WATER. 



as large as the hollow barrel into which it defcends, but it 

 does not touch the infide of the barrel. To make the clofe 

 fitting, the outfide furface of thecyhndrical pifton,or plunger, 

 as it is called, is made very true and fmooth ; and it is fur- 

 rounded by a collar of leathers fixed at the top of the barrel, 

 fo that no water can leak out of the barrel between the 

 plunger and the leather collars ; at the fame time that the 

 plunger can freely move up and down through the collars, 

 and will thereby increafe or diminifh the capacity of the bar- 

 rel, to produce the fame effeft as if the piilon fitted clofe 

 into the barrel. 



The principal circumftance to be attended to in this 

 pump is the conftruftion of the collar of leathers. To re- 

 tain thefe leathers in their places, the top of the barrel muft 

 be made with a flaunch, and pierced with holes to receive 

 fcrew-bolts. Upon this flaunch two rings of metal are ap- 

 plied one over the other, with fimilar holes : the internal 

 opening in the lowed ring is exaftly the fize of the plunger, 

 and that of the upper one a little larger. Two rings of foft 

 leather are cut out to correfpond with the metal rings, except 

 that the central holes are rather fmaller than the plunger : 

 to prepare the leather, it is foaked in a mixture of oil and 

 tallow for fome hours. One of thefe leather rings is laid 

 on the pump-flaunch, and one of the metal rings placed above 

 it ; the plunger is then thruftdown through the leather, which 

 turns the inner edge of the leather ring downwards ; the 

 other leather ring is then flipped on at the top of the plunger, 

 and the fecond metal ring is put over it, and then the whole 

 are Aid down to the metal ring ; by this the inner edge of 

 the laft leather ring is turned upwards. 



The metal rings and leathers are now fixed on the flaunch 

 by the fcrew-bolts ; and thus the leathern rings are ftrongly 

 comprefled between them, and make a clofe joint with the 

 top of the barrel ; and as the holes through the leathers are 

 fmaller than the plunger, they grafp the plunger fo clofely 

 that no preffure can force the water through between them. 

 The lower metal ringjuft allows the plunger to pafs through 

 it, but without any play, fo that the turned-down edges of 

 the lower leathern ring cannot come up between the plunger 

 and the lower metal ring, but are lodged in a conical enlarge- 

 ment, which is made round the inner edge of the upper 

 part of the barrel ; and in hke manner the turned-up edges 

 of the upper leather are received in the hole of the upper 

 metal ring, which hole is made larger than the plunger, to 

 leave a fpace all round for thefe edges : it is on thefe trifling 

 circumftances that the great tightnefs of the collar depends. 

 To prevent the leathers from flirinking by drought, there is 

 ufually a little ciftern formed round the head of the pump, 

 and kept full of water. 



This kind of pump is preferable to any other, where the 

 preflTure to be overcome is verv confiderable. The hydro- 

 ftatic preflcs are conftrufted on this principle. See Press. 



Pijians or Buckets for Pumps. — A good pifton fhould be 

 as tight as poflible, and (hould have as httle friftion as is 

 confiftent with this indifpenfible quality. The bucket of 

 the common fucking-pump, when carefully executed, pof- 

 feffes thefe properties in a high degree, and is the model for 

 other kinds of pump-buckets, or piftons, in which leather 

 can be employed. This bucket is in the form of a truncated 

 cone, with a hollow through the centre of it, which is half as 

 large as the outfide, at the largeft part ; it is generally made 

 of wood not hable to fplit, fuch as elm or beech, but in the 

 beft ki"d of pumps is made of metal. The fmall or upper 

 end of it is cut away at the fides, fo as to open into the 

 hole through the centre of it, and form an arch, by which it 

 is fattened to the iron rod or fpear of the pump, and within 

 the arch the valve or clack is fituated. The lower end of 



the conical part may be covered with a hoop of brafs, which 

 fits the barrel of the pump very exaftly ; the bucket is alfo 

 furrounded with a ring or band of ftrong leather, fattened to 

 , the wood with nails, and firmly retained by the brafs hoop 

 which is driven down on the bucket from the upper or the 

 fmaller end of the cone, and binds the leather fatt on the 

 wood ; but the leather being wider than the brafs, the edge 

 of the leather rifes upwards and furrounds the wood : this 

 part of the leather is made to turn outwards, like a cup or 

 hollow cone, which, at the upper end, is rather larger than 

 the barrel, fo a? to fpring againft the infide of the bar- 

 rel when the bucket is put into it. The leather muft be of 

 uniform thicknefs all round, fo as to fuffer equal compref- 

 fion between the wood of the bucket and the working 

 barrel, but tliis compreflion is very flight, becaufe it is the 

 upper edge of the cup which applies moft clofely to the 

 barrel. The feam or joint of the two ends of the band of 

 leather muft be tapered, and made to overlap and lie very 

 clofe, without increafing the thicknefs, but not fewed or 

 ftitched together, as that would occafion bumps or inequa- 

 lities, vi-hich would fpoil its tightnefs ; and no harm can 

 refnlt from the want of fewing, becaufe the two edges will 

 be fqueezed clofe together by the compreflion in the 

 barrel ; nor is it by any means neceflary that this compreflion 

 be great, for it occufions friftion, and caufes the leather to 

 wear through very foon at the edge of the bucket, and it 

 alfo wears the infide of the working barrel, which foon be- 

 comes enlarged in that part which is continually pafled over 

 by the pifton, while the mouth remains of its original dia- 

 meter, and then it is impoflible to thruft in a pifton which 

 fhall completely fill the worn part. A very moderate pref- 

 fure is fufficient for rendering the pump perfeftly tight, 

 becaufe the prefl"ure of the water makes the leather cup ap- 

 ply itfelf clofe to the barrel all round, and even adjuft itfelf 

 to all its inequahties. Suppofe it to touch the barrel in a 

 ring of an inch broad all round, this is a trifle, and the fric- 

 tion occafioned by it not worth regarding ; yet this fmaU 

 furface is fuflicient to make the paflage perfeftly imper- 

 vious, even by the prefl^ure of a very high column of incum- 

 bent water : for let this prefigure be ever fo great, the pref- 

 fure by which the leather is forced againft the infide of the 

 barrel will always exceed it, becaufe, in addition to the pref- 

 fure of the water, the leather will always prefs againft the 

 barrel by its own elafticity, the top of the cup of leather 

 being made rather larger than the interior of the barrel. 



This method of applying leather piftons is found to be 

 preferable to any other, becaufe if the leather is prefled 

 againft the barrel by any other means than the force of the 

 column of water, the preflure will always be too great or 

 too little. 



Pumps which are to raife hot water cannot be leathered, 

 becaufe the leather would fhrivel up ; in this cafe, ftrong can- 

 vas cloth is fometimes ufed inftead of leather ; but as this will 

 not hold water perfeAly, fuch pumps are generally packed 

 with hemp, in the fame manner as the pifton of fteam- 

 engines. 



Pump without Frisian. — When the height to which the 

 water is to be raifed is fmall, a pump may be conftrufted in 

 which the pifton does not require to be fitted clofely into 

 the barrel, nor are any leathers required. The barrel of this 

 pump muft be as long as the whole height to which the 

 water is to be raifed, and as much more as the length of the 

 ftroke of the pifton. The pifton is a foUd piece of wood, 

 fitted to the barrel as clofely as it ca.i be vithout aftually 

 touching the infide, and may be either fquare or round, but 

 a fquare trunk and a fquare beam of wood are beil, if the 

 pump is made of wood. The pifton muft be as long as the 



barrel, 



