Photograph of a water pressure tank air volume control How to Find & Repair the Water Tank Air Volume Control Device
     

  • AIR VOLUME CONTROLS, WATER TANK - CONTENTS: 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? - Photographs help identify air volume controls; How to replace or abandon an air volume control
  • 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.
  • REFERENCES

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Guide to air volume controls on water tanks:

This article describes 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.

We describe 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 - InspectApedia.com  &  americangranby.com Article Series Contents

[Click to enlarge any image]

In water pressure tanks that do not use an internal bladder, over time, the air in the tank will be absorbed into the water and the tank will become ‘waterlogged’. This means that the tank is full or nearly full of water. The pump will come on and off very quickly (short cycling or rapid cycling water pump).

This short cycling is hard on the pump, and air is added to the tank to correct the situation. - Adapted with permission from Carson Dunlop Associates Home Reference Book.

The job of the AVC is to keep air in the water tank to avoid waterlogged water tanks or well pump short cycling.

Photograph of a water pressure tank air volume control

The air volume control or "AVC" device mounted (usually) on older steel water tanks (ones that do not use an internal bladder to keep water and air separate) is designed to automatically add air to the water pressure tank when it's needed.

If a water tank loses its air charge it stops working properly and usually results in the water pump turning on and off rapidly - "short cycling" of the water pump. This condition, in turn, can damage or even burn up the water pump.

Round Air Volume Control Devices With Copper Tube

An "automatic" air volume control (AVC) device may be installed on the water pressure tank if it's an older, bladderless steel tank.

The AVC is intended to automatically put a little bit of replacement air into the tank from time to time as water pressure cycles up and down, that is, each time that the water pump runs.

If you see a round steel disc of about 4" diameter and about 1" thick on the water tank, mounted perhaps at the middle of the tank height or at the water outlet to the tank, or perhaps on the side of the tank with a plastic or copper tube connecting the disc to a fitting on the tank or nearby piping, this is the AVC..

Photograph of a sketch of the main controls and valves on a water systemUsed on jet pump water supply systems, on each pump "on" cycle the AVC draws in a small volume of air that is then pushed onwards into the water pressure tank.

The tube connecting the AVC to the pumping chamber suction side provides the pressure drop that pulls on a diaphragm on the AVC that in turn causes the AVC to draw in its air charge.

The air volume control might be found on the side of the water tank (above left) and is typically connected to the water pump itself (above right) by a flexible copper tube.

The AVC may also be located right on top of a one line or two line jet pump such as is visible at the top center in our Meyers™ well pump photo at left.

The alternative air volume control shown below does not include a disc-shaped device and has no connection to the water system's pump or other piping. The hole seen in the end of the brass screw is the air inlet for this air volume control.

US Gauge & Similar Type 310WJ, Type 300SL, or Type 6 Rectangular Air Volume Controls = Excess Air Vents

air volume control (C) Daniel FriedmanThe deep-well AVC below does not use copper tubing, all it's parts are self-contained. This is a valve that you may hear hissing if it's working.

  • The U.S. Gauge Type 300L or US Gauge Type 6 AVC is intended for use on shallow wells. Note the tubing fitting on the bottom of the valve. This part includes a tapping to accept a water pressure gauge. The AVC is designed to work in conjunction with an air inlet valve such as a Schrader valve[6] or a Dill type valve[5] mounted in the hose connection.
  • The US Gauge Type WJ or US Gauge Type 310WJ (for deep wells) Air Volume Control produced by U.S. Gauge, also located under the Ametek® brand are intended for deep wells using submersible well pumps.

Watch out: As we discuss at Snifter Valves below, in general these air volume control valves function only to release excess air in the water pressure tank; in that case air is obtained from other components (such as the snifter valve). They let air out. Air is let into the system using a separate device, usually a snifter valve discussed below.

At our FAQs section below we provide more details (and photos) explaining the difference between the US Gauge Type 300L or Type 6 AVC and the US Gauge Type WJ or Type 310WJ air volume control.

