Air Separator Question

EricPeterson

I am using a B&G "Bell & Gossett IAS 1-1/4" In Line Air Separator".
There is a section in Dan's book "Pumping Away" (see below) where he indicates that this type of air separator needs a straight 18" section of pipe at the inlet.
However I cannot find any such requirement in the B&G spec sheet

Any advice on this situation would be most appreciated.

Thanks,
Eric Peterson

hot_rod

That upstream piping dimension seems to be disappearing from installation manuals for some reason?

It's no longer in the Amtrol manual either.

The upstream distance helps the air rise up in the pipe before it enters, and also helps reduce turbulence in over pumped systems. Especially when there is an ell right against the purger.

Have you consider a much higher performing microbubble type separator? There is no mechanism in a ramp type "camel hump" air purger to grab and remove microbubbles. These tiny bubbles reduce the efficiency of the heat transfer in the boiler and heat emitters.

Use a vent cap adapter and vent the air into the compression tank. If you really want a compression tank?

So you get high performance air removal and avoid that tank fitting.

PeteA

@hot_rod
Bob is a compression tank the same as an expansion tank? Also do you have a drawing that shows what your describing in regards to the tank above the vent cap adapter?

EricPeterson

Thanks HR.
I called Xylem and left a message with the local B&G rep. No call-back yet.

I already have the IAS, but would consider other options especially if they do a better job. I do like that the IAS is zero-maintenance.

So the you can use a vent cap adapter on the microbubble separator to connect to the tank?

I also already have a steel compression tank, would rather not bother replacing it right now:

• IAS air separator
  
• Airtrol ATF-12
  
• 12" compression tank
  

but...any recommendations?

Eric

hot_rod

A compression tank aka plain steel tank, serves the same function as a diaphragm type expansion tank, commonly used on residential hydronics.

When you use a compression tank you must maintain an air bubble in the tank. It is an air management type expansion device. So any air that you purge out needs to be routed up to that tank.

With a common diaphragm tank you system is an air elimination type. Air removed can be expelled to the surrounding space. This happens because the diaphragm in the tank keeps the air bubble trapped for expansion space.

Typically a diaphragm tank will be 3 times smaller than a compression tank.

More on the science behind the two types of systems in this downloadable guide from Amtrol.

hot_rod

EricPeterson said:

Thanks HR.
I called Xylem and left a message with the local B&G rep. No call-back yet.

I already have the IAS, but would consider other options especially if they do a better job. I do like that the IAS is zero-maintenance.

So the you can use a vent cap adapter on the microbubble separator to connect to the tank?

I also already have a steel compression tank, would rather not bother replacing it right now:

• IAS air separator
  
• Airtrol ATF-12
  
• 12" compression tank
  

but...any recommendations?

Eric

Whichever air eliminator you use, it needs to direct up to the compression tank. You could add a tube onto the air vent on top of the IAS, I suppose.

Typically the Airtrol system was two parts, the air vent up top the boiler and the tank fitting
.
https://www.xylem.com/siteassets/brand/bell-amp-gossett/resources/brochure/air-management-for-hydronic-heating-and-cooling-systems.pdf

EricPeterson

From a layman's perspective:

• water expands in volume as it heats as it is non-compressible.
  
• air is compressible, thus the air bubble in the compression tank compresses when water volume expands.
  
• an expansion tank has a rubber divider (diaphragm), which stretches to accommodate increased water volume.
  

Eric

hot_rod

Here is a simple way to use the IAS and compression tank.
I believe all the IAS have 1/2" air vent top ports?

Is so a 1/2 Caleffi 5020, the adapter to change the thread to 1/4" NPT (NA102), then a compression adapter to add a 3/8 copper tube up to the tank. This shows a 1/4 fip X 3/8 compression ell,it could be a straight 1/4 npt X 3/8 compression adapter also.

So as air vents out you are putting it into the tank. Basically a homemade airtrol set up, using what you have.

EricPeterson

@hot_rod - well I already have the Airtrol ATF-12, so I might as well use it. The model I have is a one-piece, not two, that simply threads into the bottom of the tank, with a 1/2" fitting to connect it to the fitting on the top of the IAS via a suitably pitched and sized run of horizontal pipe.

As for the IAS, while it's not a microbubble type separator, it might well work well enough with the Airtrol.
Most of the microbubble separators are designed for expansion tanks, and to vent air rather than direct it to a compression tank. So adding a fitting to such a device seems a bit of a hack to me.

