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Today I have a steam locomotive question.

According to a set of diagrams in the Major Lewis Ingles Jeffries book N & W:  Giant of Steam on pages 72-74 he has diagrams of the operation of compound Mallet articulateds in simple, compound, and booster modes of operation.  I know that the booster mode was unique to the N&W Y5, Y6, Y6a, and Y6b 2-8-8-2.  But when a compound Mallet articulated is started is has to be in simple mode because there is no other way to get steam into the low pressure cylinders until after the locomotive is moving some distance and sufficient exhaust steam from the high pressure cylinders reaches the low pressure cylinders.

Until that happens the exhaust steam from the high pressure cylinders is exhausted directly to the stack, bypassing the low pressure cylinders.  So there could be eight chuffs per revolution of the drivers, unless the front and rear engines were in sync with each other.  Otherwise there should be eight chuffs, ranging from perfectly timed to various staccatos.

Am I correct in this assumption, or am I missing something?



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