STATIONARY ENGINES.

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periphery of the stones of a flour or other mill, to prevent backlash. To find the weight of the rim in cwts. multiply the constant1366 by the horse-power of the engine, and divide the product bythe mean diameter multiplied by the number of revolutions perminnte, and the quotient is the weight. To find the thickness ofthe ring when the breadth is given, in the first place find the areaof the ring in square inches, then divide the weight in lbs. by thearea multiplied by '263, and the quotient is the thickness in inches.The breadth of the rim for large wheels is generally -^th of thediameter of the wheel, to -jJyth for small wheels.

The governor .—The point of Suspension of the arms should beas near the centre of rotation as possible, and the working angleshould never exceed 45 0 ; the diameter of the balls varies from4 to 9 inches. To find the number of revolutions, divide 375 bythe square root of the pendulum, or vertical distance from the pointof Suspension to the working plane of the centre of the balls, andone-half of the quotient will be the number of revolutions required.When the revolutions are given, to find the length of the pendulum.Divide 375 by twice the number of revolutions per minute, and thesquare root of the quotient will be the length required; or other-wise, divide the constant 187-5 by the square root of the pendulum,which will give the number of revolutions. Thus, supposing the ver-tical height is 36 inches, the square root = 6 inches, we have—

T^ZT — 31'25 revolutions.

Given the number of revolutions, to find the length of the pendulumfrom the centre of the working plane of the balls to the centre ofSuspension. Divide 187*5 by the number of revolutions, and thesquare of the quotient will be the length of the pendulum:

— 6"= 36 inches long.

Formulce for safety-valve levers :—■

Weight or pressure on the valve x distance of valve from stud _ we jgktTotal length of lever from stud

(2)

Weight or pressure on the valve x distance of valve from studWeight

= total length of lever.

, v Weight on lever x total length of lever from stud A A , ,

(3) -2-—--——-2-.-— - = total pressure on valve.

Distance of valve lrom stud