# Donkey Boiler



## Prospect (Dec 8, 2011)

I'm doing a redraw of plans for a boiler for my Donkey engine. I had drawn a set 3 years ago based on the boiler in the William Harris book but basically doubling the size and building it from steel. I went by the ASME code which was no problem except for the size of the cleanout fittings. I had the calculations and design checked by a friend who is a Mechanical Engineer and He said it was OK. One of the beauties of 3D Cad is the ability to see a rendered view of your drawing and because of the fitting sizes it looked nasty so The plan is to redraw it based on the Australian Miniature Boiler Code with a few other changes. Due to the difficulty of getting approval nowadays the boiler may never be built but at least I'll have drawings I like. So, I have some questions that someone might help me with.

  My experience is with loco or traction engine boilers where all surfaces of the pressure vessel that are exposed to the products of combustion must be protected by water to prevent burning of the steel. In a vertical boiler what protects the upper part of the firetubes and is there a formula or recomendation for tube lengths? Thanks John

  The proposed boiler barrel is 10" schedule 40 pipe, and the firebox will be either 6" or 8" schedule 40 pipe. The firebox access tube is 3" schedule 80 pipe. The boiler would be 22" high with 17 - 3/4" tubes. it would measure about 14" between the tube sheets


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## GWRdriver (Dec 10, 2011)

Prospect  said:
			
		

> In a vertical boiler what protects the upper part of the firetubes and is there a formula or recomendation for tube lengths?


John,
While I've never seen this answered in respectable text my contention has always been that in the upper 1/3rd of the flues one would expect the flue gasses to have lost considerable heat, or at least enough heat so that the steam itself would absorb enough of the remaining heat to prevent overheating and in the process become to some degree superheated. There is a proven and long accepted formula for flue for ID to length ratio which I know works for horizontal fire tubes but I've never been sure it applied to vertical flues.


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## Jasonb (Dec 10, 2011)

If at the top of your boiler you have a similar sized tube to the firebox that extends down about 3" with the tube plate at the bottom of this, the minimum water level can be set at say 2" from the top of the boiler and there is a steam space all around the top of the boiler but the vertical flues are at leas t1" below water level.

John Haining's Caradoc boiler is done like this.

J


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## Dan Rowe (Dec 10, 2011)

Jason,
The type of boiler you just described is known as a submerged tube or submerged head boiler.

John, I am assuming you are talking about welded cleanout holes with threaded plugs. Hand holes with a dog is what we used on ships which is ASME code for the most part. That might be allowed and would look a lot less klunky. The manholes look similar only big enough to squeeze through.

Dan


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## Prospect (Dec 10, 2011)

Thanks Gentlemen for your replys.

  GWR, Your info confirms much of what I've been told or read. They say that the saturated steam will cool the tubes and as you say superheat or maybe dry the steam. I would like to use copper tubes. Do you think in a vertical boiler considering the tube exposure would copper or steel tubes be better.

  Jason, I have looked at that option. It appeals to me in that it would make attaching the smoke box neater. I'll do another layer in the drawing with that option. Nice thing about CAD.

  Dan, The fittings I was concerned about were the blowdown/ cleanout fittings above the mudsill. By code they were required to be 1" and that required a 1.875" hole for weld in fittings. This other than looking bad made the centerline of the fitting to high above the top of the mudsill in my opinion. I changed the design to use three 1/2" fittings on the mark 3 model. I wanted a large cleanout in the back of the boiler where it doesn't show so much and went with the Australian code and used an eliptical opening 2.5 x 3.25" a few inches above the crown sheet.

  The attachment gives some dimensions. The top tube sheet is 3/4" thick and sits on top of the barrel. I wanted to be able to tap directly into it as I'm not quite sure of the port positions. Is that likely to be a problem? I'm a welder but not B-Pressure and would not be welding this proposed boiler but I couldn't see any way to weld the tube sheet on due to it's thickness if it was down in the barrel.

 Thanks, John


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## steamer (Dec 10, 2011)

Lots of tubes there John...Have you looked at ligiment distance?....might be a bit tight.

I'm told that small boiler shouldn't use real small tubes as they carbon up readily.

Just an observation....

Dave


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## Prospect (Dec 10, 2011)

Dave, I did check the distance between the tubes when I had drawn an 8" diameter firebx but not when I changed it to 6" diameter. I will check that now. John

  Checked it and the distance between the tubes and from the tubes to the firebox inner wall is 3/8" The tubes are 3/4" diameter.


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## GWRdriver (Dec 10, 2011)

Prospect  said:
			
		

> GWR, Your info confirms much of what I've been told or read. They say that the saturated steam will cool the tubes and as you say superheat or maybe dry the steam. I would like to use copper tubes. Do you think in a vertical boiler considering the tube exposure would copper or steel tubes be better.


John,
I would use rolled-in copper, but for no other reason than I know how many small steel boilers have used them with great success over the years. I used the term "superheat" to indicate an increase in steam temperature, however slight, above 212, but drying is a better description of what is actually happening.

