AHS S130 Coalgun- Puffbacks & Explosions

The puff backs (or explosions) seem to be an operational issue more prevelent in the smaller 130 size units. I have not heard of problems with the larger units. Maybe owners of the 260 size AHS and AA units can enlighten us on their experience with puff packs.

I would not be concerned about the quality or support from AHS. They are not real active on the forum but will help you when you call the factory.

markviii wrote:My S260 Had Two Puff Back/Explosions Last Night!!!

How severe? Was anything damaged?

Did you have the small (5/8" I believe) port hole in the sight tube cover (flapper) open or closed when the explosions occurred?

Larry:

My 260 had a 2 huge explosions about a month ago: 1 big; and, about 10 seconds later 1 huge. Sounded like a 12 gauge shotgun blast in my basement---blew my type M baro right out of it's hinges. I though I had the problem solved; but, I actually had 2 more small puff-backs this morning while I was getting ready for work...

I'm starting to wish I'd bought an EFM DF520...

Dewey Watkins

I don't know how far back the Axeman-Anderson AA 130 and AA 260 boilers go in history, but I surmise they go back to at least sometime in the 1940's. The Eshland and then AHS units go back to circa 1970, and they are essentially clone spin-offs of the Axeman's. There must be a bunch of these boilers in past and current use. Is it possible for a defect of this nature and proportions to exist for a product that goes back as many decades as this design does (and for a design considered so successful that it spawned clones soon after the AA patents expired)?

I'm only in my fourth week of running mine, and now I'm wondering (and yes, worrying about) when my first puff-back will happen.

The AA130 goes back to 1946.

There is a report on the AA130 listed in this link:

Bureau of Mines Report 4936 Axeman-Andersen Anthratube Boiler

AHS built parts for Axeman Anderson at one time and then copied the boiler design.

The advice in the AA installation and operation instruction warns about too high of a fire in the combustion tube. They state that if the fire gets too high (too thick), puff backs may result. Fire height in the pot is controlled by the ashing ratchet setting.

They also state that the flapper for the site tube to the pot should be open 3/4" when the fan is off to ensure proper draft.

If I read between the lines here, the problem of puffbacks (explosions) is an operational and setup issue, not a design issue. Sufficient air must be over the fire bed to prevent combustible gas buildup and puffbacks.

I am not an expert on the AA or the AHS. I just got my (1951) AA130 operational this spring and have yet to fire it up for the heating season. I will have a better feel for operation in a couple of months.

Note: coal size and quality will have bearing on the setup and puffback issue.

If Axeman's warning is about the fire getting too high (too thick) and that is thereby casuing the puff-backs, then the suggestion made within this thread to raise the height of the fire in order to alleviate the problem certainly comes into question.

lsayre wrote:If Axeman's warning is about the fire getting too high (too thick) and that is thereby casuing the puff-backs, then the suggestion made within this thread to raise the height of the fire in order to alleviate the problem certainly comes into question.

I interpret the Axeman manual differently. I interpret the reference to a "thick fire" as being when the fire is very low in the column.

I am attaching a copy of the relevant page of the Axeman manual.

Bob wrote:

lsayre wrote:If Axeman's warning is about the fire getting too high (too thick) and that is thereby casuing the puff-backs, then the suggestion made within this thread to raise the height of the fire in order to alleviate the problem certainly comes into question.

I interpret the Axeman manual differently. I interpret the reference to a "thick fire" as being when the fire is very low in the column.

I am attaching a copy of the relevant page of the Axeman manual.

I disagree, If the fire is too thin, outfires may result. Anthracite doesn't like shallow beds and burns better in a proper thickness subject to sufficient air and draft.

To thick - the manual says overheating may result also. This could only occur with too much fire, IE too much coal burning or thick bed of coal. The heat will offgas the volatiles from coal not yet burning and result in a explosive gas mixture in the combustion chamber. Also, more coal equals less air volume in the combustion chamber. The explosive limit concetration of gas will build quicker in the smaller volume increasing the likely hood of a puff back.

