# Compound steam engine



## bille1906 (May 2, 2009)

I am thinking about building a four cylinder compound Heisler as patented but never built by Charles Heisler
The V-4 engine would have a high and low pressure cylinder on both sides and would be 180 degrees opposit each other.
In researching the subject of compound engines it appears that in full scale, the low pressure (LP) cylinder diameter is double the size of the HP one.
In our scale, it seems that the ratio is much closer to even. Aster has two compound models which both have 10 mm HP and 13 mm LP cylinders
*My questions are:*
*Does anyone have any experience with the Aster or any other G scale compound models they can share before I get too far into the design work*
*Any ideas or links to helpful information* 

I know there were a lot of problems with Mallets as the distance between engines led to a lot of condensation and pressure loss but that these engines were successful in marine and stationary applications where the cylinderss were inline. this will be the case with the two cylinders on each side so I am thinking it should help there


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## Cougar Rock Rail (Jan 2, 2008)

Bill you might also want to check out some German forums regarding the Regner compounds and other locomotives--just fire up the Google translator! 

Keith


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## Cougar Rock Rail (Jan 2, 2008)

Here is a link to a thread here on MLS where someone built one of the Regner compounds--some information that might help: 

http://www.mylargescale.com/Community/Forums/tabid/56/afv/topic/aff/11/aft/31256/Default.aspx 

Keith


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## Geoffc (Dec 27, 2007)

Bill, 

Herrmann Echtdampf makes a German Mallet (SEG Mallet #104) that runs very well (I have one). Both the high and low pressure cylinders are the same size- I'm sure that it is done that way for ease of manufacturing, and at that such a small scale it probably would not improve performance enough to follow the true prototype (looking at photos of the real SEG 104, the front cylinders look to be twice the diameter of the rear). There are no photos of Uwe Herrmann's compound design on his website, but it has appeared very simple to me- when I have had the bogies off for maintenance that is. Uwe has a great web site: 

http://www.echtdampfwelt.de/echtdampf-classic/echtdampflok-seg-mallet.htm 

Uwe speaks very little English, but his business partner Hanns speaks good English and I'm sure he would be happy to answer any questions if you sent him an e-mail (address posted at web site) 

Geoff Clinton


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## Semper Vaporo (Jan 2, 2008)

The size of the LP cylinder depends on the steam pressure that is left in the exhaust of the HP cylinder. What you want is the same amount of thrust on the drive rods from both the HP and LP cylinders.

As an example, and to keep it really simple so I don't have to get my calculator out... 

Suppose you have 40 pounds per square inch of steam in the boiler and the HP cylinders are 1 square inch of surface area (that makes it... ummm... daing gotta get the calculator anyway... sqrt(1/Pi) = 0.564 inches in diameter), thus you are applying 40 pounds of force on the drive rod. 

"IF" you lose 1/2 of the pressure moving the piston in the HP cylinder then you have 20 pounds left in the exhaust. To get 40 pounds of thrust on the drive rod you need 2 square inches of piston surface area to get that same 40 pounds of thrust. Sqrt(2/pi) = 0.798 inch diameter. Remember that big "IF" at the beginning of this paragraph. "IF" you have only 10 pounds of pressure left then you need 4 square inches of surface area to get that same 40 pounds of thrust, so Sqrt(4/Pi) = 1.133 inch diameter. "IF" you have 30 pounds of pressure left then you need 1.333 square inches of piston surface area... Sqrt(1.333/Pi) = .65 inch diameter.

To complicate matters! The pressure left over in the HP cylinder's exhaust depends on the cutoff of the steam into the HP cylinder. It could range from nearly the full boiler pressure (no cutoff) to near atmospheric pressure (maximum cutoff); it could even be negative pressure!

The cutoff to use for the calculations depends on the purpose of the engine and its normal operating state. There are trade-offs that must be considered that might offset the value used away from any "ideal" value. What kind of valve gear is being used and what levels of cut-off does it provide? Does it stop and start often? Does it run fast or slow most often? Does it need help in starting? Is there a way to feed boiler pressure to the LP cylinder when needed?

For a "toy" engine, I would hazard a guess to assume a pressure loss of around 1/2 or more and thus go with a LP piston area of at least 2 times the HP piston area (about 30% more in diameter), up to maybe 3 times the area (not quite twice the diameter).


