Air hissing sounds at the water tank: this article explains the causes of a hissing sound of air escaping at the air volume control at a water pressure tank - a condition that may be normal and may not require repair.

Hissing Sound Coming From the Air Volume Control?

What Causes an Air Hissing Sound Versus Water Leaks at AVCs

If you may hear air hissing in at this air volume control fixture (it's working). Hissing air at the air volume control means that the control is releasing excess air from inside of a bladderless water pressure tank.

But if you see water leaking out of the air volume control, that means it needs repair or more likely, replacement..

Here is a perspective view of where air volume controls are typically installed on a steel water tank. You won't see a control like this installed on a bladder-type captive air water tank.

Leaky Air Volume Control Tip: sometimes when you've taken water pressure off of the tank and are refilling it by air using one of the other methods below, you may hear a hissing coming from the tank.

Air may be leaking out of an opening at the base of the air volume control. It's valve parts may be partly "stuck" from having moved so seldom or having got clogged by debris.

Usually if this is happening you can simply push your finger over the hole where you feel air escaping.

Some air loss is common at this point, but it should stop on its own. If it doesn't, tap your finger on the hole a couple of times and the air hissing will probably stop. If not you may need to call a plumber to replace this annoying part.

Sometimes we tap the control (gently) with a wrench to see if this will stop the leaking. It has always worked for me - so far. When it does not, and when hissing is followed by water leaks we recommend replacing this air volume control.

Watch out: we do not recommend trying to disassemble this valve. And its response pressure is factory set. If you mess with the brass lock nut and vent you are changing the operating pressure range of the air volume control valve.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-08-03 by (mod)

I suspect your water pressure tank is waterlogged - it has lost its air charge.

See WATER TANK AIR, HOW TO ADD methods for replacing a lost air charge in a water pressure tank.

On 2020-08-03 by Kenny

I have a deep submersible pump , and my tank water level Is about where the air volume control is,but when my pump pressure drops at low pressure 30 psi it only takes a few seconds for it to reach about 55psi , its cycling to fast

On 2020-05-01 - by (mod) -

In case we missed this detail it's normal for some AVCs to hiss and release air. They work as follows: during a water draw-down cycle as the water level falls in the pressure tank the AVC let air into the tank.

At the end of the draw-down when the pressure reaches the CUT-IN Pressure set on the pressure control switch, the pump turns on and begins sending water back into the tank. The AVC will set some air out to avoid accumulating too much air (and too little water volume).

This design was intended for use with deep well submersible pump systems that use a snifer valve in the well to insert air through the pipe and into the water tank at each pump cycle. Without the excess air release the snifter valve system would accumulate so much air in the pressure tank as to fill it and actually send air discharging out at faucets.

On 2020-04-24 by Anonymous

I thought about that, so I took off the small pressure tube that runs to the pressure switch. It wasn't clogged. So I reinstalled it.

On 2020-04-24 - by (mod) -

Is there a possoble clog in the tubing communicating pressure to the switch.

On 2020-04-23 by Anonymous

thanks so much for replying. But I've had three different control boxes on this well. They all do it. But only once the pressure reaches a certain point. I feel I've not done something correctly installing the new AVC. ...something.

Could it be my old tank has given up its ghost, or maybe the submersible pump itself? Although flow seems fine when not hooked to the tank. The the tank and above ground check valve are old, but appear to hold pressure. So, I don't seem to be getting any backflow.

On 2020-04-23 - by (mod) -

A buzzing relay is usually shot. Sometimes people (IMO wasting time) try filing or grinding the contact points but inevitably that's a short lived repair; or the transformer itself can be shot.

If it's the device and not the TT wires we can prove that by removing the TT wires and jumping the TT terminals.

On 2020-04-23 by Anonymous

It's the actually control box and most definately not the switch or AVC. It sounds like the relay in the control box is shuttering/buzzing then after a few seconds of that, the unit turns off. If power is left on, it'll start back up after a minute or two and then do it (rattle/shutter/buzz) again and after a few seconds of that turn off again.

On 2020-04-23 - by (mod) -

Thanks for the helpful question, Ed. I think we can figure this out but I need to understand more clearly what's happening.

What is rattling: the pressure control switch, a separate pump relay that the pressure control switch is turning on and off, or the AVC, or something else?

Also let's review pressures:

You did what I'd do: drain the tank and set it's air pre-charge to get a known start point.

If a pressure control switch turns the pump ON at 30 psi and off at 50 psi, we'd set the tank air pre-charge to 2 psi below the ON or CUT-IN - i.e. 28 psi.

On 2020-04-22 by Ed

So my AVC started leaking so I replaced it. The factory setting is to 25lb, and it hisses until the tank raises the floater at which point it of course, stops. I have an old tank with no brand name on it, that looks exactly like a 42 gallon Flotec fp7235-08 air over water vertical 20" tank.

The problem is once the pressure reads roughly 30-33 lbs the control box begins to rattle and the pump shuts off. I suppose it's some sort of safety feature in the control box. I've replaced the square D switch and control box and it's still doing this. Is there some adjustment to the AVC's factory air setting that I should make? I think if I tighten it lets out less air, and if I loosen it it lets out more air.

I drained all the water out of the tank and started it fresh, and it still does this. Any advice on setting the AVC? Should I leave it at the factor setting?

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Continue reading  at AIR VOLUME CONTROL TEST or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• AIR VOLUME CONTROL ADJUSTMENT
• AIR VOLUME CONTROLS, WATER TANK
• AIR VOLUME CONTROLS, GET RID OF
• AIR VOLUME CONTROLS, HISSING
• AIR VOLUME CONTROL REPAIR - repair procedures for Brady and other air volume control devices
• AIR VOLUME CONTROL TEST
• WATER TANK AIR VOLUME CONTROLS - home
• WATER TANK AIR, HOW TO ADD - methods for replacing a lost air charge in a water pressure tank.
• WATER TANK AIR ADD BY DRAINING
• WATER TANK BLADDERS

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