lower unit: this is where the air is fed into the cylinders, turns the wheel and moves the train by a valve gear. upper unit: comprises three major parts: the air tank, the compressor and the engine. the air compressor is what fills the air tank with air and is stored on stand by, when needed, the driver operates a air valve in the cabin and monitors the air pressure coming in and out the cylinders, but to keep the air tank filled, the operator starts the engine and pumps more air into the air tank.
c2a