B&G does make a microbubble type separator designed to connect to a compression tank, but it is $$$ and I'm not sure it's worth the dough. It's like 10x the price of the IAS - SupplyHouse.

Eric

leonz

I have the same system with the B+G Internal Air Separator, ATF12 and the B+G/Wessels 15 gallon compression tank and 1/2" Gauge glass with valves piped to the end tapping's of the Steel Compression Tank that is 8 years old now and you need 18 inches of pipe from circulator for the air bubbles to migrate and rise to the Internal Air Separator and then hits the cast in place baffle and then rises up the feeder pipe to the Internal Air Separator and then on to the Steel Compression Tank.

Do you have a gauge glass in the end of the steel compression tank? It makes life much simpler.

If you need any help with it you can send me a PM.

EricPeterson

@leonz - thanks for the info. The 18" is what I recall. It's troubling that B&G does not have this in their documentation.

I do not have a gauge glass on my tank, and I do not think there is anywhere on the tank to add a tapping for a gauge glass.
My understanding is that you can set the proper water level in the tank by using the bleed screw on the ATF-12.

Thanks,
Eric

hot_rod

The IAS you have is a bit different than just a ramp style air purger. Ive never tested one on a clear pipe test bench to compare performance.

If your flow velocity is in the 2-4 fps range Id imagine it will do the job

Their drawings never show it with little  or no upstream piping🤨. So maybe it is just implied you have some straight piping upstream?

B&G does offer the micro bubble type as well as the Rolairtrol and there was another EAS type  available years ago. So someone at B&G
Must agree there are even more “improved” options

Somewhere you can find Dan article on the invention of the Microbubble resorber by Spirotherm, for some additional thoughts on air separation and removal

leonz

EricPeterson said:

@leonz - thanks for the info. The 18" is what I recall. It's troubling that B&G does not have this in their documentation.

I do not have a gauge glass on my tank, and I do not think there is anywhere on the tank to add a tapping for a gauge glass.
My understanding is that you can set the proper water level in the tank by using the bleed screw on the ATF-12.

Thanks,
Eric

-----------------------------------------------------------------------------------------

Please tell me more about your tank Eric,

Yes, you can do this, the steel compression tank has to be large enough in diameter to accept the ATF12 and its copper tube and at the same time create the 1/3 air blanket, 2/3 water ratio.

If your entire system is empty it will take a while to get all the air out of it so just open your fill valve and
use a box end 6 or 12 point wrench to open the vent slightly and open the water fill valve as boredom will ensue while it is filling.

When the ATF12 is hissing and spitting water-a lot of water it is time to close the vent and close it 1/4 of a turn then you can turn a circulator on to push water and any trapped air through the system.

Just like my system when you begin the heating season you will have the occasional air bubble.

I wish I had been able to afford a 60 gallon tank and create an open system like the one that was in this house when I bought it in 1978.

EricPeterson

@leonz - my tank is a 12" diameter B&G, 24 gallons per the lettering on the side.
The ATF-12 is the one designed for a 12" diameter tank, per the B&G documentation.

When we moved in 39 years ago there was still a tank from the open system up in the attic, from the original boiler which was apparently a coal-fired gravity system, but had been updated to a circulator with compression tank. I removed extraneous stuff like the tank, along with the 4" diameter pipes in the basement when I split the house into zones, did a lot of other stuff to make the house comfortable.

It's been an ongoing project since I've lived here.

Eric

Steamhead

Here's the manual- it covers the whole Airtrol setup:

https://www.xylem.com/siteassets/brand/bell-amp-gossett/resources/manual/s10300h.pdf

It doesn't mention the 18" straight pipe either, but does show a length of pipe before the IAS in the diagrams. I'd use that 18 inches.

I'd also use the Airtrol tank fitting. This helps keep air from migrating out of the tank, solving the waterlogging issue we often find on plain steel tanks. And it does this with no moving parts. Keep in mind, diaphragms are moving parts and will eventually fail.

hot_rod

The sheet @Steamhead attached shows the multiple installations. The one has the inline IAS up against an ell.

With their other air seps EAS and EAS Junior, they make a point of "no minimum pipe requirements"

EricPeterson

@hot_rod and @Steamhead - I saw that diagram of the IAS. It's disappointing that there is no mention of the 18" span. It's disappointing that the tech support never called me back. I'll try calling them again.

