SEW

422

SEW

might not be unadvisable to adopt the egg-shape, supposingthat they can be manufactured with the same accuracy, andat no higher cost. If they be adopted, we should advise theirbeing made in two pieces, the lower one forming the invert,and the upper the semicircular crown; a flange, or socket,might be formed at the edge of the bottom-piece to receivethe top, and make a correct joint; the same practice might beadopted in cylindrical pipes of a large size. The advantagesattaching to this method are, that the inverts can be laid withgreat nicety, a matter of considerable importance, and areopen to inspection after they are laid, so as to admit ofopportunity of testing their accuracy: the objections againstthe whole pipes, on this head, are of considerable weight.Another advantage is, that the top-half can be taken off atany time for examination or inspection of the pipes, with-out disturbing the invert, or interfering with the flow.

These pipes are manufactured of stoneware, and variouskinds of clay, glazed and unghtzed, some being glazed onthe interior, and others on both surfaces; the stoneware,glazed on both sides, are most frequently adopted, and arefound to answer best; but there is a process of manufacturewhich produces unglazed pipes equally efficient as the glazedstoneware. The peculiarity of this process consists in sub-mitting the pipe, when half-dry, to an extreme pressurebetween two polished iron surfaces, whereby a density ofsubstance, and truth of form, is attained, which is equivalentin practice to the best glaze, so far, at least, as the flow ofwater is concerned. Pipes of the above materials and manu-facture have a great advantage over brick sewers, on accountof the comparative smoothness and evenness of surface, whichoffers very little or no resistance to the current; the amountof frictional resistance being naturally greater over the rouglisurface of the brickwork. In the following table will befound the result of some experiments, for the purpose ofdetermining the advantage gained, in this respect, by glazedpipes :—

Table of Comparative Time of Run of Water throughBrick Drains and Glazed Pipes.

Inclination.

Depth of Water.

Time throughGlazed Pipes.

Time throughBrick Drain.

Level .

Inches.

5

38

50

2 Inches in 50 feet...

41

16J

25

2| ditto

H

19

27

lj ditto

3

18

26

I ditto

31

25

36

ditto

4

15

22

1| ditto

6

13J

The rate of inclination is a matter which requires someconsideration in laying out a system of drainage ; the greaterthe fall, of course the greater the velocity, and, in conse-quence, the more rapid the discharge; the scour is also pro-portionately greater. It will thus be seen, that the efficiencyof sewers depends a great deal upon their rate of fall towardsthe outlet; this, however, will depend mainly upon the natureof the locality to be drained. Supposing there exists a cer-tain fall from the highest point to be drained to the outlet, itwill be well to see how it can be laid out or expended to thegreatest advantage :—the rule is this, give the greatest rateto the house-drains; the next greatest, to the pipes with whichthey are immediately connected ; and so on, diminishing therate gradually as you get towards the outlet. The reason forthis is obvious; for, in the first place, your main object is toremove the sewers from immediate proximity to the houses,so that perfect drainage is of less consequence at a distance

than it is in the houses themselves. But beyon f or as t 'is another more important object in this arrangemen^ r gtibody of water is less in the sewers or drains fnitsCfrom the outlet, it is more likely to be sluggish tb ^

ments than where there is a large volume ot wa r »te ^tendency to slugglishness is overcome by an (he

inclination, so that the want of velocity caused * ^ by 11body of water in the smaller sewers is compe nsa e qu»l>extra fall, and thus the flow in all cases is render ^ co jlectnearly so. In the larger sewers, where the wat ^ r ; en t to P r jlfrom the tributaries, the mass of water is su r^,

serve a good velocity with even a small inclina > ^ gro" a ’will depend, as we said before, upon the nature o j nbut, as a general rule, it is advisable that the j n -se"' eIpipes should not be less than 1 in 240, and in xpe ri® e,l Jnot below 1 in 1,000. It has been deduced from ^ 0 f iu°^that no proportionate advantage is gained by a ^ e peB“ el ■'than 1 in 60. The requisite size of the P’P^g vel oC '^Jj 3 .in a great measure, upon their fall, for as ra te 0 j|,eincreased in proportion thereto, so is ,wi°e less * iU 1,6charge, and therefore the greater the fall, tl‘ esectional area required for the sewers. . a noth er > ^Where one sewer discharges its contents m g 6 nt t0 ^junction should be effected by a curve, drawn ^ ^ sti e (directions of both sewers, so that the direction ^ ©ay ^may be changed in as easy a manner as possi ’ gJ . or ei>experience any shock either in leaving the sn nt - re to 111

gtr<

ing the larger sewer. It was formerly tbe ?^ the ithe junctions rectangular, but by this me 1 . r ;ght

■actice

the

les>

ofc> iaD

J) ad a tendencwTo ch C, ° SS1 ' ng that the maui

depending- on an S e lts direction, the amount -

a ' t ‘y case, however force of tiie tW °

eddies caused and’d 6 ^°- W w the main stre!,m was Tf L t,,econtrary , th e * w e P°sit thereby accumulated. Jf, . oC .

little or To f rea “ s be tangential at the P° iut .°yV' e

both a tenden/J ped ' ment will take place, a\ th fJ.Li'

sa ble, that thJ t0 m ° Ve in t,ie same direction. 1 ‘ „s

eyctUZ “£ * «r» A .HI,,. 1«S« *

the purpose in • P‘Pe-sewers, junction-pipes are , „»aiS-JL“jS ^Junction-curve is commenced,^

of a curved one in ti lave a strai S ht P’P e > aI> t Jade i0

.suit differ ent ’ * le same length; the pipes are tff0

junctions and tl mstances > some with one, others py-pl)aspect to the ti J^ ° C ™-iom sizes as requir f ag hdifferent iunefiV„ 6 0 . ccu P ,e d by the passage ot wate j a tby Mr. R oe aft S ’ th f following results hare been at

Time occurij/ , Vai ' I . ous experimen ts ;— .• v) ai‘ f

through simifn i ^ l h e passage of equal quantities /^oLTjZlty? JithtlJsamlinclination-

With true ^ 11 ,ne ~90 seconds.true curve-100 seconds.

0ttd9 - thzj

With turn at right angles—140 seco “““' t ; 0 nS, - .- neIt is to be observed with reference to J ^ main, gnot necessary to increase the capacity o ga °f * 1 rea sO>Jevery junction with a tributary, or that 1 . 6 he ^

should be equal to the area of all the J un , a P'P e ;t3 o ut 'of this apparent inconsistency is, that alt Jh full at ^tid^at the head, it will be found to be not « 0 f the P‘ Alet, and this is caused by the increased re .^jpgd pj 11 ^ 0 f th,of water acquired by running down an e port 10a little distance from the head, thereto e > gU tB<:i en . tsectional area of the pipe will he vaca ” t : c h will 11room for the discharge of a tributary^ gn( j lea^® is, ^

- -v» 1 ..

■ts tlir

i ts { 0 r

add to the velocity of the main^ stream,^

a second tributary atcourse, a limit to the addition of tnuu,-- ^areas of the main will be comparatively

ill

1