IT) 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[January, 



DISCHARGE OF WATER THROUGH DRAIN PIPES. 



Experiment, on the Discharge of ''T'''-/'-''- /j^^^!' 7!^f ^7,^1^ 

 ,r,netion of the Metropolitan Commisnoners oj ie^e«.-L* rom tne 



Mechanicn' Magazine.'] 



T «en<l for the ffni.laiice or consideration of your readers, some 

 ,ccouTt of ex erhnents made on the discharge of water from 

 ?. pes lith a view to ascertain the requisite sizes of various aque- 



cts for tlfe purposes of drainage. It was necessary to c.mduc 

 hese expe iments,'as to arrangements of apparatus, m a different 



: ne^'thau if it had been required to know fe "ecessary s.z of 

 nioes for supplying the town with water, as, in the tormer case 

 tZl being 'no- pressure arising from head, a flow of water o 



liform seAion is maintained by the continual addition of lateral 

 s ream- and the length of the aqueduct, therefore, as an element 

 off t o.f, may have little or no influence on t^e velocity of he 

 main current; while in the case of waterworks the velocity of the 

 water epe.uing on the head at the origin of the system length of 

 nine is a most fmportant element in calculation; and the friction 



' "ng from this clmdition is often the '-■'^-f force to be o.^rconie 

 1,1 f-ict under these two circumstances, reverse effects are pro 

 I ced for in a drain, if the length he increased -"d junctions be 

 , ^ortionallv added a greater amount of discharge -11 be the 

 •esilt (1 always assume that the junctu.ns '""f "="'':, '.*7. "I" j 

 scientific manner with regard to their aiding the main line), and 



;, another respect the operations <>l - . ^^ ^ "[^'l^^:^: 

 system of waterworks are curiously dissimilar; for in t'^ former, 



tie chief current being supplied !"--'-''^ly "^Z;, timS e"l by a 

 sustained by their various ramifications, and "It""^*'^'-^ 'f' , "^J^/ 

 ; u titude of small mouths, the whole operation Pl-«7>^ ^-^f^^^ ^j^ ^^ 

 and easily bv the silent effort of gi-avitation; wh le in the latter 

 c"se the main line being first charged, the water has to be fo.ced 

 with suffid nt power to "divide itself, and "V've;"th great ve ocity 

 in a multitude of different directions, up hill and doj^'''''^ ^^ 

 intricate and narrow passages, turning at every arety of angle^ 

 In the latter work, again, the power is generated at once at the 

 he-,d of the' vs em, and is continually being expended so long as it 

 acts- but in the former, force is self-generating-.t accumulates 

 ftiie op^ralt enlarges, until the small tributaries become im 

 portant streams, and these streams an '"^P'-'^'^^X" plays in 

 easy to perceive at once what an important partyra(iO« plays in 

 the'one case to what it does in the other. , ,_ . . 



Hence with regard to formula- constructedon the basis of expe- 

 riments male wiU, heads of water at the ends of pipes, they have 

 r .el totally useless as means of ascertaining the P-per - es of 

 trains and sewers; and when tested by the ac a ^ '^charge ot a 

 drain, I have found them so much >" '^""'^^,^^' j ''^J^;^"^ p.^/ 

 ff-.essed by the eve much nearer the truth. rhe>y '"f^f ^ '^"">' 



Mher, rm' ch a^ to dc st^y confidence in any one of them unless 



c nfirmed by other evidence. The e''P»="?;V't^,;i '''^,^ J:t"^^ gZ 

 to describe were made under the sanction of the Metropolitan Com 

 missioners of Sewers, on their premises in Greek-street. 



The apparatus used was as f.dlows:-A strong platform, 00 feet 

 l„n<r w s erected fixed to move about a central axis at one enfl, 

 a T'fr^e o "emoved at the other by a chain and windlass, so as to 



llet I'Tths and a careful selection of them was made as to accu- 

 Soloi-e and dimensions. They were laid "Straight lines of 

 ^Um inclination, and the pipe joints were «"dered «. t^t^ 

 with clay. On each side of a line of pipes, fi;*^, J""'''^"!"^, Y" 

 Attached at intervals, by which tlie water was admitted, as « ell as 

 H the head f the pipe. The entrance of the water was regulated 

 by s nice o lat'w M e the head of the pipe was just hi ed, water 

 'L at the stle time admitted by the junctions sufficient to ma^i- 



i^sJi^cgeti^mnrn-iiorx^^^^^^ 



l--^:^J reduced to 5C,fe. in l.i.th, gave .^ n.iHy the 

 ::"• ,n:riea I) llln^ :' 'I'lter ne.;^ the discharging and was 



reduced to one-fifth of the corresponding area of the pipe and it 

 required a simple head of water of about 22 inches to give the same 

 result as that accruing under the circumstances of the junction'. 

