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Adjusting bladder tank pressure while the system is hot

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  • Zoso
    Zoso Member Posts: 33
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    It's an industrial building. I don't have the full history but I think it used to be straight water years ago. They kept freezing coil so they put glycol in. Then I would assume they started popping the 30 PSI relief valve. So probably under fill the system ever since and no flow ever reached the highest points.

    When I got involved I put the correct size tank and based on the 30 PSI relief valve. Everything is rated for 125 so I don't know why the hell 30 is in there to begin with. But they refuse to let me change it which would have eliminated multiple problems

    So I'm sure they did not properly fill it again and I have a lot of air in the high points. Another part of the problem is they have some maintenance people who try to do HVAC but don't really know what they're doing.

    Just waiting for them to give me the go-ahead to go out with one of my service tech and fix the system. Thanks for all the comments here. My whole point was to try to see if there was a slick way to do it hot without isolating and relieving pressure from the tanks.
  • hot_rod
    hot_rod Member Posts: 22,158
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    > @Gordy said:
    > Looking at the original problem (popping relief valves. Is it possible that the auto fill was left on, and the feed piping is/was on the suction side of the circulators. If the pressure differential was such that the suction side was below system pressure it could trick the auto feeder into adding more water to the system.
    >
    > But you also said you are pumping away from the ponpc.

    Autofill on Glycol system, I hope not?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • icy78
    icy78 Member Posts: 404
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    Okay here's a foolproof way. Set the tank pressure .
    Go to the highest point, and install a pressure gauge, pump up the system until you see that you have 5 PSI over that highest point.
    Then start troubleshooting flow or restriction problems.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
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    liveto99 said:


    STEVEusaPA said:

    liveto99 said:

    The size of the tanks does not matter just the pressure....

    Since when?
    Pressure could be correct, but if the tank(s) are undersized for the volume of water in the system, the pressure will still rise.

    The tank volume is almost 20 percent of the system, the tanks are not undersized. If there is 3 different size tanks there if there is the same air pressure in them they will all work fine. The first one is probably the correct size and 2 people have tried to fix this problem by adding tanks.
    My comment wasn't directed at you but at a poster claiming the size of the tanks does not matter, just the pressure, which is false. Other people may read this thread and think the size of expansion tanks do not matter.

    There was an error rendering this rich post.

  • Jolly Bodger
    Jolly Bodger Member Posts: 209
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    I thought they meant that the multiple sizes did not matter. I hope that is what they meant!
  • ch4man
    ch4man Member Posts: 296
    edited December 2019
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    just a silly thought, i realize you have glycol but your an engineer, however ill speak of water and a single tank.
    since water expands 4% in a 100 degree temp rise, and i have a 100 gallon system at 12 PSI, i guess i need to make room in the expansion tank for 4 gallons.
    sooo how much will the air pressure in tank (air side of the bladder) rise above the starting 12 PSI when you compress the air the amount that the physical volume of that 4 gallons would cause?
    maybe thats the answer to the hot pressure question.

    i dont know, id ask an engineer
  • Zoso
    Zoso Member Posts: 33
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    That's how I calculated the hot pressure of 25psig that I expected to see. It's Boyle's law, but you have to use absolute pressure readings not gauge pressure.
  • ch4man
    ch4man Member Posts: 296
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    maybe the smallest tank gets maxed out early on, thereby reducing the effective amount of the expansion system which may answer the reliefs blowing.
    doesnt answer why calculations are not proving out nor the lack of heat on the top floor
  • icy78
    icy78 Member Posts: 404
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    In my experience, what gets calculated compared to what is actual, are 2 different things.
    Your gpm may be off considerably.

    About the tanks. How could one tank become waterlogged before another, if they're at same bladder pressure?. Physics says they compress at the same rate.
    So forget that they are at 20 psi when you think they should be 25. That's enough for your piping height.

    Also, is the guage accurate?
    Jolly Bodger
  • Zoso
    Zoso Member Posts: 33
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    Yeah but I'm 20 psi hot. I didn't run the numbers backwards but I think that would put me down it about a 12 PSI fill which would not be enough in my case.

    I'm going to check for air at the top of the system and probably put some charge in the tanks.

    Thanks everyone for your comments.
  • Jolly Bodger
    Jolly Bodger Member Posts: 209
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    @Zoso watch out for tunnel vision. You have 20 PSI right now? that is about 45 ft. If there is air in the top floor, it is not due to low static pressure.

    It is like a car that won't start and has a flat tire. Putting air in the tire won't make the car start.
    icy78

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