR200
62
240
220 Gal
22.9
86.68
19.2
72.67
16.7
63.21
WR240
81
310
220 Gal
30
113.55
25.1
95
21.9
82.89
WR260
85
325
220 Gal
31.5
119.23
26.4
99.92
23
87.05
WR360
119
450
450 Gal
43.6
165.03
36.8
139.29
32.1
121.5
Notes to the Wel-Rite Water Tank Sizing Chart
Data based on a Well-Rite® water pressure tank [1]
When choosing an internal-bladder type water pressure tank, take note of the operating pressure range of your well pump equipment. You will see in the table above that the higher you set the water pressure cut-in and cut-out, the smaller will be the draw-down volume provided by a particular water pressure tank.
Questions & Answers regarding this article
Questions & answers about setting the air precharge pressure in internal-bladder type water pressure tanks
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Thanks to Jeremy Houser who suggested that we needed to clarify the difference between bladder type and non-bladder type water tanks when discussing air charging and diagnosis of water tank repairs.
Thanks to Jeff Garmel for discussing clarifications on water pressure tank testing and diagnosis, 8/24/2009.
Amtrol Extrol™ pressure control tanks, which they call well tanks, are described at the company's website at www.amtrol.com/extrol.htm and installation and operating instructions for these well tanks can be found at www.amtrol.com/pdf/9015A290revcWXT.pdf
Well-X-Trol: Amtrol Extrol™ pressure control tanks used on hydronic heating and other systems such as models 35LBC, 50 LBC, 85 LBC, and 100LBC to 600 LBC also use a bottom bladder containing air - see amtrol.com/pdf/LBCSeriesEXTROL9017-095.pdf for details.
Wessels Company bladder replacement store was found at westank.com/bladder-tank-store.php on 5/22/2009. Wes sell refers to "shock and surge tanks" as ASME replaceable bladder type and pre-charged hydropneumatic tanks used for commercial, industrial, and well water systems.
Thanks to reader Howard Jackson
for technical editing of proper pressure settings for the Well X Trol WX-103 - WX-203 tank bladder pressures - June 2010
[1] Well-Rite water tanks. Well-Rite water tanks are produced by Flexcon Industries, 300 Pond Street
Randolph, MA 02368
Tel: 781.986.2424, based on manufacturer data provided on the shipping carton for a 44 Gallon / 170 Liter internal bladder water pressure tank during installation in Northern Minnesota, September 2011.
Rasmussen Well Drilling, Inc., 1793 Hwy 61, Two Harbors MN. Jeremy Rasmussen provides third generation well drilling and plumbing services on the North Shore of Lake Superior. Photos by DJF. Tel 218-834-3387. Email: rasmussenwell@frontier.com
Quoting: We serve the north Shore – Lake, Cook, St. Louis, Carlton and Pine counties, including Duluth, Grand Marais, Clouqet, Carlton, Finland, Isabella, Silver Bay, Grand Portage, Saginaw, and everywhere in Northeastern Minnesota.
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