In Praise of Airtrol

EricPeterson

I recently did some re-piping and properly hooked up both the B&G Inline Air Separator and the ATF-12 Airtrol fitting to my 24g compression tank.

Prior to this I only had the IAS installed and was constantly getting air in the high point of the system (radiators on the third floor). I had meant to install an ATF-12 but gave the one I had purchased to my father-in-law for his boiler.

Since the install and an initial bleed, there has been no air whatsoever in the third floor radiators.
So I am a very satisfied customer right now.

I do have a few comments on this situation:

1. Somewhere I read that there is an requirement of 18" of straight pipe leading to the IAS. But I cannot find this anywhere in the B&G documentation. I could only manage 13" and that seems to be working well enough.
   
2. Another thing that is very hard to find is an explanation of how this setup works to prevent air in the system. The only explanation I could find is on page 26 of this Technical Manual. This manual does contain a lot of useful technical information. I also know that DanH talked about this vaguely in one of his books.
   
3. In general I find the B&G information scattered through different documents, you have to piece it all together.
   
4. The install and maintenance instructions are wanting in my opinion. I use the Airtrol fitting to verify that I have the right amount of water in the tank. I added a fitting on the compression tank drain so that I can quickly charge the system with the desired air pressure - bringing it up to pressure using the fill valve is a laborious and time-consuming activity.
   
5. If you want some light reading material to put you to sleep, read the original patent (attached). I couldn't really make out the principle of operation from the patent either.
   

Eric Peterson

jesmed1

Thanks for that history on the Airtrol. I just installed an Airtrol ATF-12 on our expansion tank, so it was interesting to read the patent description of how it's supposed to work, but as you say, the language is not exactly clear.

Anyway, thank you to Mr Edwin B. Tidd for your invention.

hot_rod

The concept of having some straight piping section is to allow air to start rising up in the pipe before it enters the purger.

I'd be more concerned about excessive velocity, compared to straight section. Above 4 fps the ability of purgers to catch all the small air decreases.

Is this in the piping that you calculated at 7 fps?

EricPeterson

hot_rod said:

The concept of having some straight piping section is to allow air to start rising up in the pipe before it enters the purger.

I'd be more concerned about excessive velocity, compared to straight section. Above 4 fps the ability of purgers to catch all the small air decreases.

Is this in the piping that you calculated at 7 fps?

Yes it is in the near-boiler piping. I'm constrained by a water heater next to the boiler, unless I send the water from the boiler first the other way then make a U-turn. Any such re-piping will have to wait until next year.
It seems to working OK right now, will see how it performs over the heating season.
The 7 FPS I calclulated is only when the Caleffi valve is closed, I have not yet tried to calculate the fps once the valve starts to open.
If I replace the circ with a lower flow model, that would improve the situation.
At any rate it's working better than ever before, even if the install is sub-optimal.


Eric

Robert_25

Eric, please see this post from years ago: https://forum.heatinghelp.com/discussion/66639/how-critical-is-the-18-inches/p1

From Dan Schaffer @ Bell & Gossett:
"Bell & Gossett's IAS requires 6 pipe diameters upstream and 3 pipe diameters downstream. This may be advantageous for some installations."

Steamhead

Nice job, @EricPeterson ! We like the Airtrol setup too. It gets the job done without the moving parts that diaphragm tanks have, and lasts much longer.

mattmia2

The tank fitting has some baffles that reduce gravity circulation of water in and out of the tank which reduces circulation of water with dissolved air out of the tank which helps keep the air in the tank.

This is a mostly obsolete system, when it was in common use B&G's sales material would have had a more cohesive description.

jesmed1

mattmia2 said:

The tank fitting has some baffles that reduce gravity circulation of water in and out of the tank which reduces circulation of water with dissolved air out of the tank which helps keep the air in the tank.

The introductory text of the patent sheds some light on this aspect of the Airtrol. In the patent text, Mr Tidd says that he found that, if the expansion tank was plumbed with 1/2" pipe, air would not travel freely up the 1/2" pipe into the tank, but would bridge the pipe ID and form a "definite block".

He says he found that larger pipe diameters would allow air to pass freely into the tank, but that when the circulator was running, it would induce a circulation in the larger pipe that caused the water and air in the tank to heat up, and would cause air bubbles from the tank to be transferred to other parts of the system. So as you say, his baffle design is supposed to prevent that circulation.

Our expansion tank had been plumbed with 1/2" pipe, which Tidd says would impede air transfer into the tank, and which also was not pitched and so would further impede air transfer to the tank. I removed our old 1/2" pipe and plumbed our new Airtrol with 3/4" copper with a 3-in-12 pitch, so we should get better air transfer to the tank. I'm hoping we see improvement similar to Eric's.

hot_rod

EricPeterson said:

hot_rod said:

The concept of having some straight piping section is to allow air to start rising up in the pipe before it enters the purger.

I'd be more concerned about excessive velocity, compared to straight section. Above 4 fps the ability of purgers to catch all the small air decreases.

Is this in the piping that you calculated at 7 fps?

Yes it is in the near-boiler piping. I'm constrained by a water heater next to the boiler, unless I send the water from the boiler first the other way then make a U-turn. Any such re-piping will have to wait until next year.
It seems to working OK right now, will see how it performs over the heating season.
The 7 FPS I calclulated is only when the Caleffi valve is closed, I have not yet tried to calculate the fps once the valve starts to open.
If I replace the circ with a lower flow model, that would improve the situation.
At any rate it's working better than ever before, even if the install is sub-optimal.


