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Who pumped up the bladder expansion tank (more like how)?

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STEVEusaPA
STEVEusaPA Member Posts: 6,505
Ok this is a new one on me. Drop boiler pressure, take bladder expansion tank off. Check the pressure, its 40 psi.

The whole story...
Oil-fired Weil-McClain Gold, coil, 1 zone baseboard loop. Only one Taco vent on boiler. Circ on return, Flow Check on supply. Expansion tank piped off the bottom of an old B&G flow check. Been like this for 20 years.

This is a long time customer, old lady, widow, rarely goes in the basement. No kids, no visitors, and says no one was in the basement, no one touched the boiler. I have no reason to doubt her.

Get a call, water on the floor, it's under the relief valve, boiler pressure @ 40 psi. I figure bad gauge & 'air' for starters.
Close the feed, close supply to coil, open hot faucet, take both of them out of the equation.
Purge the system of air, drop pressure to 12 psi, close feed again. Boiler pressure starts rising, up to 30psi. Confirmed with my own gauge, coil still out of the equation.
Drop the pressure, drain enough water to remove the expansion tank. It reads 40 psi. There's no water in the tank at all. As light as any empty tank. Confirmed with second air gauge, then went out and checked my tire pressure, still couldn't believe it.

Changed tank, replace air vent& relief valve, purge--all is well.

So my question obviously is, how did the expansion tank end up at 40 psi? My only thoughts are:
1. Someone added air, but there was really no reason to think that, and the cap over the valve had 20 year old dust on it.
2. Maybe the Flow check stuck, air in system, circ forced air into bladder tank? Sounds stupid, because it should've came back out when I removed the tank, but that's all I got.

Any thoughts, suggestions, medication appreciated.
Thanks
Steve

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Comments

  • Ironman
    Ironman Member Posts: 7,379
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    Maybe the bladder was stuck and compressed to where it had 40 psi?

    How did it get that way: fill valve slowly leaking through?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    STEVEusaPA
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,623
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    Something went haywire.
    If the tank always had 40 psi in it it would be like running a system with no expansion tank.....no cushion. Unless they ran the system at 40 relief valve would leak.....is it a 30 psi relief??

    If its a 30 psi relief and you ALWAYS had 40 in the tank the relief would constantly leak and reseat and the feeder would feed and stop feed and stop
  • HVACNUT
    HVACNUT Member Posts: 5,864
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    Domestic tanks are factory charged to 40 psi. Is it 3/4 instead of 1/2" male threads?
    Alan (California Radiant) Forbes
  • j a_2
    j a_2 Member Posts: 1,801
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    HVACNUT said:

    Domestic tanks are factory charged to 40 psi. Is it 3/4 instead of 1/2" male threads?

    Very good question
  • JUGHNE
    JUGHNE Member Posts: 11,076
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    I have seen a system with 2nd floor rads with no air in tank.
    The rads had an air cushion in the top of them.

    But you have BB, couldn't be that much air in there and still work, could it? Maybe it has always been peeing on the floor and she finally noticed it. Should be some traces though.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
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    Thanks for all the responses.
    Wasn't a domestic tank.
    Wasn't always dripping.
    Only one story, so all radiation is about 8 ft up from bottom of boiler.
    No changes to any system components in 10 years (I'm the only one to work on the system).
    Bob's response makes some sense to me. If the system pressure rose and the bladder was compressed and stuck, I assume the pressure in the tank would increase, and the system would have no room for expansion, the same as having no tank.

    There was an error rendering this rich post.

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,623
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    Sigh. It's one of those things that make no sense. Been doing this 45 years. I have a few riddles, some I think about once in a while. Dives me nuts because I will never know the answers
  • j a_2
    j a_2 Member Posts: 1,801
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    There has to be more to this 40 psig make no sense...OP picture up the unit in guestion... what gage are you going by that says 40 psig. ?
  • hot_rod
    hot_rod Member Posts: 22,259
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    It may have been over charged from the factory? The system had some air pockets to accept expansion?

    Your positive the air gauge is accurate?

    Does the boiler have a 45 psi relief, most boilers are rated to run up to 45 psi. Maybe the relief valve is stuck closed.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
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    If it's a rad system, my first guess would be air pockets that eventually got absorbed.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
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    j a said:

    ... what gage are you going by that says 40 psig. ?

