Photograph of a water pressure tank air volume control Water Tank Air Volume Diagnostic FAQs

  • AIR VOLUME CONTROL FAQs - CONTENTS: questions & answers about water pressure tank air volume controls (AVCs): How to Find & Maintain the Water Tank Air Volume Control - what it looks like, when do you need one, or is an AVC even installed on your water tank?
  • POST a QUESTION or READ FAQs about air volume controls on water tanks: how they work, why they are needed, and how to fix, repair, replace, or abandon an AVC that is not working, hissing, leaking, or just generally making trouble.
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Diagnostic questions & answers about air volume controls on water tanks:

This article presents questions & answers that help explain, diagnose, repair or isntall water tank air volume controls (AVCs) used to keep a proper air charge in a water pressure tank and thus avoid well pump turning on and off to frequently.

This article series describes what AVCs look like, we explain the types of air volume controls used on jet pumps and on submersible pumps, and we describe where to find them, and how these devices work, and how they can be repaired, replaced or just abandoned.

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WATER TANK AIR VOLUME CONTROLS - Defined, How they Work, How to Use

Bradg AV100 air volume control -  &

Question: Why Can't I Find the Air Volume Control on My Water Pump or Water Tank?

I've looked all over my water pressure tank for that round disk thingie that you show in the photos in this AVC article but I just can't find it, nor do I see that rectangular version that is sometimes on the tank side. Where is it?

[Click to enlarge any image]

Reply: your well water system may not have an AVC, or the AVC may be hidden on the well piping inside the well

Bladder type water tanks (WATER TANK BLADDERS & CAPTIVE AIR) do not use an air volume control valve: Air volume control valves are present only on steel water tanks which do not include an internal bladder to keep water and air separated inside the water tank. In other words, if your water tank is one of the newer models which uses an internal bladder, you won't find an AVC installed.

A bladder-type water tank keeps the air charge separated from the water. The air is in the tank and the water is inside the bladder inside the tank. Thus the air charge does not become lost by absorption into the water.

Hidden AVCs that may be found inside the well are discussed at Air volume control valves located inside the well

Instructions for replacing an air volume control such as the Brady AVC shown above are at AIR VOLUME CONTROLS, REPLACE

Question: does it matter where the AVC is installed?

Does it matter where the AVC is installed? i have a 1/4" opening 3/4 up from the base,probably used for pressure gauge,rather then use the 1 1/4" opening 2/3 the way up. - Schnitzl

Reply: Yes - here are some details about proper AVC location

Yes the AVC has to be installed at the proper location on the tank relative to the tank's moving water level - take a look at the instructions that come with your unit and you'll see that information, usually in the form of a sketch.

An opening up 3/4 of the way from tank base is probably OK but I'm not sure - it may depend on your particular type and model of Air volume control device. They vary.

In sum, the location of an AVC depends also on the type of device. For example on some submersible pump wells air volume in the pressure tank is controlled by a SNIFTER & DRAIN BACK VALVES mounted on well piping just ahead of the pressure tank, working in concert with a piping drain/vent located actually inside the well itself.

Question: water pressure is surging, bladderless pressure tank, what to do?

my water pressure is surging and i have a bladderless tank. Any tips? no drain at bottom of pressure tank! - Craig

Reply: check for short cycling water pump diagnosis & solutions


I if your water pressure is surging in synch with the well pump turning on and off your water tank is probably water logged and needs its air charge renewed.

Indeed if your water system included an air volume control device (AVC) that has stopped working, the pressure tank may have become waterlogged.

Take a look at SHORT CYCLING WATER PUMP to be sure of correct diagnosis of the surging water pressure.

If the problem is loss of air in the water pressure tank (very common), see WATER TANK AIR, HOW TO ADD for three different approaches to getting air back into that water tank.

Question: is changing a water tank AVC twice a year normal?

A Friend of mine has to change his AVC about twice a year is this normal? - Tom

Reply: no, look for debris clogging or improper installation

Not in my experience, Tom; if the AVC keeps needing replacement I wonder if there is debris in the water that's clogging it up. Or maybe an improper installation?

Question: Air is coming out of my water pressure tank - is that normal?

