I understand the theory behind compounding on steam equipment - "use" the steam twice or more before exhausting to atmosphere or a condenser.

My question lies in the realm of what did it really do, for say for example, N&W Y6B's? Did it really use less steam than a single expansion or produce more tractive effort (the latter I heard from a firend who I would assume knows more about it than myself). The boilers were just as massive if not bigger as that of a Big Boy's simple expansion design which made me wonder if the lower steam consumption was a real product or desire of this design.

Also, I would assume that if it worked so well for N&W, why didn't everybody else jump on the compounding band wagon?

Don't stop your field of vision in the US - check out Chapelon's work in France to find out about compounding at its historical best.

dave

Without going into too much detail at the start, the final versions of the N&W Y6, including the Y6b, were designed to perform best at speeds up to about 25-30 mph while putting out about 5,500 dbhp continuously. Above 30 mph, their output fell off rapidly. N&W used them in low speed service and they were exceptional at this type of work. On rolling profiles, the Y6's were allowed up to 50 mph. For higher speed service, i.e., sustained 35-60 mph, N&W used the Class A 2-6-6-4s.

Their boilers were about the same size as a large 4-8-4 with respect to grate area and heating surface. Big Boys' were much larger in all respects. The Y6s were an extremely compact design, and weighed about 611,000 lbs (engine weight) in their final iteration.

Coal and water usage per unit of output (DBHP-hr) has been documented in detail for the original Y6's from tests conducted in 1947, but nothing comparable has been found yet on the improved Y6's ca 1952-57. Summary data exists and has been published in books such as N&W Giant of Steam, Revised Edition (Lewis I. Jeffries), and in the series, Rail Remembered (Louis M. Newton).