Evening Republican, Volume 21, Number 156, Rensselaer, Jasper County, 19 July 1917 — HOW TO FIGURE HORSE POWER [ARTICLE]

HOW TO FIGURE HORSE POWER

Comparatively Easy Method of Making Calculation With Any Engine la Available. As an easy method of calculating horse power the following Is commended: Where practicable take an indication diagram which shows the mean pressure of steam throughout the stroke. In order to-calculate the pressure, ten ordinates are usually drawn across the diagram; the length of these Is measured on a scale representing the pounds per square inch of pressure. The ten numbers thus obtained are added’together and the sum divided by ten; this gives the average pressure per square inch of steam throughout the stroke. Calculate the area of the piston In square inches from its diameter, and multiply this by the square inch. This gives the total pressure exerted on the piston. Next multiply the number of revolutions of the engine per minute by twice the length of the stroke In feet; this gives the speed of the piston In feet per minute; multiply this by the pressure on It In pounds, and the result Is the number of foot pounds of work done on the piston per minute. A horse power is reckoned at 33.000 foot pounds per minute, the number of foot pounds divided by this figure gives the indicated horse power. A portion of this, varying from a third to a fifth, is taken up in overcoming the friction of the working parts of the engine; the remainder only Is available for useful woi;k—- ---■ . ■ - ■.. .