Double compound steam engines - any info?
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  1. #1
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    A while back there was a posting about a derelict ferry in the USA; the steam engine was described as a “double compound”. I had never heard of this type of engine, and still can’t find much info. Anyone have any experience with this type, and how they fit into the last years of the steam reciprocating engine? Some of my ideas below probably need correction please let me know [img]smile.gif[/img]

    One problem is the varied descriptions used - when searching the internet I came across what I would call a compound engine (i.e. 1xHP, 1xLP cylinder) described as a “double compound”. For example there is a surviving steam ship called “Segwun”, photos appear to show a compound engine (two cylinders, two cranks), but it is described as a “double compound”. As if life weren’t complicated enough

    It took a bit of figuring out, but a marine double compound seems to have four cylinders on four cranks on a common crankshaft. Of additional interest is that they sometimes use the Woolf cycle – revived and employed in some of these last steam engines built. There seem to be different versions, but one type has two pairs of Woolf compounds (i.e. cranks of each pair at 180 degrees), on a common crank, with 90 degrees between the pairs. This allows the engine to always start (no dead centre) while retaining the simplicity possible with cranks at 180 degrees, .e.g. no receiver, one valve per pair of cylinders.

    Arthur Woolf was one of the early builders of compound engines; he built his first in 1803. A distinctive feature of the original ‘Woolf’ system (as fitted to beam engines) is that the pistons of the HP and LP work together in the same direction, thus the HP exhausts directly into the LP, no receiver is required between the cylinders. The marine engines described above have pistons working in opposite directions, but being at 180 degrees, I believe it is the same system. The same cycle can be used with tandem and annular engines.

    Other types of two-crank compound used a receiver and separate valves between the cylinders; this allows the cranks to be at any position (expansion not dependant on piston phasing). Often cranks are at 90 degress for easier starting and better balance. This popular compound receiver system developed into the triple expansion with cranks at 120 deg, best known of all marine engines.

    I suppose another type of “double compound” is the twin tandem engine. Found both on land and at sea, the LP and HP of each pair share the same crank pin. A modified Woolf type became popular at sea – tandem with separate valves for each cylinder. Several such tandem units could be mounted on a common crank to make some of the largest marine engines ever made. However, it is really the four crank types that I am interested in here.

    I found descriptions of a few double compound engines as used in the 1920’s-50’s:

    W.A. White in the UK developed the White “New Economy” engine which first appeared in 1934, a double compound with HP and LP cranks at 180 deg, each pair at 90 deg, “easy handling and good balance” being the description applied. This engine was a little unusual in being ‘high speed’ (250/300 rpm), it drove the prop shaft via a reduction gear. The LPs’ exhausted into a LP turbine which also drove the prop shaft via the same reduction gear. This unit developed 1230 hp.

    (A whole other subject; this type of ‘combination’ machinery was popular and successful in the 20th century and made in many interesting different types by many manufacturers (i.e. using single and double compound, triple expansion, etc. etc. and low pressure exhaust turbines powering geared or hydraulic drives, AC or DC generators driving motors connected to the shaft or electric elements re-heating the receiver steam, compressors re-compressing the receiver steam etc. etc.)

    Christiansen & Meyer from Germany made double compounds (Woolf compound), four cylinders, just one valve (piston type) per pair of cylinders. The HPs’ were counterflow, the LPs’ were relieved compression uniflow. Only one eccentric per pair of cylinders, a very simple engine.

    Lentz-valve engines were also made double compound from the 1920’s, Woolf-type with no receiver, steam exhausting from HP to LP through a common valve. Once again, HP and LP cranks in each pair at 180 deg, with each compound section joined with HP cranks at 90 deg.
    I have a photo showing a Lentz-type double compound engine built in Australia after WW2 for their “D-class” ships. It is fully enclosed and the description says “individual poppet valves”, so maybe not the common valve of the earlier type.

    Anyone have info on US or other double compounds?

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    Peter,
    I think the ferry mentioned (Mary Murray?)had a four cylinder compound, basically two fore and aft compounds mounted end to end on a common bedplate. I'm sure if Joe Michaels reads this he'll be able to clarify the terminology but that's what comes to my mind. The only other thing I can think of would be two steeple compounds on a common bedplate.
    Speaking of compound engines, I'll be bringing Medea back from the shipyard tomorrow. This time I'll try and get some pictures posted.