The formula for horizontal fire tubes gives an ID for your flue length of around .465" which is close enough to 3/8" Type K or Type L copper. I didn't notice if you named the fuel you plan to use but if it's gas then the .402"/.430" ID of Types K/L would do just fine. In addition the flue-to-grate area ratio of model boilers, which I think yours must be considered, is approximately 1:10, IIRC, which means that sufficient draft and exhaust can be had with a total flue area of 1/10th the grate area. Someone please correct me if I've recalled that ratio incorrectly. Thus for your boiler, with a grate area of let's say 18sq/in, the number of 3/8" Type L copper flues would be 12-14. Whether these guidelines for horizontal boilers apply to verticals, at least so far as flues go, I don't know. I think a vertical can be easily over-flued to the point where much useful heat will go up the stack.


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## Dan Rowe (Dec 11, 2011)

John,
I just happened to have a set of plans for a 6" copper vertical boiler handy. These plans were sold by Saturated Steam in the 80's. The boiler was designed by F. B. Gittins of Rugby England.

The distance between the tube sheets is 7.25" and the design water line is 3" below the top tube sheet. Here is a photo of the boiler and the hand/cleanout holes I mentioned can be seen just above the mud ring.










This is a sketch I made of a submerged tube vertical boiler.

Dan


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## steamer (Dec 11, 2011)

Actually GWR...minor point but it is the degrees over the saturated steam temperature at the operating pressure.  The temperature above 212 would be superheated steam at atmospheric pressure and of course below that pressure....but above that pressure it would be at best saturated steam, or a mixture of steam and water or just water.

A mollier diagram would show this quite clearly.

Dave


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## Jasonb (Dec 11, 2011)

Dan that sketch is just like the boiler I mentioned

John if you want to see a reduced drawing PM me.

J


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## Prospect (Dec 11, 2011)

GWRdriver  said:
			
		

> The formula for horizontal fire tubes gives an ID for your flue length of around .465" which is close enough to 3/8" Type K or Type L copper. I didn't notice if you named the fuel you plan to use but if it's gas then the .402"/.430" ID of Types K/L would do just fine. In addition the flue-to-grate area ratio of model boilers, which I think yours must be considered, is approximately 1:10, IIRC, which means that sufficient draft and exhaust can be had with a total flue area of 1/10th the grate area. Someone please correct me if I've recalled that ratio incorrectly. Thus for your boiler, with a grate area of let's say 18sq/in, the number of 3/8" Type L copper flues would be 12-14. Whether these guidelines for horizontal boilers apply to verticals, at least so far as flues go, I don't know. I think a vertical can be easily over-flued to the point where much useful heat will go up the stack.



 GWR, This boiler would be gas fired (propane ). I had wondered if with 3/4" tubes if I wasn't creating a torch to cook my smokebox and was wondering about an arch of some kind. Did a quick redraw with 14 - 1/2" od tubes and a submerged flue design as Dan and Jason have suggested. It looks interesting as the upper submerged section would act as a stay for the upper tube sheet if necessary. John


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## GWRdriver (Dec 13, 2011)

steamer  said:
			
		

> Actually GWR...minor point but it is the degrees over the saturated steam temperature at the operating pressure.Dave


Dave,
Yes I realize that, but for the moment I decided for simplicity's sake not to go into it, just as I've decided not to point out that because the flue length has changed so has the length-to-diameter ratio, if we accept that the usual fire tube formula applies to vertical tubes, which I'm not sure of. So many slippery slopes . . . :


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## steamer (Dec 13, 2011)

GWR  No worries mate!

It's steam....it's self integrating anyway......

 ;D


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## Prospect (Dec 14, 2011)

Did some calculations today. On a submerged tube Boiler with copper tubes some dimensions I would like to go with are as follows.

1. 2" steam space above high water level.

2. A 6" o.d. Extention (smokebox ?) extending from the bottom of the upper tube sheet to the top of the boiler top sheet long enough to give a 3" operating water level measured from the bottom trycock to the top trycock. Aprox 5.75" long. Sorry if that sounds confusing. This would give an exposed to water tube length of 7.625" There would be 14 -3/8" tubes (actual .5"o.d. with .049" wall)

3. 10.75" o.d. boiler shell with a 6.625" o.d. firebox giving a water leg width of about 1 .625".

4. The hydro test volume (calculated) would be 4.24 Imp. gals (19.283 liters).
  3.66 Imp. gals (17.31 liters) at operating level or middle trycock.

5. The total heating surface would be 491.64 Sq inches which includes that upper extention ( internal smokebox?) I'm not sure what you would call that piece.

6. The grate to flue ratio would about 10.25 to 1.
  I can see I'm wrong on this ratio. I used the tube o.d. rather than i.d. Correct ratio would be closer to 15.9 to 1. This doesn't allow for any restriction in grate area due to burner jets.

Any advice would be appreciated. John


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## Prospect (Dec 16, 2011)

Hi, further to this boiler, I've been working on a spreadsheet where I can change dimensions and not make me wish I paid more attention in math class. While a work in progress it's functional.

GWR, I have searched the internet and my own book collection which is huge and I can't find any definite info on grate to flue area on model vertical boilers. On full scale boilers it appears to be about 5 to1. Just looking at the model drawing 5 to 1 appears to be excessive due to the short flue length, so I am going to go with 10 to 1 until I find other info.

In the short term could someone let me know if the mudring enters into the heating surface calculations or if it is considered a none heating surface. It would appear to me that the mudring would actually draw heat away from the water heating surface but is it included in the heating surface calcs.

