# Another steam engine shaped object



## DJoksch (Apr 1, 2022)

I was given another steam engine shaped object as a birthday gift.  Unlike last years project, I think I saw this one on E-Bay.  It appears to be an incomplete abandoned attempt at a dual in-line engine.  I did a rough rework this morning on the valve cylinder using a black felt pen and my calibrated eyes.  It works ‘sort of’.  I think I can convert it to an in-line compound engine.  l’m sketching out how I think it should look.


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## DJoksch (Apr 2, 2022)

I found a link explaining how to determine the primary and secondary cylinder bore.


			https://thermodynamicsheatengines.com/HeatEnginesVol%202%20Chapter%202%20RS.pdf
		


Lots of wasted space as it sits and it looks clunky.  The stroke is currently 1.2” and will be extended to 2.25” to use the entire cylinder length To start.  Cylinders should be round.  Feel free to criticize.


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## Jasonb (Apr 2, 2022)

With the two connections on the end it looks more like the end cylinder was intended as a pump rather than a tandem engine


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## DJoksch (Apr 2, 2022)

The larger brass fitting is a check valve.  The other is just a port to a hole.  Could make a simple reed valve.  You may be right.  It does looks like a pump may have been intended.  The rod into the second cylinder has a seal like the working cylinder, but lacks piston rings while the working cylinder piston does.  It could be made into a double acting pump since both ends are sealed.


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## DJoksch (Apr 2, 2022)

I just took the second cylinder off the frame and saw that it was ported to be a steam cylinder and later plugged.  So it looks like it may have started as a compound engine and then made it into an unfinished air pump and finally abandoned.   I‘m thinking about an in-line compound expansion engine.


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## Steamchick (Apr 3, 2022)

I agree that it looks more like a pump configuration. But conversion to a compound should be manageable. The link to the document is excellent! I have read this text before - but from a different book - but it said exactly the same words, so has been re-printed in many books I guess.
Thanks for an interesting post. I hope to read more as the project progresses!
K2


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## DJoksch (Apr 3, 2022)

I made a 2.25” throw crankshaft.  Now the entire cylinder is used.  Given a 2.25” stroke and a 1.2” ID secondary cylinder I can determine the high pressure cylinder diameter.  I have a nice 5” flywheel, but I think I need a little more mass.


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## DJoksch (Apr 20, 2022)

Slowly progressing on the tandem resurrection project.  I’m using the last resurrection project as a guide.  My plane is to get it to run, then see what happens from there.  The rule is to use only materials from the shop floor.


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## DJoksch (Apr 24, 2022)

The valve eccentric was poorly made out of thin aluminum.  I will remake it in bronze then cut the steam ports and make the slide valves.  The flywheel is not very nice and is only temporary.


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## Steamchick (Apr 25, 2022)

I would not worry about the flywheel at this stage, as "original" 19th C engines had pretty crudely cast flywheels, so yours is more authentic. (If you cast a 2 ton flywheel in the shop, you accept it "warts 'n all" as it costs too much to scrap and make another!). You can utilise "natural" imperfections that make the flywheel imbalanced, to partly balance the engine. I always do, and have very smooth running engines as a result. (As long as the valve is correctly set = balanced!).
Cheers!
K2


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## DJoksch (Apr 27, 2022)

This is turning out to be a smooth easy running beast.


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## Steamchick (Apr 27, 2022)

Testimony to the quality of your workmanship.
 Well done Doug!
(But I look forward to it running on air, then steam, then converted to a compound?)
Cheers!
K2


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## DJoksch (May 14, 2022)

I replaced the thin aluminum eccentric and used bronze clock bushings in the linkage.  I waited to mark off the steam ports so I could compensate for any incremental error.


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## Steamchick (May 15, 2022)

Hi Doug. I'll be interested to know how you set the valve port sizes and slide valve dimensions. As you'll be aware, lap on valves is quite a critical bit of the design of the engine. I am making a steam pump and the valve timing is adjustable, to compensate for (MY) inaccuracies of machining. But you don't appear to have any adjustment if a port or valve slide is a few thou "off"? I don't want to suggest your machining is as bad as mine, but I have only built engines with some adjustment in the valve train, to tune to balance (centre) the valve when I get to the running stage. That way I do get very smooth and slow running engines, without an odd "kick" or stall at the end of one stroke... 
Also, what material are you using in the glands? I always used graphited string, and have put 1 or 2 turns of PTFE tape on the shaft first,  but my latest uses silicon O-rings... which I am sure will seal, but hope they will slide smoothly, and not bind. I may be tempted to apply a layer of PTFE tape to reduce friction for when I tighten the glands "just enough" to stop steam leaks.
It looks really good anyway! - Looking forward to seeing it run and make some power!
K2


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## DJoksch (May 15, 2022)

My first steam build was a Clarkson 1” bore vertical engine with missing pages that happened to be the slide valve and steam port dimensions.  I found some sites that walked through slide valve design.  I also read an article discussing lap allowance for steam expansion.  Here is one of the sites I used as a reference in my reading list.  



			Slide Valve Design
		


The “steam shaped object”, was my second engine and slide valve calculation.  In this case an original aluminum lever with a slot allowed for minor throw adjustment.  I made a final piece out of brass with no adjustment.  For the tandem engine l set the length, but I used aluminum so I can make it adjustable if I need.  The slide valves have 0.6” of travel with a slide valve length of 0.825” running .125 x .3“ steam ports.  The exhaust port will be .25 x .3”.  I’m reworking the math this morning before I cut.  I found an old spool of graphite yarn when cleaning my parents shop.  I’ve been using this for packing material.  For this engine I used the packing nuts that came with it, but I did have to modify them to actually work.


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## Steamchick (May 15, 2022)

Thanks Doug.


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## DJoksch (May 15, 2022)

I am always amazed at the complexity of steam engine and boiler design.  They look so simplistic after they are built.  The criticism of my work has lead to very satisfying results.  On another topic.  Since I’m not using rivets on the Yarrow project, I am deciding on silver solder.  The 65% silver from Rio Grand Jewelry looks like a candidat.  Has a 1250 deg. Melting point.


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## Larry G. (May 16, 2022)

Steamchick said:


> I would not worry about the flywheel at this stage, as "original" 19th C engines had pretty crudely cast flywheels, so yours is more authentic. (If you cast a 2 ton flywheel in the shop, you accept it "warts 'n all" as it costs too much to scrap and make another!). You can utilise "natural" imperfections that make the flywheel imbalanced, to partly balance the engine. I always do, and have very smooth running engines as a result. (As long as the valve is correctly set = balanced!).
> Cheers!
> K2



Thank you for your detailed and informative comments on this and many related posts.
Can you provide some insight into the theory and practice of steam engine balance?
Particularly for simple, single cylinder, single or double acting models.