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    IIRC the term refers to a 2cyl.expansion engine,
    but usually referred to as a "compound(ed) engine as there must be two cyls. minimum for compounding.
    Triple and quadruple expansion engines were referred to by their full "titles"

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    Peter:

    IMO, the term "double compound" applies to a pair of fore-and-aft compound engines using a common crankshaft. This configuration of engine has four (4) cylinders, in-line. Typically, there are the two high pressure (HP) cylinders in the "middle", and the low-pressure (LP) cylinders are out at each end. The cranks on the HP's are usually set at something like 90 degrees to avoid having the engine stop on dead center.

    The "double compound" design was used for harbor ferryboat service. The reason for this was that this configuration provided the best combination of manuverability, power at the cost of some economy. A harbor ferry had to be able to get up to speed and manuver quickly. In the days of the double compound steam engine's popularity, harbors were a lot busier. There was a great deal of barge traffic, workboats, lighters and then there were the bigger merchant vessels. Navigating through New York Harbor, as the Staten Island ferries had to do, meant working through harbor traffic consisting of railroad car floats from several different railroads, assorted barges in tow or "on the hip" of the tugs, ship docking tugs, other ferries, and merchant and passenger vessels. It was not uncommon for a ferry engine to be slammed from full ahead to full astern to check the speed of the ferry or make a hard turn to avoid some other vessel. Approaching the slip at the end of a crossing, the ferries had considerable way still on them. Not too far out of the slip, the skippers would ring for the engines to be run astern. The ferries would shudder and vibrate when this occurred and come to a near stop rather quickly. The engines would then be stopped and the ferry would kind of glide into the slip with almost no jolt or impact against the pilings. Once in the slip and against the pilings, the skippers would ring down for slow ahead to hold the ferry in place.

    This sort of thing went on for many trips each day. The double compound engines were ideally suited for this sort of running. It was a service that did not allow the engines to be brought up to a steady crusing speed and left there. If that were the case, then an engine such as a conventional triple expansion engine would have been used as steam economy would have taken precedence over manuverability.

    There were other "double compound" marine steam engines built using what could be called "steeple compound" or "tandem compound" cylinders. These had the HP cylinders on the same piston rods as the LP cylinders. This made for a taller engine with a shorter overall length. That design, aside from saving engine room floor space, had higher reciprocating masses. I would think manuverability would be compromised with this type of double compound. IMO, this type of double compound engine, while qualifying as a "double compound" was not so widely used in marine service. I believe that when the term "double compound" engine was used, most people took it to mean double fore-and-aft compound engine.

    Skinner engine used the Woolf system to build some steeple compound Unaflow marine engines. These were typically built in multi-cylinder layouts (4 crank throws being typical). I believe the car ferry "Badger"- still in service on the Great Lakes- uses this type of compound Unaflow engines. I do not know if Skinner ever built any of the steeple compound Unaflows with only two crank throws.

    Joe Michaels

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    Peter,

    The White “New Economy” engine sounds interesting. Seems like a lot of expense for such a small power output, given the cost of the engine, turbine, and gearbox. I wonder if the fuel economy justified the cost?

    Do you know if the turbine was permanently coupled to the gearbox, or whether there was clutch to avoid spinning the turbine when manouvering?

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    Joe is correct about the Badger it is powered by 2 Skinner uniflow quadruple expansion engines. 5 auto stoker coal boilers provide the steam. The ship also uses steam steering and anchor lifting engines. It is a real treat when the Badger is in port [Ludington MI] and the Luedtke #16 dredge is also there since the dredge is a Clyde 28 oil fired steam crane. I hope someday to get a picture of these last two survivors of the Great Lakes. The Badger is a joy to watch and even more fun to ride. Marine History lives in West Michigan

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    Asquith, I don't have a lot of detail in the White engine. It was fully enclosed, forced lubrication. "Excellent results mechanically and in fuel economy." Example given was S.S. Adderstone.

