IU MP. 



only it the whole column of water to be set in motion, but there U a 

 low of useful effect : 1st, in consequence of the contraction ..f the fluid 

 vein at the foot valves ; 2nd, in consequence of the bends, or changes 

 of direction in the line of flow ; 3rd, in tho weight and friction of the 

 valves; 4th, in the friction of the pumping machinery: and . r >th, in 

 the friction of the ascending column of water against the tides of the 

 pipes, and in the inertia of the water itaelf. D'Aubuisson gives the 

 formula- usually adopted to calculate the value of these resistances 

 (pp. 519 to 5'J."'i ; but he prefaces them by saying, that it is impossible 

 to determine them rigorously. It may then suffice to say, that in 

 one mining- pump*, where the lift is very great, the sum of these 

 resistances is such as to reduce the useful effect of the pumping 

 machinery to about one-half of the power exercised. In Urge force 

 pumps the pistons are usually made of tho description known techni- 

 cally by the name of pl*grrt ; that U to say, they are formed of 

 hollow metal cylinders working in a stuffing-box, but with a small 

 annular space between their sides, and those of the cylinders. Theo- 

 retically, the quantity of water raised by each stroke of the plunger 

 would be equal to iU sectional area multiplied by the length of the 

 stroke, but in practice there is found to be a considerable loss of effect ; 

 and in cases where plunger pumps ore used in conjunction with lifting 

 pumps (as in deep mines), it is customary to make the former of t \th 

 larger diameter than tho hitter. In the force-pumps of very deep 

 mines it it necessary to counterbalance tho weight of the piston rods, 

 and to take great precautions to prevent their becoming bent und- r the 

 jars they are exposed to by their own vibration. 



The action even of connected pumps being of necessity of an inter- 

 mittent character, there is introduced near the point of delivery a large 

 vessel, called the air raarl, into which the water is forced in greater 

 quantities than can be discharged by the outlet valve, during the 

 period of inlet. The water then accumulates in the air vessel, and 

 compresses the air contained in it, sometimes even to the extent of 

 producing a pressure equal to three atmospheres. Of course when the 

 water ceases to enter through the valve connected with tho piston, the 

 reaction of the compressed air maintains the discharge through the foot 

 valve, and thus the discharge is rendered almost continuous. The air- 

 vessels also diminish in a notable manner the hydraulic jar on the 

 rising main, produced by the intermittent action of the pumping 

 machinery. 



In addition to the suction and forcing pumps, there are several 

 descriptions of machines used for raising water, such as the chain 

 pumps, norias, Archimedian screws, scoops, bucket wheels, Persian 

 wheels, flash wheels, rotary pumps, &c. ; and perhaps it would be 

 preferable at once to notice them, even though in some cases the 

 machinery con hardly be considered to come under the strict definition 

 of the word " pump." Thus, the chain pump consists of a series of 

 flat boards which ore attached to an endless chain, and the latter works 

 upon fixed wheels at the top and bottom of the course ; the flat boards 

 in ascending pass through a cylinder, and lift ill it a column of water. 

 The Noria is a machine much used in the Kast for irrigation pi. 

 and consists of a scries of earthen pots ranged upon a rope, working 

 also on fixed wheels ; so that the pots dip into, and raise the water 

 from the bottom of the well, to discharge it whan they pass over the 

 top wheel The Archimedian screws, as their name implies, consist of 

 a scries of threads, or worms, fixed upon an axis of rotation bearing on 

 a fixed pivot at the lower end, and having a winch handle at the top. 

 There are usually three threads working in a species of close fitting 

 race, or channel, open at the top ; the diameter of the thread is usually 

 made from 13 to 20 inches, but occasionally it has been made as much 

 as 6 feet ; the angle mode by the thread with the axis of the central 

 shaft (which, it may be added, is usually equal in diameter to Jrd of 

 that of the thread) varies between 45 and 78 ; but in practice an 

 angle of CO" is found to be the most advantageous. The. axis of the 

 1 shaft is usually placed so as to form an angle of from 30 to 45 

 with the hori/ontal line. The.'c Archimedian screws are much used 

 in Holland for drainage woiks; they ore driven by wind-mills, and 

 raise ti iy economically, provided the lift be not more than 



the Sambrc and Meuso canal a screw of 5 feet 4 inches 

 ' inches li; by a steam engine, has 



. ery satisfactory results. 



The scoops are, in fact, largo troughs fixed at one end on an axis, 



the otln r to a balance beam, to which an alternate 



U is communicated from some extraneous motive power; so that 



to dip into the water when the beam is at its lowest 



. line of its ovvnli* 



the beam rises. These engines arc applicable to lifts of from 12 to 15 

 feet, and they certainly work with very economical results. The 

 ! are, in principle, very similar to tho norias, and are 

 tiled in Switzerland, and in some parta of Germany, for in 

 purposes; they consist of a number of small buckets, arranged 

 iK-npbi-ry of a wheel mode to revolve in water, so that the 1 

 become filled .it, the bottom of (he revolution, and discharge their 

 contents at the top of tho same. The dynamical results of th. - 



but they do not require frequent 



repairs, uor do th y r'.|iiire attcndani" which m -.' 



