Replacing old compression expansion tank with new bladder type

Ttom

Got some conflicting information and am now second guessing the DIY fix I already finished last night. I unfortunately don’t have a picture but the tank was tapped off of a 4-in-1 device that has a “from boiler”, “to system”, “to tank” and some kind of little vacuum lock device. The old compression tank was just a straight run from the “To tank” side, so I hacked off and pulled down the old tank, gave it a new shutoff, and and redirected it to hang the new style tank right off the pipe (with hangers). Now I’m seeing a lot of info that the device should have been eliminated and moved somewhere else and with an air control device of some kind. Did I **** up?

hot_rod

The compression tank systems are what is know as an air management system. Air that comes out of solution needs to be kept in that tank. Various valves were used to move air from the top of the boiler into the tank. You cannot add an air purger unless you pipe it up into that tank.

If you switch to a diaphragm tank, now you have an air elimination system. You need to add a purger to get the air out of the system. Use a microbubble type, like a Discal for high efficiency air removal.
The diaphragm type tank will be about 3 times smaller due to its captive air bubble.

Jamie Hall

As @hot_rod said, the two approaches to maintaining pressure in your system are really very different. The compression tanks worked -- and continue to work -- splendidly well for decades. They required very little maintenance (mainly making sure that they had some air and some water in them). The device to which you refer did that quite well.

The expansion tank which you have installed now operates quite differently -- and won't tolerate any air getting into it at all, so you need an air removal device (purger) (you can lose the old air eliminator which went with the compression tank) as well as the new tank, and the new tank should be connected to the system where the pressure reducing valve is connected, and both should be a foot or so upstream from the inlet to the main circulating pump -- which is unlikely to be anywhere near where the old compression tank was conneted.

Why did you replace it?

Ttom

@hot_rod and @Jamie Hall, thanks for the info. And I replaced it because the old tank rusted through and sprung a leak.

Steamhead

Jamie Hall said:

Why did you replace it?

Unless it was leaking, there was no need to. Bladder tanks require maintenance just like plain steel ones do.

Ttom

@Steamhead, the 1.5” of water in my basement told me it was time to replace lol

WMno57

Sorry to hear your basement got wet. Did the water leak from the old tank, or did the water come out the relief valve?
The old tanks require maintenance. Over time they waterlog and require draining. However they are a better solution for old systems. Some on this forum may not agree with me on that, but they don't have a 70 year old boiler, that works perfectly, and hasn't been touched all winter. That's right, I drained my air over water tank last fall, and have done nothing since. I have the water shut off to the pressure reducing fill valve, so no leaks either.
15 minutes of maintenance once a year. Why exactly should I get a new system?

WMno57

Ok, I need to work on my reading skills. I now see your post where you stated your old tank rusted through.
My old tank also rusted through several years ago. I replaced it with an identical air over water tank. They are hard to find. I bought mine from Quality Tanks Inc in Clinton, Wisconsin.

www.qualitytanksinc.com

If you change to a bladder tank, you will need a different air management device, and should move the circulator so you are "pumping away". Easier to just get a replacement air over water tank.

Steamhead

R.E. Michel sells these tanks too.

hot_rod

I suppose if diaphragm tanks were made of the same gauge metal as compression tanks they would see 30 years or more life expectancy Either tank sees some O2 in any air that is added.

With compression tank the air keeps going in and out of solution as the water heats and cools.

WMno57

hot_rod said:

I suppose if diaphragm tanks were made of the same gauge metal as compression tanks they would see 30 years or more life expectancy

The bladder or diaphragm has an average life of about 15 years. Less if you frequently take the system to zero pressure to replace pumps, dirt mags, etc, as this flexes the diaphragm beyond its normal range. Diaphragm tanks are a good match for new systems that are pumping away, and filled with good clean water. Air over water tanks are a better choice for old large diameter gravity piped systems filled with rusty water and sediment that are not pumping away.
You can spend thousands of dollars on new pumps, dirt mags, Mr Bubble air thingamajigs, and large diameter copper pipe. Then pay a pipefitter hours of labor to pipe it all up. Or, you can do like I did and not try to improve the Deadmen's design. Their old fashioned air over water tank worked just fine for 70 years on my system.
The Mr Bubble air thingamajig works a lot better if you are pumping away. It should be located at the hottest point. It should be located at the lowest pressure point. Easy if you are pumping away. Impossible if the pump is on the return. If your system is not pumping away, stick with the air over water tank.

hot_rod

another option if you don't want water, or boiler fluid in a steel vessel. Put it in the bag, sir.
Further reduce the size of the tank also