Read page 9 of the manual under "Building a Fire". The statement "Do not smother fuel bed by completely filling combustion tube by hand as doing so puff-backs may result." further supports the fact that thick fire is a build up of coal in the combustion tube.

Steamup. I am not clear on what you are disagreeing with.

I said: "I interpret the reference to a "thick fire" as being when the fire is very low in the column."

What the Axeman manual says is: "If the fire is too thin (combustion tube 3/4 or more ashed up)...." and "If fire is too thick (combustion tube 1/4 or less ashed up)..."

I hope we can agree that the ash is BELOW the fire. If the ash is below the fire then a thin fire has more ash under it than a thick fire. To put it another way a thin fire is higher in the column than a thick fire.

Due the their auger feed The Axeman's may well be different here, but the AHS design dictates that the combustion chamber is always full of coal, and then some, as the hopper sits atop the combustion chamber and gravity feeds into it.

Interesting..."Combustion tube should be filled up at all times".
That being said, we need to only have the proper ratio to avoid problems...which can go either way.

In summer they recommend adjusting the ratchet stroke to accomplishing 1/2 ash and 1/2 fire in the combustion tube. Too thick of fire (or thin ash) will get a Puff-back.

Seems it would be important to leave ashing grate turned off to allow the fire to get higher...if it hasn't ever got there it may have a hard time being adjusted w/ controller to make happen.

AA owners refer to this as the number of teeth or clicks adjusted to.

OK, here is a newbie/rookie question for you: Is what Axeman calls the combustion tube the same thing that AHS refers to as the sight tube? As far as I can tell, my fire level has al\ways been at or below the sight tube, and I've never seen ash through the sight tube.

lsayre wrote:OK, here is a newbie/rookie question for you: Is what Axeman calls the combustion tube the same thing that AHS refers to as the sight tube? As far as I can tell, my fire level has al\ways been at or below the sight tube, and I've never seen ash through the sight tube.

I think the combustion tube is a round vertical tube where there is a column of coal with ash at the bottom, then a layer of burning coal, and then a layer of coal that is not yet burning. I believe the combustion tube is different than the sight tube, which is not vertical but rather is angled and opens to the side of the boiler.

Bob wrote:Steamup. I am not clear on what you are disagreeing with.

I said: "I interpret the reference to a "thick fire" as being when the fire is very low in the column."

What the Axeman manual says is: "If the fire is too thin (combustion tube 3/4 or more ashed up)...." and "If fire is too thick (combustion tube 1/4 or less ashed up)..."

I hope we can agree that the ash is BELOW the fire. If the ash is below the fire then a thin fire has more ash under it than a thick fire. To put it another way a thin fire is higher in the column than a thick fire.

We maybe looking at it two different ways. I may have have mis-spoke in the previous post. Once I have run my AA more I will have a better feel for it. The instructions state that the combustion tube should be filled up all the way except for the few days after starting a new fire.

Many members recommend priming the tube with ash before a new fire. This makes sense as it starts the fire off at the proper level. Especially true with ASH that gravity feeds coal.

I agree with your point on the height of the fire. I was previously thinking more in terms of coal thickness over the fire, not ash thickness under the fire.

So thinking about this more, with the fire too thick ie low in the combustion tube with 1/4 ash or less and lots of coal over the fire, there is lots of air between the spaces in the coal. This will allow more gas buildup as there is more fresh coal to burn off volatiles from and since heat is present, the right combo of gas and air results in ka-boom. We can call this the AA/AHS coal burners "big bang theory".

So to continue with this theory, to limit explosions, the ash sensor must be adjusted to permit the ash buildup in the combustion tube to limit the coal volume in the combustion tube but not so far as to cause a "thin fire" or high ash buildup that could result in poor performance and outfires.

I will test this theory in the days to come. I may fire this weekend just to get things going to experiment.

Those with puff backs need to note the height of the fire in the coal tube,(and ash level) and see if it fits the theory.

I expect the more experienced members can enlighten us. I have read several posts about puffbacks, but have not researched as to how they resolved their issues.