WATER. 



which the water comes is fomewhat higher than the other 

 end where the water is to be delivered. The water would 

 indeed (hew itfelf at the fame level at one end of the pipe as 

 at the other, but it would not run out ; and in all cafes with 

 the fame fize pipe, the quantity of water given will increafe 

 in proportion as the receptacle at the difcharge is below the 

 fpring at the other end of the pipe. Hence, if there is a 

 great deal of water to be conveyed to a place fituated but 

 Tittle lower than the level of the original fpring, a very large 

 pipe mull be ufed to convey any given quantity. But the 

 fame quantity may be conveyed in a fmaller pipe, and con- 

 fequently at lefs expence, if the refervoir is much below the 

 original level. 



If the diftance is great, the length of the pipes will con- 

 fiderably diminifh the quantity of water brought through 

 them, in confequence of the friftion of the water againft the 

 fides of the pipes ; this cannot be prevented, and we muft 

 make the bore of the pipe larger, in proportion to the length, 

 if the water be in fuch quantity and fo much wanted as to 

 make it worth the expence. The rules for calculating the 

 proper fize of pipes we have already given. 



Defaguliers mentions an experiment which he made upon 

 a leaden pipe, wiiofe inward diameter was i|^ inch, and found 

 that at 1400 yards diftance from the fpring of water that 

 fupplied it, it did not give a tenth part of the water that it 

 would have given at thirty yards from the fpring, though 

 both places were at the fame depth below the furface. 



All care (liould be taken in the conflruAion of a conduit- 

 pipe, to avoid obilruftions occafioned by lumps of folder hang- 

 ing in the infide of the pipes, or by roughnefs at the joints, 

 if the pipes are put together by fcrew-joints. All the cocks 

 and plugs in the pipe (hould have water-ways fully equal to 

 the fedion of the pipe. 



Thofe who execute water-works are moft tempted to fail 

 in this point by making the cocks too fmall, becaufe large 

 cocks are very expenfive. 



The engineer fhould be fcrupuloufly attentive to this, for 

 a fingle contraftion of this kind may occafion the extra ex- 

 pence of many hundred pounds in making a large pipe to be 

 thrown away, becaufe if the pipe will yield no more water 

 than can pafs through the fmall cock, it would have been 

 as well to have laid a fmall pipe all the length. 



It is of the moft material confequence that there be no con- 

 traftion in any part of a conduit, and it is alfo prudent to 

 avoid all unnecefTary enlargements ; for when a pipe is full 

 of water moving along it, the velocity in every feftion muft 

 be inverfely proportional to the area of the feftion : hence 

 the velocity is diminifhed wherever the pipe is enlarged ; and 

 it muft again be increafed where the pipe contrafts. 



This cannot be done without expending force in the ac- 

 celeration ; and confuming part of the impelling power, 

 whether it be that of a column of water, or the force of a 

 machine. 



No advantage can be gained by the flow motion which 

 takes place at every enlargement in a pipe ; but every con- 

 traction, by requiring a reftoration of the former velocity, 

 employs a part of the impelling force ; this force muft be 

 equal to the weight of a column of water whofe bafe is the 

 contrafted palTage, and whofe height is fufficient to produce 

 that velocity with which the water mull pafs through the 

 contraftion. 



This point has often been overlooked by engineers of the 

 firit eminence ; and has, in many inftances, impaired the per- 

 formance of their beft works. 



Another point, which muft be attended to in the conduft- 

 ilig of water through pipes is, that the motion of the water 

 ftiould not be by pulfations, but continuous. When the 



water is to be driven along a pipe by the ftrokes of a reci- 

 procatmg engine, it fliould firft be forced into an air-veffel, 

 that the elafticity of the confined air may preferve an uniform 

 motion along the whole length of pipe. If the water is 

 fufFered to reft at every fuccefTive ftroke of the pifton, the 

 whole mafs muft again be put in motion through all the 

 length of the pipe. This requires a ufelefs expenditure of 

 power, over and above the force which may be neceffary for 

 raifing or conveying the water to its deftination. By employ- 

 ing an air-veffel and double or treble adling pumps we remove 

 this imperfedlion, becaufe it keeps up the motion in the 

 intervals between the ftrokes of the pifton. The cora- 

 preffion of the air by the aftive ftroke of the pifton muft be 

 fuch as to continue the impulfe during the momentary inac- 

 tivity of the pump. 



Pipes are fubjeft to obftrudlions from the depoCtion of 

 fand or mud in the lower parts of the pipes, and from the 

 coUedlion of air in the upper parts of their bendings. The 

 velocity of the water ftiould always be very moderate, and 

 then fuch depofitions of heavy matters are unavoidable ; 

 care ftiould therefore be taken to have the water freed from 

 all impurities, before it enters the pipe by proper fil- 

 tration ; and to difcharge the fediment which is unavoidable, 

 there ought to be cleanfing plugs at the lower parts of the 

 bendings, or rather a very little way beyond them. When 

 thefe are opened, the water will iffue with greater velocity, 

 and carry the depofitions with it. 



It is much more difficult to get rid of the air which 

 chokes the pipes, by lodging in their upper parts. This air 

 is fometimes taken in along with the water at the refervoir^ 

 when the entry of the pipe is too near the furface ; but it is 

 eafy to avoid this fource of the air, by making the water 

 enter the pipe beneath the furface. For if the entry of the 

 pipe is two feet under the furface of the water at the fpring, 

 no air can ever get in, and a float may be placed over the 

 entry, with a lid hanging from it to flaut the pipe before the 

 water runs too low. 



Air is difengaged from fpring-water by the motion of the 

 water in paffing along the pipe. When pipes are fupplied 

 by an engine, air is very often drawn in by the pumps. It 

 is alfo difengaged from its ftate of chemical union, when 

 the pumps have a fuftion-pipe of ten or twelve feet, which 

 is very common. In whatever way it is introduced, it col- 

 lefts in all the upper part of bendings, and accumulates 

 till it will choke the paffage, fo that fcarcely any water will 

 be delivered. 



To illuftrate this, fuppofe that the water of a fpring, or 

 coUeftion of fprings, is to be conveyed through a pipe to 

 the place of delivery, at a mile or half a mile diftant from 

 the fpring ; and that the ground, over which the pipe is 

 carried, has many undulations, and afcents and defccnts, 

 where it pafles over fmall intermediate hills and valleys. 

 We will fuppofe the place of declivity to be but a httle 

 lower than the water at the fpring, for example 9 or 10 

 feet. If the furface of the water in the fpring comes down 

 to the entrance-mouth of the pipe, or only near it, much 

 air will run down with the water into the pipe ; and where- 

 ever the ground rifes in the courfe of the pipe, this air will 

 lodge itfelf in the upper parts of the bends of the pipe, 

 and thereby diminifli the water-way fo as to force the 

 water to pafs through a paflage of one.fifth or one-fixth, 

 fometimes one-tenth of the proper bore of the pipe when 

 full. 



Sometimes, though no air Ihould get into the mouth at 



the fpring, there will be thefe lodgments of air from the 



firft running of the water ; for when the water firft enters 



into the pipe, if after coming down from the fpring it has 



R r to 