I have a lot of air coming out of the pressure tank (a bladderless with an WJ Type ACV). There is an adjustment screw on the ACV. Which way do I turn it to stop the surging of air into the household water? - Dave M.

Reply: hissing at some air volume controls is normal excess air escaping

Dave, there are adjustments on some air volume control valves, but to be confident we know what action to take we need to diagnose the cause of the excess air. For example, if you are constantly getting air blasting out of plumbing fixtures the root cause could be a leak in well piping - not something to fix by just adjusting the AVC.

Indeed some AVCs will vent excess air in the pressure tank. This design is particularly common on water pressure tanks whose air volume control is maintained by a snifter valve (see SNIFTER & DRAIN BACK VALVES) because the snifter valve system can indeed push more air into the pressure tank than needed.

So if your water system uses a submersible well pump with a snifter valve, you will probably find a rectangular type AVC control on the side of your water pressure tank at about mid tank height, and it may occasionally vent air - that's actually normal, as we explain at AIR VOLUME CONTROLS, Hissing.

Question: I replaced my old water tank - what was that old 310WJ for - do I need it?

I just replaced my 20yo galvanized bladderless tank with an identical one from the same mfr. (yes, still being made). I was impressed with the longevity of the old tank - I called her "Old Ironsides". I simply copied the identical piping configuration onto the new tank with new fittings.

Two fittings I "scabbed" from the old tank however, were the 310WJ (as pictured above with attached air pressure gauge) and a brass Flowmatic check valve with two inlet ports. The two inlet ports (on the tank side of the check valve) were being used for a air inflator stem (with cap) and the Pumptrol electric well control valve.

Over the years, I have just emptied the old tank completely with a garden hose annually and been happy enough with the performance.

My question is: I did not know that the 310WJ was anything more than a pressure gauge until I removed the old one and saw the rusted off float arm, apparently long since useless.

According to your description, the 310WJ was to allow excess air to drain out when too much was put in by an air inlet. The only place an air inlet could have been would have been the air inflator stem, which I thought was only for adding air by mechanical means. It really does just look like an ordinary tire pressure stem and not like anything automatic. Did I misunderstand what this was all along by keeping the cap tightly in place?

This is more just for my understanding than the thought of me trying to resurrect the old air volume control valve scenario - I can't imagine the old 310WJ would last very long in any event. Also, my old system (now rebuilt) absolutely had no pressure relief valve unless one is hidden along with something else - on the output side is just a boiler drain for draining the system along with a common stop valve before being connected directly into the house plumbing. Should I worry? - Dan 3292

Reply: bladderless water tank + submersible pump + snifter valve: need changes when replacing the water tank


in the article above (see SNIFTER & DRAIN BACK VALVES) we describe a type of air volume control that was used on some wells that use a bladderless type water pressure tank along with a submersible pump. Because during well pump on and off cycles, the snifter valve system (there is a companion device in the well) can admit more air into a pressure tank than needed, that rectangular device on the side of the old pressure tank included a vent that would automatically vent out excess air when needed.

Because you replaced your old bladderless pressure tank with a new bladderless tank, if you intend to continue to rely on the snifter valve system, you'll want that air vent to work properly or your water system may begin to see too much air. (AIR DISCHARGE at FAUCETS, FIXTURES)

Of course if the in-well valve or the snifter valve have quit working, you can go back to manually adding air to the water pressure tank when needed, but honestly it's better if that chore is handled automatically.

Watch out: for readers replacing water pressure tanks: if you are changing from a bladderless water pressure tank on a submersible pump well system, check to see if your old system included a snifter valve system that needs to be properly removed - details are at SNIFTER & DRAIN BACK VALVES

Reader follow-up:

I have owned the house and well pump tank for 17 years now - only 3 years after the sticker on the tank said that it was installed by our local well driller. I don't think I ever heard the 310WJ AVC ever hiss to release air in all my years here, and the snifter valve (that's a new one on me) has had it's cap tightly screwed down for years - even with teflon tape around it as it used to leak water on the floor. This tank has been relocated around the basement maybe four times (all by me).

