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When the stroke of the bucket is either more or less than half the stroke of the piston, the pump's diameter will then be obtained by the following

Rule.-Square the given diameter, multiply by the length, and divide by the length proposed, extract the square root, and the product will be the diameter.

EXAMPLE.-Suppose an engine with a 4 feet stroke required an air pump 26 inches diameter with a 2 feet stroke, but necessity requires it to be 6 inches nearer the end of the beam, what must be the diameter of air pump, the beam being 11 feet long ?

Radius of beam = 66 inches. Then,
As 66 : 48 :: 39: 28.36 inches, length of stroke ;

262 x 24
And

= 24 inches diameter of pump

28.36 nearly. The Condenser ought to be a little more in capacity than the air pump; but in the case of marine engines, where the bottom of the condenser and bottom of the cylinder are nearly on a level, care must be taken to make the passage between the valves and condenser large enough to contain the condensing water required for one stroke of the piston, besides leaving a proper communication, otherwise, the connexion between the cylinder and condenser will be cut off by water of nearly 100° of heat, on account of the cylinder being twice filled with steam for each effective stroke of the air pump

The area of air pump multiplied by .25 will give the area of foot and discharging valves; thus, 24 inches diameter = 452.39 inches area, x 25 = 113.0975 inches area of valves.

The Piston Rod is about to of the cylinder's diameter; the air pump rod in the same proportion, unless it be made of copper, and then it may be about

of the pump's diameter.

The Cold Water Pump. It has lately been ascertained from experiments by Mr. Dalton, that when the temperature of the condenser is kept

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Hence, it appears that when water is used for condensation at a mean temperature of the atmosphere, 7 imperial gallons per minute for each horse power is found to produce the most beneficial effects; and 7 imperial gallons = 1941 cubic inches nearly.

Therefore, multiply 1941 by the number of horses' power, and divide by the number of revolutions per minute multiplied by the intended stroke of pump, and the quotient will be the area.

EXAMPLE.-Required the diameter of a pump for a 30-horse engine, making 19 revolutions per minute, the effective stroke of pump being 28 inches. 1941 x 30

= 109.45 inches area, or 11.8 inches 28 x 19 diameter nearly.

The Hot Water Pump. The same rule applies as well to the hot water pump as to the cold, only that the quantity to each horse power is 150 cubic inches.

EXAMPLE.—What must be the diameter of a pump for a 65-horse engine, velocity 22 revolutions per minute, and effective stroke of

pump

134 inches. 150 x 65

= 32.82 inches area, or 6.4 inches 22 x 13.5 diameter nearly

=

THE BEAM.

When a beam is applied to an engine its length ought not to be less than three times the length of stroke, and its breadth half the stroke, or in high pressure engines şths of the stroke ; also its best form is a parabola. To find the Thickness of a Beam when the length,

breadth, and diameter of cylinder is given. Rule.-Multiply the whole pressure of steam on the piston in lbs. by half the length of the beam in feet, and divide the product by 70 times the square of the breadth in inches, and the quotient will be the thickness in inches nearly.

EXAMPLE.—What thickness of beam is requisite for an engine whose cylinder is 25 inches diameter; the length of the beam being 15 feet, length of stroke 5 feet, and the effective pressure on each square inch of the piston equal 15 lbs ?

Area of piston = 490.875 inches, And 490.875 x 15 x 7.5

= .876 or ģ of an inch in 302 x 70 thickness nearly. To find the versed sine of an engine beam by calculation, is just to find the base of a triangle, for the radius of the beam is the hypotenuse, and half the stroke is the perpendicular, hence, subtract the base from the hypotenuse, and the difference is the versed sine.

Example.- What is the versed sine of an engine beam 12 feet long, and strohe 4 feet?

6 feet = 72 inches, and 2 feet = 24, their difference 48,

Then by problem 4 in Mensuration.

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68 = 4

✓ 72 + 24 x 48 = 68, and 72 inches nearly.

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