Articulated [Mallet]

A Mallet locomotive. A simple articulated is a mallet which had a large enough boiler to supply all four cylinders with high pressure steam direct from the boiler. A compound mallet is a mallet which had a boiler too small to supply high pressure steam to all four cylinders at once, and used steam twice, once to the rear high pressure cylinders and the "partially used" steam would then supply the front cylinders. The best known example of a compound mallet is the NW Y6b mallet, which "shifted" to compound operation at higher speed. Some well known simple articulated's are the UP BIG Boy, the UP Challenger, the NW Class A, the BO EM-1 type, and the SP AC class.