That said, I am really doubting how much the air volume control ever worked. I have never experienced excess air in the tank to the degree of getting air coming out of the faucets - more the reverse that I got short cycling of the pump from not enough air, so I started an annual program of draining the tank in the fall. I see that the AVC 1-1/4" opening on the tank is approximately half way up, implying that tank is meant to basically ever be half full of water, half full of air - another revelation. So my tank which is marked 42 gals. pneumatic actually only holds about 20 gals. of pressurized water?

I only have ever used the snifter valve to connect a small electric air compressor to aid in speeding up the annual draining process. I stupidly thought that was what it was for. Also, I have discovered that in times of extended electrical outages where I do not have 220v service, but do have my 120v generators - I can "pump up" the tank with my air compressor to revive my water service. Very handy for those multi-day outages!

What about the issue of not having a pressure relief valve?

BTW: Thanks so much for keeping this website! I rebuilt my septic system this summer and referred to your articles on septic theory over and over.



When an automatic air volume control system on a water tank is not working, it means simply that on occasion we have to use some other means to restore air to the tank, lest it become waterlogged and give us a pump short cycling problem.

Your second question: the risk of not having a pressure relief valve (required by code) on a water pressure tank is that the tank could burst, not only flooding the building but injuring someone. This problem would occur, for example, if a pump control failed to operate properly or were misadjusted by someone. Search InspectApedia for "RELIEF VALVES - Water Tanks" to read details.

Question: Water tank leaks when the pressure drops off

Hello, I was wondering if someone could tell me what this is on our 82 gallon pressure tank. When the pressure drops it leaks water at around 40 # . It also sounds like it is sucking in air. This only happens when i run the sprinklers. The well will put out about 12 gallons a minute. But i have the pressure set at 45 and 65. It only takes 8 gallons of water to drop the pressure from 65 to 45 and that is when the pump comes on. Is this some kind of automatic valve? is there a way i can stop the spitting of water or is that necessary.

I do not believe this tank has a bladder. It looks like it has a schroeder valve in that thing on the side of the tank. But that is out side the well house on the well side of the check valve along with the pressure relief valve. I thought the pressure relief valve should be on the tank side of the check valve. I do not think much of the man who installed this 3 years ago as he wants nothing to do with it now, So i need to figure this out. I will be changing the heads on the sprinklers to use less water. But the largest zone only uses 10 gallons a minute.

Thanks to anyone who can help, and i think your site is great. Bruce W


Your photo shows a rectangular type air volume control on a water pressure tank - details and more photos of that device are found in the article above, at WATER TANK AIR VOLUME CONTROLS

The valve should not spit water - it is doing so probably because your water pressure tank is waterlogged -has lost its air charge - see WATER TANK AIR, HOW TO ADD- for various methods for adding air, including using the schrader valve and an air pump

And yes Bruce, you are correct, this type of air volume control is used on water pressure tanks that do not use an internal bladder. Your photo showed a steel water pressure tank with a pressure gauge and air volume control mounted on the side of the tank.

Your valve does not include a tube connecting it to the water pump as other air volume controls sometimes used because your model uses an internal float that opens and shuts a valve to allow air to enter the water tank. I often find these valves just stop working, because of debris clogging or because the float is stuck. You can leave the valve in place and add air manually or you can replace the device.

Question: air surging out of faucets after tightening up the air volume control

I recently had to repair a small pinhole leak in the cold water line to my kitchen sink. To do so I had to shut off the well pump/water supply. After the repair I turned everything back on and then discovered a dripping leak from the air release valve on the tank's WJ type AVC and water spraying out from the snifter valve. I tightened up both valves to stop the leaks and thought all was fine but a day or two later we began to get air surging at the toilet and other fixtures.

This seems to occur for a minute or two after the pump starts up. I have not noticed short-cycling and the pressure gauge cut on and cutoff points seem ok(32 and 52psi respectively)and the tank seems to hold pressure ok as well. Any ideas/suggestions would be greatly appreciated. Thanks. Tim B. 5/3/12

Reply: replace the leaky air volume control on the water tank


Sometimes when we tighten fittings on the air volume control to stop a water leak we are also stopping the valve from being able to purge excess air - sending that excess air out at the faucets. If the water system uses a submersible pump and an in-well snifter valve that admits air into the system, that design can admit more air into the pressure tank than is needed. If the excess air can't be released at the aboveground AVC it heads for the faucets. Try replacing the leaky AVC that you found on your water tank.


