depending on whether the locomotive has an air brake or vacuum brake system. Water compartmentTank for water to be used by the boiler to produce steam. Coal bunkerCompartment for storage of fuel before being directed to the firebox. When the fuel is coal (and in the distant past, coke or wood), the fireman shovels it manually through the firebox door or, in larger locomotives, by operating a mechanical stoker. When the fuel is oil, it is sprayed into the firebox from a sealed tank. GrateSupports the burning fuel while allowing the products of combustion – ash and small clinker – to drop through. Ashpan hopperCollects the ash from the fire. Journal box Axle box Housing for the bearing on the axle of a wheel (43). Equalising beams / Equalising levers / Equalising barsPart of the locomotive suspension system. Connected to leaf springs; free to pivot about their centre, which is fixed to the frame. Their function is to even out weight carried on adjacent axles, which is especially necessary on uneven or poorly laid tracks. Leaf springsMain suspension springs for the locomotive. Each driving wheel supports its share of the locomotive's weight via leaf springs that connect the axle's journal box / axle box (40) to the frame. Driving wheelsDrivers Coupled wheels Wheels coupled to the main/side rods, through which the power developed in the cylinders (24) is transformed into tractive power at the rails. The weight of bearings and coupling rods on the driving wheels is counterbalanced with cast-in weights to reduce "hammering" on the track when the locomotive is under way. Pedestal / SaddleConnects a leaf spring to a journal box / axle box (40) on a wheel. Blast pipeExhaust pipe Directs exhaust steam up the smokestack/chimney (33), creating a draught that draws hot gases through the firebox (27) and along the boiler tubes (28). Pilot truck, Pony truck Leading bogie / Lead truck / Bissel truck Wheels at the front of the locomotive to guide the front driving wheels around curves, and minimise yawing at higher speeds with the attendant risk of derailment. The truck has some side motion and is equalised to the driving wheels (41). The names Pony truck (US+) and Bissel (or Bissell) truck (UK+) apply when there are two wheels; the others when there are four. Pilot / Cowcatcher A shield made from bars, cast steel or sheet steel to prevent an object