Steam Engine - Compound, Cross Compound & Simple

[nicknoyes]

Reading about steam engines I notice reference to Compound, Cross Compound and Simple. I assume this describes how the steam pressure is used to move the engine, but what is the difference?

 

Nick

[CSSHEGEWISCH]

A simple engine uses steam once.  After exhausting from the cylinders, the steam goes up the stack to aid the draft.  A compound uses steam more than once.  In a Mallet compound, such as a C&O H-6, the steam exhausts from the rear high-pressure cylinders to the front low-pressure cylinders, where it is used a second time and then exhausts from the low-pressure cylinders up the stack.  A cross-compound is a non-articulated locomotive with a high-pressure cylinder on one side and a low-pressure cylinder on the other side.  Most non-articulated compounds predate the development of superheating.

[nicknoyes]

Nice straight forward answer.

Thank you Paul

[selector]

...not to be confused with a Westinghouse Cross-Compound air pump.

[timz]

Most non-articulated compounds predate the development of superheating.

In the US, that is.

I guess cross compounds were never common in the US-- they must have been about all gone by 1910. Tandem compounds were another short-lived idea: coaxial high pressure and low pressure cylinders on each side of the engine. More numerous were Vauclain compounds: HP and LP cylinders parallel to each other on each side of the engine. Many US railroads tried balanced compounds -- two HP cylinders inside the frame, driving on a crank axle, and two LP in the usual spot-- but only SFe had a large fleet of them, and they rebuilt them to simple by the 1920s.

Lessee-- who still had any non-artic compounds in the US in, say, 1930?

[gbrewer]

The Manitou & Pike's Peak Cog Railway used Vulclain compounds until they diesalized. Most (possibly all) are still in existance.

[erikem]

Lessee-- who still had any non-artic compounds in the US in, say, 1930?

Delaware & Hudson 1400, 1401 and 1402 - the 1403 came in 1933.

The 1400 used 350 psi superheated steam, the 1401 used 400 psi and the  1402 used 500 psi. See the June 1967 issue of Trains.