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MODERN STEAM PRACTICE.

must be a known quantity, as likewise the diameter of the crankpath, when the opening of port by the valve is determined on, aswe now propose to do, the slide valve can be set out as generallyadapted for all classes of engines.

OPENING OF PORT BY VALVE.

The diameter of the cylinder and speed of the piston must also bedetermined on to find the opening of port by the valve. Sup-posing it is required to find the opening of port by the valve, witha piston speed of 300 feet per minute giving out for a single cylinder200 nominal horse-power, multiply the constant 33,000 by the powerrequired, and divide the product by the speed of the piston perminute, multiplied by the constant 7 lbs., and the quotient addedto half the area of the piston-rod will give the number of squareinches of cylinder area; thus,

33000 X 200 .0 -1

300 x 7 =3142 + 28 = 3170 square inches,

or say 63^ inches, is the diameter of the cylinder, this being therecognized rule for the nominal horse-power of marine engines. Forhigh-pressure engines we simply take the steam pressure in boilerinstead of the constant 7 lbs., making an allowance of 1^ of thepower required, and the rule for finding the cylinder’s diameter isthe same as for the marine engine. Thus, supposing the powerrequired was 20 horse, and the speed of the piston 200 feet perminute, with a steam pressure of 30 lbs.,

200 x 30 5 = r 7 8 '7 = say 15 inches diameter.

To find the full area or opening of port by the valve we will take theformer example as for the marine engine, namely 3170, as area ofthe cylinder in square inches, with a piston speed of 300 feet perminute. Multiply the cylinder area by the speed of the piston infeet per minute, and divide the product by the constant 10,000, thequotient gives the area of port by the valve—

3170 x 30010000

= 95 square inches.

Thus the area of the steam port by the valve, divided by thelength of the steam port, will give the opening. The le ngth ofthe port is found by dividing the cylinder diam eter by 17 ; thus,63-5 -3- 17 = 37*5, or say in round numbers 38 inches, is the length