3io

MODERN STEAM PRACTICE.

RULES FOR THE BEAM ENGINE.

The beam .—The length of the beam should not be less thanthree times that of the stroke, and its breadth one-half of the stroke;for the breadth at the ends multiply the breadth at the middle by vpTo find the thickness of web at the centre multiply the total pres-sure on the piston— i.e., steam and vacuum—by one-half of thelength of the beam in inches, and divide the result by the constant500 into the depth in inches; the quotient is the sectional area insquare inches for cast iron.

Wrought-iron tubulär beams :—

l = length.

d = depth.

a — area of bottom flanges.

C = constant.

W = breaking weight in tons; hence

28 feet 8 inches.

5 » 6 ,,

56 ‘67 square inches.

80

50^07 x 5*5 xöo

870 tons,

28'66

as the breaking weight in the middle. The load on the beam beingfrom 85 to 90 tons, we may safely consider the ratios of strengthas 870 :90, or nearly 10 to 1. The thickness of sides for a beam ofthe above dimensions is inch, supported between the flangeswith T-iron over the joints, and corresponding strips outside; upperand lower webs or flanges 2 feet wide, with four plates in each,’if inch thick, rivetted to the sides with double angle iron. Thecentre boss is cast with a plate, which is rivetted to the sides; theend and intermediate bosses have also cast-iron plates. Instead ofthe box form of beam, the side plates are sometimes made ofsufficient strength, having no angle irons at the top or bottom, butmerely secured with bolts and nuts, and sometimes rivetted to thecast-iron bosses. The diameter of the main gudgeon is generallyone-fourth of the diameter of the cylinder, and for the piston-rodgudgeon divide the cylinder diameter by 6'5 ; or they may be cal-culated taking them as round beams loaded in the middle.

To find the versed sine described by the beam of an engine. —Divid-ing the square of the stroke of the engine by 8, multiplied by theradius of the beam, gives the versed sine nearly, viz., S 2 -^(8 X R) =versed sine.

A ir pump and condenser. —The air pump has generally a stroke