Everything about Cow-calf totally explained
In
North American
railroading, a
cow-calf set is a pair of
switcher-type
diesel locomotives: one (the
cow) equipped with a driving cab, and the other (the
calf) without. The two are coupled together (either with regular
couplers or a semi-permanent drawbar) and are connected with
MU cables and brake lines so that both locomotive units can be operated by a single cab. Cow-calf sets were used in heavy switching,
hump yard switching, and transfer runs between yards.
Cows are analogous to
A units and calves to
B unit road locomotives. Unlike them, cow-calf sets were almost always permanently attached.
Some 3-unit cow-calf-calf sets were built, but this was rare.
Each unit in a cow-calf set was powered. As
diesel engines became more powerful, they exceeded the practical limit to the power that could be applied to the rail at low speeds in a single four- or even six-axle locomotive. Thus, the concept of the
slug was born—like a calf, these attached to a switcher or other locomotive needing extra low-speed tractive effort, but a slug doesn't have its own engine—instead, it takes electrical power from its "mother", allowing more of the power of that engine to be applied.
Most cow-calf sets were built between the
1930s and the
1950s. They were built by several different makers, although
General Motors'
Electro-Motive Division built far more than the others.
The cow-calf concept was adopted on Queensland 2ft gauge sugar cane railways with two locomotives being coupled permanently in multiple-unit mode with the cab of one removed. This was utilised by Isis Mill (1980-1993) and by Mackay Sugar (2005).
The concept was also used in the
United Kingdom by
British Rail to produce the unique
Class 13 locomotives, composed of two
Class 08 locomotives. British terminology is
Master-and-Slave Unit.
List of cow-calf models
EMD TR
EMD TR1
EMD TR2
EMD TR3
ALCO SSB-9
British Rail Class 13Further Information
Get more info on 'Cow-calf'.
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