Drain back valve removed from well piping tee (C) Daniel FriedmanDrain Back Valves & Snifter Valves
AVCs,Water Tank Air Volume Controls, & Snifter Valves as Well Pipe Freeze Protection Devices

  • SNIFTER & DRAIN BACK VALVES - CONTENTS: what are the drain back valve & snifter valve used on a well water system and how do they work? Hidden & antique air volume control valves can explain well pump rapid cycling or air discharge problems
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Drain Back Valves, Bleed-Back Systems & Snifter Valves for Well or Lake Pipe Freeze Protection & Air Volume Control:

This article series describes snifter valves and drain-back valve , what they are, how they regulate air in a well water system, how they work with an air volume control,& how these components protect well piping against freezing. We describe how & where the snifter valve, drainback valve and air volume control are installed & what they look like.

This article also discusses how these valves are maintained, replaced, or eliminated. Snifter valves & drain-back valves along with AVCs are a three-part air volume control system designed to allow water to drain out of well piping and back into the well while also maintaining water pressure in the building and the air charge in a well water pressure tank. These devices are used on some submersible pump systems or lake water supply systems where a bladderless water tank is installed and where well piping is exposed to freezing.

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Snifter Valves, Drain-back Valves, & Air Inflators Offer Protection From Well Pipe Freezing & Air Volume Control

Snifter valve on submersible pump system can protect against well pipe freezing (C) Daniel Friedman

Article Series Contents

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Why are Drain Back Valves & Snifter Valve Air Type Volume Control Systems Used?

There are three reasons why a snifter valve & drain-back valve may be used along with a submersible well pump, bladderless-type water tank, and check valve.

  1. Water line freeze protection: the main one is to allow water to drain out of well piping and back into the well to prevent freezing of well piping that is not buried below the frost line. Drain back valve systems may be used to freeze-protect water supply piping from drilled wells (well bores) or from other water sources such as freshwater lakes in freezing climates.
  2. Air supply to the pressure tank: a second feature of drain-back / snifter valve systems is the injection of air into the water pressure tank, a process that involves further air management by an air volume control valve that will vent excess air from the tank.
  3. Water odor & taste improvements: A third feature claimed by some installers is a reduction in both iron and smelly sulphur odors, though the level of this benefit is questionable.

Snifter Valves, Air Inflator Stems, & Drain-Back Vents Inject Air Into the Well or Lake Water Piping System

Synonyms for this well pipe freeze protection system include: snifter valve system, drain-back valve system, bleed-back system, well pipe freeze protection system, bladderless water tank air injection system as well as Brady valves or Dill valves.

Air inlet and air purge snifter valve photos (C) D Friedman Snifter valve on a submersible pump well system (C) D Friedman

In our well pipe freeze protection system photo (above left) the green arrow points to the air release valve opening on the water tank's air volume control (AVC) and the red arrow points to the snifter valve air inlet fitting mounted on a check valve. At above right my finger points to the snifter valve at its mount on the check valve.

We give a closer look at these components shortly.

Snifter valves (photo above right, shown mounted on the 1/8" tapping on a check valve) provide an air inlet, typically located on a check valve on the water line near the bladderless water pressure tank. The air inlet snifter valve works in concert with a water drain-back valve (a bleeder orifice) that you cannot see - located on well piping inside the well where a submersible pump is used.

At the end of a well pump on-cycle (when the well pump stops) this snifter air valve mounted on a check valve on the well line ahead of water pressure tank opens to allow air into the well piping.

This incoming air allows water to drain out of the well piping at the drain-back valve: a bleeder fitting mounted on a tee on the well piping, inside the well.

A photo of the drain back bleeder mounting tee on the well piping is shown at below left. We've pulled the piping out of the well for this photo. A close up of the drain back bleeder valve itself is shown at below right.

Air inlet valve tee on well piping (C) D Friedman Rasmussen Well DrillingAir volume control air inlet valve for well piping (C) D Friedman

A check valve located near the bottom of the water tank on the incoming well piping (on which the snifter valve is mounted in our photo) keeps water in the pressure tank from draining back down into the well when the well pump has stopped.

Because the snifter valve system will usually push more air into the water tank than is needed, an air release valve mounted on the water pressure tank is also installed to purge excess air from the water tank as necessary. So if you hear air hissing from the air purge valve, that's normal.

Watch out: The snifter valve stem looks like any other air inlet valve but it uses a weak internal spring to allow the valve to open on its own, admitting air into the piping. DO NOT tighten the valve stem cap found on the snifter valve and don't replace a vented valve stem cap with a solid plastic one - if you do so your well pipes may freeze to death.

