Expansion Tanks/Pumping Away

swellman

Hi, I was reading Dan's post on "pumping away" (https://heatinghelp.com/systems-help-center/pumping-away-piping/) and it left me with a couple questions:

(1) What's a maximum rule of thumb for just how far away a diaphragm expansion tank can be installed from the air separator? He gives "near or very near to" the air separator but I'm not much of an expert whether that's a foot away or whether the tank (for instance) could be 5 feet above the air separator in the joist space more out of the way.

(2) I currently have an old (and large) steel expansion tank. I'm wondered if (in your opinions) it's worth replacing an old steel tank with a newer model. If we didn't, is there a general rule of thumb for how far away these steel tanks ought to be form the air separator as well? What is the best way you would suggest I roughly calculate the size of tank I need? (I'm finding kind of mixed stuff with google results).

Thanks!

Ironman

There's no set rule of thumb as to how far away the tank can be. The issue is the point of connection. Anything reasonable should be fine, and if it wasn't, the connecting line could be up-sized.

If you have the old style compression tank, the air removal system works differently than with a bladder tank. With a bladder tank, you must have some form of air separator (air scoop, MBR); with a compression tank you can NOT use an air separator. The air must be directed into the compression tank to maintain an air cushion at the top.

hot_rod

The tank can mount most anywhere, the important point is the connection into the piping, that needs to be near the inlet side of the circulator. You could copper or pex over to a remote tank location.

The air purger should always be on the boiler supply, the hottest point, the expansion tank doesn't necessarily need to be below the air purger.

If the pump is on the return side of the boiler, the expansion tank should connect there also.

Some examples.

Jamie Hall

To further add to @Ironman 's post -- first, reemphsize that if you have the older steel tank (probably hung from the ceiling), you must NOT have any other air separator in the system! Further, though, the connection to the tank needs to be a T with the leg of the T connecting to the tank -- and the leg pointing up. That way air in the system can get to the tank and keep it properly charged.

If the existing tank is controlling the system pressure adequately, there's no good reason to replace it. They -- and the related Airtrol fittings (or equivalent) -- are pretty sturdy and reliable.

swellman

These are really helpful comments. Thanks so much. 

@Jamie Hall - is there a simple way to tell if 
the pressure is being adequately controlled? E.g. pressure isn’t fluctuating wildly on the gauge perhaps? 

Also, our steel tank is currently teed in on the return side of the boiler. Is that normal? And, if we were to keep our steel tank should we look to tee it off the supply side coming out of the boiler and *not* use an air separator as you have kindly pointed out?  

Jamie Hall

The only real way to tell if the tank is controlling the pressure adequately is to heck the pressure gauge on the system -- it should probably be somewhere around 15 psi cold, and rise perhaps to 20 psi hot. More or less. Or something like that... it varies.

As to reconnecting the tank to somewhere else... if it ain't broke, don't fix it. If you are repiping things for some other reason, then the connection should be close to the inlet side of the circulating pump. "Close to" being one of those variables... and yes, don't use an air separator.

swellman

Re: re-piping. We are doing some... installing a new circulator and fixing a leak in the pipe a couple feet after the circulator. So we have the option of piping it to a new point before the circulator. Right now it looks like it’s connected to a drain point and also goes into the boiler (picture attached). Should I leave this one as is or should I still move it to before the circulator while I have the supply piping all apart? 

Jamie Hall

Personally... I'd leave it be.

hot_rod

yeah, unless you are changing out the tank to a diaphragm style, I'd let the sleeping dog lie.

jumper

Old type is better. When relief wets floor you know that tank is flooded and requires drain job. Far easier than dealing with bladder tank. That happens maybe every ten years. Preferable to check gauge each leap year rather than look for water on floor. I also prefer checking gauge to add water rather than deal with automatic make up.
Agree that if system works then don't move expansion tank. But when locating tank the higher the better. Hopefully air comes out of solution and ends up in tank instead of someplace else where it can create problems. Air separators can only remove entrained air, I think?