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## bille1906 (May 2, 2009)

Keith, Geoff
Thanks for the info
I couldn't get the Regner build to open even after I installed Picasso but the rest of the info was helpfull


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## redbeard (Jan 2, 2008)

Hi Bill, 
I have read the patent information and studied the patent drawings for the four cylinder Heisler many times. I do not see how you could balance the reciprocating weight of the pistons if they were different sized at all. Why a compound engine for this locomotive? 
Larry


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## bille1906 (May 2, 2009)

Semper 
It looks like 30% may be the way to go 

Aster who usually gets it right uses a 30% larger LP with a 75% cutoff on the HP and 80% on the LP for it's SBB A 3/5 which I guess is a fairly high speed engine so I think a 82% cutoff on both sides should work on the Heisler. 
I'll be using Walschaerts gear with slide valves per the original Patent drawing 
The drawing shows both cylinder outside diameters to be the same size, as when he originally designed it, it was to be either simple or compound. In fact the drawing looks to have simple piping but the text I read indicates he was leanin tward a compound engine. 
In any event, it will be hard to have too much variation in cylinder size and keep with the scale Heisler proportions


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## bille1906 (May 2, 2009)

Hi Larry 
There will be one small piston on each side of the locomotive connected to a common crankshaft journal as in all Heislers. 
In addition, there will be one larger piston on each side connected to a common journal which is 180 degrees ofset from the aforementioned one. 
This is the way I interpret the drawing. 
I have made some drawings but am away from my computer and scanner so I can't post them but I will when I get home in a few days 
Why a compound engine? 
That's what my friend Henner asked me. 
This will be the first G scale three truck Heisler (I think), the first four cylinder Heisler (I know) so why not go all out and compound it. 
I am sure it would be easier, run smoother and have more power with four 1/2" cylinders which I may end up doing but, I do enjoy a challenge so I am probably going to at least try this first 
This will be a narrow gauge version so it will be fairly large and should have power consistent with the size.


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## lotsasteam (Jan 3, 2008)

http://www.buntbahn.de/modellbau/viewtopic.php?t=6630

With pics (in german) page 2 (Henry might be able to translate)

Manfred


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## HMeinhold (Jan 2, 2008)

@Semper

In these small scales condensation is a big problem. The theoretical area ratios don't work. 1:1 to 1:1.3 are empirical values.
@Manfred
We have an internal E-mail/personal discussion and I provided Bill already with some of the results in the buntbahn threads.
This will be another fascinating project by Bill.


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## rodblakeman (Jan 2, 2008)

Hi Bill, 
I believe we met at Rob Lenicheck's steam up a couple of years ago, I have built both the Regner IV K and TSSD Mallett engines and they run well. 

The HP cylinders are 12mm and the LP 14mm. 

Normally 3 - 3.5 bar of steam is needed to get the compounding started, once well warmed the engines run ok on lower pressures. 

I find cylinder drain cocks are essential to enable clearing of condensate especially for the LP engine. 

I also lagged all the steam pipes to try and keep them warm. 

In this clip of the IV K it starts in simple and when switched over to compound one can hear the reduced exhaust beat noise. 

https://plus.google.com/photos/1140...5909772484938531874&oid=114036153408224749848 

I hope you can access the video, since Google screwed up Picasaweb with Google + which frequently prevents me from viewing my own input. 

One also has to take care starting in simple mode as it is easy to "spin" the LP engine at "full" pressure and just drag the HP engine, especially on slippery track. 

Good luck with your new project, have enjoyed following all your build threads. 

Regards


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## bille1906 (May 2, 2009)

Thanks Rod
I do remember meeting you
I am curious as to why the Regner needs to start in simple mode.
Is it because it doesn't have the power to get started or that it spins the HP wheel set


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## rodblakeman (Jan 2, 2008)

Bill, 
As far as I am aware it was normal practice to start off in simple and then switch to compound when the engine was cold. 

In the model, I have to admit that I don't know how much power the LP engine produces in compound or if it is just a pump for the exhaust at these low ( 2 - 3 bar ) pressures.  

My experience with these models is that on a good day with warm cylinders one can restart in compound but usually I switch to simple and frequently open the LP drain cocks for a second to get going. 

If there is any condensate in the LP cylinders and one tried to start in compound then yes the HP engine will spin up. 

It is all a matter of practice with each engine. 

The one thing that I do find critical is the drain cocks, from cold at these steam pressures there is a tendency to condensate up the LP engine. 