    The various combined systems usually uncoupled the turbine somehow when going astern, and also bypassed the LP steam direct to the condensor via a changeover valve. But it doesn't tell me how the White does it.

    Bauer-Wach used an oil-filled coupling.

    Brown Boveri actually fitted an astern turbine as well.

    Parsons used a 'springloaded friction plate drive in the second motion gear hub'.

    Other combined systems used reheat and compressor turbo systems, or electric drives.

    Chris and Joe, thanks for your replies - you both use the term "fore and aft" compound - another term I have never come across in books - maybe it is an Americanism?

    Ken, I think your description is probably plain wrong and needs to be stopped. Basically you (and others I found on the internet) are calling a compound engine with two cylinders on two cranks a "double compound". What would you call a "normal" double compound with four cylinders and four cranks?

    Joe, the tandem compounds had a period of popular use on the North Atlantic run - huge engines with maybe three tandem compounds fitted to a single crank, the City of Rome being a monster example. This appeared in 1881 with 10,000 ihp from its single engine. I can't see them ever called double compounds, but then many of them were "triple" compounds anyway.

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    If the description is "double compound" I think a double tandem would be a better description on a ship ( HP and LP on same piston rod but situated HP over the LP) I have seen engines with this configuration before and in this config would use alot less valuable deck space on a ferry.

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    Mcandrew1894,
    I don't think we are talking about the same engine type here.

    There is an engine type which uses four cylinders (2xHP, 2xLP) on four cranks on a common crankshaft. Each cylinder has its own crank. I believe this is a double compound, at least I find it given this name in the few brief accounts I have in books.

    I have to say I was very surprised and fascinated when I read about it (on this forum), I had completely missed it after many years of interest in steam. Of further interest is that this design was used in the early days of marine compounding (1860's) and was criticised as having excess of parts. So it is interesting to see this type appear in some of the last marine steam engines made, and sometimes in highly efficient form.

    The twin tandem compound or twin steeple compound has half the number of cranks. BTW, the tandem layout didn't always share a piston rod, there were various methods to sometimes get around this, however I guess they did share the same connecting rod and crank.

    Apologies for going over the same stuff again and probably stating the obvious, not sure where the misunderstanding is, maybe just different terminology at work...

    --------
    "For and aft compound" - any idea where this term comes from? I think I understand its meaning, just curious as to its origins as I have never seen it used in books.

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    Ken, I think your description is probably plain wrong and needs to be stopped
    Did I write that? [img]redface.gif[/img]

    kenh, sorry, that comes across badly. I meant to question your description, but not intending to be rude.

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    Peter,
    A fore and aft compound has the cylinders inline on a fore and aft axis as opposed to a steeple compound in which the HP is above the LP and has a single crank throw. There are also V compounds and triangle compounds which really stir things up.

    I'm posting pictures of Medea under a separate thread.

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    Hi Peter,

    Do you have a picture of this beast? I would imagine the receiver plumbing ( both of them) on such an animal must be quite impressive. Though possible, its just seems odd.

    Your comments about the differant steeples and various methods of routing piston rod(s) is right on point, I was trying to keep it simple as it gets complicated enough all by itself.

    I have to ask though, are we sure we are not talking about a "4 legged triple"? For those of you who think I am speaking in giberish,I will explain. The steam navys of the world in an effort to make their battleship engines more powerful, started running them at higher speed. With an ordinary triple ( three cylinders on three throw crankshaft like a liberty ship) the LP piston starts getting very large. When run at high speed the unbalanced loads between cylinders just due to mass cause excessive vibration that is very difficult to address. This is where a "4 legged triple" comes from. The LP is split into two seperate pistons, eg HP - IP - LP - LP. Designing it this way makes the pistons near to the same dimensions. Example, the USS Ohio of 1904 ( if my memory serves) had cylinders of 35 x 51 x 66 x 66 x 48" stroke running at 125 RPM.
    If you go to the USS TEXAS web site you will see a very large "4 legged triple" with photo's

    Pete the reason I ask is that the cylinder arrangement can be such that it looks like two compounds bolted together
    Check this out
    http://www.gwpda.org/naval/w07tex4l.gif
    Here the LP's are on the ends ( like the OHIO's)
    Again this was for balance and to make the crank effort smooth. If you have 100' of prop shaft spinning, you need all the help you can get!


