weight, and the quotient is the weight in lbs. required to be placed upon the lever at that distance it to sortune motfod art yightfoM 2. When a certain pressure is required upon the valve, the weight upon the lever and distance of the valve from the centre of motion given, to find where that weight must be placed.or From the required weight upon the valve in lbs. take the weight of the valve, add the effective weight of the lever, multiply the remainder by the distance between the fulcrum and the valve, and divide the product by the weight in lbs upon the lever, and the quotient is the distance in inches from the fulcrum that the weight must be placed. 52 3. When the distance of weight, distance of valve from the centre of motion, and weight upon the lever are given, to find what pressure is upon that valve 20 Multiply the weight in lbs upon the lever by the distance in inches to the fulcrum, divide the product by the distance between the fulcrum and the valve, and the quotient, plus the weight of the valve and effective weight of the lever, equal the weight upon the valve in lbs. aowoq gatod fanisión 6 di lampo g0068 yo Jəbivb Bas 24 inches in EXAMPLE 1. Suppose the lever A length, and the A, what weight must be placed upon the lever 20 inches from A, to equal 80 lbs., on the valve C, the weight of the lever being 2 lbs., the weight D, which balances the lever, 41 lbs., and the weight of the valve 3 lbs. di bogolivah nyroy octod eany add quitalsblea 20lbs. weight of the lever seed off yd vods droquty 7545 moto balance ditto. EXAMPLE 2. Suppose the weight upon the lever equal 17.625 lbs., it is required at what distance from A the weight must be placed to equal 80 lbs. at C. etunim noq encitulovor 68 words EXAMPLE 3. Suppose, as before, that a weight of 17-625 lbs. is placed upon the lever 20 inches from A, required the pressure at C, the distance from the centre of motion being 5 inches, and the effective weight of the lever at that point equal 6 lbs., also the weight of the valve 3 lbs. suply su To Find the Proper Diameter for a Safety-Valve.or Multiply the bottom surface of the boiler, or surface immediately exposed to the action of the fire, in feet, by the multiplier opposite to the pressure in lbs. on each square inch of the safety-valve, and the square root of the product is the valve's diameter in inches at the e narrowest part. If the boiler is to have two safety-valves, then the square root of half the product equal the diameter of each 12 .. 356 *348 *344 30 336 40 *329 45 50 *321 315 $305 *293 *289 *282 *275 **270 264 26 In constructing steam-engines, the following simple f obtaining the nominal horse power is now generally adopted: for The area of the cylinder in square inches multiplied by 7 lbs. pressure, multiplied into the speed of the piston in feet per minute, divided by 33000, equal the nominal horse power. Thus, area of cylinder × 7 lbs. × feet per minute __ The length of stroke and relative speed of piston, and number of revolutions per minute, will be found by the following table. In calculating the gross horse power developed in any cylinder, as shown by the indicator, it has been customary to allow one-tenth, and sometimes one-eighth, for friction; this is now very properly abandoned, and the following rule for calculating the indicator diagram should be always adopted: the mean pressure as shown on the card, multiplied into the area of the cylinder, multiplied into the speed of piston, in feet per minute, when the card was taken; this product, divided by 33000, will give the gross or indicated horse power: O stroke 30 revolutions per minute 180 per minute. 76 STEAM POWER AND THE STEAM-ENGINE. The Air-P to contents more than Pump half the the air-pump of the cylinder, or the diameter of the cylinder in inches multiplied by 6 will give the diameter of the air-pump in inches, the length of stroke to be one-half the length of stroke of the piston, dn adehizak to JacTMOS The Condenser should never be less than half the capacity of the cylinder and in engines where the pressure on the boiler ranges from twelve to twenty pounds on the square inch, a much larger condenser should be given.y-secx »*2 The foot and delivery-valve passages should have an area of onethird of the air-pump, 10 The Steam-Ports. The area of the steam ports on the cylinder should never be less than one-twentieth of the area of the cylinder. If the speed of the piston is above 250 feet per minute, the ports should less than one-fourteenth the area of the cylinders. The Cold-Water Pump. The capacity of the cold-water pump should be not less one-thirty-sixth of the capacity of the cylinder. The Fly-Wheel To find the weight of the fly-wheel rim the following practical