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Auto air vents.

Another discussion in the office. 🧐 One side (him) is saying auto air vents on a hydronic system should only used for a period of time until the air is pulled out of the system then isolated. The other side (me) is saying the auto air vents should function continuously. The reason for this question rises from a recently installed auto air vent that is spitting fluids. 40/60 glycol water mix. System flushed with degreaser, fresh water flush and drain. Thank you

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 20,440
    I suspect that the discussion arises because one side (you) assumes that the auto air vent will work as intended, and keep working, and the other side, probably through sad experience, says well, that is as may be -- but they don't.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EdTheHeaterManGGross
  • hot_rod
    hot_rod Member Posts: 18,208
    edited August 2022
    Auto air vents or air purgers?  Auto air vents used at high points in a system, an air handler mounted on the ceiling for example. Sometimes those are turned off, cap tightened, after the system has run for a period of time. Mainly for fear of discharge causing damage.

    Air purgers or air separators located near the boiler or chiller need to be active.

    Every time a boiler fires, small micro bubbles form on the surface above the flame. When the boiler is off, cold that air will go back into solution. A working air purger has the ability to expel that formed air. That air is mainly nitrogen as the O2 will be consumed when oxidizing any ferrous metals in the system, pumps, expansion tanks, steel pipe, etc. Unless you have non barrier tube😉then O2 continues to enter the system.

    Most air seps have the ability to add a discharge tube to deal with spits or discharge.

    My opinion, for what it is worth.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterMan
  • MikeDurigon
    MikeDurigon Member Posts: 24
    Thank you gentlemen. I think I have lost the bet to him. (The boss) 😂
    EdTheHeaterMan
  • leonz
    leonz Member Posts: 682
    My past experience with air vents is they fail at the worst times and leak. You either plan on having the elbows lower and adding a pipe nipple, ball valve, pipe nipple and pipe coupler before you thread in the $10.00+ air vent or you are lucky enough to have the head room for the piping and ball valve before the air vent.

    Having a spare vent on hand is also a must on a Sunday night I no longer have to crawl around my baseboard (which I hate) to bleed air from the system as I have a 15 gallon steel compression tank (I wish I had a 30 gallon steel compression tank. I can always add a second steel compression tank later.

    Knowing what I know now 40 years later I should have requested that the open to air steel expansion tank was left in place when they installed the hand fed wood and coal boiler) as I would have had heat when the drilled well failed-the auto feed valve failed and leaked back-insert stupid kid here.

    The 10 gallons of water in the 15-gallon steel compression tank are a great asset to have if you have baseboard as the bladder tanks can and will fail over time and you lose your point of pressure change.

    If you have an air scoop already in your system you can still use a steel compression tank by plumbing the vent line to the airtrol valve under the steel compression tank and still have a good way to strip air bubbles from the heating system if you have the head room to install a steel compression tank.

    With a steel compression tank there are no moving parts; the only thing that is moving is the heated water as it passes through the Air scoop or Internal Air Separator where the air bubbles enter to the airtrol valve and rise into the steel compression tank and are absorbed by the air blanket above the water level in the tank. As the water cools it gradually drops back into the water flow in the system.

    First, a thank you Dan for your writing and convincing me to use an Internal Air Separator, Airtrol Valve and Steel Compression Tank, and I also wish to thank the Dead Men.



  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 13,121
    Cap the auto air vents after the system is running and purged. Any minor air after that should be elevated at the boiler main air removal device which should be kept operational.