    Re-read original post
    hot rod said:

    It may have been over charged from the factory? The system had some air pockets to accept expansion?...

    The tank has been on that unit a for at least 10 years, never had high pressure.
    hot rod said:


    Your positive the air gauge is accurate?

    I have 2 tire pressure gauges, both read the same.
    hot rod said:



    Does the boiler have a 45 psi relief, most boilers are rated to run up to 45 psi. Maybe the relief valve is stuck closed.

    Regular 30 psi relief, probably was stuck.

    If it's a rad system, my first guess would be air pockets that eventually got absorbed.

    Its fin tube, but I never heard of a bladder tank absorbing air like that, or knew that it could. Makes sense along with @Ironman idea.

    Thanks for all the responses.

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  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
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    If it's a rad system, my first guess would be air pockets that eventually got absorbed.

    Its fin tube, but I never heard of a bladder tank absorbing air like that, or knew that it could. Makes sense along with @Ironman idea.

    Thanks for all the responses.


    I didn't mean it that way. Suppose the x-tank always had that much air in it. The only logical conclusion. Then suppose the system had a air pocket in it somewhere that acted as a cushion. Throughout the years, that air was slowly absorbed into the water and when the water was reheated, the air released exited through the air sep. Once all the air was gone, the system lost it's cushion and thats when the problems started.

    That would be my best guess as to what occurred
  • Phil_17
    Phil_17 Member Posts: 178
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    Perhaps if you were to cut it open you would find something out of the ordinary (bladder adhered to itself, or the tank wall?) that might help explain the situation.

    Also, did you release the air and recharge it to the proper setting? If you let the air out, did it release an appropriate amount, or was it under what you would expect? Again, I'm thinking that the bladder somehow adhered itself to something that changed the volume or shape of the chamber.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
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    @Harvey Ramer I got ya now Harvey. Thanks for the clarification.

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  • Lance
    Lance Member Posts: 271
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    The answer is a defective bladder tank. Your solution to replace was correct. Why is unknown. However, some tanks, including well water tanks during manufacture, after setting too long in storage may have the bladder make a seal between the steel and the bladder or fold the rubber bag onto itself making a smaller or no chamber at all. Also, the Schrader valve may let air in but not out. In this case unless the air pressure is being measured while pumping in, the "false check valve" caused by a bladder seal will not let air out making us think it is empty when the needle is pressed in by hand or gauge. Many a tank installed without being pressurized first will be subject to the system pressure constantly pressing the bladder flat. One must check first and realize if too little air volume pumped in makes a big pressure difference it may be the bladder chamber has reduced to almost nothing and should be rejected. Test 1) put air in and see if it comes out. Test 2) is harder to gauge but ask did the air volume that goes in match the volume out? Test 3) compare with another tank of same size.
    Rubber is an amazing product.
    But you observed 40 psi. It is perfect to assume it was charged that way, irregardless of dust. But you hypothesize it may have been at zero or 12psi and somehow got to 40psi. But all the pressure symptoms show the tank is too full of air or fluid. The tank was obviously not providing room for expansion. But I am curious could a tank fill itself or increase its pressure by itself? The answer is no. But what force could cause this? I can only assume an element such as refrigerant with a vaporization point when cold could be filled at 12psi and later when heated expand to 40PSI. But I believe the relief valve was stuck closed even against higher pressures, or air in the system above created the expansion space required to keep the relief valve from blowing. Relief valves can leak and still hold back higher pressures without leaking too much. Perhaps the assumptions made are wrong. The customer does not know all? My bet is the tank started with too much pressure, had no impact on system until air venting occurred. Many right things happen for all the wrong reasons.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    edited October 2017
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    Interesting thoughts Lance, thanks. Without rehashing, I took the tank off, measured 40 psi, no water. Checked it with 2 different gauges. Pushed the schrader valve, and air came out just like bike tire. Of course I checked new tank before install and it was at 12 psi.

    There was an error rendering this rich post.

  • Harvey Ramer
    Harvey Ramer Member Posts: 2,239
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    If it was a stuck bladder or reduced/compressed air chamber in the tank, one would certainly think that the tank should be partially filled with water. @STEVEusaPA said it was devoid of any water.