Thanks for any replys, John


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## Jasonb (Dec 17, 2011)

Have a read through this thread about another vertical boiler, I'm sure we talked about flue sizes there quite a bit.

http://www.homemodelenginemachinist.com/index.php?topic=12736.0

J


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## Prospect (Dec 17, 2011)

Thanks Jason, Interesting thread. I'll run the tube calculations shown in the thread later. I finally found my copy of the Model Engineers Handbook and I think there is some info on tube calculations there too. John


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## Prospect (Dec 20, 2011)

OK, doing the steam consumption calcs on this donkey engine set with the engine set at its maximum load (100psi), would you design the boiler steam generation (heating surface) for that demand? I think that full load would only occur for a fraction of the running time. My concern is that to achieve that constant output might require a fairly large increase in heating surface (more tubes) when I would like to keep things fairly simple? John


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## Dan Rowe (Dec 20, 2011)

John,
I saw on the other thread you are working the problem with 120 rpm. Well I will say it has been a number of years since I have seen steam winches in regular service but that seams a bit high and as you say that is not continuous running.

With logging the cable is only under load while lifting just like the old ship rigging I saw as a cadet. The duty cycle has to be less than 50%.

Did you work the calculations for the original design for heating surface? If you worked that backwards you might get close to the model design RPM for your heating surface check. 

Dan


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## GWRdriver (Dec 20, 2011)

Prospect  said:
			
		

> GWR, I have searched the internet and my own book collection which is huge and I can't find any definite info on grate to flue area on model vertical boilers. On full scale boilers it appears to be about 5 to1. Just looking at the model drawing 5 to 1 appears to be excessive due to the short flue length, so I am going to go with 10 to 1 until I find other info.


John,
I almost certainly I would have gotten (and hopefully accurately remembered) this ratio from one of three sources, either KN Harris, Martin Evans, or Jim Ewins, all of who wrote in Model Engineer. I am also certain this would have been in the context of horizontal locomotive type boilers in the cases of Evans an Ewins, but could have been either horiz or vert with Harris. How's THAT for authoritative and conclusive evidence!


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## Dan Rowe (Dec 21, 2011)

John,
I checked both Martin Evans book_ Model Locomotive Boilers_ and the boiler book by K.N. Harris and I did not find anything about the ratio of grate to tube area for a vertical boiler in writing.

The formula given by Martin Evans for length to area of tubes is based on best practice for full size locomotive type boilers so using it on vertical boilers will not have any basis to proven designs for either full size practice or model work in my opinion.

N.K. Harris does give us a vertical design to reverse engineer. If we look at design #5 and work out the ratio of the grate area to the tube area I got 4.87: 1. We could also try the length to area on the tubes but they need to be as long as possible so why should we really bother with that math?

I checked the 6" vertical boiler I mentioned in this thread for grate to tube area. It has a single flue tube that is larger for a superheater element which I assumed to have the same cross section as the other tubes with the superheater installed. The ratio I worked out is 4.3:1. This boiler has a 5" OD 13 SWG firebox and 52 3/8" OD 22 SWG tubes 7-11/16" long. It has a single flue tube with superheater element 1" OD 16 SWG. I did the calculations with 53 of the 3/8" tubes for simplicity.

It seams to me that a ratio of 5:1 is a much better design goal than the 10:1 ratio given by GWR from memory.

If you are working the heating surface calculations using Harris as a guide please give the bore and stroke of the engine and design RPM in this thread. I have done more than a few of these calculations over the years but as to this point I have never built a model boiler. 

Dan


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## Dan Rowe (Dec 21, 2011)

Prospect  said:
			
		

> In the short term could someone let me know if the mudring enters into the heating surface calculations or if it is considered a none heating surface. It would appear to me that the mudring would actually draw heat away from the water heating surface but is it included in the heating surface calcs.



John,
Any surface that has water on one side and combustion gas on the other side can be considered heating surface. So no the mud ring does not count. If you are going with the submerged tube design the whole upper head and chamber below the the design water line does count. I did a few calculations on a small one of the submerged tube designs and there is very little if any loss of heating surface from a normal design with 2/3 of the tube submerged.

The #5 in Harris has the water line at 2/3 of the tube length and 60 sqin of heating surface. This is was my reference point.

Dan


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## Dan Rowe (Dec 21, 2011)

John,
The reason I know about submerged tube boilers is because they were used with early Shay locomotives.

None of the Shay vertical boilers survived and the drawings are not known to exist. We do have some engineering knowledge of them because the main dimensions were listed in early catalogs.

They came in 2 sizes. The 7 ton Shay with 2-7"x7" cylinders had a vertical boiler with a 44" OD shell 78" tall. The 125 tubes were 2" OD and 30" long. I made two assumptions a 3" mud ring making the firebox 38" ID and simply use the OD for the tubes. This gave me a 2.9:1 ratio for the firebox to tube area.

The 9 ton Shay had 2-8"x8" cylinders and had a boiler shell 48" OD and 90" tall. The 155 tubes were 2" OD and 34" long. Making the same two assumptions the firebox is 42" ID and use 2" for the tubes. I got 2.8:1 for the firebox to tube area ratio.

Now it is clear to me at least that the tubes are really short on a submerged tube design and most likely a standard design would use the very same tube OD as 2" is a very common boiler tube size. So that throws any rule of thumb relating the tube length to diameter ratios out the window. We could make a rule for normal vertical boilers and one for submerged tubes if we had a bunch of data points but I do not think a single simple rule of thumb will cover both types of vertical boilers.