That's because if no air can enter the snifter valve, no air can enter the well piping and the well pipe freeze protection system won't work. If you find water leaking out of the snifter valve it needs repair or replacement.

Air introduced by a snifter valve / bleed-back system may reduce unwanted tastes, iron or odors of sulphur in the water supply

Rasmussen points out that in Northern Minnesota and on water systems in other very cold climates, the system's ability to drain water back into the well, leaving just air in the higher sections of well piping can help protect a well system from freezing. According to our well driller friends, on water systems whose well provides water high in smelly hydrogen sulfide (that rotten egg smell) or perhaps high in iron, the high absorption of air into the well water provided by this design might help oxidize and thus reduce those contaminants in the water supply.

By contrast, a bladder type water pressure tank keeps the water supply physically separate from the pressure tank's air charge - air is never absorbed into the building water supply and other treatment methods would be needed to remove sulphur, hydrogen sulfide, or high iron levels.

Really? We have read this claim in several articles about drain-back or bleed-back systems but have not [yet] found research supporting the claim that added air induction into the well water system was alone able to remove significant levels of iron (FE) nor hydrogen sulfide (H2S). Contact us if you've found such data.

We are not confident that air injection ALONE will cure a serious sulphur odor in the water supply.

More likely we'll need to install a treatment system such as a potassium permanganate "green sand as the plumbers call it" system or a chlorine injection system, combined with filtration, or some equivalent.

Drain-Back Systems Work with Submersible Pump Systems

But the use of a drain-back system to prevent well piping systems is long established as a method that works on well water supply systems that use a submersible pump and a bladderless type water pressure tank.

Why only with submersible well pumps? If we drain the water out of well piping in a jet pump system the pump is going to lose prime and may be unable to re-prime itself, thus losing water supply and risking pump burn-up.

Why with bladderless type water pressure tanks: those tanks can be fitted with an AVC or air volume control that will release the excess air allowed into the system by the drain-back valve and snifter valve.

Drain Back Valve, Dill Valve, & Snifter Valve Components, Definitions & Functions

This discussion has moved to a separate article

How the Drain Back System Actually Works on Well or Lake Water Piping to Protect from Freezing & to the Keep Air Charge in the Pressure Tank

Steel bladderless water pressure tank using a drain-back valve and snifter valve (C) Daniel Friedman

The bleed-back or drain-back system on a water piping system works automatically to drain water out of piping between the water pressure tank or check valve and the bleed back or drain back valve opening found on the well or lake water piping in the well casing or at a level below the frost line. By allowing air to enter the piping system it is protected from freezing.


Troubleshooting Frozen Well Pipes on Drain-Back Valve, Dill Valve, & Snifter Valve Systems


Drain Back Valve & Snifter Valve Installation, Repair or Replacement


Converting a Bladderless Water Tank to a Tank with an Internal Bladder? Remove all the Snifter Valve Components!

Snifter valve on a submersible pump well system (C) D Friedman

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In our snifter valve photo (above Rasmussen Well Drilling, Inc., Two Harbors MN & DJ Friedman) ) my finger points to the stem of the snifter valve: an air inlet valve mounted on a bronze check valve. Stains on the floor show that there has been leakage at this particular valve.

In that photo we have a clue that the snifter valve had not worked for years and was also leaky. You can see the copper stains on the floor below the valve (my finger points to the snifter valve stem). How did the owners get away with this? Their well piping was buried at more that eight feet below ground: below the frost line in their areas of Northern Minnesota.

So the owners didn't have a problem with freezing well piping. But they did report a long-standing problem with a water-logged water pressure tank whose well pump short-cycling shenanigans had been dealt-with by manually adding air to the pressure tank at frequent intervals.

Because the well piping between the well bore and the building was buried sufficiently to eschew the worry about freezing well lines, the owners decided to tackle the recurrent short-cycling problem of their well pump not by replacing the snifter valve (which was the real culprit) but by replacing the steel bladderless water pressure tank with a new internal bladder water pressure tank.

To complete that installation the well-plumber would keep a check valve at the pressure tank outlet but remove the snifter valve and he'd also have to remove the drain-back or bleed-back valve located in the well piping.

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.

If you fail to remove these components you will suffer from constant air discharge at the building faucets and other plumbing fixtures as the air injected into the piping system will be pushed into the water-containing bladder in the new pressure tank: a location from which there is no escape as there is no air volume control and no mechanism to remove this air on an internal-bladder pressure tank set-up.

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