Coalgun- Puff backs & Explosions

I have been watching this thread sitting on the fence on purchasing a AHS 260 over this explosion issue. I can't not understand how AHS has not responded to this thread or come up with a solution to resolve the issue? The average oil or natural gas boiler cost 1/2 of what a coal boiler is going for.....If you came home and saw your brand new Lennox blow the door off on the floor of your basement the factory would be all over it not to mention all the product enforcement agencies . Am I missing something? This sounds like a very dangerous problem to me not to mention all the confusion on operation of what is to be a trouble free boiler. I know what I went through with the DS hand fed and I just keep asking myself if I want to fuss with something all day or go solar and take on another part time job to pay for it all. When I started mixing pumps and electronics to control a hard fuel device the mystery just seems to begin.
The simple ratchet design on the EFM is looking better every day!!
Mac

The simple ratchet design on the EFM is looking better every day!!
Mac[/quote]

Any coal boiler has its learning curve. To run a coal boiler, it requires some brain activity. A little adjustment can have a great impact on operation and efficiency.

there no problem with the 260 the burn pot is much larger than the 130
BDD

steamup wrote:Any coal boiler has its learning curve. To run a coal boiler, it requires some brain activity. A little adjustment can have a great impact on operation and efficiency.

Steamup,

I agree with your post but based on the posts thus far concerning the explosions, there is more then a "little adjustment" needed to make the AHS 130 safe to operate. I have been burning coal for 5 years and feel it is the best heat source for me. It takes extra work on my end to fill the hopper and dispose of the ash but it is the best option for me. All I want to do is to be able to leave my boiler running unattended for a few hours a day,or sleeping through the night without the fear of explosions damaging my house. I have made adjustments to my controls and hope I figure out a solution by trial and error.

One thing I've done (so far) is to keep my hopper pretty much full. I've never (to this juncture at least) ran it down to where 60-65 lbs. of coal wouldn't fill it right back up to the brim. I wonder if that has anything to do with my not having had any puff-backs to date? I'm also running at 180 degrees. Many who are having puff-backs seem to be running at 150 to 160 degrees. I wonder if that has anything to do with it as well?

There have to be a series of common denominators among those who are experiencing puff-backs, and also among those who are not experiencing them.

I've made the following changes to my S260 boiler system since my huge ka-boom in October:

1. Significantly loosened the sight tube flapper cover---per Darren at AHS, the flapper doesn't have to seal completely when the boiler fan is running. The boiler needs to get air when the fan stops running.

2. Lowered the PLC SV to 130 Fahrenheit from the factory 140 setting.

3. Added fresh air to the bottom of the "tombstone" cover.

4. Removed my type M baro (for now). The ka-boom back in October damaged my original baro. I believe this original baro stuck open, leaving the boiler without draft, resulting in the explosion... I plan on installing a new baro this Saturday.

5. I've also purchased some new 6" black pipe. I plan on significantly increasing the slope of my horizontal run to keep gases flowing to the flue---another job for Saturday...

6. I've also started burning Jeddo coal; versus, the Blashak bagged which I was previously using.

I think the problem is due to multiple factors. In my case, putting a binder clip on the inspection door, allowing it to always be open a bit, and thus allowing a small stream of air over the fire, seems to have made the most difference. I have not had puff-backs (booms, whatever) with any frequency since I added the clip. In addition, when I was first using my S-130 I did not use the "tombstone" cover. Big mistake. When a boom would occur, it would blow back and bend my inspection door. With the cover in place, that issue goes away and it may have operational benefits as Yanche stated previously. I also got rid of my baro damper; for me is was just a source of draft leakage, as I have marginal draft anyway. Just my $ 0.02.

lsayre wrote:One thing I've done (so far) is to keep my hopper pretty much full. I've never (to this juncture at least) ran it down to where 60-65 lbs. of coal wouldn't fill it right back up to the brim. I wonder if that has anything to do with my not having had any puff-backs to date? I'm also running at 180 degrees. Many who are having puff-backs seem to be running at 150 to 160 degrees. I wonder if that has anything to do with it as well?

There have to be a series of common denominators among those who are experiencing puff-backs, and also among those who are not experiencing them.

I have had puff-back problems even when the hopper is nearly full so I am inclined to think that is not a factor--of course if you let the hopper empty and then add coal too fast that will definitely cause puff-backs but in my experience so long as there is any coal in the hopper the level doesn't seem to be related to puff-backs.

I had puff-backs when I was running at 180 but then I also was running at a higher SV. I think there may be a "required" relationship between boiler operating temps and SV.

I share your view that there must be some "common denominators". I am inclined to think that controllable variables have relationships--for example perhaps a boiler temp of 150 works fine IF the SV is adjusted appropriately downward AND draft is sufficiently high.

What I think are definite contributors from reading both the AHS and AA manuals is that the following may contribute to puff backs:
1. Coal Quality
2. Fire bed thickness
3. Introducing too much fresh coal too quickly

The subject of this thread seems like a good reason not to buy such a badly designed unit.

