Steam pressure entering the cylinders drives the piston back and forth. The piston rod is attached to a connecting rod which drives a small wheel located centrally between the locomotive wheels. The band that encircles this small center wheel is the band brake. This small wheel is attached to the countershaft which has two small gears driving two larger gears located on each side of the pinion, or cog wheel, that's the gear that connects with the rack rail. The shaft through the pinion has excentric's mounded on each end. Connecting rods from these excentric's link to excentrics on both the front and rear driving wheels. Consequently the driving wheels are powered even when the rack is not engaged on adhesion trackage.