 With re-rard to varying sizes and inclinations, we found, sufficiently 

 for practical purposes, that the squares of the discharges are as the 

 fifth powers of the diameters; and again, that in steeper declivi- 

 ties than 1 in 70, the discharges are as the square roots of the 

 nclinations; but 'at less, declivities than 1 in 70, the ratios of the 

 discharges diminish very rapidly, and are governed by no constant 

 law At a certain small declivity, the relative discharge is as the 

 fifth root of the inclination; at a smaller declivity, it '* found as 

 seventh root of the inclination; and so on as it approaches the 

 horizontal plane. This may be exemplified by the following results 

 found by actual experiment : — 



Discharges of a &-inch Pipe at Several Inclinations. 



Inclioat'nn 



1 in 60 



1 in 80 



1 in 190 



1 in 120 



1 in 100 



1 in 200 



1 in 240 



Pischarges in loOft. 

 per minute. 



75 

 .. 68 

 .. 63 

 .. 59 



6-1 

 .. 52 



50 



Inclination. 



1 in 320 



1 in 40(1 



1 in 4B0 



1 in 640 



1 in bOO 



1 in 120(1 

 Leiri 



Discharges in 100ft. 

 per minute. 



49 

 . . 4S-5 



'U 

 .. 47-5 

 .. 47 2 

 .. 4l>-7 

 .. 4li 



1 in 240 "" , r • ■ 



The series of hydraulic experiments from which the foregoing is 



selected, has be/n in operation for the last two years, at a„ expense 



of upwa ds of 2000/. 'fhe experiments conducted at .^reek-st eet 



were a continuation of similar experiments made in the Fleet 



Tewer: in the latter place the sewage was used, and .n the former 



pure water supplied by the New River Company. ri ■„, 



•^ The conclusi.m arrived at is, that the requisite sizes of drams 



an.^ ewers can be determined (near enough for practical purposes 



as ai im^-ortant circumstance has to be considered in provu^ing for 



the depSn of solid matter, which disadvantageously alters he 



/bm of the aqueduct, and contracts the water-way) by taking the 



result of the 6-inch pipe under the circumstances before mentioned 



as a"«°«m, and assuming that the squares of the discharges are as 



the fifth powers of the diameters. , ,. . . ,i,„ 



That at greater declivities than 1 in 70 the discharges are as the 



snuare roots of the inclinations. ,t„i.ta;n. 



That at less declivities than 1 in 70 the usual law will not obtain , 



but near approxLatioiis to the truth may be obtained by observing 



tl e relative discharges of a pipe laid at various small luclina ions 



That u^easing the number of junctions at intervals accelerates 

 the velocity of the main stream in a ratio which ^f eases as the 

 snuare root of the inclination, and which is greater than the ratio 

 of resistance due to a proportionable increase in the length of the 

 anueditr The velociiies^t which the lateral streams enter the 

 main 1 ne is a most important circumstance governing the flow of 

 wa er In piactice, these velocities are constantly variable con- 

 ^dered individually, and always different considered collectively 

 othaXelr united' effect it is <'iffi'^f ^o estimate Again ;^t^h^ 

 same sewer at different periods may be quite filled, but discharge 



^•'Thr:^:^^usi:^:^'^nX^.:^"of^r':uUic.s of the several 



for!;!::i:rforequo.d^le.tlij^ie.;c.o^ 



that no man, ^^cept by li own r „.ould' discharge. 



what a." a.p.educt u„d r a ^^^^^ Uke the trouble to 



^:e^a:,:^^:^^^e:^r.L formul. the one with tl. ^he. 

 need dwell on it no lon^ci. ^i- e r„,.t<i npi'iirrimr in their 



own expe nence -,/uo^. «f "'' ^^^ ^^^ scattered, or appro- 



exist in ^"""'"'nt ab ndu.ce • ^^^^ ^^^^. ^^ to assume 



'""':?U^Wudi r; has nt had an .fpportuuity of verifying by prac- 

 results «hKh he "as mi i^ current, the formulae of 



\^:\^::^^ns Si r 'l-: been received as orthodoxy by the 



scientific world. ^ ^ ^^^^^^ 



1, Greek-xtriet, Soho, 

 Dec. i, 1S49. 



Civil Engineer. 