Dan


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## Prospect (Dec 21, 2011)

Dan Rowe  said:
			
		

> John,
> I saw on the other thread you are working the problem with 120 rpm. Well I will say it has been a number of years since I have seen steam winches in regular service but that seams a bit high and as you say that is not continuous running.
> 
> With logging the cable is only under load while lifting just like the old ship rigging I saw as a cadet. The duty cycle has to be less than 50%.
> ...



Dan, 120 was the engine crankshaft rpm. The winch drum speed would be 30rpm. Playing with my toy this afternoon I think 250 crankshaft rpm would be a more realistic speed for the engine.

After reading your posts, I checked the heating surface of the W. M. Harris model I scaled up from, and the heating surface is about 322 sq. in. with an engine set adjusted piston area of 3.08 sq. in. and total displacement of 3.08 C.I. My donkey engine was scaled up by 2 and thus the engine piston area and displacement are over 4 times the origional model. This seems to make the heating surface of my boiler design small in comparison. 615 sq. in. vs 322 sq. in.

I'm going to have to think on this a bit. John


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## Dan Rowe (Dec 21, 2011)

John,
The point I was trying to make is you can reverse engineer the original design. As this is a simple boiler the safe assumption is that it will evaporate 1 cu in of water for every 100 sq in of heating surface. This is Chapter 1 of N.K. Harris. Now with the boiler design pressure you can figure out how much steam the original boiler design can produce. This figure can be used to get a ball park figure for the RPM of the original design.

You can change the RPM but that might require a larger boiler. At any rate the same assumption of 1 cu in of water evaporated for every 100 sq in of heating surface apples to the larger model. You need determine the heating surface required for your chosen engine RPM.

I knew you were talking about the crank speed with 120 RPM and I still think that is fast but it is your model so you are the one to pick the design RPM and match the boiler heating surface to the steam requirement of the engine.

My copy of _Model Boilers & Boiler Making_ is somewhat dog eared form too many trips to in my sea bag when I was a Marine Engineer.
Dan

Edit: the evaporation rate of 1 cu in water per 100 sq in of H.S. is per minute.


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## Prospect (Dec 21, 2011)

GWR, I quite sure I've seen the 10 to 1 ratio somewhere too. I dug out my very crisp (literally) Little Engines drawings for their Pacific Loco. and checked the total flue (6.75sq.in.) area and the grate area (144 sq.in.). This gives a ratio of about 21 to 1. My Pacific loco. boiler was built by a licenced company as I wanted a stamped code boiler and when I measured it today the ratio is 15 to 1. While my loco has never run on a track, it has spent many hours running on its roller stand and its boiler works well. As Dan has suggested I checked the no.5 boiler in the Harris book and it is about 5 to 1. Lots and lots of tubes. Doesn't look like it would be fun to build or maintain. All this does confuse things a bit. I know 2 gentlemen both retired now who have built 1/3 scale traction engines. One has his first class steam ticket and the other a third class. After Christmas I'll try and get there opinions on the subject. Thanks again to all for your help. John


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## Prospect (Dec 21, 2011)

Thanks Dan. I do appreciate your input. It makes me think which is a good thing. John


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## Dan Rowe (Dec 21, 2011)

Prospect  said:
			
		

> One has his first class steam ticket and the other a third class.



John,
I am also retired but for what is worth my ticket said Chief Engineer unlimited horse power.

Dan


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## GWRdriver (Dec 21, 2011)

John,
Perhaps compiling an average of flue area ratios of a number known (and successful) vertical model boilers would give us a reasonable number to use, lacking any more definitive value. My recollection could certainly not be considered _definitive_, I wouldn't. A friend of mine produces vertical steel boilers commercially (installed in his 7.5"ga locomotives) of maybe 12" diam and it would be interesting to know the flue area ratio of those boilers. They are known as free-steamers, but then he uses a large number of small flues over a strong propane burner. I also have the drawings for the old "Dianna" (model) steam launch boiler. There have been many of those built, but I've never read a 1st-hand report (or any report) of their steaming attributes. I'll try to pull out those drawings and pull a ratio on that boiler. One thing these two boilers share in common, aside from a large number of small flues, is they are short and squat, larger in diameter than they are tall, so the flues need to be smaller in diameter.


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## Dan Rowe (Dec 22, 2011)

Prospect  said:
			
		

> I checked the no.5 boiler in the Harris book and it is about 5 to 1. Lots and lots of tubes. Doesn't look like it would be fun to build or maintain.



John,
Yes it is a lot of tubes in a small space. If we check the length of the tube to the internal diameter squared I got the length is about 65 times the diameter squared. This is what Martin Evans recommends for a locomotive boiler. He states that the best practice for full size locomotive boilers is 50 to 70 times the inner diameter of the tube squared and uses a figure in the middle of that range.

Now maybe you can see my point of the dangers of using design rules for locomotive boilers for vertical boilers. 