    Glycol makes a lot of foam and auto vents don't work well with glycol.....doesnt work well.
  • HomerJSmith
    HomerJSmith Member Posts: 1,923
    Caleffi, an inovative company, has a cap for the air vent with hydroscopic discs that prevent liquid discharge while letting air out when dry.
  • hot_rod
    hot_rod Member Posts: 18,208
    You will see auto air vents used at boilers in lieu of an air purger or air sep. It is not a good substitute. If that is intended to be the only air elimination device, then yes it needs to be left open or functioning.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • hot_rod
    hot_rod Member Posts: 18,208
    leonz said:
    My past experience with air vents is they fail at the worst times and leak. You either plan on having the elbows lower and adding a pipe nipple, ball valve, pipe nipple and pipe coupler before you thread in the $10.00+ air vent or you are lucky enough to have the head room for the piping and ball valve before the air vent. Having a spare vent on hand is also a must on a Sunday night I no longer have to crawl around my baseboard (which I hate) to bleed air from the system as I have a 15 gallon steel compression tank (I wish I had a 30 gallon steel compression tank. I can always add a second steel compression tank later. Knowing what I know now 40 years later I should have requested that the open to air steel expansion tank was left in place when they installed the hand fed wood and coal boiler) as I would have had heat when the drilled well failed-the auto feed valve failed and leaked back-insert stupid kid here. The 10 gallons of water in the 15-gallon steel compression tank are a great asset to have if you have baseboard as the bladder tanks can and will fail over time and you lose your point of pressure change. If you have an air scoop already in your system you can still use a steel compression tank by plumbing the vent line to the airtrol valve under the steel compression tank and still have a good way to strip air bubbles from the heating system if you have the head room to install a steel compression tank. With a steel compression tank there are no moving parts; the only thing that is moving is the heated water as it passes through the Air scoop or Internal Air Separator where the air bubbles enter to the airtrol valve and rise into the steel compression tank and are absorbed by the air blanket above the water level in the tank. As the water cools it gradually drops back into the water flow in the system. First, a thank you Dan for your writing and convincing me to use an Internal Air Separator, Airtrol Valve and Steel Compression Tank, and I also wish to thank the Dead Men.
    Nothing against the technology, but what would it cost to put a compression tank in? Tank, airtrol, sight glass, etc. $1000 bucks or so for parts?
    A $50 diaphram tank should last 20 years, a bag type a bit more so you don’t worry about a moving diaphram😉
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • leonz
    leonz Member Posts: 682
    edited August 2022
    hot_rod said:


    leonz said:

    My past experience with air vents is they fail at the worst times and leak. You either plan on having the elbows lower and adding a pipe nipple, ball valve, pipe nipple and pipe coupler before you thread in the $10.00+ air vent or you are lucky enough to have the head room for the piping and ball valve before the air vent.

    Having a spare vent on hand is also a must on a Sunday night I no longer have to crawl around my baseboard (which I hate) to bleed air from the system as I have a 15 gallon steel compression tank (I wish I had a 30 gallon steel compression tank. I can always add a second steel compression tank later.

    Knowing what I know now 40 years later I should have requested that the open to air steel expansion tank was left in place when they installed the hand fed wood and coal boiler) as I would have had heat when the drilled well failed-the auto feed valve failed and leaked back-insert stupid kid here.

    The 10 gallons of water in the 15-gallon steel compression tank are a great asset to have if you have baseboard as the bladder tanks can and will fail over time and you lose your point of pressure change.

    If you have an air scoop already in your system you can still use a steel compression tank by plumbing the vent line to the airtrol valve under the steel compression tank and still have a good way to strip air bubbles from the heating system if you have the head room to install a steel compression tank.

    With a steel compression tank there are no moving parts; the only thing that is moving is the heated water as it passes through the Air scoop or Internal Air Separator where the air bubbles enter to the airtrol valve and rise into the steel compression tank and are absorbed by the air blanket above the water level in the tank. As the water cools it gradually drops back into the water flow in the system.

    First, a thank you Dan for your writing and convincing me to use an Internal Air Separator, Airtrol Valve and Steel Compression Tank, and I also wish to thank the Dead Men.
    =================================================================



    Nothing against the technology, but what would it cost to put a compression tank in? Tank, airtrol, sight glass, etc. $1000 bucks or so for parts?
    A $50 diaphram tank should last 20 years, a bag type a bit more so you don’t worry about a moving diaphram😉
    =================================================================


    The thing is, one's sanity (mine) is important; once the system and piping is filled and purged of excess water and there are no leaks the valves are shut off and the water is captive and the air blanket like the water in the steel compression tank is captive and unless there is a leak in the piping or a bad seal in a circulator the water volume never changes.

    The only thing that occurred was a vacuum condition over time that was caused by loose stem packing nuts for the gauge glass on the tank which I finally narrowed down with the help of the members of the forum. The vacuum condition was eliminated, water level normal, water added to increase system pressure slightly to improve circulator performance and it's been fine ever since.

    All I need to do now is isolate and remove the B+G NRF 25 circulator insert a check valve and then begin the heating season.

    The parts 7 years ago were about $700.00 The cost of the clowns who put the tank, IAS and airtrol and coal stoker in at the time was a great deal to me because of thier screw ups and the bad hydrolevel units.