Thanks,
Larry in NJ


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## Steamchick (May 16, 2022)

Hi Larry,
I use a text book on locomotive design from (I think?) The 1930s... I'll dig it out for the title, author, etc.
On my little models, parts weighed in grams, calculations become a bit meaningless, but I use a bit of trial and error with plasticine and lead shot (from when I used to fish). Or I have some (scrap) weights from car wheel balancing, so have some 10gm steps. Sometimes one of those strapped on a flywheel gives me a useful balance value, to incorporate into the model.
Catch you later, K2


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## Steamchick (May 16, 2022)

Hi Larry, there is a comprehensive thread on the subject of Balancing Engines by Jorgensen Steam, in the HMEM Break Room,  from 2011, elsewhere on this site, so look that one up and see if it covers your query?
I'll try and help properly tomorrow.
K2


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## Steamchick (May 16, 2022)

My text book on balancing is Steam locomotive design data and formulae, by E. A. Phillipson, dated 1936. A new copy available from Camden Miniature Steam  Services.
Pages 290 onwards...
Other books, (my Dad's and Grandfather's) are out of print.
K2


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## Larry G. (May 16, 2022)

Steamchick said:


> Hi Larry, there is a comprehensive thread on the subject of Balancing Engines by Jorgensen Steam, in the HMEM Break Room,  from 2011, elsewhere on this site, so look that one up and see if it covers your query?
> I'll try and help properly tomorrow.
> K2



I'm off to the Archives!  

Thanks


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## Bentwings (May 16, 2022)

Steamchick said:


> Hi Doug. I'll be interested to know how you set the valve port sizes and slide valve dimensions. As you'll be aware, lap on valves is quite a critical bit of the design of the engine. I am making a steam pump and the valve timing is adjustable, to compensate for (MY) inaccuracies of machining. But you don't appear to have any adjustment if a port or valve slide is a few thou "off"? I don't want to suggest your machining is as bad as mine, but I have only built engines with some adjustment in the valve train, to tune to balance (centre) the valve when I get to the running stage. That way I do get very smooth and slow running engines, without an odd "kick" or stall at the end of one stroke...
> Also, what material are you using in the glands? I always used graphited string, and have put 1 or 2 turns of PTFE tape on the shaft first,  but my latest uses silicon O-rings... which I am sure will seal, but hope they will slide smoothly, and not bind. I may be tempted to apply a layer of PTFE tape to reduce friction for when I tighten the glands "just enough" to stop steam leaks.
> It looks really good anyway! - Looking forward to seeing it run and make some power!
> K2


As far as acting what you did is what I did toot works untill the packing nut gets bottomed out. My shaft happens to be 3 mm so I purchased some Teflon tubing used in 3 d printers that has a 3mm inside diameter I just count an o ring out of this then let the packing gland form it you can make what ever size you need  Teflon o rings are a bit hard to find this small but the tubing works fine on compresee air  hot steam will probably be even better as it will compress just a little. 

I also discovered the need for adjustment in the piston port valves . I just establish top  dead center of the piston then set the piston valve some distance down its bore. So it it just barely opens the port to provide the cushion . This can be quite critical as my holes for gas flow are pretty small  and you really can’t see where the pist is . I just set it so the enginge runs smoothly . I record the settings then make minor changes and record results . Monitor rpm at given pressures steam could radically change this but I have not tried this yet. I use a split shaft collar that grips both the hub of the eccentric and the crank shaft so it’s relatively easy to adjust . When. Make new eccentrics I’ll incorporate the split collar into the piston valve connecting rod hub so it easier yet to adjust


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## DJoksch (May 16, 2022)

I have been loosely following a tandem project at “https://glasgowengineering.com.au/history/steam-engine-restoration” for artistic ideas to soften the bar stock look.  He run into problems with balance and added counter weights to the crankshaft.  I have been looking up articles but thought I would get it running to see what I am up against.


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## Steamchick (May 17, 2022)

Hi Doug,
When you have created the "valve diagram" - as per the explanation, it will be good to see it as a "worked example". I drew one in the dim and distant past for a piston valve (central admission) Stuart SUN engine, but have lost that in the depths of 20-odd years...
I must draw the diagram for the steam pump I am making. (I don't think it considers lap!). I am curious, because the steam pump has a simple link between the piston rod and valve rod, not a crank and eccentric. Therefore there is no lead (advance) on the primary valve. To make the main valve operate, the primary valve has to supply steam to a slave piston valve, that drives the main slide valve. I'll try and make a drawing, as the machining drawings do not do it justice. Ooooh! I feel an Excel spreadsheet coming on....  (my stupid brain!).
K2


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## Steamchick (May 17, 2022)

Hi Again Doug, 
My experience for silver soldering. 
A really nice silver solder for flow and building-up beads is the 55% solder. But to have a couple of different solders for different parts of the assembly I also have stock of 2 others. That way I can make first sub-assemblies in the "hotter grade", build them into "second level" assemblies with the "middle temperature grade" and final assembly with the "coolest" grade.
A quote from a welder: "_The most widely used silver solder melting points are 1328° Fahrenheit at 33 percent silver volume, 1247° Fahrenheit at 40 percent silver content, and 1202° Fahrenheit at 55 percent_ " - I have used Johnson Matthey silver solders if I want something "special",
Silver-flo-filler-metals - matthey.com 
(I ordered some "flux-less" silver solder for a Works job for joining wires once - contains Phosphorus - Not the best for a boiler, but good for gas fittings.). But generally, the "cheapest" market quality 55% is OK for most of my final assembly work, and regular "cheapest" is a 33%~35% grade. I guess you'll get ASTM grades in Yuba?






 In theory, you should only use certified material for Boiler-work. Talk to your BOILER TESTER/INSPECTOR, in case he wants to know what solder grades you are using, and he may want to see prepared but unassembled parts, and drawings for the boiler. I have never needed to present calculations to the Boiler Tester (they just do a visual exam to be sure all joints look OK, before doing the pressure testing), but (now) always do those FIRST, as it is easier to increase a material thickness or change a design before making anything! But I have had to De-Rate some boilers (even one I designed and made) following a more comprehensive study of ASME, some university papers and "industrial practice" papers. But your Yarrow is relatively simple and we have already discussed sizes and strengths of tubes.
There is a curious effect when silver soldering: (A metallurgist should be able to explain?). When the pool of silver solder is molten, some of the adjacent copper diffuses into the solder, changing the metal composition, so it moves to a different place of the "liquidus" curve, and later needs a higher temperature to melt the joint. Too much heat (prolonged or too high?) can increase this diffusion, but what it does for joint strength I cannot say.
Cheers!
K2


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## Bentwings (May 17, 2022)

DJoksch said:


> I have been loosely following a tandem project at “https://glasgowengineering.com.au/history/steam-engine-restoration” for artistic ideas to soften the bar stock look.  He run into problems with balance and added counter weights to the crankshaft.  I have been looking up articles but thought I would get it running to see what I am up against.