Maybe when someone is killed they will take the time and trouble to fix it.

franco b wrote:The subject of this thread seems like a good reason not to buy such a badly designed unit.

Maybe when someone is killed they will take the time and trouble to fix it.

franco b,

I don't agree that the AHS is a badly designed unit, it is essentially a copy of the tried and true AA units that have been modified with additional designs that are intended to make it more user fiendly with less hands on care. I do believe that there needs to be more research done by the current AHS owners to correct the settings we need to use to make the unit safer, no more puff back explosions. The forum contibutors are doing a fantastic job of finding a solution to the problem. The AHS 130 is a great boiler and made very well. Once we get to the bottom of the problems we will all be much happier and safer.

1. I agree that the full hopper does not eliminate the explosions.
2. The ash dump temperature settings need to be adjusted per forum recommendations.
3. The use of a barometric damper is not necessary for all applications as long as your draft is sufficient.
4. Coal quality may be a problem but it does not explain why I am having explosions this season when I didn't have them in the past. I have been using the same coal for 5 seasons.
5. The ash can't be dumping without the fan running and the coal bed needs to be hot when new coal is added.
6. Is the Fuji controller sufficient are are the new controllers on all new AHS units needed to eliminate the explosions?

We will figure it out ourselves without manufacturer help even though that would be nice.

franco b wrote:The subject of this thread seems like a good reason not to buy such a badly designed unit.

Maybe when someone is killed they will take the time and trouble to fix it.

I'm more convinced that they require proper setup and operation in order to function properly. My wish is that someone from AHS and/or AA would chime in and enlighten us with their full knowledge base and experience with respect to this issue. With 65 years of proud history and many satisfied users as well as a solid historical reputation for making a top shelf product (as supported by the 1953 United States Department Of The Interior's 'Bureau Of Mines' extensive real world test conducted in a families home over a period of several years, and with purely glowing test results and conclusions), this thread should IMHO never have been permitted to get to the point of view expressed above without representation from the manufacturers (though given only what has been seen within this thread I can respect how some would reach the above conclusion).

I believe that permitting the ash grate motor to run only when the fan is on seems to be a huge step in the positive direction. Good draft seems to be a positive factor as well. Another positive is the small window that can be rotated open within the sight tube cover to permit air flow at all times (draft permitting). The 'tombstone' cover seems to be a positive as well.

I'm beginning to wonder if sometimes the sight tube cover hangs up in the closed position after the fan shuts off and this leads to the puff-backs due to volatile gasses evolving from the freshly drawn down coal not having sufficient draft induced air infiltration to burn them off. My thought is that perhaps an electromagnetic device which reverses its polarity would be the ticket to solve this. When the fan is on the electromagnet would pull the sight tube cover (which would be endowed with its own permanent magnet) closed by magnetic attraction, and when the fan shuts off and the polarity of the electromagnet is reversed the sight tube cover would be thrust open by magnetic repulsion.

Or a simpler idea along the same lines would be to have two permanent magnets of the same polarity, one on the sight tube cover bottom and one on the sight tube bottom. The natural tendency (state) would thereby be for the sight tube cover to be thrust open. An additional electromagnet on the sight tube bottom which would be of the opposite polarity and would overpower the fixed magnet on the sight tube would strongly snap the sight tube cover closed only when this electromagnet is energized, and it would only be energized when the fan is running.

One potential drawback here might be the "Curie Temperature", which is the temperature at which permanent magnets lose their magnetism. The materials of the permanent magnets would have to be selected for their very high Curie temperature properties. This may preclude the use of permanent magnets, and limit this concept to only the use of electromagnets.

Well, this thread has reached 13 pages so far and a lot of ideas have been added to the pot.

How many more pages is anybodies guess??? Shouldn't we assemble some collectible data that might lead us down a narrower path?

Perhaps there needs to be a gathering format of some of the many variables into one locations to see what pattern of common denominators may surface???

I believe *Bob* had a substantial start in his post of a couple post above.

Bob wrote:What I think are definite contributors from reading both the AHS and AA manuals is that the following may contribute to puff backs:
1. Coal Quality
2. Fire bed thickness
3. Introducing too much fresh coal too quickly

I totally agree with his 3 comments.
And I'd like to add to *Bob*'s comment number 3.
Yes, introducing much fresh coal quickly is a factor, but I think it is more the problem when doing such just after a longer idle period, see after loafing along for a longer period the response is slower, when cycles are closer together the response is more robust and volatiles are consumed (nearly) as fast as they are generated. Which I believe is NOT the case when response is slow...assuming in both cases the same given amount of coal was added to the pot. Every boiler load is unique as is the seasons...this will make it hard to find a exact cause when looking elsewhere.
And one thing you will NEVER be able to control is "How much coal is added at a given time"...solution will have to come from some where else...Sorry
Make sense? Am I way off here?