Of course this may all be down to the user/ builder


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## bille1906 (May 2, 2009)

Thanks Rod 
I know that condensation was a big problem with the full size Mallets and that many were converted over to straight simple engines. 
As Henner points out, it is more of a problem with our models. 
A couple of things I will have going for me is that the LP and HP cylinders are butted together so there will be a short pipe connecting them and there will be heat transfer from the HP to the LP cylinder. 
Also, both cylinders will be connected to the same crankshaft so the spin factor will not be an issue 
Do you know if the original IV K or TSSD had the simple/compound switch or is that something Regner came up with?


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## HMeinhold (Jan 2, 2008)

Bill,

the newly restored rack railway loco 97 501 was a compound. However shortly before it entered the rack section, the rack cylinders were warmed up by slowly running them on live steam. Once on the rack section, they switched to compound. I have asked my "sources" in Germany to inquire about the Tssd and IVK. But it looks as if both locos (the real ones) had single/compound valves.


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## Reg Stocking (Sep 29, 2010)

Starting simple and switching to compound was standard practice with the French de Glehn four-cylinder locomotives. In 1964 I was delighted to observe the departure of the boat train from Le Havre Maritime to Paris from the deck of SS America. The shiny Pacific started with crisp high-pressure exhaust blasts for the first few driver revolutions, then made soft and slushy chuffs in compound. The performance was most impressive.


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## bille1906 (May 2, 2009)

Here are the drawings I have been fooling around with








Here is the original drawing by Charles Heisler in 1897. Note the admission piping indicating this engine would be simple.
Heisler however was contemplating building a compound engine 









Here is a 70 Ton three truck engine which was available in both standard and narrow gauge.
My thought is to do this one in narrow gauge (1:20.3) but with four cylinders. 









Here is what the LP and HP cylinders would look like. This shows the left side. The right side would be the same but offset by 90 degrees 
The right side connecting rods are shown just to the right of the left side on the crank journal 









This shows the engine mounting and crankcase clearances. This is slightly modified from Kozo's drawings and scaled down
It also has an extra crank journal for the third and fourth cylinders
It looks like the engine may be removable through the diamond frame using these dimensions


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## Charles (Jan 2, 2008)

Billy

We are going to be sending your some expert gauge one reading material on compound steam engine via PM.


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## bille1906 (May 2, 2009)

Thanks Charles


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## zephyra (Jan 2, 2008)

Bill, I have the Aster BR96 Compound Mallet. The HP cylinder are 13 x 18 and the HP cylinders are 10 x 18. The machine works well. The key is to use the LP bypass valve intelligently when first getting the machine going. 

Happy to bring these to a Pacific Live Steamers event for inspection.


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## xo18thfa (Jan 2, 2008)

Hi Bill: It was good to see you at Sacramento again.


What kind of boiler are you planning for this engine? Rod says 3.5 bar, that's 50 PSI. Go with a full up loco style boiler. It will make full time 50 PSI no trouble

Bob


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## bille1906 (May 2, 2009)

Bob 
I was thinking of a ceramic burner loco style similar to the Uintah. 
I am still leery of alcohol and there isn't much access for coal with the cab configuration 
Not sure about wet or dry fire box yet. 
Still not sure if I should go with a wagon top boiler or just a straight one with a wagon top wrap 
Any suggestions?


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## HMeinhold (Jan 2, 2008)

Posted By zephyra on 19 Sep 2013 09:48 PM 
Bill, I have the Aster BR96 Compound Mallet. The HP cylinder are 13 x 18 and the HP cylinders are 10 x 18. The machine works well. The key is to use the LP bypass valve intelligently when first getting the machine going. 

Happy to bring these to a Pacific Live Steamers event for inspection. 

Bill lives just 12miles north of your place near 280. Why don't the two of you meet?


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## Garratt (Sep 15, 2012)

Posted By Semper Vaporo on 17 Sep 2013 02:07 PM 
...
... 
Suppose you have 40 pounds per square inch of steam in the boiler and the HP cylinders are 1 square inch of surface area (that makes it... ummm... daing gotta get the calculator anyway... sqrt(1/Pi) = 0.564 inches in *diameter*), thus you are applying 40 pounds of force on the drive rod. 
...
... 
Semper, I think your calculations should read 'radius' not 'diameter'. 

