Expansion Tank

Paul_28

I have a blader type expansion tank on my system. Can I just remove the water pressure and then test the air pressure or must the tank be removed from the system before testing.

Al Letellier_2

expansion tank testing

Just lower the system pressure to zero and check the tank pressure. It should be equal to your normal system operating temperature.

G. Gibbs

Correction

Al, I'm sure you wanted to say...lower the pressure of the system, and then charge the tank to the normal fill pressure
of the system. Greg

Michal

yes lower the pressure

Basically drain enough water so the arrow reads 0 pressure, that way you do not have to refill the whole system, Then check the air in the tank should be like 12 to 15 depending on manufacturer.

Joe Mattiello

Expansion tank should be isolated from the system when checking the precharge pressure of the tank. There should be an isolation valve located at the system connection. Captive air bladder type tanks are factory charged to 12 psi, to accommodate most systems. However, if the system static pressure is 20 psi, it would be your responsibility to increase the tank pressure to 20 psi, so there is equilibrium in the system, and the only water that enters the tank will be the thermally expanded water in the system. If the tank pressure is less than the system pressure, you can stress the bladder, and risk a premature failure.

Taco, Inc.
Joe Mattiello
Technical Service Technician
joemat@taco-hvac.com
401-942-8000 X 484
www.taco-hvac.com

Ragu

Yet Another Thing

If you do need a new expansion tank, check the pressure in the tank before installing it. I'd say that 75% of new tanks I've put in only had 2-5 psi in them, right out of the box.

Timco

So...in a system operating normally @ 15 lbs, if the pressure is dropped to 0, the tank should ideally be charged to 15#? if the tanks drops to 0 as well, bad tank?

Tim

Mark Eatherton1

Or...

bad air charge. Don't condemn the tank until you find water where theres only supposed to be air, it may just need recharged with air.

And don't forget to include a means of bleeding the water charge to zero if you isolate the expansion tank.

Isolation is of no earthly good if you can't take the water pressure to 0 on the tank:-(

ME

Timco

soooo...why not just bleed the tank with the system charged, and see if any water is present on the air side, then recharge it if not?

T

Mark Eatherton1

You won't get

the air charge properly done with water pressure on the bladder. It'll work as a quick diaphragm check, but isn't the proper way to check and adjust the air charge.

There is no right way to do things wrong:-)

ME

Timco

grasshopper.....your wisdom exceeds my understanding every time!! :-) I appreciate all your posts as I read the wall, Mr.E. After bleeding the tank thus doing the 'quick diaphram check', could the system be lowered to 0, then charge the tank, then fill the system? I missed my chance to install an isolation valve on the tank this fall when I rebuilt my manifolds in 1" from 3/4".

T

joe j

expantion tank isolation valve

Isnt it against code to install an isolating valve on a diaphram tank? I like the idea of installing atee with adrain valve inline to prevent getting a face full of water hopefully not too hot.

joe j

expantion tank isolation valve

Isnt it against code to install an isolating valve on a diaphram tank? I like the idea of installing atee with adrain valve inline to prevent getting a face full of water hopefully not too hot.

Timco

someone suggested it to me, but all I really want to do is check my tank to ensure it is working properly. The pressure reading is the same as the system pressure, and drops with it.

T

Mark Eatherton1

Yes...

We normally check the air side prior to installation, and adjust if necessary, IE a 30 foot tall system would require approximatley a 20 PSI fill pressure, therefore the air charge should also be at 20 PSI. After checking and adjusting, we write the findings on the tank with Magic Marker and date it. That way, there is a reference point for future service techs.

ME

Mark Eatherton1

Not illegal where I work...

but may be in your area, but I can't see why. An expansion tank is not considered a final safety device like a safety pressure relief valve. THAT would be illegal to isolate with a valve, although the low water cut off is REQUIRED to be isolatable in order to test. Sometimes, I just shake my head and wonder why....

Check with the jurisdiction having authority whenever in doubt.

ME

Timco

thanks, ME.

thanks for the advise, as always. just trying to keep things in good shape, and really enjoy learning and doing most things myself. system is cooling down prior to draining. I have found a basement rad that has a tiny drip I will fix as well. do you use the wrenches that fit the 'dogs' in the rad nipples or an internal type expanding wrench?

t

Weezbo

it is a case of observation...could be that you can make a ..

determination by draining it down and refilling it.and reheating it.you have to Be There as it were...i have ways i test things that arent in a book....

Weezbo

touche`

Mark Eatherton1

You're welcome..

Thanks for the kudos and keep on learnin'. As long as someone like yourself is interested in learnin', people like myself and others are willing to teach.

As for the radiator tail piece, I prefer to try and used the radiator wrench first, and if that fails, then an internal wrench, and in the event that that fails, a saw and chisel.

Try lost of rust buster on the threads first, let it soak for a long time, keep adding to it, THEN try the rad wrench.

I generally lay the radiator down, get my spud wrench tightly engaged into the pawls, then apply a good sized pipe wrench with a 2 foot cheater bar, then, while applying steady pressure to keep things properly engaged, i JUMP on the cheater (literally) and the SNAP torque shock will generally break the fitting loose. Kinda like sneakin' up on it:-)

Be prepared to land on the ground hard if all hell breaks loose. I've thrown my back out of place more times than I care to remember using this method.

Good Luck, and hang around, you might learn some more:-)

ME

Timco

ME,

If I was able to master electricity and welding, I'd like to hope I could pick up how to maintain my HW system :-} My wife and I do love the feel it gives us. I posted about filling & purging, but figured that out....keep filling while draining each zone individually. By the way, with the tank off, pressure was 0, and held for a few minutes, and had water in the air side. Charged & replaced it (with new)and my pressure gauge has only differed 2#s! Used to go from 3-17 or so. Is it OK to have an undersized boiler? Set the aquastat to bring a single zone to 180, but when 2 or 3 zones are running, never breaks 120-130.

Really grateful for guys such as yourself who help...I posted on that flat rate thing and some Ken guy wasted no time insulting me for not doing as he does.

you 'da man,

t

Mark Eatherton1

Undersized boilers...

IMHO are better than grossly oversized boilers provided that they get the job done. If it is so extremely undersized that it can't get the job done, or it is continuously operating in the condensing range and its not designed to, then THAT is a problem.

I use a condensing boiler in my own home, and it is intentionally undersized by a factor of 50%, and it works just great. But that's just MY home...

Ken is the straw that stirs. He makes and keeps thing interesting. He's actually a pretty nice guy in person. Kinda like a 6'6" teddy bear.

ME

GermanPlumber

Nitrogen

Good posts again. One thing so. We charge tanks in Germany with Nitrogen . Molecular structure is bigger than air and charge will hold longer.

Mario

Michal

need a lock valve

expansion tanks can have a valve, it must be a lock shield valve locked open.

Wayco Wayne

Interesting

about the Nitrogen thing. I always isolate a bladder tank with a ball valve and then put a 1/2 threaded tee on the tank inlet that has a 1/2 boiler drain on one side of the tee and the tank on the other. That way you can isolate the tank with the ball valve and then put a hose on the boiler drain and comfortably drain the pressure from the tank to zero without spraying water all over the place. Then you take a deep breath, blow it out slowly and check the air pressure while visualizing a mountain stream deep in the woods. Ohmmmmmmmm. WW

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"