How does a US Gauge Type WJ or similar air volume control work? Drainback air volume control.

Using a US Gauge Type WJ or similar air volume control to manage air in the water pressure tank is a different approach that is unfamiliar to so many homeowners that we've seen some odd advice like "take off the part and throw it away" - which is usually not a good idea.

The air volume control approach used with these valves is also called a drainback system. When water level falls inside the pressure tank to a level below the valve and its float, the valve opens, bleeding excess air out of the pressure tank. Separately, a snifter valve (see below in this article) in the well piping (usually hidden inside the well) is the device that forces air into the water piping from the well and thus into the pressure tank at each pump on-cycle.

Our photo (below left and right) shows a U.S. Gauge Type WJ - so we know this installation is for a deep well.

air volume control (C) Daniel Friedman air volume control (C) Daniel Friedman

As U.S. Gauge points out,

U.S. Gauge Air Volume Controls are designed for domestic water supply systems which deliver a quantity of air to the pressure tank with each cycle of pump operation.

Insufficient air in the pressure tank causes frequent operation of the pump.

Too much air in the pressure tank will permit large bubbles to be carried into the piping system. This causes a disagreeable noise and sputtering at the faucets.

It is the function of U.S. Gauge air volume controls to maintain the correct relationship between the volume of air and the quantity of water in the pressure tank.

As we illustrate below, this air volume control device uses a float that moves as the water level inside the water tank changes. The float movement allows air into or out of the water pressure tank as needed.

Adjustment of the US Gauge type WJ AVCs is in a separate article found
at AIR VOLUME CONTROL TEST

At DRAIN BACK / SNIFTER VALVE TROUBLESHOOTING we detail how the AVC is tested on a drain-back system or bleed-back system is tested to see if it is in fact releasing excess air as it should.

An excerpt is given just below
at AIR VOLUME CONTROLS on DRAIN BACK SYSTEMS

Drain-Back Water System Air Volume Control Valves

Snifter valve on a submersible pump well system (C) D FriedmanAir Volume Control Valves on drain-back pump and water systems are one component of a three-part system designed to protect well or lake water supply pipes from freezing and to maintain the air charge in a water pressure tank on some submersible pump systems where a bladderless water tank is installed.

A snifter valve is installed at a check valve at the water tank (photo at left) and works with a drain-back valve located in the well or lake below the frost line to insert air into the water piping system for freeze protection.

Because the snifter valve & drain back valve will result in a large charge of air pushed back up the water piping and into the water tank at each water pump on-cycle, the air volume control used on the pressure tank must release the excess air to avoid over-charging the water tank with air.

At DRAIN BACK / SNIFTER VALVE TROUBLESHOOTING we detail how these drain-back system or bleed-back system components are tested, including the AVC on the water pressure tank.

An excerpt is just below:

If the air volume control is working on a drain-back system you will at least occasionally hear air hissing out of the excesss air release port on the AVC (blue arrow in the photo at below left).

If the air volume control is not working on a drain-back system, because each pump on cycle is pushing a lot of air into the water tank you will ultimately see air spurting out of the building's plumbing fixtures such as faucets. That's because the AVC is not releasing the excess air in the system.
See AIR DISCHARGE at FAUCETS, FIXTURES

Air volume control on a snifter valve bleed back valve water system (C) Daniel FriedmanIf the AVC is not working properly on a non drain-down water systems you will find the opposite problem: a water-logged pressure tank causing well pump is short cycling.
See WATER PUMP SHORT CYCLING

Watch out: short cycling can still occur on a drain-down (bleed-back) system too, but not because the AVC isn't working.

Rather, if the snifter valve stops admitting air into the piping system OR if the drain-down valve becomes clogged and stops draining water out of the water piping, then because air isn't entering the piping no air is being pushed back up into the bladderless pressure when the pump runs. Eventually the water tank will become water logged and the well pump or lake pump will cycle on and off rapidly when water is run in the building.

Watch out: On a drain-down / bleed-back water system with either of these two problems, because the well piping is not able to drain and not able to fill itself with air at the end of each pump-on cycle, there is also a risk of frozen well or lake water piping.