Andrew


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## Semper Vaporo (Jan 2, 2008)

Posted By Garratt on 21 Sep 2013 11:07 AM 
Posted By Semper Vaporo on 17 Sep 2013 02:07 PM 
...
... 
Suppose you have 40 pounds per square inch of steam in the boiler and the HP cylinders are 1 square inch of surface area (that makes it... ummm... daing gotta get the calculator anyway... sqrt(1/Pi) = 0.564 inches in *diameter*), thus you are applying 40 pounds of force on the drive rod. 
...
... 
Semper, I think your calculations should read 'radius' not 'diameter'. 

Andrew 


ACK! You is absolutely right! It is Pi R squared (even if it is the da crumb-bread that is really square!)


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## Garratt (Sep 15, 2012)

Mmmm, pi. My favorite! 

Andrew


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## xo18thfa (Jan 2, 2008)

Posted By bille1906 on 20 Sep 2013 07:19 AM 
Bob 
I was thinking of a ceramic burner loco style similar to the Uintah. 
I am still leery of alcohol and there isn't much access for coal with the cab configuration 
Not sure about wet or dry fire box yet. 
Still not sure if I should go with a wagon top boiler or just a straight one with a wagon top wrap 
Any suggestions? 
Hi Bill. According to the Australian model boiler code, boilers under 77mm diameter and running at less then 520kPa (75.4 PSI) do not require flanged boiler plates. Flat plate for firebox ends, tube sheets etc is satisfactory. According to the code the plates can be 2mm thickness. If you used 2-1/2" or even 3" copper pipe for the barrel, then 1/8" thick plates would be plenty. Without the flanging, there would be no difficult fit-ups to do. Everything is nice square corners.

Kozo's "New Shay" book has a very detailed explanation to calculate stay requirements for the firebox. I don't think you would need that many.

Kozo's first Shay has a wagon top boiler. He rolls the transition piece from flat. Could make a wooden transition piece and use to to make a pattern from a file folder.

I'd go all the way


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## bille1906 (May 2, 2009)

Thanks Bob 
I have the KOZO Heisler book and see how he did the boiler. 
I won't follow it exactly as I have better things to do than 20 or 30 boiler solderings 
My dimensions will be different so Dennis will probably make me a pateren for the transition piece in CAD 
I'm thinking maybe wet fire box with dry backhead. 
The dry firebox on the Uintah works well with the ceramic burner but I haven't done a wet one yet so here is a good place to start. 
The dry firebox allows for more tubes but the wet one has better water circulation. I guess.


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## du-bousquetaire (Feb 14, 2011)

Aster French and Swiss compounds function perfectly well as compounds and the economy is such that a compound will do at least two laps more than a SE engine with the same train and track. However the advantages of compound engines are mainly the balancing out of piston masses and the resulting hammer blow. I wouldn't see the point of doing one as a Heisler, except as a freak project just for fun. They were known to be better at climbing grades than simple engines so you might find an advantage there, and you could also use the booster effect of admiting some HP steam to the LP cylinders although that would lead to a complex system of derivation valves (to exhaust steam from the HP cylinders directly out and feed steam directly from the boiler at reduced pressure to the LP cylinders.) The N&W used to call it a Booster! The problems linked to condensation can be solved with an appropriate superheater. The other lesser known advantage of compounds over simple was that there was less carry over or leakage across the piston rings as there was a smaller pressure drop from one side of the piston to the other, this led to a good deal of the economy of modern compounds. It must have been especially nice on a loco say a few weeks or months from general overhaul. 
The Etat Pacifics Red stocking talks about actually had two regulators one regular to the HP cylinders the other to the LP cylinders, they are terific engines almost Chapelon pacifics as the Etat engines were copied with detail mods from the Paris Orléans engines Chapelon transformed in 1929. the Etats ones were transformed with two oscilating cams per side for both HP and LP cylinders, some Houlet (an improved type of) superheater elements and of course Kylchap exhaust they were practically Chapelons. I rode the 2-3-1 G 150 km from Alencon to Caen. The 1,2% grade just out of Alençon was eaten up in fabulous style. the loco could really accelerate a train.


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## bille1906 (May 2, 2009)

Thanks for that background 
Yes I am doing it mainly as a fun project. 
It will be superheated and the LP and HP sharing basically the same cylinder block should help with the condensation. 
Rather than go into a complex plumbing job, my thought is that I can easily convert it to simple if it doesn't work.


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