From: brownp@cs.unc.edu (Peter Brown)
Newsgroups: rec.railroad
Subject: Re: compound locos (was Re: High Speed Rail Query)
Date: 9 Nov 92 06:28:06 GMT
	<36546@cbmvax.commodore.com> <1dicm2INN3l8@usenet.INS.CWRU.Edu>
Organization: UNC Department of Computer Science
In-reply-to: elw4@po.CWRU.Edu's message of 8 Nov 92 06:38:58 GMT

In article <1dicm2INN3l8@usenet.INS.CWRU.Edu> elw4@po.CWRU.Edu (Evan L. Werkema) writes:

      I know Garretts were used in Australia and Africa (still?), but I can't think
   of a North American railway which used them.  Is there any particular reason 
   why it didn't catch on in the USA?  

Kenya Railways has a Garratt they fired up as recently as 1988; I
don't know if they still run it or not.  I don't know why they didn't
catch on in North America.

	[This next is Mark quoting a previous article of mine]

   >Something Mark doesn't mention about the Vauclain is that the high-
   >and low-pressure cylinders also shared a common valve chest
   >(presumably rather more complex than a standard valve chest);
   >generally this was a piston valve (as opposed to the slide valve
   >standard in American practice in the 1890's), mounted inboard of the
   >high-pressure cylinder and actuated by inside valve gear.  You can see
   >the front of it pretty clearly in photos of the early Vauclain
   >compounds.

      This may be what you're talking about anyway, but some Santa Fe Atlantics
   were built as four cylinder compounds with the high pressure cylinders mounted
   beneath the smokebox between the low pressure ones, but with each high pressure
   cylinder sharing a common valve chest with the neighboring low pressure 
   cylinder.  The low pressure cylinders angled in at 45 degrees and the high 
   pressure ones angled out, meeting at two common sets of valves beneath the 
   running boards.  _Iron Horses of the Santa Fe Trail_ by Ed Worley goes into 
   some detail on these beasts (though I'm typing this from memory too).  His 
   comment on them was essentially, "Handsom is as handsom does, and these 
   Atlantics were about the ugliest locomotives ever put across the rails."

You're right - they're different.

To draw something of a picture (O, the joys of ASCII graphics):

Vauclain (seen from the end):               

                           valve chest
                            |      |
			    v      v
high-pressure cylinder->  o o      o o
low-pressure cylinder->   O          O
                           |        |
                           ^        ^
                          driving wheels

The valve gear is inside, between the drivers; the two cylinders on
each side drive a common crosshead, so you get only one main rod on
each side, outside the drivers.  (This drawing represents case where
the locomotive had fairly large drivers.  Small-drivered Vauclain
compounds had the cylinder assembly the other side up, with the
low-pressure cylinders on top.)

Santa Fe (seen from the end):

                            high-pressure cylinder
                             |
                  valve chest|
                            ||
			    v|
                            ov     o
low-pressure cylinder ->  O  o    o  O
                           |        |
                           ^        ^
                          driving wheels

I have drawn them as if the valve gear were inside; I suspect it was,
but could be wrong.  What I _am_ sure of is that the low-pressure
cylinders in this arrangement were outside the drivers, and the
high-pressure cylinders were inside, so it took two main rods on each
side to get the force from the cylinders to the wheels.  Lots of extra
complexity, lots of extra maintenance headaches.  Ugh.

Peace,
--Peter
--
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
"In this is love, not that we loved God but that he loved us and sent
his Son to be the atoning sacrifice for our sins." - I John 4:10
Newsgroups: rec.railroad