I’d suggest reading articles on automotive crank balancing. There are ways to come up with what  is  at called bob weights which are based on some percentage of parts that rotate and those that swing like connecting rods the weighs are then added to the crank and it is balanced as an assembly . It’s been a long time since I was in the automotive machine shop it’s something like all of the  rotating weight and some percentage of reciprocating weight . It’s quite involved if you have many cylinders and connecting rods . The balancing machine itself is complex.


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## DJoksch (May 17, 2022)

Thanks.  I’m still at the deciding how to do the counter weight calculations for weights.  I knew I had to address this and I am at the point where it will be an issue.  I will ask about the silver solder to make sure I’m following the requirement.  I’m hoping to run it on air next week.


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## Steamchick (May 17, 2022)

Doug, an easy way to balance primary....
Set the engine so the piston rods are vertical. Set the engine at half stroke. If "no friction" the imbalance will cause pistons to drop. Add some weight opposite to the crank pin, until it is almost balanced. 
Then set the engine on the bench and run slowly.  
The primary balance weights  will then cause a secondary imbalance, partly negated with the weight of con-rods plus big end, as when at TDC, The balance weight will drop that side of the flywheel, but at BDC will have to raise the balance weight. Watch study and work it out. For slow running, the secondary imbalance is not significant. You'll see when it runs. You can reduce the balance weight by 1/3rd to get a good compromise.
Enjoy the balancing act!

K2


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## DJoksch (May 22, 2022)

Just made a temporary steam inlet pipe and am about ready for a test run.  I acquired this little mechanical oiler and was planing to use it, but it seems to just crank to its limit and binds.  Unless I’m missing something, you have to stop the engine, load more oil, then manually crank to its upper limit and start over or risk damage.


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## Steamchick (May 23, 2022)

No idea about your oiler, but it does look to have a simple displacement oiler in the pipe-line... So maybe you can just use that? Usually quite adequate for models.
I use them as intended for steam, or inverted (reservoir above the line) for running on air. But you must also use the appropriate lube, depending on steam or air: Proprietary steam oil, of Air-tool oil, are my options. Hope my 1-minute sketch helps?




K2


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## Steamchick (May 23, 2022)

Awaiting the first run with bated breath....
K2


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## DJoksch (May 29, 2022)

Update: Finishing up the base.  I decided on a planked floor.  I saw a similar floor with same sized planks.  I didn’t like the even pattered result so I cut random sizes and thicknesses then picked and matched at random.  While I’m varnishing, I’ll mill the sides of the cylinders so I can clad them.  That leaves the split main bearing modification and the cross slide.


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## Steamchick (May 30, 2022)

Beautiful! I used thick "planks" of balsa wood on boilers for insulation. Very effective! But on the (plywood) deck of a boat I cheated. Instead of planking, used 2mm thick 3-ply, with drawn planks (random lengths) using a fine ball pen (pencil did not work for me). When varnished it looked real enough.
I like your proper job!
K2


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## Steamchick (May 31, 2022)

Doug, do you want a design for a ceramic gas burner to suit this boiler? If so, send me sizes and I'll do you a design. I'll probably need to have the enclosure sizes as well. (I once made a burner to someone's sizes, but it didn't  fit the access hole). Needs >1/2" clearance between the bottom of the lowest tube and the ceramic.
K2


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## DJoksch (May 31, 2022)

That would be terrific.  I will get that to you.  I’m on my Summer beak after tomorrow which will speed up the engine and boiler project.


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## Steamchick (May 31, 2022)

I am retired, so every day is a beak!
K2


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## DJoksch (May 31, 2022)

Work definitely gets in the way.  I keep getting asked to teach Summer classes.  I respond by saying if I wanted to work year around, I would have stayed at Lockheed. This is a sketch of the boiler.  I also have a 5-1/4 X 3-5/8” piece of ceramic I did not use on the last burner project.  I was not sure if this would work.  The overall size of the engine and boiler still fits on my glass to backyard table.


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## Steamchick (Jun 1, 2022)

DJoksch said:


> Work definitely gets in the way.  I keep getting asked to teach Summer classes.  I respond by saying if I wanted to work year around, I would have stayed at Lockheed. This is a sketch of the boiler.  I also have a 5-1/4 X 3-5/8” piece of ceramic I did not use on the last burner project.  I was not sure if this would work.  The overall size of the engine and boiler still fits on my glass to backyard table.


Excellent Doug. If you want to stick to the single ceramic, it should be rated around 2kW. (I'll check properly later). But if you want to fully exploit the full capacity of the boiler's steaming ability, I suggest a burner about 7" long and 4" wide between the 2 bottom tanks. You could even go full width of the bottom tanks if you wanted to mount a burner beneath those?
The fun is working out how to join panels of ceramic to the size you want. I join them with firebrick cement, and cut to size using a fine hacksaw, or junior hacksaw on smaller burners. But you need to fully support the ceramic on a flat board, up against a bench stop, when cutting. Follow the holes so the swarf (dust) drops through. Gently and carefully cut with long smooth strokes and very little down pressure. I'll send picture of a similar large burner I made - using an appropriately sized biscuit (cookey) tin.
Cheers, 
K2


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## Steamchick (Jun 1, 2022)

Hi Doug. Now on my proper PC... 
This picture shows a large burner, made from 2 ceramic slabs. It is about 5" x 7 1/2". Using a 0.022" jet, in a 16mm ID mixer tube, with Propane gas at around 15psi (It would take 20psi but was roaring! - I suspect too hot and the ceramic could fail after >10 mins.). Note the zoning, due to some weird pressure variations beneath the ceramic. Hardly perceived "By eye" - by the camera is more sensitive and clearly shows the non-uniformity of the combustion, which could lead to differential expansion and early life failures. I should do a better job next time! (The mixer tube needed more tuning!). The diagonal line was a stainless steel wire support beneath the ceramics. 



This fitted beneath a 9" diameter vertical boiler:
as seen in 
*The International Toy and Model Steam Hospital*




Gas jet was providing gas for over 7kW of heating.
I estimate that you could use a 7" x 7" square burner, which should manage about kw: using a No 72 or 71 jet (0.65mm or 0.025" or 0.026" diameter hole) to give around 9kW of heating. The mixing tube should probably be 19mm - you may get away with 16mm? The air holes should be 3 off x about  12mm diam. - maybe as big as 14mm? (Start smaller!). You'll need about 140mm from air-hole to end of mixer tube: - I'll have to sit down later and design a diffuser tube, as I can't do that "off-the cuff". I'll do some drawings later as well, with a "proper" set of sizes.
Hope this gives you an idea about the largest burner you could have to fire that boiler?
When you design the enclosure, please consider how the heat can radiate from the burner - e.g. between gaps in the water tubes - and arrange that the inside surface is shiny (stainless steel?) to reflect the heat back onto copper tubing. Very effective! I have incorporated internal reflectors in fireboxes on some boilers to improve efficiency (reduce lost-heat that only heats the casing!).
Cheers!
K2


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## DJoksch (Jun 1, 2022)

I will order another panel.  Your double panel burner looks great.  I had not considered joining them in the middle.


