440

MODERN STEAM PRACTICE.

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Fig. 323. — Box Valve Seat with square sides, arrangedfor twelve Valves for Air Pumps.a, Box with twelve valves. b, India-rubber valve.

C, Guards. d, Stud for guard.

the free entrance and exit of the

lift of valve as in the former examples, five times the area isobtained; or with excessivelyfast-going engines, the lift ofvalve can be reduced, a greatdesideratum even with india-rubber valves, for undoubt-edly the wear and tear cannotbe so great, while the areafor the passage of the wateris always greater than in asingle valve. In another ar-rangement four valves areplaced on the top of a squarebox, and two on each side,making twelve valves in all.

These sets, and indeed allindia- rubber valve arrange-rnents, can be placed upsidedown, or at any angle thatmay be considered best forwater from the air pumps. In-stead of round valves, somemakers cut the india rubberinto oblong flaps, hinged atthe centre and folding upagainst the guard on eachside; by this means the holesfor the bolts do not weakenthe india rubber so much aswhen they are placed alongthe edge. The holes for thepassages of the water arehexagonal, formed aroundcircles 1 inch in diameter,with webs similar to a honey-comb. The area through thevalves should be as large as

possible, and the grated Space Fj... 324.—Double Oblong Valve with Hexagonal

equal to the length and Gräting for Air Pumps.

. . - r - - . . a, Gräting, b, India-rubber valve. c, Guard.

breadth of the hole m the dd, studs.