1180

THEORY AND PRACTICE OF ENGINEERING.

Book II.

sentod will be ton ml infinitely preferable : it consists of a copper box forming the IkxIv ofthe piston, in the form of a truncated cone, with a small flange, C C. The tigs. 1799. lHthi.

Fig. 1799.

Fig. 1801. P

Fig.1802.

show the section with the upper plan, where it is seen that this box is traversed by a bar1)1) pierced by a mortice E: on the surface of the box is a leather band A A, confinedby an iron ring let into the leather, which is ^ of an inch thick.

The piston is covered by a leather valve strengthened by iron or copper plates G, G,(fig. 1800.), made in the segment of a circle : above the valve are similar plates, but of ratherless diameter, so that they may enter the piston, as indicated by the circle 1 K in fig. 1808.,having only therein the leather and upper plates, which rest on the edge of the box ; thus theleather is screwed between the two by four nuts and screws, II : this valve is fitted to the box,so that the centre FF is placed on the bar 1)D; to tie the whole together an iron cross isused, L M N O P, in fig. 1801., which is a section through the bar D D of fig. 1796. Thepart M N is placed, on the middle F F of the valve ; then the tenon 0 P traverses the hole E,and passes through an iron bar Q It, whose extremities, X, X, are halved into the thicknessof the box, as well as the circle B B, which is sustained by this means, and secured to thebox by passing a key into the hole T, as shown in the section of the piston at right angleswith the preceding.

The rod L O is adjusted to an iron bar by a tenon at its summit, a mortice in the middle,and two screws serving to tighten one against the other; this bar is suspended to a crank orlever.

To remedy defects in the common plungers of wood, a much more solid one is now sub-stituted, as shown in fig. 1S03. The body of the piston consists of two copper cylindersA R C D, E F G H, of a screw N O, and a ring p

Z, all cast together ; the diameter CD is ratherless than the barrel Q It S T, and the diameterE F only half the preceding ; the thickness A C may be one-fourth the diameter A B, and E Gtwice E F.

A number of leather roundles, whose dia-meter is rather more than the pump-barrel,pierced in their centre by an aperture of thediameter G H, are fitted on the cylinder E FG II,and beaten with a hammer to press them to-gether ; others are then added, supported by acopperplate I K, the thickness of which shouldbe half A C , and being pierced in the centre isfitted to the screw I, Si, after which the wholeis pressed together by the nut X, The piston

is then placed on a lathe to reduce the whole to the same diameter as the piston head,form a cylinder I A B K, having a uniform surface. The piston is then introduced intothe pump-barrel without difficulty, and water being poured above the leather it swells, andall the roundles unite against the barrel, and form a new cylinder Y, whose diameter isequal to that of the barrel, leaving no admission for air during suction, nor passage for thewater when forcing: in proportion as the surface of the cylinder Y wears by friction, theleather swells, not having attained its maximum of dilatation in the first instance, especiallyif it be of the best quality.

Tlie ring Z serves to hook on the rod P, so that it may play freely, and enable the piston

p i

I

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Fig. 1804

, and