The only bit I could find by Jim Ewins on the web is this link. He gives 80 for Kt which is the same ratio of tube length divided by the tube diameter squared. Again this is for a locomotive boiler not a vertical boiler.
http://www.modeleng.org/articles/loco_research_je.pdf

I did find a table of vertical boiler dimensions in _Boilers Types and Design_ ICS 1907.
The table lists 14 boilers ranging from 20" to 48" OD. I calculated the ratios of the grate area to the tube areas given and the values ranged from 3.4 to 5 to one. The average of the 14 boilers listed worked out to exactly 4:1 for the grate area to the tube area.

The grate sizes for the 48" boiler is 42.5" OD and the grate diameter for the 44" boiler is 38" OD in the table so my assumptions for the Shay submerged tube boilers was a good estimate.

I can work out the L/d2 ratios for the table for vertical boilers given in the table to get a ball park figure for vertical boilers as it is a good historical source of information, and that is what was done by other model engineers for locomotive type boilers.

Now why do you not want to simply double the size of the boiler like you did the engine? That seams like the simple approach to me. And speaking of successful vertical boilers it seams to me that the original W. Harris donkey boiler or the steam roller boiler have to fall into that category as I am sure many examples have been made to those plans.

Dan


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## Dan Rowe (Dec 22, 2011)

John,
I consider this type of discussion a learning exercise and a refresher course for more experienced boiler makers.

As most of the readers of this section of the forum have a copy of K.N. Harris handy and most likely have worked a few boiler calculations could you PLEASE give us the bore and stroke of the engine in question so we can use Chapter 1 of the book to follow along.

Dan


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## Prospect (Dec 22, 2011)

Dan, The twin engine bore is 2" and the stroke is 2". The pston rod is 3/8" in diameter. I know there is controversy about it, but I used a Viton o-ring for a piston rings. I've always had good luck with o-rings. The cylinder blocks are cast iron and the slide valves are bronze. John


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## GWRdriver (Dec 22, 2011)

I don't know why this should raise a controversy? A couple of things come to mind . . . .
1. Many model steam cylinders now operate perfectly happily with O-rings, as long as the ring material and cylinder wall finish is appropriate for the application and the grooves are properly proportioned. Yes 2"OD is a bit out of the ordinary as most O-ringed model cylinders are smaller, but _most_ ain't *All.*
2. In the end do whatever you want to do. If you like and have time, report your experiences. It's the way model engineering works, . . . or used to.


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## Prospect (Dec 22, 2011)

GWR, The main reason I use o-rings is that i use them frequently on the farm and are readily available. In three steam engines the previous 2 being smaller bores, they,ve worked well. it's very true that the initial cylinder wall finish is important and one has to remember that 0-rings swell a touch in fluids and that has to be taken into consideration. On this engine I bored the cylinders, lightly removed the bit of fur with a brake hone and then lapped or polished the bores using an extended aluminum piston with 3 quadrings so that I could run one ring completely through. I used some Bon Ami and oil for abrasive. It was fast and the finish was very nice. John


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## Dan Rowe (Dec 23, 2011)

John,
The best answer to this is found in K.N Harris Chapter 8 about tubes and spacing.

K.N. Harris gives the proper credit to the formula found in both Martin Evens books and _Model Engineers Handbook_ by Tubal Cain. The formula L/D2=60 to 80 where L is the tube length and D is the tube external diameter was produced by the investigations of C.M. Keiller.


I have read this several times over the years and missed the differences. The formula given by Martin Evans is very similar but slightly different. Slightly transposed the formula is L/d2=65. In this formula given by Martin Evans d is the internal diameter. Tubal Cain gives the same formula from Martin Evans book and it is the same with source credit given.

Martin Evans says that the length of the tubes divided by the square of the inner diameter is 50-70 for the most successful FULL size locomotives.

Tubal Cain says The most economical length to diameter for both models and full size boilers with induced draft is 70-90. Then he mentioned that that tests on FULL sized locomotives proved that the last 25% of the tubes only evaporated 10% of the total output.

The tests at Altoona PA on of course full size locomotives indicated that no advantage was gained by having a tube longer than 100-120 times the length of the inner diameter. This is from _Steam Locomotive Design: Data and Formulae_ E.A. Phillipson 1936.

Tubal Cain then says that Martin Evans formula leads to ratios of 25-30 for loco boilers. This is the L/d ratio not the L/d2 ratio.

L is defined as tube length and d is defined as tube internal diameter.

Tubal Cain then talks about vertical boilers with natural or slight forced draft, and states that the L/d rations are as small as 15 due to mechanical issues with very small tubes.

To answer the grate to flue area question we turn back to K.N. Harris Chapter 8. The type of draft is an important consideration in selection a grate to flue area ratio. The numbers given by K.N. Harris for a locomotive boiler doing locomotive work or with induced draft is the tube area should be 1/7 the grate area and can be made as high as 1/6. The ratio for natural draft is given as 1/4 as a good all round figure. This is the same figure I got with the ICS vertical boiler data.

Dan


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## steamer (Dec 23, 2011)

I don't see any reason why Orings should be controversial. I use solid teflon piston rings on my launch engine and have run 3 seasons now at 165 psi. with cast iron cylinders...with no worries or issues..

Orings should work a treat!

Dave


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## Dan Rowe (Dec 24, 2011)

John, 
Here is the ICS vertical boiler data. The Stuart Swan is a 2.25"x2" twin cylinder vertical engine that can produce 3 HP @ 800 RPM and 100 Psi. I have a Cygnet which is the single cylinder version.

