The New Student's Reference Work/Indicator

In′dica′tor (steam-engine), an instrument for drawing automatically a figure showing the instantaneous expansions and also the corresponding pressures of the steam in a steam-engine cylinder. The figure is called an indicator diagram. The expansion of the steam multiplied by the pressure gives the work the steam is doing. By letting vertical distances represent volumes, the area of the figure equals average pressure times change of volume or area equals work done.

A STEAM-ENGINE INDICATOR

The common indicator is due to Richards. It consists of a small cylinder which can be connected to the cylinder of the steam-engine. The pressure of the steam acts on the piston in the indicator cylinder and compresses a spiral spring. The amount of this compression is indicated by a pointer and measures the pressure. The pointer moves up and down with the changes of pressure, tracing a line on a paper wound on a small drum. This drum is attached to the piston-rod of the engine, so that it rotates backward and forward with the motion of the piston. But the position of the engine piston gives the volumes of the steam in the cylinder. The pointer thus traces a figure in which horizontal changes represent expansions or changes in volumes and vertical distances represent changes in pressure. The indicator diagram is used to study the performance of the valves of an engine and also to calculate the work the steam is doing. This is called indicated power as distinguished from brake-power, which is the power

CHIEF YELLOW BOY GIVING THE PEACE SIGN

Note that he has dropped his cartridge belt and war bonnet at his feet

delivered at the fly-wheel. The brake-power is the indicated power less the losses by friction and similar causes in the engine.