!e I' r the class of work they arc usually appliixl to. I 

 ! for raising water from the i: 

 it are now almost entirely abandoned ; tln-v 



1'UMl 1 . 



of a series of hi-li--.-id.il channels Conned in large wheels, wh 

 made to dip in the water, .md <lves the water : 



Way to the- centre of the wheel, win .-vided for it. It 



! fc, t. The d:i>h 



wheels are, however, the m -iiis description of tin 



omnium use, and in tho polders of Holland they may In- seen in almost 

 : with windmill.*, whilst in our own fens 



tttey arc as frequently employed will w. Tiny 



consist of a series of floats fixed on tho p. i iphery "f a w i. 

 revolve in the water with gnu 1 

 applied to the water itself is sufficient to raise it to a height of 



i very efficient wheel of this description at work in 

 the Deeping Ken. near Spalding, set in n, 

 80-horno power; the wheel is i!. 1 - feet in diameter, with 

 54 feet 1 ; with a velociiy of ti t 



: the ouan: i is l'I. r > cub: 



At Ten-mile bank, near l.ittleport, in th- ! 

 there is a win -1 of In feet in di.iun !"i .d.-o moved by .steam. 



The Itntiii , p ,ini|w are those in which . 



vertical motion is communicated to the water to be raised, by i 

 of a wheel, bearing a series of fixed arum rotating at a high velocity in 

 a close drum, and receiving it* supply through the ajwrtures in the 

 side of the drum close to the axis. The h ipe of the arms has 

 material influence upon the useful effects of these pumps; and 

 many experiments, it has been found th-it the mo~t advant 

 to be given to them is to curv e , -.vards to th, .if the 



movement, so as to form a tangent to the circumference of the wheel 

 at the points where they intersect it. Amongst the most valuable 

 forms of these centrifugal pumps for drainage purposes, those manu- 

 factured by Mr. Appold, or by ' vane and Co., an 

 generally known; and perhaps it may be desirable to add tha' tin- 

 latter work with the smallest loss of power compared to the useful 

 effect with small lifts : Appold's pumps, however, pnsent more satis- 

 factory results when higher lifts arc required. All these engines are 

 inferior to the best forms of force-pumps when large volumes of water 

 have to be raised to great heights ; and their use would appi --, in 

 their present forms at least, to be most advantageously limited t 

 of about 30 or 40 feet vertical as a maximum. 



The discussion of the motive powers to be applied for the raising of 

 water by pumps, or other machines, will be more conveniently 

 reserved to WATKII Srri'LY. 



In Air-Pumps the objects to be obtained are twofold : 1st, to 

 exhaust the air under a receiver, for the sake of obtaining a vacuum ; 

 and 2nd, to condense the air so as to produce on increased pressure 

 upon the enclosed surface. The former object is sought to be obtained 

 in philosophical experiments, or in chemical or physical im 

 the condensation of air has lately been applied to many important 

 operations in the arts of construction. The exhaustion of the air is 

 effected by means of one or more pistons working through air-tight 

 cylinders, and provided with a series of valves which allow the air to 

 pass from the receiver to the exterior, but without admitting any 

 return ; so that the air of the interior becomes more and more rarificd 

 in proportion to the effort employed, and the perfection of the 

 machinery. No instrument of this description has yet secured a 

 perfect vacuum, though from what has been said in the article 

 Am-PuMP, some remarkable results seem to have been attained, 

 approximating very closely to that condition. As the mechanism 

 of air-pumps for exhaustion has been described in the article, 

 thus referred to, it will suffice here to state that in machinery they 

 are principally used for the purpose of overcoming the rcsi- 1 



1 by the steam left in the cylinders of steam c- 

 for removing the contaminated air in mine?, or in diving br 11s. The 

 condensing air-pumps, in their turn, are mode with valvog opening 

 inwards only, so as to allow air to be forced into t' 

 without being able to return. They arc employed for the pnrpo.-e. 

 of forcing air into diving-bells, into blowing machinery of r 

 and latterly into the iv 1 for making the fonndal 



bridges upon running sands. In the latter e Ion . .f 



tho air reaches to the extent of an <!!.] t o.|u.-d to at least three 

 pheres, and the workmen are obli;-.-.! to cany on tln-ir operations in a 

 medium of that density. A description of the machinery of this 

 description used in the Rochester bridge, was given some year- 

 by Mr. Hughes, who executed the works of that remarkable monument, 

 and the system has since been applied with success in tho cases of the 

 bridge er the Rhine, and of the railway bridge over the 



Thciss in Hungary. Coulomb appears to have b. en the li 

 introduce thi i-lrcssed to the A' 



-in 177>; and the French engineers have 



I'le.jin-ntly employed it in hydraulic, or ill milling operations, when 

 the pressure to be overcome has not exceeded the above quoted 

 limit of three atmospheres. 



>Vii'yw' /';/./. . F. T a number of years the chain-pump, . 



of metallic discs, regularly arranged upon 

 disc acting as a piston, w a- the only one in use on board large 

 and it. nny still 1 seen in several of our sea-going old line-of-paHlc 

 ships, although ni.-w chain-pumps are no longer fitted in her Mai 

 service. 



Pumps of various descriptions are in use lioUi in the navy and 



