Rotary Pumps.

287

Chap. 5.]

and compelled to rise in the discharging one, as indicated by the arrows.Other pumps of the same dass have such a portion of the small cylin-der cut off, that the concave surface of the remainder forms a continuationof the case in front of the recess while the pistons are passing; and thenby a similar movement as that used in the figure described, the convexpart is brought in contact with the periphery of the drum tili the piston’sreturn.

All rotary pumps are both sucking and foreing machines, and are gene-rally furnished with valves in both pipes, as in the ordinary foreing pumps.The butments are always placed between the apertures of the suckingand foreing pipes.

No. 133.

No. 132.

There is another dass of pumps that bears some relationship to the pre-ceding—the eldest branch, we believe, of the same family. One of these isfigured in the 133rd Illustration: the butment consists of a curved flap thatturns on a hinge ; it is so arranged as to be received ;nto a recess formedon the rim or periphery of the case, and into which it is forced by thepiston. The concave side of the flap is of the same curve as the rim ofthe case, and when pushed back forms a part of it. Its width is, ofcourse, equal to that of the drum, against the rim of which its lower edgeis pressed; this is effected in some pumps by springs, in others by cams,cog wheels, &c„, fixed on the axles, as in the last one. The force bywhich the flap is urged against the drum must exceed the pressure ofthe liquid column in the discharging pipe. The semicircular pieces on theouter edge of the case represent ears for securing the pump to planks orframes, &c., when in use. The arrows in the figures show the directionin which the piston and water is moved.

Such machines have often been patented, both as pumps and steam-engines. In 1782 Mr. Watt thus secured a “rotative engine” of this kind,and in 1797 Mr. Cartwright inserted in the specification of his metallic pis-ton a description of another similar to Watt’s, except that the casehad two flaps, and three pistons were formed on the drum. In 1818 Mr.Routledge patented another with a single flap and piston, (Rep. of Arts,vol. xxxiii, 2d series ;) but the principle or prominent feature in all thesehad been applied long before by Freneh mechanicians. Nearly a hun-dred years before the date of Watt’s patent, Amontons communicatedto the Freneh Academy a description of a rotary pump substantially thesame as represented in the last figure. It is figured and described in thefirst volume of Alachines Approuv. p. 103 : the body of the pump or case