USRA Designs

USRA Mikado Steam Engine






Franklin Type B Ragonnet Power Reverse Gear



The Ragonnet power reverse, patented in 1909 by Eugine L. Ragonnet (see patent here), was a true feedback controlled servomechanism. The power reverse amplified small motions of reversing lever in the locomotive cab made with modest force into much larger and more forceful motions of the reach rod that controlled the engine cutoff and direction. It was usually air powered, but could also be steam powered. (Source: Wikipedia)


The diagram below shows the valve linkage going from full forward cutoff to full reverse cutoff.


Cutoff, usually quoted as a percentage, is the point in the piston stroke at which the supply of steam to the cylinder is cut off by the closing of the valve. Maximum cutoff (typically 75%) is used for starting a train and is reduced by the operator as the train accelerates to speed.


The reversing lever, or "Johnson Bar", does more than simply provide the reverse function of the valve gear. Its control of the cutoff is equally important. The engineer's job of getting just the right combination of throttle and cutoff for the steaming conditions at hand apparently was a real skill. You may read about notching up, hooking back, hooking up, or company notch in the context of economizing the use of steam at speed. (Source: Robert A. Booty)


The light USRA Mikados' used the Franklin Railway Supply's Type B Ragonnet Power Reverse. These could either be powered by steam or air from the brake system.



(click on picture for a larger view)

Raggonet Power Reverse Raggonet Power Reverse

Source: Railroad and Locomotive Engineering, November 1917

Source: Franklin Railway Supply 1925 Notebook

Raggonet Power Reverse

Southern Railroad (2-8-0), ALCO Type B Reverse

Source: Wikipedia