    Dave

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    Hi again,

    Check this link also, amazing what the old timers could do with big stuff on short notice

    Dave

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    Hi,

    Joe I just read your post..."4 legged triple" is the name told to me...

    ...and no, I don't know who dreamed up the "4 legged triple" name.


    dave

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    Hello McAndrew:

    No disrespect, but a "four legged triple" is, in fact a triple expansion engine with two (2) LP cylinders. This was done to avoid having one overly large LP cylinder. The overall arrangement then would be: HP cylinder, IP cylinder, and two (2) equally sized LP cylinders. Years ago, an oldtime marine engineer (turned millwright) told me he had shipped on vessels with "four legged triples" and gave me this explanation. The "four legged triple" name would make sense since the engine was a triple expansion, but, having two LP cylinders it then had the "four legs" (in the form of four connecting rods or four mainframes). A double compound, while having "four legs" was a very different engine in that the steam was only expanded in parallel , through two (2) compound engines. The "four legged triple" was a true triple expansion engine in that the steam expanded from the HP exhaust into the IP receiver, thru the IP cylinder and then went on a parallel path through the two (2) LP cylinders.

    Some of these "four legged triples" had the LP cylinders on each end-throw of the crankshaft, and some simply had the pair of LP cylinders right next to each other.

    As for "four legged triples" and who dreamed up the name: old marine engineers tended to have their names for things, just as other trades and professions did. Chances are some marine engineer used to a conventional triple expansion engine stood looking at a triple expansion engine that had four cylinders and, while it wasn't a quadruple expansion engine, it DID have four cylinders. At the time that guy must've stood there pondering this "new" engine, horses were commonplace, so the "four legged" term was easy enough to come to mind.

    I had another friend, another old marine engineer (turned machinist and machine shop owner) who first shipped in the depression days as a workaway. He shipped as a workaway to get a warm berth and something to eat. He and countless other workways during the Depression years shipped for something like a penny a week. This princely wage being paid to avoid appearances of outright slavery or piracy. My old friend shipped for several years as a workaway, doing any kind of heavy grunt work in the engine and fire rooms. He and countless others were shipped as "coal passers and wipers", but put to any work in the engine and fire rooms. He said he was taken ashore only to "write for his tickets"- to sit exams for fireman and oiler as he got his sea time in, and later for third assistant engineer. Anytime the ship tied up in a port, the ship's officers would tell the workaways there were a couple of thousand men waiting to get aboard as workaways, all looking for a warm berth and somethign to eat. The message was clear: "shut up, get below and do what your'e told". So, they knew the ship's officers along with crooked businessmen were invoicing the shipping line for all kinds of work done by "contractors", when, in truth the labor was done by the workaways. My old friend said he wound up seeing and doing quite a bit of work on recip engines and boilers, learning quite a bit as he went along. He claimed he drew his first real paycheck only after he got his license as a third assistant engineer. He shipped right through world War II, in the North Atlantic finishing as a Chief engineer, Steam Vessels, Horsepower Unlimited. He sailed on all kinds of steam vessels, and had lots to say about the various types of engines and boilers. He had even more to say about the shipping lines, ship's officers and businessmen ashore who got rich off the workaways. He'd sailed on steam vessels with all manner of recip engines and some with steam turbines. This guy referred to any recip marine engine as a "walking turbine". He's dead and gone a good few years now, a gruff, tough oldtimer who took the time to teach me a few things when we worked together.

    Having got the "four legged triple" explained to me by two old time marine engineers, I'd go with their explanation of it. OTOH, "Walking Turbines" takes a bit of poetic license as that term makes no engineering sense.

    Joe Michaels

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    Hi Joe,
    I have commented below, I think we agree completely. But read through and make sure.
    Power loading must be balanced on any recip and especially multi expansion engines. Power balance is attained by adjusting cut-offs and receiver volumnes to obtain a card with equal area's ( power) and minimum drops between cylinders. But reciprocating engines running with piston speeds of 1000 feet/minute Also need to be balanced mechanically.


