Chap. 4.]

Double acting Fump.

271

CHAPTER IV.

Forcing pumps continued: La Hire’e double acting pump—Plunger pump: Invented by Morelaud ;the raost valuable of modern improvements on the pump—Application of it to other purposes than rais-jng water—Frictionless plunger pump—Quicksilver pumps—Application of the principle of Bramah ’spress bybees inforcing honeyinto their cells. Forcingpumps with hollowpistons: Employed in French water-works—Specimen from the works at Notre Dame—Lifting pump from Agricola—Modern liftingpumps—Extract from an old pump-maker’s circular—Lifting pumps with two pistons—Combinationof hollovr and solid pistons—Trevethick’s pump—Perkins’ pump.

Op the various modifications which the forcing pump has undergonein recent times we can notice but a few, and of these the greater partwere rnost likely known to ancient engineers. The most prominent oneis that by which the machine is made double acting. Now the device bywhich this is effected has not only frequently occurred to quite a numberof ingenious men in their endeavours to improve the pump who were ig-norant of its having been accomplished; but it is an exact copy of onethat has been applied to the wind pump of China from time immemorial,(see No. 112;) it probably therefore did not escape such men as Ctesibius ,and Heron, and others who appear to have exercised their ingenuity andsagacity to the utmost in Order to improve this machine, and who wereenthusiastically attached to such researches. The remarks on modernimprovements of the atmospheric pump, pages 225-6, are equally applica-ble to those of the forcing one; and it is worthy of remark, that notwith-standing the present improved state of mechanical Science , the ancientforms of both now prevail—for the forcing pump as made by Ctesibius inEgypt , and as described by Vitruvius as used by the Romans, is still morecommon than any other.

The double acting pump represented in the figure, was devised by M.La Hire in the early part of the last Century. His description of it waspublished in the Memoirs of the French Academy in 1716; and from oneof his expressions we perceive (what was in-deed very natural) that if he was not indebtedfor the improvement to the contemplation ofbellows, these instruments were at least close-ly associated with it in his mind. The pumpI propose [he observes] furnishes water con-tinually, “just as the double bellows makesa continual wind.” The piston rod passesthrough a stuffing box or collar of leathers onthe top of the cylinder. The latter has fouropenings covered by valves or clacks; twofor the admission of water and the same num-ber for its discharge. A B is the suction pipe,and C D the ascending or discharging one.Suppose the lower end of the suction pipe inwater; then if the piston be thrust down,the valve near B will close, and the air in thelower part of the cylinder will be forcedthrough the valve at I> and up the pipe D C ,and in consequence of the rarefaction of theair above the piston, the valve at C Mull be

No. 122. Double Acting Pump.