Booster engine

For the term in rocketry, see Booster (rocketry).
Booster engine with the cover removed to show the mechanism. The driven axle is on the right; the booster normally hangs behind it.
Diagram showing how a booster is installed and connected.

A locomotive booster for steam locomotives is a small supplementary two-cylinder steam engine back-gear-connected to the trailing truck axle on the locomotive or one of the trucks on the tender. It was invented in 1918 by Howard L. Ingersoll, assistant to the president of the New York Central Railroad.[1]

A rocking idler gear permits the booster engine to be put into operation by the driver (engineer). A geared booster engine drives one axle only and can be non-reversible, with one idler gear, or reversible, with two idler gears. There were variations built by the Franklin company which utilized side rods to transmit tractive force to all axles of the booster truck. These rod boosters were predominately used on the leading truck of the tender, though there is an example of a Lehigh Valley 4-8-4 using it as a trailing tender truck.[2]

A booster engine is used to start a heavy train or maintain low speed under demanding conditions. Rated at about 300–500 horsepower (220–370 kW) at speeds from 10 to 35 mph (16–56 km/h), it can be cut in while moving at speeds under 12–22 mph (19–35 km/h) and is semi-automatically cut out via the engineer notching back the reverse gear or manually through knocking down the control latch up to a speed between 21 and 35 mph (34–56 km/h), depending on the model and gearing of the booster. A tractive effort rating of 10,000–12,000 pounds-force (44–53 kN) was common, although ratings of up to around 15,000 lbf (67 kN) were possible.[3][4]

Tender boosters are equipped with side-rods connecting axles on the lead truck. Such small side-rods restrict speed and are therefore confined mostly to switching locomotives, often used in transfer services between yards. Tender boosters were far less common than engine boosters; the inherent weight of the tenders would decrease as coal and water were consumed during operation, effectively lowering the adhesion of the booster-powered truck.

  1. ^ "Locomotive Boosters". Railway Mechanical Engineer. Vol. 98, no. 10. Simmons-Boardman Publishing Corporation. October 1924. p. 590-591 – via Internet Archive.
  2. ^ Van Nort, Darryl E (28 March 2023). "Class T-2a 5210". Retrieved 28 March 2023.
  3. ^ "Dynamometer Tests of the Locomotive Booster". Railway Mechanical Engineer. Vol. 96, no. 10. Simmons-Boardman Publishing Corporation. October 1922. p. 562-565 – via Internet Archive.
  4. ^ "Dynamometer Tests of Type E Booster". Railway Mechanical Engineer. Vol. 118, no. 9. Simmons-Boardman Publishing Corporation. September 1944. p. 399-401, 408 – via Internet Archive.