Class V.]

HYDRAULIC MACHINES—CENTRIFUGAL TUMPS.

181

might have been avoided, it is evident that power musthave been expended unnecessarily in producing that visviva. And in like manner, if any vis viva remain un-necessarily in the water when it leaves the wheel, it isevident that the power by which that vis viva was createdmight have been saved.

The expedients by which the water may be brought tothe wheel with the least loss of vis viva are common tothis and to other hydraulic machines ; those by which itenters and is delivered from the wheel are peculiar to thecentrifugal pump.

If the vanes be straight, it is evident that whatevermay be the velocity of the water in the direction of aradius, when it leaves the wheel, its velocity in thedirection of a tangent will be that of the circumfereuce ofthe wheel, so that the greater the velocity of the wheel,the greater will be the amount of vis viva remaining inthe water when discharged, and the greater the amount ofpower uselessly expended to create that vis viva.

If, however, the vanes be curved backwards, as regardsthe motion of the wheel, so as to have nearly the direc-tion of a tangent to the circumference of the wheel at thepoints where they intersect it, then the velocity due tothe centrifugal force of the water carrying it over the sur-face of the vane in the opposite direction to that in whichthe wheel is moving, and nearly in the direction of atangent to the circumference, will—if this velocity ofthe water over the vane in the one direction be equal tothat in which the vane is itself moving in the other—produce a state of absolute rest in the water, and entireexhaustion of vis viva. And in whatever degree theequality of these two motions—of the water in one direc-tion over the vane, and of the vane itself in the oppositedirection—is attained, in that same degree will the water bedelivered in a state approaching to one of rest. The ex-pedient of curved vanes is adopted in Mr. Appold’s pump.

With regard to the admission of water to the wheel, itis obvious tliat it should pass directly from the suction-pipe into the wheel without the intervention of anyreservoir in which the vis viva of the influent stream—communicated in the act of rising through the pipe—mayexpend itself, and tliat such space should be allowed atthe centre as not to alter the dimensions of the influentstream. It would further seem expedient, by means ofproperly constructed channels, to divide the water intoseparate streams, and to give to these divergent streamssuch curvatures as would facilitate their entrance uponthe channels formed by the vanes; as in the turbine.

It is obvious that the tendency of the centrifugal forcecontinually to increase the velocity of the water over thevanes as it recedes from the centre cannot take effect inrespect to all the particles of water in the same section,unless the sections of the channels diminish. If they donot, some of the particles of water in each section mustbe continually retarded, and power be uselessly expendedin producing this retardation; whilst the current cannotbut suffer from it a disturbance destructive of its vis viva.

This diminution of the sections of the channels mightprobably best be effected by giving to the sides of thewheel the forms of conical discs; an expedient which isadopted in Mr. Lloyd’s blowing-machines, and in Mr.Bessemer’s centrifugal pump.

The communication of motion to the water of thereservoir in which the wheel revolves, and into which thewater is discharged, should by every practicable expe-dient be avoided; and for this object the water should bekept as much as possible from the sides of the wheel.This is effected in Mr. Appold’s pump, by fixing thewheel between two cheeks which project from oppositesides of the reservoir. The velocity with which thewheel must be driven depends upon the height to whichthe water is to be raised. Beyond a certain height thisvelocity is practically unattainable. But long before thislimit is reached, it becomes inconsistent with an econo-mical application of the power which drives the pump.It is probably therefore only in comparatively smalllifts, where a large quantity of water is to be discharged,that the centrifugal pump will be found useful.

No. 420, p. 232 (England). The Council Medal hasbeen awarded to J. George Appold, 23 Wilson Street,

Finsbury Square, London , for a centrifugal pump,* onefoot in diameter, having curved vanes, separated bv acentral diaphragm, perpendicular to the axis and inter-secting the vanes, so as to form a double wheel; to the twoparts of which access is given for the water by centralapertures six inches in diameter, on opposite sides of thewheel, whose axis is fixed to the diaphragm.

To determine the useful effect of this pump, a series ofexperiments were made under the direction of ColonelMorin, the Vice-Chairman of the Jury. The results ofthese experiments are detailed iu the following Table.(See page 1S2.)

The work of the motive power was determined by thewell-known dynamometer, constructed by M. Morin, ona principle proposed by General Toucelet*. It is the dis-trintcive feature of this dynamometer tliat it registerseach effort of the motive power with the space throughwhich the machine is driven by that effort, however

* The centrifugal-pump is by no means a new invention.Without entering into further particulars of its history,which appears to date back more than a century, it issufficient to state that it was used in America as far backas 1830; that one was erected in the Navy Yard, New York ,by our colleague, Mr. M‘Carty, in the year 1838, and tliatimprovements in it were patented in the United States inthe following year. The curved form of the vanes wasadopted in some of the American pumps. * The true prin-ciples of that part of the invention would seem, however,not to have been generally understood; and it is a fact notwithout interest in the history of the invention, and strik-ingly illustrative of the importance of other views of theprinciples of mechanics than are common among practicalmen, that these curved vanes appear to have been discardedfor straight ones.f In an able memoir by M. Ch. Combes,Member of the Institute of France , entitled, “ Sur Ies Rouesde Reaction,” read before the Academy of Sciences on the23rd of July, I83S (see k ‘ Comptcs Rendues,” vol. vii., 2meSemestre, 1838, p. 306), the theory of the centrifugal venti-lator is discussed and its obvious relations to the theory ofthe centrifugal pump arc pointed out. The curved formproper to the vanes is insisted on in this paper, and itstheory investigated.

In August, 1838, this gentleman took out a brevet (Vin-vention, entitled, “ Pour line machine universelle, a forcecentrale, propre a deplacer les liquides et les fluides aeri-formes,” &c., which appears to have been a centrifugal-pump ; a name which indeed he applied to it in a noteaddressed to the Academy of Sciences in February 1839.From this period M. Combes appears constantly to have ad-vocated the use of the centrifugal-pump, and with this viewto have caused a model of such a pump to have been con-structed, which still exists in the collection of the “ EcoleNationale des Mines,” at Paris . The expediency of giving acurved form to the vanes could not but be apparent to himfrom those scientific considerations on which his investiga-tions were founded, and it is insisted upon or implied inthem all.

In 1843 he published a work entitled, “ Recherches theo-riques et experimentales sur les Koues a reaction ou atuyaux,” in which, treating specially and principally of theturbine, lie nevertheless establishes principles applicable atthe same time to the centrifugal-pump, and arrives at for-mula? which are applicable to it by a slight modification ofthe symbols. This relation and this application he speciallypoints out. This explanation has been considered due tocur distinguished colleague, M. Combes. The question ofpriority, either in the invention of the machine or in themathematical discussion of it, is one on which it is not theprovince of the Jury to enter.

* A model of one of them was exhibited to the Jury, by Mr. Gwynn,having this form of vane.

+ The following passage is from the prospectus of the inventor ofa centrifugal-pump : “In attempting to construct a centrifugal-pumpa very large number of inventors have exhausted their skill in makingarrangements of spiral or curved arms on an axle, or in endeavours tofind the supposed angle or curve, with the diameter, which the fluidwould make in passing off, being in utter ignorance of the fact, tliatin obedience to the law of central forces, the escaping fluid takes theshortest line to reach the circumference; or, in other words, that eachparticle of matter in a state of rotation, when free to escape, movesdirectly in the line of the radius until it reaches the circumference,and thence follows the tangent line until influenced by gravity crsome other disturbing force.”