Photograph of a water pressure tank air volume control Air Volume Control (AVC) Test Procedures
How to inspect & test the air volume control to determine if it is working

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Air volume control inspection & testing:

this article explains how inspect, test, & listen to the air volume control (AVC) on a water tank to determine whether or not the AVC is doing it's job.

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How to Test Air-Volume Controls (AVCs) on Water Tanks - is the AVC Working?

Photograph of a water pressure tank air volume controlHow do we know if the AVC is working?

Our photo (left, courtesy of reader Doug Mehak ) illustrates still another type of air volume control. The red arrow at the left of the photo points to the AVC and the right arrow points to the tubing connection on the water pump, in this case a one-line jet pump.

In our photos above and at left, most AVC controls that use a pressure sensing tube connected between the AVC and the water pump.

You will see a small diameter tube which connects the air volume control valve to a fitting (usually) on the water pump itself so that the valve can respond to the cycling on and off of the water pump (and changes in water pressure).

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. Makeup air is needed in these water tanks because over time the air charge in the tank is absorbed into the tank's water.

The most common versions of air volume controls, illustrated at the top of This article , look like a disk of about three inches in diameter, as we show in the photographs here. A copper or plastic tube that extends from the AVC to a fitting on the water pump itself, as we showed on the photograph above. Look at the fitting screwed into the side of the water tank about 2/3 of the way up from the tank bottom and on the right side of the water tank in the photograph above.

Photograph of a water pressure tank air volume controlIf 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.

Also illustrated earlier in this article, a second common version of air volume control valve is shaped like a small rectangular steel box with fittings shown in our two photographs above.

You also can see the small object connected to the side of the water tank near the top right side of the tank in this photograph at left.

There is no copper tube connected to this AVC. Here is a close-up photograph of this more rectangular type of air volume control.

If this AVC is working you will occasionally hear air hissing out of the fitting, as we discuss


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