Thanks for the help..
Eric

Robert_25

I found an old thread on a similar topic: 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."

I have an IAS installed with these lengths of straight pipe and it works well.

EricPeterson

@Robert_25 - thanks for the link. Too bad all the images are stripped out.

After reading through all the comments, I homed in on the exact same comment as you did regarding the pipe diameters.

So for 1-1/4" that would be 7.5" upstream, so not sure where the 18" from Dan's book came from - unless he was presuming 3" near-boiler piping which is hard to believe.

Eric

hot_rod

EricPeterson said:

@hot_rod and @Steamhead - I saw that diagram of the IAS. It's disappointing that there is no mention of the 18" span. It's disappointing that the tech support never called me back. I'll try calling them again.

Thanks for the help..
Eric

If you have the room I would give it as much upstream as possible. I don't know of any actual testing showing the result of different inlet lengths? So a lot of hearsay.

I recall the number being based on pipe diameter instead of a set 18" or whatever.

As close to the boiler outlet seems to be a recommendation that is still in installation guides.

Being in the hottest fluid and lowest pressure zone "pumping away" probably is the more important point, compared to piping distances.

Above 4- 5 fps seems to throw typical ramp style purgers into a panic. From my shop testing with clear piping to observe.

Here is my latest test assembly that I'll take to our lab in Milwaukee where we have more accurate test equipment.

My take is with shrinking high performance boiler heat exchanger design, thinner metals and castings, the micro-bubble removal becomes more of a concern.

In your case with a cast boiler and probably low flow velocity, your plan should work fine.

Robert_25

Eric, I would guess the 18” recommendation is for a traditional airscoop.  The B&G IAS is a different design.  I have some old B&G literature somewhere that discusses the difference, will see if I can locate it.

EricPeterson

@hot_rod and @Robert_25 - thanks for the updates. @hot_rod that's an interesting test setup and I like that garage floor treatment.

Yes I am pumping away, the boiler is cast iron with 1-1/4" near-boiler piping, and there is a mix of 3" and 1" distribution piping (1" to the 1st floor and 3rd-floor baseboard CI radiators, 3" that branches out to the 9 free-standing radiators in the original parts of the house, plus some CI baseboard in the basement).
LOTS of water. I only get air now in the 3rd floor.

The IAS is one 90° elbow from the boiler output and I have room for the 18" section.

Eric

WMno57

Link to my 100 year old high volume system with 1950 Thrush air scoop and bladder-less air over water tank.
https://forum.heatinghelp.com/discussion/181774/replacing-ceiling-mounted-thrush-compression-tank/p1
Eric, in my opinion, you don't need a gauge glass, micro bubble, or 18 inches of horizontal. If you are capable of draining the tank once a year, and occasional bleeding of top floor radiators, I think you will be fine.

leonz

Again:

You need the 18 inches of horizontal flow to allow the air bubbles
to rise and then migrate to the Internal Air Separator.

A micro bubble absorber added to an existing system with a
steel compression tank eliminates the air cushion blanket in the
steel compression tank and floods the steel compression tank and
loses the point of pressure change.

If the system is left alone after the excess water is drained from the
steel compression tank and the water feed valve is shut off he should
have no issues with his heating system.

EricPeterson

@leonz - that is a very interesting point that you make.

The micro bubble absorbers are designed to remove all air from the system. That is good for systems with expansion tanks, but not for systems with compression tanks as @leonz indicates. I found only one micro bubble remover (the B&G EAS) that was designed to divert air to a compression tank.

I agree I should be fine with the IAS, Airtrol, and the compression tank. These are all simple devices which I prefer and are very low maintenance. They also never wear out.

OF course being a homeowner and part-time stationary engineer I will monitor the system to make sure it is working properly.

Eric

leonz

How many steam/chilled tons/Megawatts Eric?

EricPeterson

@leonz - haha just me and my little old boiler. It's how my father-in-law used to jokingly refer to me.

Steamhead

EricPeterson said:

...... I found only one micro bubble remover (the B&G EAS) that was designed to divert air to a compression tank.

That's our go-to air separator. Not only can it work with plain steel tanks, but it can be installed with either a vertical or horizontal inlet. The outlet is always horizontal.