How Steam Engines Operate
"Changing heat into mechanical power"



A new era began during the second half of the 18th Century caused by a radical development of the steam engine; this heralded the industrial revolution. The various improvements were largely due to James Watt, the most significant being the change in design that permits the steam to drive New-comen's piston on both the forward and return stroke, thus increasing the efficiency. This to and fro motion was converted into rotary movement by either a crank, patented in 1781 by James Pickard, or by a Sun and Planet, patented by William Murdoch, Watt's assistant. Once rotary movement was possible the way was open for the development of steam engines for transport as well as stationary engines for industrial power.

THE PROCESS: Heat being converted into mechanical energy via water (steam) as an intermediary.

Though this process is seldom seen in transport today our electricity supplies are generated by steam but the engines are nowadays the sophisticated turbine and the heat source may well be nuclear.

The diagrams on the left show what actually happens inside the power converting system (piston and cylinder) when "fire and water" are brought together to produce mechanical energy, energy to drive a drilling machine, a saw, locomotive or steam roller.

Key to the diagrams:

#1 The water in the boiler is heated by the fire, this generates steam and because it is trapped in the boiler pressure builds up. Steam can pass, however, to the cylinder (blue dotted lines) via the slide valves.

In the second diagram the steam can be seen passing to the left side of the piston, pushing the piston to the right. At the same time the exhaust steam from the previous stroke is directed, by the other port on the slide valve, out into the atmosphere, having done its work, (dotted green (line) Just before the piston reaches the end of its travel, on the extreme right, the slide valve cuts off the steam from the boiler. This is the point where the crank is at the limit of its movement and is known as "top-dead-center" or "bottom-dead-center", referring to the two possible geometric positions. The flywheel carries the crank over this critical position by the energy it has stored from previous power strokes. The slide valve continues to move in the same direction this time opening the inlet port to admit steam to the right hand side of the piston, again pushing the piston but now to the left, exhausting the steam through the left hand port. The whole cycle being repeated when the "dead center" is reached once more.

Today Electric motors and gasoline engines have replaced the steam engine, nevertheless they still hold the interest of young and old alike. WILESCO engines cater for this ageless interest in demonstrating the basic principals of changing heat into mechanical power.

Back to the Steam Engine Home Page