page_title: Booster engine
hierarchical_section_title: Booster engine
caption_attribution_description: English: Booster engine installation layout.
context_page_description: A booster engine for steam locomotives is a small two-cylinder steam engine back-gear-connected to the trailing truck axle on the locomotive or the lead truck on the tender. A rocking idler gear permits it to be put into operation by the driver. It drives one axle only and can be non-reversible, with one idler gear, or reversible, with two idler gears.
  A booster engine is used to start a heavy train or maintain low speed under demanding conditions. Rated at about 300 horsepower at speeds of from 10 to 30 mph, it can be cut in while moving at speeds under 12–20 miles per hour and is semi-automatically cut out via the engineer notching back the reverse gear between 20 and 35 mph, depending on the model and design of the booster. A tractive effort of 10,000–12,000 pounds-force is common, although ratings of up to around 15,000 lbf were possible.
  Tender boosters are equipped with side-rods connecting axles on the lead truck. Such small side-rods restrict speed and are therefore confined to switching locomotives, often used in transfer services between yards. Tender boosters were far more rare than engine boosters.
context_section_description: A booster engine for steam locomotives is a small two-cylinder steam engine back-gear-connected to the trailing truck axle on the locomotive or the lead truck on the tender. A rocking idler gear permits it to be put into operation by the driver (engineer). It drives one axle only and can be non-reversible, with one idler gear, or reversible, with two idler gears.
  A booster engine is used to start a heavy train or maintain low speed under demanding conditions. Rated at about 300 horsepower (220 kW) at speeds of from 10 to 30 mph (16 to 48 km/h), it can be cut in while moving at speeds under 12–20 miles per hour (19–32 km/h) and is semi-automatically cut out via the engineer notching back the reverse gear between 20 and 35 mph (32 and 56 km/h), depending on the model and design of the booster. A tractive effort of 10,000–12,000 pounds-force (44–53 kN) is common, although ratings of up to around 15,000 lbf (67 kN) were possible.
  Tender boosters are equipped with side-rods connecting axles on the lead truck. Such small side-rods restrict speed and are therefore confined to switching locomotives, often used in transfer services between yards. Tender boosters were far more rare than engine boosters.
caption: Diagram showing how a booster is installed and connected.
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