You should be able to produce 1.5-2 HP with that engine depending on what RPM and boiler pressure you choose.

Proportions of Vertical Boilers ICS 1907

HP  Shell Height  Tube  Tube L   Tubes  H.S.  Grate  Grate  Total Tube
    OD          OD           #         OD   Area   Area
    In   Ft   In   In   Ft  In         SqFt  In   SqFt   SqFt

34   48   10  8    2.5  7   8      91  340   42.5   9.722  2.584
28   44   11  4.5  2.5  8   5.25   64   282  38    8.08   1.8176
24   42   9   4.5   2   6   7.375  96   247  36    7.068   1.6992
23   40   9   8.5   2   6   11.25  85   233  34.25  6.398   1.5045
20   38   8   9.25  2   6   1      85   201  32.5   5.76   1.5045
17   36   8   8.5   2   6   1.25   73   177  30.5   5.073   1.2921
15   34   8   7.25  2   6   1.5     61  152  28.25  4.352  1.0797
12   32   7   6.25  2   5   1      61  124  26.5   3.83   1.0797
11   30   7   6.75  2   5   2.25    55  117  24.5   3.343  0.9735
10   28   7   8.5   2   5   5      42  100  232    2.885  0.7434
8    26   7   4.25  2   5   2      37   81   31     2.335  0.6549
6.8  24   7   10.75 2   5   9.5     26   68   19     1.967  0.4602
5    22   7   4.25  2   5   4      22   53   17     1.527  0.3894
4    20   8   3.5   2   6   4.5     14   42   15     1.227  0.2478

When I bought the plans and the castings for the Saturated Steam vertical boiler I asked about the steam capacity of the boiler. They contacted the designer and he did not know no one had ever asked that question. I still do not know but I see a large heavy package under the tree that I think is the 6" and 5" copper tube I need to build the boiler so I will have to build it to find the answer.

Dan


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## Prospect (Dec 25, 2011)

Thanks Dan, Interesting information. I'll work it back to my size and see how it looks. John


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## Dan Rowe (Dec 25, 2011)

Hey guys I would appreciate some feed back here so I know if I am cutting the wrong side of the tree branch that I am standing on again.

John
Now that I know that the bore and stroke of the original W.M. Harris engine is a 1x1 twin and your calculated boiler H.S. of 322 in2 the data can be used to approximate the RPM of the original design.

This calculation is nearly the same as the example problem in K.N. Harris Chapter 1. The area of the piston is .785 in2. That times the stroke of 1 gives us .785 in3 per stroke. There is no need with this type of rough calculation to consider the diameter of the piston rod which is how K.N. Harris made the calculations.

The cylinder is double acting and there are two cylinders so 4 times .785 in3 gives us 3.14 in3 per engine revolution.

The H.S. of the boiler is 322 in2 so using the figure given for a pot boiler as a conservative figure we can evaporate 1 in3 of water for every 100 in2 of H.S. per minute. That gives us an evaporation rate of 3.22 in3 of water per minute. 

Turning to Table 1 we find from the steam tables provided that @ 100 Psi 1 in3 of water converts to 237 in3 of steam. That times the evaporation rate gives us 763.14 in3 of steam per minute @ 100 Psi.

Now we can calculate the revolutions per minute by dividing the boiler steam output by the volume of the engine per revolution and the answer is 243 RPM.

Well it looks like 250 RPM is a good design number for the engine. The scaled up calculations go just like the example in the book with a 2x 2 twin cylinder engine.

I did get copper for the Saturated Steam boiler so I will be doing the calculations for that boiler again. 

Dan


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## Prospect (Dec 27, 2011)

Hello again, The present configuration of my boiler uses 20 .625 o.d. tubes. This would give me a heating surface of about 500 Sq.In. I think this is more than adequate for the demand. I do have 5 tube patterns ranging from 14 - .625 tubes up to 31 - .500 tubes in Excell so It's easy to fiddle with. Most of the tube patterns seem to produce a heating surface in the 475 to 540 Sq. In. area, so 500 was chosen. The 20 - .625" pattern has a web spacing of between .450" and .475" spacing.

  As I've mentioned I want to stay with commonly available sizes of Pipe. Looking at the attached drawing the water leg would have a spacing of 1.625. Going to a 7" pipe would reduce that space to about .750" which would increase the heating surface by about 50 sq. in.,but I think that spacing would be too narrow.

  The upper tube sheet extention would use the same 6" pipe and thus the same spacing as the water leg. I'm wondering if that is going to leave enough steam space? I also wonder if the bottom tricock which is .5" above the bottom of the upper tube sheet and would be the absolute minimum water level should be raised?

  Thanks for your input, John


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## GWRdriver (Dec 28, 2011)

Prospect  said:
			
		

> I want to stay with commonly available sizes of Pipe. . . . Going to a 7" pipe would reduce that space to about .750" [snip] I'm wondering if that is going to leave enough steam space?


John,
I don't see a 7" steel pipe listed in schedules very often, probably because like 5" and 7" copper those sizes have been discontinued as stock sizes. Engineers and designers went to a 4"-6"-8" standard years ago. If you need enough of it the mills will draw it for you, but otherwise you won't find it in warehouses except as old old stock. If you haven't done so already, I have always found it handy to keep a listing of standard pipe sizes in my notebook. Here's a good one for steel: http://www.google.com/url?sa=t&rct=...sg=AFQjCNGBL0q-0BCv1Q8Ew4gRsmd_HsR97Q&cad=rja  I keep them for copper also.

