Stack temperature

[Lopez Mike]

I'm thinking about placing a small dial thermometer near the bottom of the stack of my wood fired VFT boiler. One with a probe that would be in the flow of the stack gasses.

What sort of top temperature would be enough? There are plenty of them available that read up to 600F. I will probably be adding a blower in the future but I can arrange that the steam won't blow on the thermometer probe.

Mike

[fredrosse]

A stack probe thermometer that ranges to 600F may be OK, but some steamboats have stack temperatures that are higher. The same type of thermometers are sold at any wood stove store, and these range up to about 1000F, and cost about $20USD.

A fairly efficient steamboat boiler with economizer should have a stack temperature in the vicinity of 350F - 450F, and without economizer 400F - 500F.

[JonRiley56]

thanks Fred ! I will try to pick up a thermometer. I might be able to get back on the water this weekend.

jon

[Oilking]

Fred beat me to it. I second the Temp range he stated. I have a Dwyer 200-1000F, similar to what's in his picture, that is part of a furnace combustion test kit. If you don't have luck with the stove shops, Brannom Instrumets my be a source in our (WA) area. Mind you price goes up with the pedagree, no sense paying for precision that isn't warranted. You might also be able to order one from Dwyer direct? That's how I got the combustion kit some years back.

Dave

[PeteThePen1]

Hi Folks

Having not logged in for a while, I have homed in on this topic as it is one that I would like to expand with a few more questions.

The context is that I have just had a boiler casing for the my water tube pressure vessel made out of 2mm aluminium. I collected the parts on Wednesday and have been busily screwing them all together ever since. A funnel stub is provided over which the funnel sits and I specified that should also be 2mm aluminium, not thinking about its relationship to the flue gasses. The funnel is a 200mm tube that has an inner tube tapering from 200 to 150 at the top. The taper tube does not start until 100mm up the funnel because the steam dome projects up nearly that far. Doing some sums based on advice from the Forum, I realised that I could not take the 150 mm funnel tube right down to the top of the casing as it would constrict the gas flow. A cross section drawing that may make this clear is shown below:



So, question one is, will that stud be up to the job with typical steam launch stack temperatures?

The second question also needs an introduction. The sheet metal firm that I commissioned to cut and bend up all these pieces has also made the funnel. I explained that it was important that the funnel was light in weight and should be made of thin sheet, less than 1mm thick. Unfortunately, somebody there has homed in on the 1mm measurment and made it of that. It is beautifully made, but weights a ton (well 9.2kg). So, it will have to go back. I am wondering about 1mm aluminium as an alternative as I know that they can get that material easily enough. Will that do the job or am I asking for trouble?

It looks the business, apart from the boiler casing standing a little too high:





Regards

Pete

[Lopez Mike]

An aluminum boiler? I've never heard of that. Any particular reason for it? Weight? Is there a specification for that? I'll bet you are going to get some raised eyebrows about this (to say the least!).

I guess you have thought out the electrolysis issues. Probably less oxidation from the water. But the transitions to steel need to be electrically isolated. Do they make schedule 80 aluminum fittings. Bronze and aluminum don't work together. We'll, they work just fine. The bronze comes out smiling and the aluminum turns to bauxite! Stainless steel eats the aluminum just as bad.

Probably you have this all under control. This will be educational for me.

Mike


By the way, your pictures didn't make it onto your post.

[gondolier88]

Hi Pete,

With the thickness of ali' you are playing with at the flue spigot you might just get away with it, but under forced draft conditions it could easily become weakened, if not even deformed, under the weight of the funnel/flue.

For the funnel I would have been more tempted to use .5mm stainless, well keyed with etch primer it will paint perfectly well, of course, a traditional option is a polished brass funnel...! For the flue I wouldn't contemplate using ali' for one second, stainless steel every time if you have a budget that can cope, mild steel if not. Minimum thickness of 1mm, preferably 1.5mm. It is not only a matter of temperature, but also it's ability to cope with the volatile environment of hot, damp and acidic gases.

Greg

[PeteThePen1]

Hi Folks

Apologies - the photos disappeared because I tidied up my photo folder after copying the IMG codes - how daft is that?

So, the boiler pressure vessel is all stell and weights a lot, but the casing is aluminium to save weight and some expense. However, getting it all cut and bent still cost an arm and a leg...

So now you can see what I muttering about, I would welcome your thoughts.

Regards

Pete

[gondolier88]

By the way, the boat is looking stunning! The casing is a very tidy piece of work, they've done you proud.

Greg

[Lopez Mike]

Much relieved about the boiler being steel! Yes, I would find out what sort of aluminum things are made of and research the strength/temperature relationship. A lot to be said for S.S.

On my VFT, the cone on top is mild steel and the stack is S.S. and it's kinda heavy to be so high up. Once I get some temperature data under hard steaming I might consider an aluminum stack. Or maybe even painted stove pipe. I'm not that excited about my existing stack. What ever happened to blued stove pipe? I haven't seen it in years.

Mike


Mike