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.
Green links show where you are. © Copyright 2017 InspectApedia.com, All Rights Reserved.
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.
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
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.
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.
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.
Continue reading at DRAIN BACK & SNIFTER VALVE OPERATION or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see SNIFTER & DRAIN BACK VALVES - home
Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
(Jan 22, 2014) joe said:
Hello I am writing about the snifter valve. If you read your article on why are snifter valve air volume control systems used one it states that the high absorption of air into the system helps oxidize and thus reduce hydrogen sulfide or perhaps iron. But in your last email to me you said it would not. So you have me confused. Thanks for your reply. JOE
Thanks so much Joe, I will review these articles and fix that inconsistency.
Honestly, I am sure that I added the statement to which you refer while I was reviewing research about snifter valves, but in replying to your email I simply forgot about it.
You were right, I was mistaken. However we need some clarification:
A snifter valve is only used on deep wells that are operated by a submersible pump AND that feed water into an older-style bladderless expansion tank. The snifter valve, installed in the well piping lets air into the system at each pump on cycle. A companion vent valve installed above ground, close to the pressure tank, or in some cases ON the pressure tank, vents excess air out of the tank to keep the tank's air charge at the proper level.
A water supply system that uses a "captive air" type water pressure tank that incorporates an internal bladder does not need this automatic injection of make-up air, so will not have a snifter valve. In fact when a plumber converts a water supply system from bladderless-tank to internal-bladder tank, s/he needs to also pull the well piping and remove the old snifter valve if one was installed. That is what was going on in my photo series about snifter valves.
So if your water system uses a bladder type tank you wouldn't have a snifter valve installed.
Finally, and here is where we need to do more research, despite the claims of the snifter valve camp, I am doubtful 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.
Do keep me posted, and thank you VERY much for helping me out with clarity and pointing out an inconsistency on this topic.
(Oct 13, 2014) Ray said:
I recently had a new well installed, drilled w/ a submergible pump. a internal bladder tank was installed .
I was concerned about the water in the tank and water line freezing in the winter , so a sniffer valve was installed on the the check valve.
I was told when shutting the system down for the winter, to open and drain the water tank, and to open the green valve cap on the sniffer/check valve to introduce sir to the system , that would allow the water in the line to drain back into the well. Will this advise work? is their any problem with the sniffer valve installed with an internal bladder water tank? thank You
Yes there's a possibility that the advice you were given will work, Ray. But just removing a valve cap won't do it. That cap is supposed to be loose and able to admit air at all times. You shouldn't have to open the snifter valve (found on a check valve usually mounted at the bottom of the water pressure tank) as it should open to admit air on its own - at the end of a pump-on cycle.
If your snifter valve is not working it probably needs a replacement. If you're replacing just the valve stem core don't buy one at your auto parts store - those schrader valves and valve cores operate at different (higher) pressure ranges and are not designed for this application.
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Search the InspectApedia website