If it was me I would want a larger steam space, but this isn't a deal-breaker depending upon demand. If it's a "working" boiler, one which will carry a load, then as steam space is reduced you can expect the firing rate (fuel & water) to need to be increased, that is, more fuel and more water per time period, to the point where firing might be continuous. A flash boiler, which typically has essentially no steam space, carries this to its logical extreme where heat and water must be continuously force-fed into the system. A demonstration or test boiler usually has less demand, so the steam is drawn off at a slower rate, so it doesn't require continuous firing although the basic thermodynamics, energy-in for energy-out, are about the same.


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## Prospect (Dec 28, 2011)

GWR Thanks for the link. The site is a lot simpler and clearer than the one I was using.

  The steam space does concern me. I think I'll lower the upper tube plate and see how it looks.

I don't think it will effect the heating surface that much.

 I had though of maybe adding a - call it a steam dryer - into the well at the top of the boiler since it

is such a large availabe space, but if it was likely to prime and mounted after throttle it can cause 

some very erratic engine operation. I'm not sure if I would want to mount it ahead. Nice space maybe 

for a feedwater heater but I'm getting ahead of myself. John


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## te_gui (Dec 28, 2011)

DOM tubing comes in a 7" ID. It may have a heavier wall than you want, but that's easily remedied. If you know any hydraulic repair shops you might check and see if they have any old cylinder barrels you could whack a length off. It's kind of miserable stuff to machine, stringy chips and all, but plenty of strength for a boiler shell. 

Just a thought 
Brian


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## Dan Rowe (Dec 28, 2011)

John did mention in the very first post that he was building to AMBSC rules. If that is the case not just any old chunk of tube from the scrap pile will be suitable. The types of steel allowed in the AMBSC steel code are listed in the front. Some of them are AS specs which are not easy to find on this side of the pond.

The thing to search for is Pressure Vessel Quality or PVQ steel.

Here is a post by a steel boiler maker in the US who has been building quality steel and a few copper boilers for a while now that states the types of steel suitable for boiler construction.
http://www.chaski.org/homemachinist/viewtopic.php?f=8&t=82955

Anyone in the US looking for State boiler code information can check this link:
http://www.homemodelenginemachinist.com/index.php?topic=8846.0

I do think it will be hard to find 7" PVQ tube but I have not searched. I had a similar problem as I needed 5" copper for the Saturated Steam boiler. There is a guy on ebay selling 5" copper at this time so I bought 16" so I am now redrawing the whole plan set because it used true 6" and 5" tube and the US standard is 1/8" larger.

I will start a thread on that boiler when it makes it to the workbench stage.

Dan


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## te_gui (Dec 28, 2011)

I'm by no means a boiler expert, but I routinely use DOM tubing in various sizes for hydraulic cylinder designs with working pressures exceeding 3500 psi with a 3x minimum burst pressure. Typical yield is around 70 ksi for A513/1020 DOM with good weldability. Obviously establishing the pedigree for a chunk of cylinder would be difficult if a specific certification with heat and melt number is required, but this material is so widely used in the cylinder business by all the OEM's I would be very surprised if it was anything else but. I have never seen the PVQ designation on a steel spec sheet, but would assume it applies to this. I took a look at the links you referenced, and in Marty Knox's first post he mentions 

"Up to about 5 1/2 - 6" diameter and 100 PSI copper has many advantages,above that,low carbon steel is the material of choice. I worked as a boilermaker for DuPont. They have a whole department that works on material specifications. They never hesitate to buy the best material for the application. We worked with a wide variety of materials - Inconel, Hastelloy, and Carpenter 20 to name a few - yet all our boilers were low carbon steel!"

I think most people would consider Marty one of the leading experts in boiler construction, I know I have certainly benefited from his contributions to various forums over the years. It seems like we are definitely in agreement here with this material. 



Brian


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## Dan Rowe (Dec 28, 2011)

Brian,
I agree that Marty Knox is one of the most leading boiler experts around. He has several very well written articles in hobby and historic preservation magazines.

The important bit he had to say about the steel to use and why is this:

"The first quality of a boiler material that comes to mind is ductility - you want a material that will withstand many,many heating and cooling cycles, with out fatiguing and cracking. Strength is almost secondary - the strength of a boiler is in its structure." 

I have not had much luck with PVQ in searches but others have mentioned it with steel boilers on this forum. Here is a link to a firm that carries the types of steel Marty mentioned in his post.

http://www.amerpipe.com/products/carbon-pipe/a53/specifications

A53 was not mentioned by Marty I got that from the AMBSC Part 2 1995 Steel Boilers.

Dan


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## te_gui (Dec 29, 2011)

1020 is a low carbon steel, can certainly take lots of pressure cycles, based on my hydraulic experience.My only question would be the heating/cooling. It has a similar carbon content to the A53 spec you referenced, so potentially about the same ductility. The pipe spec didn't give a % elongation which would help equate the two materials better. 

 I'm a mechanical engineer by education and experience, but not a boiler maker. I might mention as a side note, I helped restore a full size Willamette logging donkey and ran the calculations necessary to get the boiler certified here in Washington by the state boiler board, but that had more to do with the existing material thicknesses and riveted joints. 

