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wwww Member Posts: 242
There is an expansion tank above the Delco Boiler...DB4S...12inch Diameter x 30 inches...grey in color with drain valve.

I looked in the museum on this site and saw a DB4 and it says 125,000 btu's..What is the S for?

I've drained the tank a number of times. Initially the boiler gauge is just above 12 and then a bit higher when water gets hot and expands. In a few days the gauge is higher...20 or more. That seems not too bad but it seems the first radiator in the line on first floor above boiler always has to be bled..and has between a count of 5 or so of air in it more than once a day.

1. I know the air may cause a flow problem and since this tank doesn't have a bladder air and water are mixing in tank.
2. Will the system perform better if I put a tank with a bladder in and what effect on heating does the air have in that radiator?
3. This old tank is about 2 cu ft. How do i size this tank properly..should I get the same size tank or use another formula?
4. Should I be concerned about this? Thanks!


  • SnowmeltSnowmelt Member Posts: 1,191
    Send a pic of the serpt up, let's make sure everything looks somewhat ok, I hate to say just add a extrol - 30 and be done with it
  • GordyGordy Member Posts: 9,523
    edited February 2015
    Are,you leaving the fill valve on? If yes Could be the PRV is malfunctioning and letting water seep by. Try resetting everything and turn the valve off to the PRV.

    Do you have an indirect water heater?

    Installing an airtrol tank fitting on the compression tank will help with the air problem.
  • wwww Member Posts: 242
    the fill valve is only facing up when i fill up the boiler after putting a circulator in or servicing it. the valve is in the position to autofill the boiler and it stops when the pressure reaches 12. it doesn't seem like the prv is bad although i've seen it drip is factory set at 30..and have never seen the pressure that high. the hot water comes from the boiler.

    this airtrol fitting..i'll look at that..if it turns out this tank is any good..if not will replace and look into that fitting too. thanks.

    i can't take a photo now but it's a tank in the rafters..maybe an old b and g tank.
  • GordyGordy Member Posts: 9,523
    edited February 2015
    When I refer to prv I mean the pressure reducing valve not the pressure relief valve. Is the water supply to the pressure reducing valve always on?
  • RJ_4RJ_4 Member Posts: 484
    Check top of tank for any pin hole leaks, and the gauge glass gaskets, also have you inspected the strainer on the dual valve, internal corrosion in the valve can cause the water to leak through the valve causing overfilling. This valve may need to be replaced if it is corroded up inside. I have always preferred the compression tank like you have over the diaphragm or bladder tanks, when repairs are done in the system which require draining , it is easier to remove air from baseboard heaters or fan coils as it eventually will migrate into the compression tank. Also make sure there are no auto vents on high spots in this system
  • hot_rodhot_rod Member Posts: 13,313
    That type of tank is an air management system. You need to trap an air bubble in the tank, As RJ mentioned look for small air leaks, a bottle of spray soap is one way.

    If you chose to use a bladder or diaphragm style tank, now you have an air removal type of system, use a good air separator and high point vents to get it started, then it should remain air free. assuming no leaks.

    Amtrol and Wessel both have free online tank calculators for sizing a replacement tank.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • wwww Member Posts: 242
    edited November 2019
    Gordy...the water to the prv is always on yes....and when the boiler starts off cold the gauge reads 11 to 12....when the heat is on and temp in house is up and radiators hot the valve drips and gauge reads 26 plus...if i turn the boiler off and let the water go cold the gauge on the boiler is between 11 and that means the prv is working and not filling more water into system..right?...I called a plumbing supply regarding the airtrol and he didn't have doesn't mean i can't get one i guess...if i take the faucet type water drain off can this still be drained through the airtrol?
  • Jamie HallJamie Hall Member Posts: 12,853
    Please read my comment on your other thread.
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
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