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## Steamchick (Jun 1, 2022)

I have seen double panels, and other larger sizes, on €&@¥.
I shall try and find a link.
K2


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## Steamchick (Jun 1, 2022)

Found stuff on aliexpress.com item no.  1005003645000707 .
Hope you can find it (using my tablet so don't know how to copy urls, etc.).
K2


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## Steamchick (Jun 1, 2022)

200mm x 143 mm would cost £25.. + delivery to UK. You could easily trim that to less than 200 mm if you chose, or join one on the side to get 286 wide, then thim to 10mm or so to suit your width?
I have also glued these together with the car exhaust assembly paste. When the ceramics get hot the paste fires into a ceramic.
K2


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## Steamchick (Jun 1, 2022)

Hi Doug, A simple option that may suit your boiler could be a unit for a doner kebab cooker. A double plaque burner is available about $70. Looks like it just needs the jet and gas tap.
I'll try and paste a link when I get to my PC.
K2


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## Steamchick (Jun 2, 2022)

Hi DOug:
The sites I had found...
Gas Heater Parts Burning Honeycomb Ceramic Plate Infrared Burner Replacement - Bbq Grills - AliExpress 
GENUINE ARCHWAY GAS DONNER KEBAB MACHINE CERAMIC RADIANT BURNER HEATER PANEL | eBay 

This is a manufacturer in the USA - may be of interest? Wire Mesh Gas Burner - Gas Burner Metal Mesh | Solaronics (solaronicsusa.com) 
Burner revision textoutline 5 9 | Solaronics (solaronicsusa.com) - In this it explains the heating ability of each medium. If you ask "nicely", they may supply a free sample the size you want? (I know someone who did that with a Belgian supplier - they sent him 2 burners!).
Here's another burner... PBR03E02-TECHNICAL-BURNERTECH-FRYERS.pdf 

I hope some of these links inspire you?
K2


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## DJoksch (Jun 2, 2022)

I will send them an inquiry.  It looks like you still need to supply the jet and gas tube.  Drilling a jet was not a problem.   Thanks for the information.  I appreciate your time researching this.  These projects take on a life of their own.  I’m about to set up one of the lower drums on the mill and drill actual holes.


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## Steamchick (Jun 2, 2022)

I have been out today, so will have a proper look at the jet size tomorrow, or over the next few days. I think it is 1.2mm for use with 33 mbar propane, but want to check further for HP propane, etc.
K2


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## Steamchick (Jun 3, 2022)

Hi Doug.
Scaling a photo of a jet for the double panel Kebab machine burner: It is a standard 1BA threaded jet: the hole scales from a photo as 1.2~1.25mm diameter for use with LP LPG (Propane: 34.5mBar?) - but I guess the photo may be from a different gas and pressure... not the correct one! However, if it is of the correct jet/gas/pressure... I have estimated from my tables of jet sizes versus gas and pressure that it is a 0.049" jet: which would deliver about 16500BTU/hr (4.8kW) of gas.... Commercial "kebab" machines are rated at 7.3kW for a 3-panel grill to 16.5kW for a 5 panel grill, so there is obviously some variation, but maybe they are looking around the 3.5kW for a double panel burner? 
To use Propane at 20psi, I should need an equivalent gas-power jet: which would be 0.018" diameter drill.  So this is comparable to my double panel burner experience:
Now checking my notes of the "double plague" burner I made, I estimated a 0.55mm jet, but finally settled on a 0.47mm jet - for use at 15~20psi Propane: This was into a 16mm bore mixer tube: (I didn't make a note, but I think this gave me better versatility for turning down the gas power without spoiling the gas-air mixture - something my "customer" wanted. 
His 9" boiler had very limited flue-tube CSA. Thinking ahead to my burner in his boiler, I was expecting the limitations of the flue tubes to cause back-pressure that richens the mixture at "max gas pressure" (effectively reducing the pressure differential between air-intake and burner), so I thought I needed a way to allow him to open/adjust the air holes as suited his boiler. I also decided to reduce the "designed" air holes by masking most of 1 hole, so I was on a slightly richer gas mixture: This gave a more uniform colour across the burner, which should lead to a longer life of ceramic. I remember the final condition had a 1/2" or so of blue (CO combustion) flame above the ceramic. As I didn't have the boiler (to study the back-pressure from exhaust restriction in flue tubes) to test the final condition in-situ, I decided a slightly richer mixture - with a sliding collar on the air holes - would give my customer the flexibility to weaken or richen the mixture as suited the final application and "power" setting the customer would be using. 
For control of larger burners, I think it practical to adjust the gas pressure, so the system is "balanced" at full throttle of the engine. Then this can be reset at any time by the fireman to the known "max pressure" for running. Of course, it is reasonable then to reduce the gas pressure for "below max power" running of the engine, and gas pressure control on a pressure regulator is a repeatable way of doing this. As well, for more rapid raising of steam initially, the gas pressure can be turned to "full" setting (for stability of flame/burner inside the boiler) and the power should then be suitably limited by the jet size (to avoid overheating the ceramic). For your Yarrow boiler design, visible flames should not reach within 5 mm of ANY metal surface (that prevents full CO combustion), but there is a very good space if running at "max gas" does cause some top flame ( up to maybe 3/4"?) above the burner. Such combustion conditions appear to be "clean enough" so my CO alarm does not sound, while keeping the ceramic temperature from being too high (which causes early-life failure of the ceramic - cracking - and possible dangerous flash-back combustion).
Here is a Yarrow boiler design from a book - similar to your boiler: It shows the fire between the bottom tanks.




Hope this is useful?
K2


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## DJoksch (Jun 3, 2022)

I see that the entire boiler is enclosed.  I was planning to leave the ends of the drums visible for convenience adding the site glass, injector and blow down ports.  As long as I have to tin smith an enclosure, I can see the use of sliding or rotating  louvre system and a larger chimney.  I’ve seen several boiler examples with D shaped lower drums.  I plan to stay with simple round tubes.  I have a test pipe ready to do a test cut using an end mill.  Today I am convincing two steam cylinders to balance.  I’m redoing slide valve rod for the second cylinder to use a left hand thread.  I naively thought I could set the spacing and install them as a unit.  The left hand tap and die just arrived and it should be a quick fix. 

The adjustable propane regulator will work nicely for the burner although I will likely need to use the larger tank.  I did not go with a supper heater because I was concerned if the engines would take the high temperatures.