I have a 60 gal vertical tank. after a lot of water use , it contains only air, which then comes out of facets . draining tank cures it for a while. what can i do? - George Cain 10/15/2012



Usually air overcharging is due to a faulty air volume control device. If your system uses a submersible pump perhaps your sniffer valve and excess air bleeder are clogging. I've added both AVC adjustment and AVC repair text in the article above.

Question: short cycling waver pump, plastic bowl type AVC

My water pump cycles on for about 8 seconds then off for about 35 seconds. I have replaced the (plastic bowl type) Air Volume Control. I thought it was ok but it is back to cycling too often. I have checked for tank leaks with soapy water but found none. What do you think would cause this?

Where does the AVC get the air it puts into the tank? Could the line from the pump to the AVC be restricted? - Wayne 12/24/12


The air source depends on the air volume control type - byt typically from a vent on the control.

Question: should I scrap the old unused water tank

We have one of these in our crawl space - it hasn't been used in over 40 years - I suspect it is much older. It looks very much like the picture above (Horiz_Tank_PumpBefore_022_DJFss) Should I just scrap it out for the metal or is there any value in it? - Karen 2/16/2013


Karen, if the water pressure tank is no longer connected and thus really no longer in use there is no reason to keep it around - it's scrap metal. Just be sure someone takes a careful look to make sure that the tank is not connected to working plumbing before it is scrapped.

Question: I don't see how to adjust the US Gauge Type air volume control

I have read through all of your pressure tank articles searching for some details.  I am not the first to ask this question as I see where others have asked the same question but never answered.  I don't think the correct answer is switch to a bladder tank as bladderless with the volume control can be found new for sale in most plumping stores in my area at high altitude mountains. It is very simple.

You have a well, deep or shallow and on your air volume control (bladderless tank) has a valve with an adjustment screw with no tubing.  You are curious if adjusting this screw could eliminate or help troubleshoot extra air coming out of the faucets.  If you choose to adjust the screw (troubleshooting or maintenance) to either let air pressure out or let air in, what direction on this screw provides these benefits?

Additional question is: I get air coming from faucets, showers, sinks and toilets equally when the pressure tank nears 30psi and begins to refill.  The cold side is always the culprit, and it is very difficult to ever detect if hot water, if ever, sends any air to the faucets.  I never get any kind of hissing from the air control valve.  I am considering replacing the part US Gage 310WJ,  but don't want to waste my time if the above issues signal more conclusively something different. - Mike 4/5/2013


Thanks Mike, I reviewed the article above and added details on adjustment as well as repair of these air volume controls.

Basically, if you're getting air hissing out of valves and fixtures in the home, and provided that your water system indeed is using an air volume control like the US Gauge float type controls above, the device is intended to vent excess air from the system. Air is entering elsewhere at a snifter valve or similar device, usually on the vertical water pipe riser inside the well. You may be able to correct the problem by simply following the adjustment procedures in our article above.

Question: what are normal pressure gauge readings on a water tank?

(Apr 10, 2014) Anonymous said:

what is the gauge reading on a deep well sopose to be


Anon, the water pressure gauge reads water pressure, not a function of well depth. The pressure will range between the pressure switch cut-in and cut-out pressures, typically 20/40 psi or 30/50 psi.
IF the gauge seems stuck try tapping it gently; it may be debris clogged and need replacement.

Question: what does the float do in a water tank?

5/26/14 robert said:

What does the float do in a water pressure tank


The "float" in a water pressure tank is probably referring to the small float that actuates an air volume control on a water tank that does not use an internal bladder.

For details see


in that article where we discuss the US Gauge & Similar Type 310WJ, Type 300SL, or Type 6 Rectangular Air Volume Controls = Excess Air Vents

Question: air coming out of faucets after fixing a pump

2/1/2014 Author: Rchard (no email)

Comment:i have a bladder tank; and i recently changed the well pump after 25 years of use. Since then air has infiltrated my system with spurts of air.Any advice would be truely appreciated. Thanks!!


Rick, s

about air discharge in the system after changing a pump, I would look for an air leak into the system or a bad air volume control, or a snifter valve that should not be in use with a bladder tank.


