Older style Compression tank question

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HVACRTEK83
HVACRTEK83 Posts: 8
in THE MAIN WALL

So I realize each year its a good idea to drain down and reset the air charge in these compression tanks,I have a system with 2 20 inch tanks overhead with site glasses,and each year at the start of season I drain them down because the water levels in both are almost full but not quite. The tanks are piped in parallel,each with their own shutoff valves upstream of the b&G ATF-20 tank fittings where the system is connected to them. On the opposite end there is those airtrol boiler drain type valves with a stem that rises up into tank. I just want to make sure im doing this rite because I find the tanks become quite full even before water is even heated. From my understanding you should drain each tank until you start to suck air up through that airtrol drain fitting correct? Which in my case would start at about 1/2 tank or a bit more. Before that point it just spits out solid streams of water because the water is over the tube. So I stop draining when it gets to that level, I changed site glass nuts/washers/gaskets,so when I open up system valves,pressure in system dropped down to 6 to 8 psi and I started bypassing the prv to bring system up to 12,but the level in my tanks were rising as well while doing this. I also opened the drain on the atf-20 fittings while filling system back up,as the instructions say to have that vent/drain open while filling to push air out,and close it once a solid stream of water occurs. So I did that as well. But I guess my problem is the level in the tanks ended up around 3/4 up the glass roughly. And system was around 86f at the time. So im worried what the level will be once water is 200f. I tightened all fittings around gage glasses,packing nuts,ect. Because my thoughts were I may be losing air somewhere causing it to keep filling. But didnt seem like It was. Where do you guys like to see the tank levels,I know not all have gauge glass but am I doing something wrong maybe? Thanks

Comments

  • Jamie Hall
    Jamie Hall Posts: 27,949

    Almost. The tank should be drained until it is empty. Completely empty. Then when you open it back to the system, water will compress the air and give you your cushion. The Airtrol will, if all is going well, attempt to maintain that more or less half full condition when the system is under pressure.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    HVACNUT
  • leonz
    leonz Posts: 1,990
    edited 9:04PM

    If your system is intact and has no leaks you should not have to refill it OR drain it every year BECAUSE this allows excess oxygen to enter the system and you do not want that ever if your system has no leaks.

    Why are you running your high limit to 200 Degrees Fahrenheit when 170-180 degrees Fahrenheit will do if you have baseboard heat???????

    How much water do you have in your system?

    Is your fill valve shut off completely? If not, it should be.

    Have you reached a point where you have had a screaming vacuum leak when you started a circulator and traced it back to the sight glass packing gland nuts???

    You have to remember that you are compressing the air in the tank when the water in the system expands when the boiler is heating the water so that is not a problem.

  • HVACNUT
    HVACNUT Posts: 7,775
    edited 10:19PM

    Forget about the gauge glasses. Don't even look at them. Drain both tanks completely, as Brother Jamie said.

    The boiler should be cold while doing this. After the tanks are empty and you open the valves to pressurize them, the Pressure Reducing Valve should fill the system to 12 psi. Regardless of the level in the glass. Don't look. If you notice the system over filling past 12 psi (like approaching 15 psi), shut off the feed valve and get a 0-60 psi gauge with a hose adapter to check the accuracy of the boiler gauge.

    Now turn the power on and run the heat. Make sure all radiators heat and pressure doesn't rise above 15-20 psi at 180° water temperature. 180° should be limit. No need for 200° unless its colder than design day temperatures. Which is almost never.

    If you think the tanks might be filling too quickly, are there any air eliminators on the boiler, or an indirect water heater?

  • EBEBRATT-Ed
    EBEBRATT-Ed Posts: 21,295

    My method is to drain the system. Fill the boiler to operating pressure with the tanks isolated. Once the boiler and system are full and pressurized open the tanks.

    The top gauge glass washers are prone to leak and dry out because the never see water so changing them every few years is a good idea.

    I wouldn't stress about the tank level unless the system over pressurizes from a water-logged tank. You could close both gauge glass valves to prevent any loss of air and just open them if you want to check the water level but most jobs don't even have a gauge glass.

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