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## Steamchick (Jun 3, 2022)

Hi Doug. 
Just my thoughts on your plans - of course you can make- up your own mind, based on lots of ideas, not just mine.

I would keep boiler ends enclosed, but the water gauge should pass through the cleading so it is outside and always visible.
I'm not sure I understand what your sliding louvre system is for. But a large chimney will be needed, I GUESS  2 inches is better than 1 1/2"? For a single page sized burner, I have a boiler that my Father had to change from 1" => 1 1/2". Hence I guess 2" for yours?
I have no idea between D-shaped and cylindrical bottom drums. But my boiler-making book advocates D-shaped, though the flat part may be stressed more by the internal pressure, while the hoop stress on cylindrical pipes will put uneven loading onto the water tubes..... I do not have the knowledge nor ability to do a FEA on the alternatives. Just make sure the silver soldering is sound, with correct clearance between water tubes and larger tubes. I suggest about 55% silver solder, as it is better to generate fillets and make stronger joints. But other professional advice may give better answers. (I am just an amateur copper-smith!).
Having the ability to finely adjust the valve timing between the 2 cylinders sounds like "a proper job". Pity it didn't  work with your solid linkage. I know all my stuff doesn't have the accuracy for "absolute" sizing, so everything needs to be a bit adjustable. Welcome to the real world!
I advocate a super-heater tube. Even a single horse shoe loop around the inside of the boiler space will make a huge difference to the performance of the engine, in my experience. I always fit super-heaters, even if not complex big ones. It clearly reduces the condensate in the model cylinders, which can be very problematic (hydraulic lock!), especially during warming the engine. Model engines have such tiny spaces at the cylinder ends.... unless you fit auto-drain-valves or something? Using a good steam oil, you should be OK for normal model use, if you have a superheater.
Using a gas regulator has made controlling the firing of my boilers much easier.
Anyway, you are going "great guns" on this project. Enjoy it!
K2


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## DJoksch (Jun 3, 2022)

As I get the actual boiler built, I will post my ideas for the enclosure.  Enclosed it is.  If I’m going through this effort, I should go for efficiency.   I have a couple ideas for a super heater and will post sketches.  On the engine, the solid bar is actually threaded onto the end of the first stage.  The problem was that all the threads are right hand so turning the rod does not affect the length so the outer end will be left hand.  I’m ordering 55% silver solder.  I have 65% silver I use for instrument repair, but not enough for the job.  I also plan on stays for each drum.


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## Steamchick (Jun 4, 2022)

Hi again Doug, a new day dawns - colder today. Do you have a means of dishing the boiler ends? - Domed end plates are hugely stronger than flat ones, and eliminate the need for stays.
I've lost the thread with more information of this boiler... Was it on a different thread somewhere, or am I simply getting a bit demented? (Or maybe I always was a bit that way?). I found my Tube calculations - for 50psi NWP:
IF Flat ended:
2.5" dia end plate with single centre stay: Min thickness = 0.065"
1.125" dia end plate without stays: Min thickness = 0.055"
So a dished end without stays: Spherical radius 2" or below: Min thickness = 0.040": But at 4.5" spherical radius: Min thickness = 0.090"
Combining the two:

For the 2.5" ends: Unstayed flat >0.125" thick, dished to 4.5" radius >0.090" thick: dished to 2" radius > 0.040" thick, Single stay >0.065" thick.
For the 1.25" ends: Unstayed flat >0.055" thick: If you wanted a single stay the end plate: >0.030" thick.
So if you use a piece of the 2.5" tube, opened out and flattened to make your end plates (>0.070" thick), only the top drum needs a central single stay.
Size of stay:
If Phosphor Bronze >1.6mm diameter "at root of thread":
BUT: the stress concentration factor at thread root is ~3... (My best estimate!) so you need at least 2.8mm root diameter (M4): I don't know what you plan? I suggest nothing smaller than 4BA, or 3/16" x 32tpi? - Or similar "US" fine thread? (Is that UNF where you are?). I.E. a root diameter at least 0.128" diameter.
Incidentally, Stainless steel comes in many grades, but for sake of argument, if using "bottom draw" stock of unknown quality you should consider it as the same strength as Phosphor Bronze. NOT better (unless a known better grade). 
I hope this helps you decide on your design?
K2.


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## DJoksch (Jun 4, 2022)

I will post my ideas for the enclosure.  It will be fully enclosed and include inspection doors.  This alcohol burner was my fist spinning project.  The end caps will be made the same way.  If I can eliminate the stays, I don’t need to poke holes.


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## Steamchick (Jun 5, 2022)

Hi Doug,
I tried (and failed!) to find strength info on silver solders, to suggest the 65% silver wasn't as strong as other grades, and propose "the best". BUT failed.
On Spinning ends. I thought you may go that route, when you appreciated how strong these can be. What radius do you expect for the 2.5" Top drum ends? If hemi-spherical, then it is 1.25", but if elliptical a bit harder to calculate. And Hoop stress is very dependant on internal radius (max). => define local minimum thickness. (I assume the spinning will thin the material slightly).
K2


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## DJoksch (Jun 5, 2022)

My air compressor has a compound curved dome.  Given it’s 12” diameter the actual domed section is 10” with 2” used to transition  the dome into the main cylinder (I’ll post a sketch). Based on this design, I planned on 2” of the dome at .4” protrusion.  The remaining .5” to create the blend into the cylinder.


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## Steamchick (Jun 5, 2022)

DJoksch said:


> My air compressor has a compound curved dome.  Given it’s 12” diameter the actual domed section is 10” with 2” used to transition  the dome into the main cylinder (I’ll post a sketch). Based on this design, I planned on 2” of the dome at .4” protrusion.  The remaining .5” to create the blend into the cylinder.


Thanks Douģ. I shall try and deduce the largest radius of curvature for the top drum end dome, from your sketch.
Might take a few days though, as my wife is having an operstion tomorrow, so I am spending a lot of time on other jobs (washing and ironing, etc.).
K2


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## DJoksch (Jun 5, 2022)

I will be sending good thoughts for you and your wife.  

I have the first stage of the little engine working nicely.  The original aluminum cross slide has a lot of play and clunks.  I will deal with it after I finish the second stage.  It has a lot of torque with just one cylinder.  The wobbly flywheel was a base for wind chimes and I decided to buy an actual flywheel casting.  As for the boiler, I’m just making an alignment tool to keep the tubes straight so I can make one of the lower drums so I have plenty of time.  It will take me a few week to cut pipes, tubes and make jigs.


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## Mechanicboy (Jun 6, 2022)

DJoksch..

