286

Rotary Pumps.

[Book III.

of Serviere’s, besides several modifications of it equallj interesting. Onehalf of the third part is occupied with descriptions of machines for raisingwater: these consist of gutters, swapes, chain of pots, gaining and losingbuckets, norias, tympanums and other wheels ; and lastly, pumps, amongwhich is the rotary one figured above. Breval, in his “ Remarks on Eu-rope,” part ii, page 89, mentions several machines in Serviere’s “ famouscabinet of mechanicks” that are not noticed in the volume published hyhis grandson; while others are inserted that were not invented tili afterhis death, as Du Fay ’s improvement 011 the tympanum.

Rotary pumps may be divided into classes according to the forms ofand methods of working the pistons, or those parts that act as such : andaccording to the various modes by which the butment is obtained. It isthis last that receives the force of the water when impelled forward bythe piston ; it also prevents the liquid from being swept by the latter en-tirely round the cylinder or exterior case, and compels it to enter the dis-charging pipe. In these particulars consist all the essential differencesin rotary pumps. In some the butments are moveable pieces that aremade to draw back to allow the piston to pass, when they are againprotruded tili its return; in others, they are fixed and the pistons them-selves give way. It is the same with the latter ; they are sometimes per-manently connected to the axles by which they are turned, and some-times they are loose and drawn into recesses tili the butments pass by.In another dass the pistons are rectangular, or other shaped, pieces thatturn on centres, something like the vanes of a horizontal wind mill, sweep-ing the water with their broad faces round the cylindrical case, tili theyapproach that part which constitutes the butment, when they move edge-ways and pass through a narrow space which they entirely fill, and therebyprevent any water passing with them. In other pumps the butment is ob-tained by the contact of the peripheries of two wheels or cylinders, thatroll on or rub against each other. No. 131 is of this kind—while theteeth in contact with the ends of the case act as pistons in driving thewater before them, the others are fitted to work so closely on each otheras to prevent its return. The next figure exhibits another modification ofthe same principle.

In 1825 Mr. J. Eve, a citizen of the United States , obtained a patentin England for a rotary steam-engine and pump. No. 132 will serve toexplain its application to raise water. Within a cylindrical case a solid orhollow drum A is made to revolve, the sides of which are fitted to moveclose to those of the case. Three projecting pieces or pistons, of the samewidth as the drum, are secured to or cast on its periphery ; they are atequal distances from each other, and their extremities sweep close roundthe inner edge of the case, as shown in the figure. The periphery of thedrum revolves in contact with that of a smaller cylinder B from which aportion is cut off to form a groove or recess sufficiently deep to receivewithin it each piston as it moves past. The diameter of the small cy-linder is just one third that of the drum. The axles of both are continuedthrough one or both sides of the case, and the openings made tight withstuffing boxes. On one end of each axle is fixed a toothed wheel of thesame diameter as its respective cylinder ; and these are so geared intoone another, that when the crank attached to the drum axle is turned, (inthe direction of the arrow,) the groove in the small cylinder receives suc-cessively each piston ; thus affording room for its passage, and at the sametime by the contact of the edge of the piston with its curved pay;, prevent-ing water from passing. As the machine is worked the water that en-ters the lower part of the pump through the suction pipe, is foreed round