If your drain-down system pump is short cycling and your water piping between well (or lake) and the water tank is not buried below the frost line, you may find you have two problems: you had a warning of trouble when the well pump was short cycling, and now you've got frozen pipes too.

Watch out: if on a submersible well pump system that uses a snifter valve for air volume control you later convert a bladderless water pressure tank to a tank using an internal bladder, you should remember to remove both the snifter valve located on the check valve near the water pressure tank and the bleeder orifice or drain-back valve located on the well piping.

See SNIFTER & DRAIN BACK VALVES for a complete discussion of drain back systems, snifter valves, drain back valves and their related components.

Definition of Schrader Valves, Brady Valves & Dill Valves

Water tank air inlet or air pressure adjustment valve (C) Daniel Friedman Water tank air inlet or air pressure adjustment valve (C) Daniel Friedman

Definition: Schrader valves (American Valves) and Dill Valves are used principally on vehicle tires to insert (or release) air to a specified pressure. The valves are also used, often in modified form with an internal spring with strength matched to the application where air inlet or outlet or water or air pressure management require adjustment on water pressure tanks and similar systems.

The Schrader valve, Brady Valve, Dill valve ( different companies) consists of an externally and internally threaded metal stem. The external valve base and stem connect (using appropriate seals or washers) to the vehicle wheel rim, or in plumbing to a water pressure tank or water piping at an appropriate location.

The internal stem of the valve accepts a replaceable part, the actual control valve that opens (when a center pin is pressed) to admit air or to release air. In reverse, pressure inside the system pushing against the valve stem core closes the valve when its center pin is not depressed. [5][6] Similar control valves but of different diameters are used in other countries than those comprising North America.

An example of a special class of these air valves is the snifter valve discussed just above and used on drain-down water systems. This valve includes a low-pressure valve stem core that will open to admit air into the valve at about 10 psi. Special versions of snifter valves can operate with as little as 5 psi.

Details are at SNIFTER & DRAIN BACK VALVES

A different range of air inlet valve is used at other (non-drain-down) water systems at the water pressure tank to add or adjust the air charge in the pressure tank. Photos of a typical air inlet valve located at a water tank tee is shown above along with a typical valve stem core. These may be found on both bladderless and internal-bladder type water tanks.

Watch out: when replacing an air inlet valve stem core be sure to select a valve core whose opening pressure (to admit air) is properly-matched to the application. Installing an automotive tire valve stem core into the stem of a snifter valve will make you sorry.

See WATER TANK AIR INLET VALVE

and WATER TANK AIR VALVE REPAIRS

Other Air Volume Controls on Large Water Storage Tanks

On some water storage tanks such as the antique 450-gallon tank shown at left (courtesy of reader Craig Revill), the air volume control may not be so obvious (photo below right). The device shown is (we should say "was") an air volume control produced by Penn Electric Switch Co., Des Moines Iowa.

You could guess at the function of this device even if the manufacturer hadn't generously given an identification tag: notice the small diameter brass tube connecting the water tank to the well pump.

Large water storage tank (C) D Friedman C.R. Large water storage tank (C) D Friedman C.R.

Shaw Air Volume Control Pennsylvania Electric Co - US Patent Office
The patent for this air volume control switch was published in 1943 and patented by Burton E. Shaw. At left we illustrate (from the patent application) just how this air volume control switch worked.

Here is the air volume control patent text and an explanation of how this AVC worked.

Shaw explained this air volume control or AVC was intended as a deep well device - by this he probably meant not shallow or "dug" wells.

The device was intended to be mounted in the wall of a water storage tank (as above) and adjacent to the water level in the tank so that the valve could respond to both air pressure and the water level in the tank itself.

The valve relieved air from the tank when the water level was low as a result of excess air from the pneumatic head of the tank, but it would prevent the release of air from the tank when the working pressure inside the tank was below the required amount.