With more thin water pipes, more steam is produced than smaller numbers of thick pipes. This means that you have a larger heating surface to heat the water to steam quickly and get greater pressure. Yarrow boiler is efficient to produce more steam pressure, but must supply with preheated water in relation to water consumption as the Yarrow boiler there is not much water in the upper boiler that it can quickly run out of water. Use electronically monitored water level to supply via feed water pump + bypass valve controlled by servo connected to Boiler with automatic boiler water level control system.


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## Steamchick (Jun 6, 2022)

Doug, you'll need some oilers on the crank journals. 
And Mech-boy is right, you should plan a feed- water heater coil - in the post boiler exhaust. I.e. outside the water tube array. (Superheater loop inside the water-tube array). And it will need a continuous water feed pump. I arrange my boats to have an engine driven pump, so faster speed =more water.
K2


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## Steamchick (Jun 6, 2022)

Hi Doug, My wife is in the chassis shop getting a new rear ball joint fitted now. Life will get better when the broken part is replaced.
Meanwhile, I checked (using the ellipse curvature calculation) the largest radius for your Top-Drum end plate.
It came out at ~1.6" radius.
Then checking ASME - which struggles with small parts (Model boilers) - it simply says everything UNDER 2.2" rad shall be at least 0.040" thick. 
BUT then there is a further requirement for the Stress Concentration Factor to have 3.3 times the thickness when material is pierced - as for the bushes for the water gauge, etc.  Which means it shall be 0.123" thick ... (1/8")! A bit thicker than perhaps we expected?
Can you spin that thick?
Hope this news isn't a problem?
K2


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## DJoksch (Jun 6, 2022)

I was planning on adding an engine powered water feed pump.   Here are a couple older excerpts from a lab text I have written.  I need a different level sensor, but a three level sensor system would provide a nice automatic feedback system with an alarm level sensor that could shut off the burner.  I should covert the water supply on the first boiler project to act as a preheated version and add an oil separator for the exhaust.  I will see if I spin this.  I may need to use something else such as 1/4” plate to make the end caps.?  









						Liquid transfer and refill system.
					

Altera PLD based liquid refill system with level sensors.




					youtube.com
				











						Alarm system
					

PLD based 4 digit combination alarm system.




					youtube.com


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## Mechanicboy (Jun 6, 2022)

DJoksch said:


> I was planning on adding an engine powered water feed pump.   Here are a couple older excerpts from a lab text I have written.  I need a different level sensor, but a three level sensor system would provide a nice automatic feedback system with an alarm level sensor that could shut off the burner.  I should covert the water supply on the first boiler project to act as a preheated version and add an oil separator for the exhaust.




See this link: Automatic boiler water level control system with phototransistor.


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## DJoksch (Jun 6, 2022)

Doing the cosmetic stuff and turning a better flywheel with more mass.  Time to make decorative copper bands and decide on a color for the metal base.  Two pounds of air and watch out for your fingers.


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## Steamchick (Jun 7, 2022)

Hi Doug, I like your slightly unconventional way of making things. It tells me we are often constrained by "History" - because "that is how it has always been done"?
Well done on a great finish to this model. - The wood and hexagon shape do look good.
K2


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## minh-thanh (Jun 7, 2022)

Hi DJoksch ! 
How do you clad wood panels? glue or..?
 Thanks !


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## DJoksch (Jun 7, 2022)

I used thin walnut veneer and super glue in this case.  For my other engine, I cut a piece of weathered mahogany into thin planks.


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## DJoksch (Jun 7, 2022)

I just bought some 1/8” copper to make end caps.  I will need to make a spinning tool with a ball bearing roller and convince my South Bend 10L to turn it.  I also have a 3 foot 3” wide 3/8” thick bronze bar that could make nice caps all the way around.  This would be an easier solution.


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## Steamchick (Jun 8, 2022)

If annealed and you can spin it, the copper is still a good option.
K2


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## DJoksch (Jun 10, 2022)

Need to add copper bands to the cylinders, and cut channels in the steam chest for appearance.  Still waiting on copper for end caps.  Things are coming together nicely.


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## Steamchick (Jun 11, 2022)

I like the dark blue finish... Is it a gun-finish or something?
K2


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## DJoksch (Jun 11, 2022)

It’s just automotive paint with a clear coat.


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## Steamchick (Jun 11, 2022)

I like the finish. Very presentable.
K2


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## DJoksch (Jun 18, 2022)

I’m adjusting and shimming.  As always, I learned a new set of “what not to do”, but I was trying to use some of the original engine.  Would have it together, but I was ask to be a guest woodwind musician for a conductor’s symposium this week.  I’m deciding if it should have a common displacement oiler on the steam feed or if I should put a separate oiler for each stage.


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## Steamchick (Jun 19, 2022)

I should use the common displacement oiler, as I have adequate lubrication with all mine. Didn't know you are a whistler! Flutes? Reeds? favourite pieces? Tell us more! As an ex-Tympanist, I like the rhythm of your engine. But have you balanced the flywheel yet? It is smoother than I recall of previous posts?
K2


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## DJoksch (Jun 19, 2022)

For orchestral work, I’m on an oboe or English horn.  I occasionally cover bassoon.  We are looking at Beethoven’s 6th with some nice oboe work.  Recently did E. Horn for New World Symphony.  I’m also a Mendelssohn and Korsakoff fan.  I also do pit orchestra work with my wife.  Pits are as much choreographing the instruments as playing them.  I find that engineers are typically accomplished musicians.  I knew you played something, I just didn’t know what.  

As for the engine, the first flywheel had very little mass.  The new flywheel is much better and runs fairly smooth.  I’m off to a concert today so I’m letting paint dry.  I’ll see if it still runs smoothly with two cylinder stages.


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## Steamchick (Jun 20, 2022)

Hi Doug,
Keep playing! It is a skill, talent and a gift from the musicians to the rest of us! (I do not count myself a musician, as I stopped over 40 years ago when I realised I wasn't the same calibre as the brass band players I performed with! +  a few other reasons. - But I was pretty rubbish! Weak left-hand, strong right-hand, and you can't disguise that imbalance in a roll!).
My favourite Tympani piece is the end of Beethoven's 3rd movement of the fifth Symphony.... leading to the 4th Mov't..., with Sibelius' Finlandia a close second.
Enjoy the music!
K2


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## DJoksch (Jun 23, 2022)

It’s coming together.  Have a few things to clean up.  Making a hard line to connect to my boiler.


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## Steamchick (Jun 24, 2022)

Hi Doug, For running on air, there is no condensate to displace the oil in the lubricator. But if you invert it, so the reservoir is above the connection to the intake manifold, then a bit of air in the reservoir will start to oscillate with the pressure and pump a tiny amount of oil into the manifold, that will find its way into the engine. I use regular air-line oil when running like this on air with my engines. Seems to use the oil slowly...
Then when running on steam, you can reset the oiler in the normal orientation. Some Condensate will collect in the reservoir and displace the oil that has to get heated by the steam in the intake manifold, and thus carried into the engine where it condenses as the steam expands and cools. - Use 50W steam oil for this operation.
After steaming, when you clean, dry and re-oil the engine, don't forget to drain the water for the lubricator. And before running you can top-up the oil reservoir as part of the pre-running oiling routine.
I'm sure you'll figure out what to do.
Enjoy a splendid engine! - Well done!
K2


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## DJoksch (Jun 24, 2022)

Just finished a hard line for my current boiler.  I’m curious to see if the boiler keeps up with the engine.


