Ex gravity sys w/circulator blowing off water

Big Ed

The tank in the attic is disconnected ,if not it should be with a circulator. Look for a expansion tank in basement.It could be a diafram type tank that lost its charge or need replacing.Or a tank up in the ceiling that needs to be fully drained to be affective...

Daniel Nolan

Non-pro engineer homeowner with tools needs help

I know - we can be dangerous. That's why I am doing my homework.... trying to save some $$ since we just bought this old place as our first house last year.

I have what I believe (after reading up on this site) to be an ex gravity system that has been converted with a "newer" boiler circa 1970 and a circulator and expansion tank.

The issue is water coming out of the relief valve on the top of the boiler when the circulator comes on. This does not happen every time or last very long, but I get 1-2 gals per day out of it.

Some observations:
- I believe I have an old style expansion tank (big welded thing in the rafters about 1'dia by 3' long)
- The F&R pipes in the basement are HUGE (3"+)
- I can only find shutoffs on the returns
- I have observed the pressure on the gauge on the front of the boiler to be above 20psi when the blowoff is happening
- For this reason I suspect the infeed supply valve (forgive me if not correct name) and not the relief valve
- I did try shutting off the water feed and it dramatically reduced the issue, but it did happen once over a 1-2 day test


Now the questions:
- What is the best way to get in there and replace the suspect valve?
(I am guessing shut off the incoming water supply and close all the return shutoffs and drain the system - possibly with all the bleeders open - and then refill and close the bleeders on each floor as it fills up)
- What is the probability that I need a new expansion tank?
- If so, where can I get the same type I have now?
- What else should I be checking?
- I have town water and a whole house filter - should I be conditioning the water in my system?

Thanks in advance. This site has proven to be quite informative!

-Dan (staying warm in Boston)

Brad White_9

Just a hunch

but I suspect the expansion tank is either too small for the system volume and/or is waterlogged hence not serving it's full purpose.
What happens when you shut the feed valve entirely? Does the system pressure continuously drop (indicating a leak)?

Daniel Nolan

Shutting off supply

After shutting off the supply the pressure did not seem to drop noticeably over 24 hours.

Also, I am not clear on how an older style expansion tank works. Does it have a diaphragm? Can it be over filled / pressurized / overloaded? There is a drain on the bottom like a garden hose connection and it is on the opposite end from the inlet pipe. Can I check the integrity of this tank by using this drain somehow? When I change the supply valve should I be re-setting the pressure in the tank or purging it or ???

Thanks again.
-Dan

Barbarossa

Hopefuly the expa. tank is attached to the suction side of the circ pump. The tank have a sight glass and the boiler a presure gauge? That info would help.

Daniel Nolan

More details

The tank is in the rafters in the basement, sorry. It is a big black welded cylinder on its side. It's piped off the feed with a big green valve thing on the top of the boiler. The tank has a big drain like a garden hose hookup on the bottom. No sight glass anywhere. No tank in the attic. Boiler has a pressure gauge, seems to be 11.5 - 14 psi most of the time, but I have seen it over 20 psi when it was blowing off.

If a non-diaphragm tank needs to be drained, perhaps that is part of my trouble too. What is the procedure for this?

And does my system drain & refill procedure above sound ok?

Thanks,
-Dan

Brad White_9

Older style expansion tanks

are simply tanks. No diaphragm and nothing separating the air cushion from the water. Indeed it can fill with water and that is where the problems usually start. When full of water there is no cushion hence no place for water to go when volume increases with expansion. Normally when the system is at its maximum operating pressure, the tank should be half or less full. If no sight glass as you state (I believe you, this is to state so), then you can tap the tank with your fingers to "listen for hollow". You will hear a difference rapping air or rapping water. If full (I suspect it is), then drain the tank about half way and see what happens to the pressure.

As the other posting said, you should be pumping away from the tank, not towards it. I suspect you may be pumping away already because the valve lifted when the pump came on. When you pump toward the tank, the suction pressure deacreases but the discharge pressure does not. (Same total pressure, just on the wrong side of things.)

What affects tank sizing also is the elevation. If at the top of your system it will be smaller than if at the bottom.

Diaphragm or bladder tanks are cheap insurance if sized correctly.

Open tanks incorrectly applied are a continual source of air re-introduction (when you drain the tank and re-charge it) then you vent the air out of your radiators, lose the air charge, your relief valve trips, you drain the tank again, and on and on and on... Stop the ritual. Stop the madness

Big Ed

Normal Problem

Your tank needs to be drained.Isolate the tank from the system by shutting off valve leading to tank. Drain off water and let air take its place in the tank. The problem you will face is a water logged tank.Air has to take the place of water first in the tank which allows the water to exit or drain out. By using a vent if your lucky enough to have one or drain it with a short hose .Let water drain out and let the tank suck in some air between drain cycles.... Yes it sucks