Practical talks on farm engineering : A simple explanation of many everyday problems in farm engineering and farm mechanics written in a readable style for the practical farmer . £/tSINE STROKE Fig. 27.—A typical indicator card. A is the point where thesteam is cut off, B the point where the exhaust is opened, Cis where compression begins, and D is where admission of livesteam starts, the pressure rapidly running up to live steam pres-sure at E shows the shape of such a diagram, and this isknown as an indicator diagram. Mathematicalcalculations show that the area of such a dia-gram as this is
Practical talks on farm engineering : A simple explanation of many everyday problems in farm engineering and farm mechanics written in a readable style for the practical farmer . £/tSINE STROKE Fig. 27.—A typical indicator card. A is the point where thesteam is cut off, B the point where the exhaust is opened, Cis where compression begins, and D is where admission of livesteam starts, the pressure rapidly running up to live steam pres-sure at E shows the shape of such a diagram, and this isknown as an indicator diagram. Mathematicalcalculations show that the area of such a dia-gram as this is proportional to the product ofthe average pressure on the piston during thestroke and the length of the stroke. In otherwords, the area of this diagram is proportional 124 FARM ENGINEERING to the work done on the piston of the engineby the steam during one stroke, so that know-ing the number of strokes per minute made bythe engine piston we may easily find the workdone per minute. This divided by 33,000 givesus the indicated horsepower (I. H. P.) of theengine, because 33,000 foot-pounds per minuteequals one horsepower. jm J -l,. S Z=) Fig. 28.—One form of prony brake To measure the brake horsepower of any en-gine, an instrument known as the prony brake or,more technically, the absorption dynamometer,is used. This, as shown in the drawing, con-sists of a band which may be tightened aroundthe engine pulley, creating great friction on thepulley and requiring constant force acting toovercome this friction. As this force is acting HORSEPOWER OF AN ENGINE I25 constantly on the rim of the pulley, in one revo-lution of the pulley the force acts through adistance equal to the circumference of thepulley. The circumference is three and oneseventh times the diameter. The product ofthe length of the circumference and the force offriction acting will give the work done in onerevolution. Then by counting the number ofrevolutions per minute and multiplying thisnumber by the work done in o
Size: 1444px × 1730px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookidpracticaltal, bookyear1915