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## Steamchick (Jun 24, 2022)

Looks superb!
K2


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## DJoksch (Jun 25, 2022)

This is the very first time it has seen steam.  I need to tighten up the gland packings.  Needs a boiler feed pump and a water preheater as pointed out.  You have to watch the water level.   Back to the larger boiler project.


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## Steamchick (Jun 26, 2022)

Doug, While I love the rhythm of the clicking and clacking.... but wonder what bits are making the noise?
I noted the shortage of steam, so I guess that if it were a single cylinder it would be OK...? Does that inspire you to convert it to a compound?
The limitations of your current boiler (from what I remember? - must check what we said when you were building the boiler) are simply in the burner....  The circle of ceramic won't last long if you increase the jet size - if it can draw the extra air - and the limitations of vertical boilers, that are fired from beneath with a ceramic, is really one of surface area. Then when you try a "bigger" burner (Alternative design), you simply get a limit of the restriction of the flue tubes, as they cannot cope with much extra exhaust gas. I must connect my compound engine to my 3inch vertical and see if it can cope? - as a comparison. (It will have a similar sized burner).
I have checked my notes on what I figured for your engine running at 150rpm... with bore 1.2" and stroke 2.25". Needs 2.0kW burner (min.). 
The jet at  
The burner at 3" dia has 7sq.in. = 45.6sq.cm. => 0.55kW at "industrial" power (for longevity) rated at 120kW/sq.m. (12W/sq.cm., or 77w/sq.in.). But I rate the burners at more like 200W/sq.in. (based on jet sizes and gas tables) - which seems OK for the lifetime I get for use in my boilers. So your 3" diameter ceramic should produce about 1.5kW of heat... so maybe just shy of the need of the engine? (Remind me of the jet size you are using, and the air-intake tube bore?).
Cheers.
K2


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## DJoksch (Jun 26, 2022)

Rear piston contacts the head on back stroke.  The burner jet is .25 and I was using 5lbs of pressure.    The first engine has a 1.5” bore and a 1.5” stroke and the boiler seems to keep up.  This was the thought when I decided to build a larger boiler.  I am also thinking it needs to be a compound engine.  The simple solution is to sleeve the outer cylinder.  I also have a nice piece of smaller hex bar stock for a new cylinder.  I was not sure of the calculations.  If I want a 3 to 1 cylinder ratio, a .7” bore high pressure would feed a 1.2” cylinder at 2” stroke.  I also read that I need to account for an early cutoff to allow complete steam expansion.


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## Steamchick (Jun 26, 2022)

Hi Doug. Just a couple of thoughts.
Obviously, you need to adjust things to get rid of the contact between piston and cylinder cover. That will quickly knacker the big-end bearing, or cross-head bearing, or both. To put it simply. Been there, fixed it.
I like the idea of the compound engine, as I have seen a few in England. Trencherfield Mill engine, etc.
To sleeve the high pressure cylinder is a good idea. But the sleeve needs to be parallel, a press fit in the existing bore, and don't forget the ports will need to be machined in the liner. And a new piston, of course.
If you need to adjust the valve timing cut-off, then you will need to draw a diagram of the timing you have, the timing you need, and probably make new steam valves to give the new timing. I doubt you can simply reset the eccentric to achieve what is needed? What is the text you have been reading on this? I can help if you need a "number cruncher". Probably worth a direct communication if you want to send drawings of what you have, to avoid cluttering-up this thread?
The 0.7"bore HP will be about OK for 3:1 required for the 1.2" dia. LP. cylinder.
Thanks for including me, I am enjoying your project!
K2


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## Steamchick (Jun 27, 2022)

Hi again Doug. When you say "The burner jet is .25 and I was using 5lbs of pressure." - I assume the "5lbs of pressure" was steam pressure? - Or did you mean gas pressure on the 0.25" jet?
Ta,
K2


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## DJoksch (Jun 27, 2022)

Actually I miss read my own notes.  I was running 5lbs of propane.


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## Steamchick (Jun 27, 2022)

Aha!  You could run up to 20psi propane on that jet on your burner, if I remember your boiler development?
that could be 3 or 4 times the steam? Try 10 or 15 psi propane and you'lloyds probably have plenty of steam, compared to the video where you were  short of steam for continuous running.
Enjoy,
K2


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## DJoksch (Jul 1, 2022)

I now have two sets of pipes.  In a compound configuration, it runs better on steam.  It definitely has more power in non-compound mode.  Time to work on the boiler.


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## Steamchick (Jul 6, 2022)

Hi again Doug. 
I found a picture of the compound twin that I hold  - belongs to the local model engineering club and I run it on show days. I only have a picture of it away from the boiler, so must make a video of it "next time" it runs...
Re-watching both your videos, the "clanking and knocking" present in the earlier "twin-steamed" video has greatly improved in the "compound" run... Testament to you fettling and tuning I think.
Very good to watch (or am I a bit "sad" in the head?). How do you feel about the ability (limitation?) of the boiler to run it as a compound compared to the Twin configuration? - e.g. at "full fire", what actual speed difference is there (at the crank) between the 2 configurations? (at higher pressure, the compound "effect" will increase).
Ken


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## DJoksch (Jul 6, 2022)

As a compound engine the boiler seems to keep up although it still requires a lot of water pumping to keep up.  You can definitely see a pressure drop as water is added.    I will run it with the boiler at full fire next time and alternate compound and non-compound configuration.  I saw an interesting oil trap condenser and water preheater which might be the solution.  I built another eccentric which could run a water pump.

Oh yes,.. I was given another box.  In this case, I need to work from the steam ports back to the required stroke and slide valve.   I just put it back in the box for later.


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## Steamchick (Jul 6, 2022)

Superb! Another twin, this time a marine vertical. You can either make it a Generator engine, with just a simple eccentric at either end, or a reversing (marine) engine with pairs of eccentrics at either end and some fancy linkages to the valves. Either way, an extra drive for a boiler feed water pump is a good idea.
Enjoy!
K2


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## minh-thanh (Jul 6, 2022)

DJoksch said:


> I now have two sets of pipes.  In a compound configuration, it runs better on steam.  It definitely has more power in non-compound mode.  Time to work on the boiler.




Run Great .
  Congratulations  !


