Democratic Sentinel, Volume 18, Number 17, Rensselaer, Jasper County, 11 May 1894 — How Horse Power is Calculated. [ARTICLE]

How Horse Power is Calculated.

Horse power measures the rate at which work is done. One horse power is reckoned as equivalent to raising 88,000 pounds one foot high per minute, or 550 pounds a second. In measuring the work of a horse the estimates of the most celebrated engineers differ widely from each other. Boulton and Watt, basing their calculations upon the work of London dray horses working eight hours a day, estimated it at 88,000 foot pounds per minute. D’Aubisson, taking the work done by ‘horses in whims at Freiburg, estimated the work at 16,440 foot pounds working eight hours a day. Under similar circumstances Desagulier’s estimate was 44,000, Smeaton’s 22,000 and Treadgold’s 27,500 foot pounds. Horse power is called nominal, indicated or actual. Nominal is used by manufacturers of steam engines to express the capacity of an engine, the element being confined to the dimensions of the steam cylinder and a conventional pressure of steam and speed of piston. Indicated shows the full capacity of the cylinder in operation involving elements of mean pressure upon the piston, its velocity and a just deduction for the friction of the engine’s operation. The original estimate of Watt is still counted a horse power. The general rule for calculating the horse power of a steam engine is to multiply together the pressure in pounds on a square inch of the piston, the area of the piston in inches, the length of the stroke in feet and the number of strokes per minute. The result divided by 88,000 will give the horse power.—[San Francisco Call.