40psi expansion tank

Cdcox · November 21

Are tanks precharged to 40 psi ever used on a boiler system, or do I need to relieve some of the air to 15psi as for the past 20 years the tank in the photo states 40psi. I am not sure if the installer bled some pressure off during installation

GGross · November 21

The expansion tank pressure should be set close to the static pressure of the system it is installed on. I would imagine if you take the tank off it is probably not set to 40 psi, someone probably changed it and didn't write it down. are you sure it is piped to the boiler system and not DHW? What is the static pressure of the system? and do you have issues with the relief valve blowing off? any other issues?

GGross · November 21

I'll add that this tank, and any other expansion tank built for domestic water, is usually OK to use on a boiler so long as the pressure is set correctly. Sometimes they are desirable to use as they are generally lined and resist corrosion much better than standard tanks. Sometimes there is a max temperature limitation which you would need to check with the manufacturer. I'd say since it has lasted some 20 years, that the temp was not an issue in this case

Cdcox · November 21

after replacing the gas valve and upon firing it up for the first time this season, it would not regulate the pressure and pop off several times. I noticed the tank had that “thud sound” all the way to the top. So I purschaed a new tank with the same criteria as the old one and not sure if the inlet was cutting off as 12 lbs so I replaced it. The pressure would climb near 25lbs and all radiators were releasing water instead of air. I sat there until it kicked off at 180° during this process I would bleed water out of the system at the drain valve to walk it back to around 12 to 18 psi. And I did replace the PRV since it wouldn’t close off after about the 5th time releasing pressure. My thought process is get the tank pressure down to 15lbs because at 40 it’s seems useless

BDR529 · November 21

It is for potable water not for a boiler. Read the tank.

hot_rod · November 21

yes you can use a potable dhw expansion tank, but only if you lower the precharge pressure to match the fill pressure

The new Amtrol Pro series for hydronics is basically a domestic tank with a 1/2” stainless nipple instead of 3/4”. Also pre charged to 12 psi

Intended for non barrier tube systems

EBEBRATT-Ed · November 21

You air pressure in the tank needs to be set with the tank removed from the system. The air pressure needs to be set at the pressure the boiler operates at…usually 15psi.

If you have too much air pressure in the tank then you will get no expansion and the relief valve will blow. Too much air pressure=no expansion cushion

Cdcox · November 24

it seems the tank never gets any water in it when I tap it with a wrench. Do they come ready to use? Meaning is there a plug on the water end I am missing. And I think my next move is to invert it so the water will be at the top. The old one was mounted with the air at the top

Jamie Hall · November 25

https://forum.heatinghelp.com/discussion/comment/1822353#Comment_1822353

A domestic tank does come ready for use… for domestic water. At 40 psi. As has been said above, you need to detach the tank from the system (or, if you have the right valves, close the valve to the system and open the tank drain) and reduce the air pressure to 12 to 15 psig. Then reattach it…

neilc · November 25

there's a bladder / diaphram between the air and water side,

let's see a wider view of the whole boiler, tank, and circulator(s)

neilc · November 25

did you set the tank pressure as everyone above has written?

set air to match desired water fill pressure, tank must be disconnected from any system pressure prior to setting air,

if you put that same type domestic tank, preset at 40 or higher, you need to air it down to 12, disconnected from water pressure

Cdcox · November 25

yes I checked it from the box and was at 12psi same as the inlet psi

neilc · November 25

is this a large system ? big house? large cast iron rads?

let's see that wider view,

are you making domestic hot water with the boiler, maybe domestic pressure is leaking in ?

Cdcox · November 25

large 2 story 1890 home with 10 radiators. I been using this boiler for the past 16 years. The only fresh water in the inlet valve. Should I close it off because it was closed off for 16 years. And no I am just heating with it

Cdcox · November 25

I just purchased a Caledactio RG-30 tank because the old one was for DHW and had a 40psi charge on it. But it was bone dry when I removed it. Now the new one I am thinking about pluming it so the air side of the tank is at the bottom of the tank because I still have high pressure and been bleeding water off the drain Bibb. The radiators are bled and emit water only. Maybe I should bleed them longer because there could be air trapped below the water

Jamie Hall · November 25

An expansion tank can be adjusted for any pressure within its rated range. Domestic water tanks may be lined differently (or may not).

If it was set at any pressure greater than the system pressure, of course it would be dry — the water couldn't get into it.

There is one way, and one way only, to set the pressure in an expansion tank (whether it is for heating, domestic water, well control, it doesn't matter). First, determine the low pressure expected of desired in the system to hand. Then, with the tank disconnected from the system on the water side, adjust the air pressure on the air side to that pressure. Then, and only then, reconnect it to the system and put it into service.

SuperTech · November 25

Air usually rises to a high point and doesn't stay trapped below the water. If you are bleeding the radiators and getting only water out then air is not the problem.

Cdcox · November 26

I am going to replumb the expansion tank to have the air in the bladder down low with the water on the top and have the plumbing set to add a second one if needed.

Cdcox · November 26

Cdcox · November 30

repositioned the tank yet the pressure relief valve opened up during the night. I am confused

neilc · November 30

what is your preset air charge on the tank? you checked it and or set it prior to install, correct

I see your tank drain, but do you have isolation between tank and system?

you're going to have to sit and observe a heat call, set a stat to 80 and watch

cold start pressure, and does it build to 30ish?

if 30 doesn't show on the gage, then maybe the relief valve is compromised from repeated opening, it is a 30 psi relief, and not a 15, correct?

or the tank isn't large enough for the entire system,

and I missed it before, you said the fill was closed before the issues began (?)

fill to 12 psi, and close the feed, then keep an eye on it for a cycle as above,

Cdcox · December 1

correct for 18 years even with the fresh water inlet turned off it worked flawlessly

Cdcox · December 2

I turned off the inlet valve and it was at 12psi. Watched it carefully top out at 180°. But it was approaching 30psi three different times and each time i bled some water off the system. I let it cool down and the pressure was at 0lbs. Ran it through a couple of short cycles up to about 120 and turned the sta set point down past the call on point not realizing it kicked on by itself and when I heard it kick off i ran downstairs expecting to see a discharge but it held at 180 and the pressure topped out at 28 psi

neilc · December 2

without being there and touching things, and assuming air is set correctly, it sounds like you might need to double the tank,

0 - 28 psi, pressure should not fluctuate that much

Jamie Hall · December 2

If the expansion tank air pressure was set right, you need a MUCH bigger tank — or the tank has failed.

Cdcox · December 2

I did check the preset and it was 12psi. If I have to add a second tank I will install a shut off valve

hot_rod · December 2

this looks like a fairly large tank already, what model is it?

IMG_9075.jpeg

40psi expansion tank

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