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## Steamchick (Jul 10, 2022)

Hi Doug,
On the " I built another eccentric which could run a water pump."... Feed pumps need to be sized to the engine, and steam usage, so the "feed-water" balances the "used steam".  If you send me the following data (I have some, but worth a re-check) then  I can let you know the displacement, bore and stroke, of the pump for feeding continuously from your crank eccentric.  
Engine Bore (1.2"?);
Engine stroke (2.25"?) = double acting;
Cylinders being fed with steam (1 = compound, 2 = twin-feed)
Crank speed: ( max - guessed from video of twin, post #82) = (250rpm?);
This gives me 1272 cu-in of steam per minute... which equates to 3.14cu.in. of water per min.  (at steam NWP = 50psi). This also proposes a need for 2.3kW of heat developed into steam. (at 60% efficiency, because the boiler loses heat to the room, heat is lost up the chimney, etc.) you need a 3.8kW burner. Maybe your burner is smaller than that, so maybe the engine is actually running at lower pressure than 50psi...?
Of course, change any of these parameters changes the (Simple) calculation. e.g. at 20psi it would be 1272cu.i. steam, 1.75 cu.in water and  1.3kW of heat transferred to steam (needing a 2.2kW burner?). (Possibly this is what I can see on the gauge in post #82?). 
Now translating the 1.75cu.in/min. of water: 
a pump at 250rpm would need a displacement of 0.007cu.i. per REV. 
So a single-acting pump, stroke = 1/2", would be 0.1335in bore...  Just over 1/8". ~3.4mm?  
I am sure you can plug-in your actual numbers - (or I can?) to get a more accurate design of pump.
Hope this is useful?
K2


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## Steamchick (Jul 10, 2022)

Hi Doug, reply to post #91: here is a similar twin for when you decide to start on your twin compound  in the box...





						Stuart Twin Launch
					

The Stuart Twin Launch Engine    I have admired the Stuart Models Twin Launch desktop steam model for many years.  It is a lovely classical 19th century marine engine design that is self-starting and reversible with Stephenson valve gear.  It runs nicely on compressed air, has a pleasing...




					www.homemodelenginemachinist.com
				



Cheers!
K2


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## DJoksch (Jul 10, 2022)

Here is the engine info.
Bore: 1.2”
Stroke: 2”
Eccentric stroke: .5” (easy enough to change)
Compound running configuration.

It runs smoothly as a compound engine.  Speeds over 300 rpm starts to demonstrate the need for counter balancing.  At about 250 rpm, it seems very happy and I can watch the Rube Goldberg action.  I was thinking about using casting clay and pouring lead between flywheel spokes once I decide how much weight is needed. The counter balancing should actually go on the crank.   I came across a lucky counter weighted flywheel allowing for high speeds for the previous engine project with no vibration.

The Stuart twin looks real close to the engine in the box.  The boxed twin has the crank at 180 degrees so compound operation would be pretty straight forward.  There are no screw holes drilled in the head or the valve chest so I don’t have any non-symmetric drilling issues.  The big blue engine cylinder caps were randomly drilled and the cylinders were not bored straight.  In fact, when it arrived, the cylinders and cross slide were glued to the base.  It was pretty hysterical, but there was no drag.  I do have a nice aluminum crank, eccentric, and crank rod bearing left over that will likely never use.


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## Steamchick (Jul 12, 2022)

Hi Doug: Here goes: 
As compound running means you are only filling 1 cylinder from the boiler, and I was using a longer stroke, the numbers now work out at:
- Bore: 1.2”
- Stroke: 2” = double acting;
- Compound running configuration. 
- Crank speed: 300rpm.
- Steam pressure 20psi (guessed from what I think I can see on the pressure gauge?).

So:
This gives me 636 cu-in of steam per minute... which equates to 0.88 cu.in. of water per min. (at steam NWP = 20psi). This also proposes a need for 0.6kW of heat developed into steam. (at 60% efficiency, because the boiler loses heat to the room, heat is lost up the chimney, etc. you need a 1.1kW burner). 
Now translating the 0.88cu.in/min. of water:
a pump at 250rpm would need a displacement of 0.0035cu.in. per REV.
So a single-acting pump, stroke = 1/2", would be 0.095in bore... IF I have crunched the numbers correctyly! (I can't even type correctilly!).
The way many manage this is not with a direct acting eccentric/pump, but with a geared shaft that has the pump attached. The tiny bore (~3/32"?) will have some dead spaces at "TDC" (due to valves etc.) that will cause it to not function if they have any entrained air. The draw-back then is that the engine can appear to speed-up in the "intake" stoke, and slow on the "pressure" pumping stroke when it is working against boiler pressure. I compensated for this with a weird eccentric drive motion that gave the pumping time approx. 3 x the inlet time... and evened out the pressure variation somewhat.
I'll have to strip the system to show you with picture and video.
K2


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## DJoksch (Jul 12, 2022)

Steamchick said:


> Hi Doug: Here goes:
> As compound running means you are only filling 1 cylinder from the boiler, and I was using a longer stroke, the numbers now work out at:
> - Bore: 1.2”
> - Stroke: 2” = double acting;
> ...


Good point.  Did not consider the speed imbalance due to pumping.  I have some nice indexing tools for cutting gears.  Old clocks can wind up storing the power of a garage door spring.  I’ve had to make a gear or two.


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## Steamchick (Jul 13, 2022)

Hi Doug (and watchers all!).
Just a quick post as I am off out with my beloved lady to enjoy the sun!
Here is a VERY quick sketch (NO CAD!) to indicate how a simply wheel driven lever can vary between one stroke and the other for the pump. 
Rotate the pin clockwise in your mind (or YOUR CAD model!). When the drive pin approaches l1, it has a good velocity ratio for quick priming of the pump, sucking against atmospheric pressure.
As it approaches L2 it has a very good mechanical advantage to push against the pressure in the boiler.
Hope this makes sense? 
K2


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## DJoksch (Jul 14, 2022)

Steamchick said:


> Hi Doug (and watchers all!).
> Just a quick post as I am off out with my beloved lady to enjoy the sun!
> Here is a VERY quick sketch (NO CAD!) to indicate how a simply wheel driven lever can vary between one stroke and the other for the pump.
> Rotate the pin clockwise in your mind (or YOUR CAD model!). When the drive pin approaches l1, it has a good velocity ratio for quick priming of the pump, sucking against atmospheric pressure.
> ...


I like the concept.  That’s exactly what this engine needs.  I would have responded sooner, but I was asked to play in a pit orchestra for a show opening this weekend.  The proceeds of course go directly into my projects.


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## Steamchick (Jul 14, 2022)

I understand "MUSIC" comes before "Machining".... in my alphabet of life...
K2


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## DJoksch (Jul 14, 2022)

Steamchick said:


> I understand "MUSIC" comes before "Machining".... in my alphabet of life...
> K2


It’s a close match, however music helps pay for the machining supplies.


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