 

Test Air-Volume Controls (AVCs) on Water Tanks

Photograph of a water pressure tank air volume controlDetails about how to inspect & test the AVC to determine if it is working to keep a proper air charge in the water tank are
at AIR VOLUME CONTROL TEST.

Excerpts are below.

If the air volume control valve is working properly, it uses the pressure changes caused by the cycling on and off of the water pump to automatically add air to the water tank when it's needed.

If the air charge in your water pressure tank is not being maintained, either there is a leak in the tank or the AVC is not working. Usually the case is the latter.

If an auto-venting AVC is installed (a type that expels excess air charge in the water tank) and if the AVC is working you will occasionally hear air hissing out of the fitting, as we discuss
at AIR VOLUME CONTROLS, HISSING.

Adjusting a US Gauge Type WJ Air Volume Control

Details about AVC or air volume control adjustment are now
at AIR VOLUME CONTROL ADJUSTMENT

Note: On a water tank that uses an internal bladder (keeping water and air separated), the air charge is not normally lost and the air volume does not normally need adjustment.

How to Repair a Leaky US Gauge Type WJ or Type 300L Drainback System or Snifter Valve System Pressure Tank Air Volume Control

Photograph of a water pressure tank air volume controlOur complete article about repair procedures for AVCs - Air Volume Controls - is now
at WATER TANK AIR VOLUME CONTROL REPAIR. An excerpt is below.

  • Leaks at the valve mount: this is a standard plumbing problem. If your pressure tank or the valve mount tapping threads are not badly corroded, remove the valve, clean all threads, reassemble using pipe sealant or teflon tape.
  • Leaks at the Type WJ adjustment screw: you may be able to disassemble, clean the tapping, and replace the existing parts. Replacement parts are available from US Gauge at AMTEK [2] The company sells a Type 310 valve assembly, Spec No. 085043A
  • US Gauge Type 310 WJ not working: AMTEK sells Type 310 valve seat replacements, Spec No. 085392A.
  • US Gauge Type 6 or Type 300L Shallow Well AVC not working: contact the company's customer service line 727-536-7831 to ask about spare parts.
  • Air leaks or hissing at the AVC are discussed
    at AIR VOLUME CONTROLS, HISSING

Recapping, both types of these air volume controls are used only on bladderless water pressure tanks - tanks that do not use an internal bladder. At above left a photo of a US Gauge a Type 6 Air Volume Control showing its operating float (that you cannot normally see as it is inside the water tank).

This control is used on shallow wells and jet pumps.me controls are
at AIR VOLUME CONTROLS, HISSING

Replace an Air Volume Control Valve

US Gauge air volume control valveDetails about replacement options for AVCs are now found
at AIR VOLUME CONTROLS, REPLACE. Excerpts are below.

U.S. Gauge makes rectangular type AVCs, as we illustrate above. So do some other companies.

Watch out: rectangular AVCs like the U.S. Gauge unit illustrated here from the company's product literature, incorporates a float inside the water tank. If you look closely at our photos you 'll see that the gauge mounts through a 1 1/4" diameter ANPT threaded pipe connection into the water tank.

Watch out: also to be sure to order the proper air volume control model. For example the U.S. Gauge AVC Type 300L is designed for shallow well operation, and the U.S. Gauge Type 310WJ Air Volume Control is designed for deep well operation. These devices do not work in an identical fashion, so buying the wrong model for your well would be a mistake.

Eliminate the Air Volume Control Valve

Details about getting rid of the AVC as well as some advuce about making that change a success are
at AIR VOLUME CONTROLS, GET RID OF

If you convert from a non-bladder type water pressure tank to a water tank using an internal bladder, part of that installation will include the removal of any air volume control valves on the system, including an AVC that may be mounted on the well pump (above-ground jet pumps) or a hidden AVC that is found inside the well piping (submersible well pumps only).

 

 

Continue reading at WATER TANK AIR VOLUME CONTROL REPAIR or select a topic from the More Reading links shown below.

or see WATER PUMP SHORT CYCLING or select a topic from the More Reading links shown below.

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WATER TANK AIR VOLUME CONTROLS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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