. The steam-engine and other heat-motors . ds per squareinch. Suppose the pressure in the con-denser is reduced to absolute zero and^ the mercury rises to some point Gthen HG represents the weight of theatmosphere. Evidently then GE +FH, or twice GE, represents the ab-solute pressure in the condenser whenthe vacuum therein is not perfect. Now the height HG, at thesea-level, is ordinarily 30 inches of mercury, and the height EFis the quantity marked on all forms of vacuum gages. Hence,ordinarily 30 inches minus EF in inches is the absolute pres-sure in the condenser. To be exact, instead of 30
. The steam-engine and other heat-motors . ds per squareinch. Suppose the pressure in the con-denser is reduced to absolute zero and^ the mercury rises to some point Gthen HG represents the weight of theatmosphere. Evidently then GE +FH, or twice GE, represents the ab-solute pressure in the condenser whenthe vacuum therein is not perfect. Now the height HG, at thesea-level, is ordinarily 30 inches of mercury, and the height EFis the quantity marked on all forms of vacuum gages. Hence,ordinarily 30 inches minus EF in inches is the absolute pres-sure in the condenser. To be exact, instead of 30 inchesthe height of the barometer in inches should be used. If,for instance, the barometer reading is inches and thevacuum is inches the absolute pressure in the condenseris = inches. Fig. 20. ELEMENTARY PRINCIPLES. 29 If we call the atmospheric pressure 15 pounds per squareinch and the barometer 30 inches, it is evident that 1 inch isequivalent to \ pound pressure, but more accurately, 1 inchequals Names of Parts.—It is desirable that the student learn, as soonas possible, the technical names of the different parts of the steam-engine, the steam-boiler, and the various auxiliaries and appliancesof a steam-plant. He should recognize, know the use of, and make 30 THE STEAM-ENGINE AND OTHER HEAT-MOTORS fair sketches from memory of pistons, piston-rods, cross-heads,cross-head pins, cross-head slipper, cross-head guides, connecting-rods (both strap and club end), gib and key, crank-pin, crank-arm,crank, crank-pin brass, crank-pin journal, bearing, liner, cap-nuts,frame back-bone, holding-down bolts, cylinder-bonnets or covers,cylinder-heads, junk-ring, follower, springs, rings, boss of a wheel,eccentrics, eccentric-sheaves, eccentric-rods, stuffing-boxes, pack-ing-glands, Stephenson link, dash-pot, reach-rod, parallel rod,saddle-plate, rocker, separator, steam-loop, steam-traps, sight-feed lubricator, indicator-cocks, reducing motion, stea
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