Pistons and Cylinders

The high pressure superheated steam is then passed to the cylinders. Her the energy stored in the
steam is converted into mechanical energy to drive the Locomotive along.
Most locomotives use Double Acting Cylinders. This is a way of getting twice the power with the
same number of cylinders by introducing the steam alternately on either side of the piston so the
piston rod is both pushed and pulled generating power on both strokes.
The cylinder valves control the access of the steam to the cylinders. The operation can be simply
described as follows by considering only one side of the double action cylinder:-
· When the piston is at the end of the cylinder the inlet valve opens and allows high pressure
steam to enter the cylinder in front of the piston.
· This high pressure steam pushes the piston back.
· The inlet valve then closes and the steam in the cylinder expands and cools producing more
power to the piston.
· After this expansion the steam has given almost all of its energy up to the piston and the
exhaust valve opens.
· On the return stroke the exhaust steam is forced out up the Blast Pipe.
The linear backwards and forwards motion of the pistons is converted into rotary motion by the
Connecting Rods and the Cranks