    "No disrespect, but a "four legged triple" is, in fact a triple expansion engine with two (2) LP cylinders. This was done to avoid having one overly large LP cylinder."


    No disrespect taken...we have the same description and understanding.


    The overall arrangement then would be: HP cylinder, IP cylinder, and two (2) equally sized LP cylinders. Years ago, an oldtime marine engineer (turned millwright) told me he had shipped on vessels with "four legged triples" and gave"


    ...again we agree completely....


    ..."mainframes). A double compound, while having "four legs" was a very different engine in that the steam was only expanded in parallel , through two (2) compound engines."


    ...I agree....I just hav'nt in 20 years seen many of them in this particular configuration...but there have been some really off the wall designs infinitely more bizarre than this so .."I'm with ya" I would like to see one of these, could you send out the post again?


    "The "four legged triple" was a true triple expansion engine in that the steam expanded from the HP exhaust into the IP receiver, thru the IP cylinder and then went on a parallel path through the two (2) LP cylinders."

    .....YUP...We still agree...and an old timer explained it to me the same way...

    "Some of these "four legged triples" had the LP cylinders on each end-throw of the crankshaft, and some simply had the pair of LP cylinders right next to each other."


    ...Absolutely.......


    go with their explanation of it. OTOH, "Walking Turbines" takes a bit of poetic license as that term makes no engineering sense.


    Engineering sense..no, but engineers are human
    ...my "handle" comes from a poem called "McAndrews Hymm" by Robert Stevens
    It's long and in Scottish broque...I won't repeat it. There is a passage early into it though where the Chief Engineer McAndrew was talking to his engine...

    ..."An Ferguson relievin' Hay. Old Girl, ye'll walk to-night!

    I think we can picture that...

    Warm Regards, and I would like to talk to you some more about this.

    Dave

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    Do you have a picture of this beast? I would imagine the receiver plumbing ( both of them) on such an animal must be quite impressive. Though possible, its just seems odd.
    mcandrew,

    I don't have a good photo of a double compound. I have one in "Workhorses in Australian Waters", but it small, poor and shows a fully enclosed engine - no detail visible. (It is a Lentz-type built after WW2).

    There is no doubt the double compound was built by quite a few manufacturers, in the way I have described above. I have found it described in several of my books with specific mention of the cylinder and crank layout. The same articles were describing all sorts of different engine types. Four-cylinder triples were not being confused with double compounds (or steeple compounds - they were popular to in the last years of engine building eg Ajax, Skinner etc and were covered in the same articles).

    As to the receiver part of your question - it seems most of the double compounds I read about were Woolf compounds - they don't require a receiver. With the cranks at 180 degrees, the steam goes direct from one cylinder end to the next, in (most?) cases via a single valve. This must have been one of the attractions of the layout.


    p.s. seems to be a link missing on your 2nd to last post?

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    Hi Peter,

    No disrespect meant.....Just checkin.... [img]smile.gif[/img]

    I understand the plumbing now too,

    I would love to see this, can you post a picture?

    Here's the link ..sorry about that...
    http://www.bb35library.com/OperatingSystems/EngineRoom

    Go to the top and click on trial report. Interesting reading!

    Dave

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    Hi again,

    here is another link for those who like big marine recips.

    This gentlemen mad a working model of one of the titanics engines...Nice work.

    http://titanic-model.com/db/db-03/hahn.html

    Dave

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    Hello Mc Andrew:

    It is Great to trade replies with you and glad of the nice level this forum is at ! I have a copy of "McAndrew's Hymn" on my desk at the powerplant. As you note, it is a lengthy, somewhat epic poem that gets into the life and times of a merchant marine engineer who'd come up from the coal scoop and slice bar.

    Peter S.:

    I do not think marine engines with Lentz valve gear ever caught on her ein the USA. To my knowledge, only one vessel ever got built with a Lentz engine. She was an ore-carrie ron the Great Lakes, possibly from the old Pickands-mather Interlake Line. She was in steam in the 1970's but I never got aboard her. I imagine the Lentz design, using poppet valves and finer control of cutoff, made for a mcuh more efficient engine than the usual piston or slide valves commonly used on marine engines. It would be interesting to learn about the Lentz engine and the vessel it was used on.

    Joe Michaels


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