rule is generally adopted: Horse power of the engine x 2000-90 (velocity of circumference of wheel in feet per second) 2 the weight of the fly-wheel in cwts. The Fly-Wheel, or Crank-Shaft. The nominal horse power of the engine and speed of the shaft being given, the diameter of this shaft, whether cast or wrought iron, will be found in the Tables of Strength of Shafts. The Governor. To find the number of revolutions, divide 375 by the square root of the length of the pendulum; half of this quotient is the number of revolutions the balls ought to make per minute. To find the length of the pendulum, divide 375 by twice the number of revolutions; the quotient squared is the length of the pendulum. General Proportions of Locomotive Engines. For the area of the steam-ports when the stroke is 18 inches, the square of the diameter of the cylinder x 068. the area in square inches. For the area of the eduction ports, the square of the diameter of the cylinder in inches X 128 the area in square inches. The breadth o induction bridges between the eduction ports and the inch and 1 inch. The diameter of the chimney the diameter of the cylinder. For the area of the fire-grate, the diameter of the cylinder in inches × 77 the area in superficial feet. H For the effective heating-surface of the boiler, the square of the diameter of the cylinder in inches x 5 ÷ 2 area in square feet. For the diameter of the feed-pump ram, the square of the diameter of the cylinder in inches x 011 the diameter in inches. For the cubical content of the steam-room, the square of the diameter of the cylinder in inches x 9÷40=content in cubic feet. For the cubical content of inside fire-boc above fire-bars, the square of the diameter of the cylinder in inches 4 content in cubic feet. For the inside diameter of the steam-pipe, the square of the diameter of the cylinder in inches x '03 the diameter in inches. For the diameter of the branch steam-pipe, the square of the diameter of the cylinder in inches x 021 the diameter in inches. For the diameter of the top of the blast-pipe, the square of the diameter of the cylinder in inches × 017 the diameter in inches. For the diameter of the feed-pipes, the diameter of the cylinder in inches x 141: the diameter in inches. For the diameter of the piston-rod, the diameter of the cylinder in inches 7 the diameter in inches. For the thickness of the piston, the diameter of the cylinder in inches x 27the thickness in inches... For the diameter of the connecting-rod at the middle, the diameter of the cylinder in inches x 21 the diameter in inches. For on the diameter of the plain part and inside bearing of the crankaxle, the cube root of the square of the diameter of the cylinder in inches x 96 = 96 the diameter in inches. For the diameter of the outside bearings of the crank for axle, the cube root of the product of the square of the diameter of the cylinders in inches x 396 the diameter in inches. For the diameter of the crank-bearing, the diameter of the cylinder in inches x 404 = the diameter in inches. For the length of the crank-bearing, the diameter of the cylinder in inches x 233 the length in inches. 1 Remarks on Steam-Engine Boilers and their Proportions. For engines designed to give a gross indicator horse power of at least twice the nominal horse power, the grate surface should be 66 or 69 square feet per nominal horse power, but may be increased to 75 square feet, and should never be diminished to less than 60 square feet as a minimum. The area of opening over the bridges or through the tubes, should be 125 square feet, or 18 square inches per horse power, and may be increased to 143 square feet, or 20 square inches with advantage, particularly in tubular boilers, and should never be diminished to less than 15 square inches, or 109 square feet per horse power The area of chimney should be 076 square feet, or 11 square inches, but may be increased to 13 square inches, and should never be diminished to less than 10 square inches per horse power. The heating surface in fire-places and flues should be 14 square feet per horse power, exclusive of all bottom surface, but may be increased to 15 square feet, and should never be diminished to less than 12 square feet per horse power. In calculating tubular boilers the whole surface of the tubes should be taken, and there should be a total of 17 square feet per horse power in the fire-places and tubes. In engines designed to work to a gross power in the cylinder by the indicator greater than twice the nominal horse power, these proportions must be increased; or, if the reverse be intended, they may be diminished in proportion. Of the Pressure of Steam, in Inches of Mercury, at Different Temperatures... |