draining STANDARD expansion tank?

Charles G.

No, you shouldn't have to drain the tank. Especially on a regular basis. The only time it's necessary is if the tank is completely water logged as indicated by the press/temp gauge rising rapidly and/or a leaking relief valve.

IF you're going to drain the tank (and I know that's what you really want to do)drain it completely. But every time you let water out of the system, you're bringing fresh (oxygenated) water into the system (hopefully). And then you heat the water, driving the oxygen out of it, and there's the air @ your 2nd fl radiators. And that air isn't necessarily bad. It will compress as the system heats so the radiator will emit heat to capacity. That air also augments the expansion tank, minimizing the high pressure conditions mentioned earlier.

jimbo_6

draining standard non bladder tank how to?

Howdy!

Super basic question--we've got a new house and Im trying to get things in shape.

In past houses ive always considered the expansion tank a necessary maintenance task.

Well, anyhow--I've had houses with bladder tanks but never one without. Well, I take that back--the house I grew up in had a regular tank, but i dont remember what to do. We had someone out to tune the boiler, but he only looked at the gas burner and nothing else.

So--just to describe things: Hot water, only one system or zone. Boilers about 3 years old, and was converted from an old gravity system. They didnt change the tank though, its obviously 50-60 years old (clearly there was once one in the attic).

Theres a pump on the return if that matters.

so--should I drain the tank? I see an isolation valve for the tank, and then a drain cock and a short capped pipe coming off the other end of the tank.

And if I should drain it, How much? Completely empty? Part way?

Finally, would it be a good idea to replace the tank with a bladder type some time? The current tank is in fine shape, but I do need to bleed the radiators on the top floor fairly frequently.

Thanks mucho for any advice!

Uni R_2

Expansion tank

Is it waterlogged? Does water come out of the PRV when your boiler gets hot enough? If so, it is waterlogged and you need to drain it. Otherwise, if you drain it, you'll just be adding more water with more entrained air for eventual delivery to those upstairs rads.

I'd get it changed, others might want to add an Airtrol fitting to the tank instead.

jimbo_6

OK, no mess w/tank. But is 20 PSI high for 1 1/2 story system?

Thanks for the advice, I'll leave it alone unless I see problems. I thought the frequent bleeding WAS the problem, but perhaps not.

I tried draining a little water but there was no change in system pressure at all, so I didnt add any water. I took maybe a gallon out of the tank (I'd guess its a 20 gallon tank?) to see what happened (with isolation valve closed) but it changed nothing--although I think the system runs quieter--less "rushing" water sound in pipes.

By the way, its wired so the circulator runs constantly.

This leads me to one more question:

SYSTEM PRESSURE
When I aksed the gas company guy what pressure the system should be it should be at he said around 20lbs.

Its just a 1 1/2 story house. Shouldnt it be more like 12 or 14?

Next year I'll use a real boiler guy but having already paid the gas company $150 bucks I was hoping to just get a few answers here.

So to summarize?

1) Leave the tank alone unless it causes safety valve pops, etc.

2) Consider at some point replacing tank with bladder tank

3) DONT bleed rads on top floor. Leave a litle air in them.

4) Possibly drain system to lower pressure?

Uni R_2

20psi

It should be around 12psi cold although 20psi hot is fine. Obviously, if it starts going over 25psi when it's hot, eventually it will trip the PRV. At that point you're going to need to drain the tank.

I don't understand the logic of leaving air in the rads. That increases the system pressure.

Don't drain the system to lower the pressure. Just have the tank drained if you think it is getting waterlogged or try and time its replacement at that point.

I battled my old tank far too many winters and it always won - until it went to the scrap dealer.

brucewo1b

UniR

In days of old with gravity hot water they used the tops of the rads as their compresssion tank why not air space is air space as long as you have enough water to meet the heat load. But please explain to me how leaving air in the rads increases the system pressure. Too Much air pressure will lead to high system pressure but an air space is an air space and the bigger the air space the more room for expansion of the heated water.

Uni R_2

In the days of old, when men were bold...

Bruce, whenever I had air migrate from my old expansion tank to the upstairs branches I would see an increase in system pressure. It was always creeping up over 20psi cold. With the compression tank it holds rock solid at 12psi cold. I have no idea how to explain why that was the case.

I can't see the point of having air anywhere in the system other than it being on the other side of the rubber membrane in a properly sized compression tank.

brucewo1b

I see your point

but what was happening was that you were pumping toward your PONPC and lowering the pressure at the fill valve, seeing lowwer pressure it would feed more water, you were doing the same at the compression tank and the air was going into solution and findings its way out at the highest point in the system. Not a problem of too much air but of lower water pressure at the feed and tank.