To see diagnostic details

Question: changed bad AVC, now no water pressure, pump won't come on

(Mar 27, 2014) said:

I have changed bad AVCs before but this time is a mystery. My AVC was discharging water and needed replacement so I cut power to the well, drained some water off the 200 gal galvanized tank, disconnected the tubing at the AVC, unscrewed the AVC from the tank and installed the new AVC. I did not completely drain the tank becacuse there was water coming out of the fitting when I took out the old AVC.
I closed the drain valve at the bottom of the tank, turned the power back on and the pump ran for a little while and shut off. There is 60 lb pressure on the well and I do not have a gauge on the water tank so do not know.

There is almost zero water pressure in the house, looks like the tank has water in it because I removed the AVC again just to see if there was water in the tank. Reinstalled AVC but no water to the house.

What did I do wrong. When I checked the new AVC installation, I took off the copper tubing and water was shooting out of the AVC so I screwed it back on. Pump won't come on because pressure is already at 65 lbs and no water to the house or out of the hose at the bottom of the tank. HELP !



Try turning off power and draining the tank completely. Then close tank drain and turn on the pump - assuming its a submersible pump, right?

You did make sure that water was turned on between the tank and the building, right?

Question: hissing at the air volume control?

(Apr 8, 2014) AVC - WJ said:

I just install a new one. If my cut-in pressure is 30 and my AVC unit is set to 25, I should hear hissing out this until the float closes the valve, correct? I don't hear a thing ever. The only thing it could be is the water level never goes down far enough?


You didn't tell us the brand and model air volume control, WJ; in some cases you will never hear air hissing unless there is excess air in the pressure tank.

Reader followup


The air is noticeable when ever it fills. It's not bad, but when you are running the water out of the faucet and the pump cycles, we get air out the faucet.



See the article titled AIR DISCHARGE at FAUCETS, FIXTURES
linked-to in the Q&A's just above.

Question: will a tipped water tank affect water pressure?

Apr 26, 2014) Anonymous said:

My submersible pump and steel galvanized water tank are located outside no protection. The ground is sinking a little on one side and the tank is listing a little. Would this affect water pressure (low to lower)? I think it has something to do with the AVC/water level not being level inside the tank anymore, but not sure. Help?


Anon, a slightly tipped water tank won't affect the water pressure and even total loss of the air volume control AVC won't affect water pressure. Instead, loss of air charge in the tank would lead to short cylcing on and off of the well pump.


(Mar 10, 2015) Ray Coker said:
I have a galvanized water tank, 5 ft tall probably 100 gallons and an above ground pump. I replaced the Brady AV 100 AVC last week because the water tank was water logged and the pump was short cycling on and off every few seconds. All was well for a few days until it began short cycling again and I noticed water dripping out of the air port on the new AVC unit. I'm assuming the new AVC unit is bad so I will replace it again. It is mounted on top of the water tank and has been for years. Is there a problem with the mounting location.


Ray just replacing the AVC, while a good idea, won't be very quick to fix a waterlogged tank. You probably need to put a proper air charge in the tank manually.

In More Reading above


Question: donde va conectado el air control volume del taque ?

(June 29, 2015) doalicea said:
donde va conectado el air control volume del taque ? A la bomba de agua o al pressure swicht ? Gracias

Reply: Repuesto:


Si estas hablando de un air volume control por cierto, puedes ver en el cima de este pagina, eso tipo de air volume control esta conectado entre el tanque y un conector directamente en la bomba.

Si estas platicando sobre el control de presion, Se depende in el tipo de control que tienes. Normalmente hay un connector (un tubo) entre la mangera que contiene agua (o el tanque) y el control de presion. Por eso el presion de la systema esta comunicado al control. Porque el presion es lo mismo en el tanque y en los tubos or mangeras de la sistema de agua en la structura, se puede conectar en qualquier lugar que cabe.

Se me mandas unos fotos de su sistema puedo comentar mas. Usas mi email que se encuentras en el CONTACT al fondo de este pagina.

Question: copper tubing on air volume control

Anonymous said:
is water suppose to be in the copper tubing going into the diaphram


The tubing may contain water or air depending on conditions in the water tank. For example, if there is excess air to be vented through some AVCs the the tubing will certainly contain air.

Article Series Contents


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