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Snifter valve on submersible pump system can protect against well pipe freezing (C) Daniel Friedman Drain Back Valve & Snifter Valve Components & Definitions
Explanation of bleed-back valves, drain back valves, snifter valves & AVCs used with bladderless water tanks & a well or lake water supply

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Definition of Drain Back Valves, Bleed-Back Systems & Snifter Valve Components & Air Volume Controls:

This article defines drain back valve or bleed-back val and the , snifter valve and describes how these components work to protect water pipes from freezing by allowing water to drain out at the end of a water pump cycle. These same components, working with an air volume control valve on the water tank also keep the proper air charge in the tank, avoiding well pump rapid on-off cycling.

We describe how & where the snifter valve, drainback valve and air volume control are installed & what they look like. 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.



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

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

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.

Observing and working with a Minnesota well drilling company in Two Harbors we were told that the Snifter Valve's job was to keep an air charge in the pressure tank by admitting air into the well piping at the end of each pump on-off cycle. Actually this well pipe freeze protection system has three key components that work together to get water out of well pipes that might otherwise freeze.

On bladderless water pressure tank and submersible well pump water systems we find the air volume control or AVC, an air outlet on bladderless water tanks working with drain-back systems (the air volume control valve that may actually let air in or out of the water pressure tank depending on model and application), an air inlet, the snifter valve that allows air into the well piping when the pump stops, and a drain back valve that lets water drain out of the well piping when the pump stops.

Below we expand and illustrate these definitions in more detail and with some photos of each device.

Definition of the Air Volume Control (AVC) & Its Functions

Air volume control working with a drain back valve and snifter valve (C) Daniel Friedman

Click to enlarge any image]

The AVC is operated by a float that is in turn operated by the water level in the pressure tank to open or close the AVC properly.

The pressure tank used on drain-back water supply systems is normally a steel or fiberglass water tank that does not make use of an internal bladder to keep water and air in the tank separate.

At each pump-on cycle, air in the water piping is pushed back up into the water pressure tank. This air volume (inside all of that well piping) is more than is needed in the pressure tank to prevent short cycling of the water pump. The excess air volume in the tank would then result in air discharge at the building's plumbing fixtures.

So an automatic air volume control (AVC) mounted into a tapping (or "tank bung") at the middle of the water tank's height is designed to vent excess air from the water tank.

Our photo shows the air volume control. The AVC float mechanisms inside the tank where it rises or falls according to the water level in the pressure tank. The float opens (on water level fall) the air vent on this AVC to vent excess air in the pressure tank. When water in the tank reaches a little below the level of the AVC valve itself, the float closes the vent to stop releasing air from the tank, keeping the proper air charge in this bladderless pressure tank.

See WATER TANK AIR VOLUME CONTROLS for more about these devices.

If the AVC is not working properly on non drain-down systems you may find a water-logged pressure tank causing well pump is short cycling.
See WATER PUMP SHORT CYCLING

But if an AVC is not working on a drain down system or you will find air discharge at the building's faucets.
See AIR DISCHARGE at FAUCETS, FIXTURES

Definition of Bleed-back Valve or Drain-Back Valve & Its Functions

The drain back valve is installed on a tee on the vertical well piping, making it a device that you won't see unless you're paying attention while a well pipe and submersible pump are being installed-in or removed from a well bore or casing. This device is used to allow air to enter the well piping between the drain-back valve tee and the building water tank at the end of each pump-on cycle.

The drain back valve opens when the submersible pump stops and pressure in the well piping drops. At that point a ball inside the snifter valve moves towards the well piping center (away from the outer face or air vent in the valve). This allows air to enter through a small opening in the snifter valve. With no foot valve or check valve on the bottom of the well piping, admitting air into the vertical well pipe allows water to flow out of the well pipe bottom and back into the well.

Drain back valve removed from well piping tee (C) Daniel Friedman Drain back valve removed from well piping tee (C) Daniel Friedman

The result is that as long as the drain-back valve itself is located below the frost level, water in the well piping above the valve will drain back into the well, leaving the well piping empty of water and full of air. (No, this scheme is not a lot of hot air.)

At above left the internal ball that forms the valve inside this drain-back valve is away from the small1/8" opening on the face of the drain-back valve: a position that occurs when pressure drops in the well piping (the pump has shut off) and one that permits air to enter through the small drain back valve orifice.

You can see the drain back vent's ball pushed into the valve body in our second photo - above right. In this position the small air inlet orifice is closed, preventing water from squirting out of the drain back vent's air opening while the well pump is running.

If the air inlet vent fails to close when the submersible pump is running, some water pressure, quantity, and flow delivery to the building will be lost.

Definition of Snifter Valve & Its Functions - with submersible well pumps & bladderless water pressure tanks

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

A special Schrader valve [it looks like the air valve on a tire], the snifter valve, also referred to as a Brady air vent valve basically a one-way valve that allows some air into the well piping system at the end of a pump cycle but prevents water from exiting the piping system (at the snifter valve) when the the pump is running and the well piping is pressurized with water.

This special schrader valve, referred to as the "snifter valve" allows additional air into the well line to allow well piping water to drain back into the well.

The snifter valve looks like a tire valve or air valve and is mounted on an 1/8" tapping on a check valve typically at or close to the bottom of a steel bladderless water pressure tank. A snifter valve works in concert with a drain-back valve and an air volume control valve as part of a triumvirate of air admittance and air volume control used with submersible well pumps installed in areas where shallow well piping is at risk of freezing.

Why doesn't the snifter valve also allow drain-back of all of the water in the pressure tank too?

A check valve is located at the point where the well piping enters the bottom of the water pressure tank. This valve keeps water from leaving the pressure tank in an attempt to head back into the well each time the pump stops.

More about how each of these components works is
at DRAIN BACK & SNIFTER VALVE OPERATION

If you're not sure how check valves work or where they are needed on water and well piping systems
see CHECK VALVES, WATER SUPPLY

 

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.

Article Series Contents

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