exp tank

[ej45]

Anyone ever replace a rubber bladder in a commercial style expansion tank? Do you charge with air before filling with air? Should air pressure match system static?

[boilerman]

I have replaced the bladder in an expansion tank before. You must install the new bladder before you charge it with air. The air is actually on the outside of the bladder while the water is in the bladder.The air charge should match your operating pressure.

[boilernazi28]

this one you wont believe!!!!!!!!!!!! asme blatter tanks MUST not repaired in the field ,,,,i know sounds like b.s.,,,,reason as of hartford stean is once the vessel is broached [opening an passing your hands into the vessel,BREAKING THE PLANE.]you resume all responsability,,yea you can replace the blatter but another way for the ins company to f%%% you,again over 30 psi operating pressure,,,or you dont need asme

[ej45]

Originally posted by boilerman
I have replaced the bladder in an expansion tank before. You must install the new bladder before you charge it with air. The air is actually on the outside of the bladder while the water is in the bladder.The air charge should match your operating pressure.

Should I charge with air before filling with water? I thought with out the air pressure the bladder could burst. Thanks Erik

[hvac-tech-lane]

Originally posted by boilerman
The air charge should match your operating pressure.

I belive air pre-charge for a bladder or diaphram tank should be non operating static +1PSI, as this will give the maximum acceptance factor for the tank. Also of note is the tank location in the system which should be at the same location as the feed line, this is referred to as the point of zero exchange as the pressure will never be less than the setting of the feed water regulator.

[jogas]

Originally posted by boilernazi28
this one you wont believe!!!!!!!!!!!! asme blatter tanks MUST not repaired in the field ,,,,i know sounds like b.s.,,,,reason as of hartford stean is once the vessel is broached [opening an passing your hands into the vessel,BREAKING THE PLANE.]you resume all responsability,,yea you can replace the blatter but another way for the ins company to f%%% you,again over 30 psi operating pressure,,,or you dont need asme

Actually, I was very surprised at this post as I had NEVER heard of anyone replacing a bladder. I've heard of many tanks being replaced though.
Why assume that responsibility and liability?
I'm sure Hartford has some cases they can show you that prompted their stance.
I remember when I was an apprentice, the contractor I worked for would give us the Hartford mag showing boiler explosions. I'm still amazed at what damage a little 5 gallon hot water tank can do.
Jogas

[boilerman]

Originally posted by ej45

Originally posted by boilerman
I have replaced the bladder in an expansion tank before. You must install the new bladder before you charge it with air. The air is actually on the outside of the bladder while the water is in the bladder.The air charge should match your operating pressure.

Should I charge with air before filling with water? I thought with out the air pressure the bladder could burst. Thanks Erik

Yes you should charge the tank with air before any water is added. The way our tank supplier told me was the correst way to charge a blaader tank was to take the static pressure of your system, then add 5lbs. The added pressure assures a flooded system.

just alittle more insight on my changing the bladder: It was done by direction of the supplier. The tank was hung in the ceiling horizontally, and on initial fill the rubber tube in the tank was pinched off by the bladder due to it shifting forward, thus not allowing for any expansion in the tank.They had never heard of it happening so we had "class" in the field and tore the tank apart..

[hvacpope]

Yes you should charge the tank with air before any water is added. The way our tank supplier told me was the correst way to charge a blaader tank was to take the static pressure of your system, then add 5lbs. The added pressure assures a flooded system.

Boilerman
can you explain to me, how adding 5lb to the air side of a bladder type exp. tank will assure a flooded system?

[73dart340]

The fill pressure should be the static head (2.31 foot per pound) plus an additional 2 to 3 pounds of pressure will insure that the highest point in the system stays filled with water. The highest point in the system will not have water in it if the fill pressure is less than the height of the hydronic system. 5 pounds of additional fill is probably OK too as long as the system pressure doesn't get too high when the water is really hot (180 to 200 deg?).

Example:
2 story building with 20' height difference between fill water connection and top of piping. 20' / 2.31 = 8.7 pounds of static head + 3 pounds of additional fill pressure = 11.7 pounds (pretty darn close to the initial 12# setting on the PRV).

I have opened vent lines at the top of a hydronic system only to have air get sucked into the system because the system pressure at the fill was less than the required fill pressure.

[pbcd]

Wouldn't the feed water regulator setting be base upon the same calculation as the expansion tank?

[hvacpope]

[QUOTE]Originally posted by pbcd
[B]Wouldn't the feed water regulator setting be base upon the same calculation as the expansion tank?

That was the way I done it, I can't figure out why adding more pressure to the air side of the tank could be good for the system, all you doing is leaving less room for the water to expand.

[hvacker]

You have to charge the air presure first otherwise you wouldn't know if you were reading air or water presure. The same applies when doing maintence you need to isolate the tank, draw off water presure so you can read the air presure. If the air presure is not correct the feed valve will not get the feedback it need to regulate and will continue to feed water until the relief valve pops.

Same in a non bladder tank. Don't look at the sight glass as you might just be looking at a partial vacuum. Isolate the tank, empty it and allow it to recharge with water.

BTW The reason non bladder tanks waterlog is during off cycles the boiler water absorbs free air ( the stuff fish live off of) and finds it in the tank. During on cycles the free air is released due to heat and finds a system vent. After enough cycles all the air has been vented and replaced with water and it's waterlogged. Next on cycle no more air cushion and out the relief it goes.

[cg2]

Interesting point to make at parties too.

BTW The reason non bladder tanks waterlog is during off cycles the boiler water absorbs free air ( the stuff fish live off of) and finds it in the tank. During on cycles the free air is released due to heat and finds a system vent. After enough cycles all the air has been vented and replaced with water and it's waterlogged. Next on cycle no more air cushion and out the relief it goes. [/B][/QUOTE]