Eric

Let us know how the lower cartridge works. If you can try both the 130F and the 115. Add this to the list of to-dos

EricPeterson

Robert_25 said:

Eric, please see this post from years ago: https://forum.heatinghelp.com/discussion/66639/how-critical-is-the-18-inches/p1

From Dan Schaffer @ Bell & Gossett:
"Bell & Gossett's IAS requires 6 pipe diameters upstream and 3 pipe diameters downstream. This may be advantageous for some installations."

@Robert_25 - thanks for that. I've got the upstream covered but used a close nipple on the downstream.
Basing the distance on the diameter makes sense rather than a fixed number.
Maybe I'll re-pipe it next year.

jesmed1 said:

mattmia2 said:

The tank fitting has some baffles that reduce gravity circulation of water in and out of the tank which reduces circulation of water with dissolved air out of the tank which helps keep the air in the tank.

The introductory text of the patent sheds some light on this aspect of the Airtrol. In the patent text, Mr Tidd says that he found that, if the expansion tank was plumbed with 1/2" pipe, air would not travel freely up the 1/2" pipe into the tank, but would bridge the pipe ID and form a "definite block".

He says he found that larger pipe diameters would allow air to pass freely into the tank, but that when the circulator was running, it would induce a circulation in the larger pipe that caused the water and air in the tank to heat up, and would cause air bubbles from the tank to be transferred to other parts of the system. So as you say, his baffle design is supposed to prevent that circulation.

Our expansion tank had been plumbed with 1/2" pipe, which Tidd says would impede air transfer into the tank, and which also was not pitched and so would further impede air transfer to the tank. I removed our old 1/2" pipe and plumbed our new Airtrol with 3/4" copper with a 3-in-12 pitch, so we should get better air transfer to the tank. I'm hoping we see improvement similar to Eric's.

@jesmed1 - My previous install also had 1/2" pipe, and a couple of elbows - now I've used 1-1/4" copper that I had laying around and pitched up to the tank with no elbows.
As I said it seems to be working well so far.

Eric

hot_rod

One issue with compression tanks is the water is in direct contact with the air. that air bubble is trapped in the tank. If it never goes through the boiler, to be heated the O2 is still in solution, which in contact with steel, turns to rust.

Reading the Amtrol Engineering Handbook explains how problems like chronic air bubbles in upper radiator or piping is all part of compression tank dynamics.
As air makes it way from the tank, yes there is movement in and out of the tank, (Dalton and Henrys Laws), that air pocket in upper "spaces" like radiators, creates a second PONPC. The disappearance or movement of the PONPC changes the hydraulic dynamics of the system.
An accurate gauge at the inlet of the circ, with the pump flowing and not flowing will indicate the presence of an upper point air bubble. And the amount relative to the air remaining in the compression tank.

Of course a 1/3 smaller sized diaphragm tank eliminates all these concerns

Anyone using or installing compression tanks should read the Amtrol book, so much to learn that helps with both design and troubleshooting.

jesmed1

EricPeterson said:

My previous install also had 1/2" pipe, and a couple of elbows - now I've used 1-1/4" copper that I had laying around and pitched up to the tank with no elbows.
As I said it seems to be working well so far.

Eric

Sounds good. We don't have air scoops like you do, but we do have integral air separators that are cast into the Weil-Mclain boilers. There's a separate 1/2" port at the air separator location, and the pipe to the expansion tank comes out of the boiler there. Will be interesting to see how well those integral separators work. One guy in the old discussion that Robert_25 linked to above said that he used Weil-McLain boilers exclusively, and he found that the cast-in air separators worked well enough that he didn't need to install air scoops. Of course, he put his circulators on the supply, not on the return like we have, so our results may not be as good.

EricPeterson

hot_rod said:

One issue with compression tanks is the water is in direct contact with the air. that air bubble is trapped in the tank. If it never goes through the boiler, to be heated the O2 is still in solution, which in contact with steel, turns to rust.

Reading the Amtrol Engineering Handbook explains how problems like chronic air bubbles in upper radiator or piping is all part of compression tank dynamics.
As air makes it way from the tank, yes there is movement in and out of the tank, (Dalton and Henrys Laws), that air pocket in upper "spaces" like radiators, creates a second PONPC. The disappearance or movement of the PONPC changes the hydraulic dynamics of the system.
An accurate gauge at the inlet of the circ, with the pump flowing and not flowing will indicate the presence of an upper point air bubble. And the amount relative to the air remaining in the compression tank.

Of course a 1/3 smaller sized diaphragm tank eliminates all these concerns

Anyone using or installing compression tanks should read the Amtrol book, so much to learn that helps with both design and troubleshooting.

That's quite a homework assignment - 112 pages.
I found a downloadable copy here.
My tank is pretty old, around 70 years, so I have no idea if it's rusting inside. But when I took it down for repainting (surface rust from a pet damage) I saved a quart of water from it and it looks clear. So that seems like a good sign.

As for todo list, the 115F element (from a different discussion) is at the top of the list. A different circulator is next on the list. From other discussions regarding ECM I think I would need a DirtMag installed if I were to go with an ECM circulator (so that's also on the list). Right now I don't have a good place to install it because my pipe runs near the boiler do not have the vertical space for the DirtMag and would involve some re-piping which I am reluctant to do at this time. Is there an optimal place to install the DirtMag?
So I may opt to go with the NRF-25 after all if I make a swap this year.
Also, I was talking to my sister's boyfriend who does maintenance at a school, including boilers, and he emphasized getting the water tested, just like you said @hot_rod.
So that is also on the list:

1. 115F element
   
2. water test / treatment
   
3. circulator
   
4. DirtMag
   
5. Amtrol Engineering Handbook
   

Eric