I saw a photo of a B&M locomotive, 080 with 23 by 28 inch cylinders, taken in 1929. the caption says, note the BOOSTER or AUXUILIARY LOCOMOTIVE TRACKS UNDER THE TENDER.I have never heard or seen them before. question I have is what are they fore & what do they do?

A booster is a 2-cylinder engine mounted on the rear axle of the trailing truck, under the firebox. The engineer could engage or disengage the booster but there was a speed limit on the use of a booster. Steam locomotives needed boosters at low speeds only.

Reading T-1's, such as RBMN 2102, were built with boosters. The main engine produces 68,000 lbs Tractive Effort and the booster adds 11,400 lbs.

There was another type of booster, a powered tender truck. Many more engines had trailing truck boosters than the tender truck type.

Phil Mulligan

Phil, thank you again for the response to my question on a BOOSTER. so as the engine took off it gave it a greater amount of traction on very long drags? was it only used on starting off and then cut off after the consist got up to speed? if you already answered it, please excuse me fore a senior moment, 80+ yrs.

Boosters were used for extra tractive effort getting a heavy train started or for a slightly quicker getaway on a passenger train. You'd cut them out and disengage them at around 20 mph depending on the type of booster. They're low speed devices meant to get you going, not for continuous running.

Eric, thank you sir so much for the reply to the purpose and the function of boosters. now I know the rest of the story.

Some B&M H-3 0-8-0s had not one but TWO boosters!

https://sites.google.com/site/bostonandmainerailroad/home/b-m-steam-locomotives-class-a-and-b/bm-class-c-d-and-e/bm-class-f-and-g/bm-class-h-and-j

liftnerd, what in GOD'S green acres were they hauling that they needed two boosters? was one on the engine and the other one on the tender? that is an Uber amount of traction power. thanks for the post on the boosters, I am impressed with the ingenuity of there engineers seeing fit to introduce them on the engines and or tenders.

At low speeds, the boiler can generate more steam than the locomotive can use. If the Railroad wants to lug as much as possible at walking speed, a booster is the answer.

If the locomotive has no trailing truck, you use a tender booster. It's basically an 0-4-0 engine (no cab or boiler) installed in place of one or both tender trucks.

Phil Mulligan

Phil, again thank you so much for sharinging your knowledge with us.