I'm curious about the Australian materials, I should get a copy of their code. My company has a plant in Brisbane, with a full engineering staff. I could probably get some of the Australian material specs crossed into US or ISO material equivalents with my colleagues assistance down under if there was interest.

Brian


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## Dan Rowe (Dec 29, 2011)

Brian,
I could tell you were an engineer by your second post. I am a retired Marine Engineer also by education and experience.

The weak point of the AMBSC for some one in the US is the specs do not match what I can find. 

I think that this issue is important enough to have its own thread. I will start with Marty Knox's post on the specs for an ASME steel boiler and add the AMBSC steel specs so maybe home builders can source the proper steel to make boilers with.

Dan

Edit: For boiler steel specs see:
http://www.homemodelenginemachinist.com/index.php?topic=17071


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## Prospect (Dec 29, 2011)

If it was me I would want a larger steam space, but this isn't a deal-breaker depending upon demand. 
[/quote]

 GWR, I think you'll appreciate this. I was out in the shop today and out of curiousity I tacked together some pipe which gave me the approximate spacing of the upper drum to boiler shell which is about 1,625". Filled with non pressurised water and with a venturi mounted on the outlet location using air and filled to 2" from the top it sucked water like a darn. 3" down there was just a mist. It would be very interesting to make something up out of lexan so you could actually see what's happening. My current attached drawing is 3" to high water and 4.5" to middle trycock. This has dropped the heat surface from 500 to 450 sq in. and the operating water level to 3.5 Imp Gals. I'm really thinking that the maximum load I'm basing my engine demand calcs. on is probably excessive, but I.ve been wrong before - mostly. I was pleasantly surprised to find out that the Boiler Inspector for my area is a fellow I know who is very involved with local museums and "Model Engineers". I'm going to try and get a hold of him after the new year in case He does the snowbird thing. Take care, John


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## GWRdriver (Jan 10, 2012)

Sorry for not responding sooner . . . I've been busy building a boiler . . .


			
				Prospect  said:
			
		

> I was pleasantly surprised to find out that the Boiler Inspector for my area is a fellow I know who is very involved with local museums and "Model Engineers".


John,
I would be pleasantly surprised and very thankful to discover I had an ME-friendly boiler inspector too. When I started out our State (TN) had a chief inspector whose career began in the 1930s and he was rigid and inflexible and would not allow that amateurs could build or operate a boiler safely. Thankfully his preoccupation was with backwoods "skonk works" mine and sawmill boilers and we ran under the radar until he retired. Keep posting on your progress. And I would do the snowbird thing also, if I could.


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## Dan Rowe (Jan 10, 2012)

GWRdriver  said:
			
		

> I've been busy building a boiler . . .



 th_wwp


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## GWRdriver (Jan 11, 2012)

In a new thread . . sometime soon.


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## Prospect (Feb 4, 2012)

Things got busy between farm work and Med Appoints since the new year so I.ve finally got back to my drawings. I talked to a Boiler Inspector ( not the one I want Yet ) and He gave some general info which I was already aware of, but talk is good.

I currently doing some drawings for weld preps. The lady who cleans house for me decided quite rightly that my Library needed cleaning. Unfortunately I can't find the books I need now - yet. Could someone enlighten me in regards to the asme code and butt welds, if I'm using a 60 degree combined angle for two plates, what is the required unbevelled root size and separation?

Thanks for your help. John


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## Maryak (Feb 4, 2012)

Prospect  said:
			
		

> what is the required unbevelled root size and separation?
> 
> Thanks for your help. John



I think that has something to do with the thickness of the plate.

Hope this helps

Best Regards
Bob


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## steamer (Feb 5, 2012)

A sketch of the joint would help,,,,

Dave


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## Prospect (Feb 5, 2012)

Sorry. This should be clearer. All other joints are similar but may be bevelled and welded from both sides depending on access. John

Found My Australian code book so far at least. The recomendation in it is for a maximum dimension of 1.5 mm, so that's what I'm going to draw. Also talked to a B-Pressure welder welding repair sleeves on a live 36" oil pipeline close by and He said 1/16".


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## pkastagehand (Apr 30, 2012)

Prospect  said:
			
		

> Hi, further to this boiler, I've been working on a spreadsheet where I can change dimensions and not make me wish I paid more attention in math class. While a work in progress it's functional.
> 
> <other stuff clipped>
> 
> Thanks for any replys, John



Have you done any more on this spreadsheet? Willing to share it? I was thinking of doing something similar but didn't want to reinvent the wheel, so to speak...

Paul


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## Prospect (Apr 30, 2012)

Hi The spreadsheet is kind of a hodgepodge mess specific to where my mind was at the moment. I just haven't had time since the beginning of the year to play much. I'll post it if only to give you an idea of what not to do. John 

View attachment BOILER CALCULATOR.xlsx


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## pkastagehand (Apr 30, 2012)

Prospect  said:
			
		

> Hi The spreadsheet is kind of a hodgepodge mess specific to where my mind was at the moment. I just haven't had time since the beginning of the year to play much. I'll post it if only to give you an idea of what not to do. John



Thanks, I'll take a look and see if I can make it work or adapt it. I'm trying to size safeties.

Paul


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