Imágenes de páginas
PDF
EPUB

the arm is made by slotted holes on the horizontal leg of the angle, so that the adjustment for position may be exactly made. The face of the valve and all wearing parts are made of bronze, the rest being of cast-iron.

Fig. 147 shows the simple regulator used on the Brookline sewers. A bent arm acts as a lever, one end forming a sliding gate, which opens or closes the exit from the main village sewer. The other end is attached to a float which moves up and down in a float chamber. When the level of the sewage in the intercepting sewer rises to a point where it overflows into the chamber, the

Fig. 147

float is lifted and the valve closes, forcing the sewage into an overflow pipe leading out from a manhole on the left (not shown). A small drain pipe leads out from the chamber so that as the level in the intercepting sewer falls, the float descends, opening the gate. This device has worked admirably for twelve years.

Fig. 148 shows a regulating device furnished by the Coffin Valve Company. A copper float moves up and down in its chamber, the motion being communicated through a rocker arm to a valve which slides across the entrance to the intercepting sewer as the float rises. The cut apparently shows the outlet to the outfall, which then comes into play, the inlet not being

visible. The side motion of this valve differs markedly from the other valves, which are all of the flap-valve type.

Fig. 1491 shows a regulator installed at Woburn, Mass., about twenty years ago. A large copper float rises and falls in a well, built by the side of the manhole. The float is attached to a lever which, working through an opening in the manhole wall, causes

[blocks in formation]

the flap valve to open and shut as the sewage in the well falls and rises.

The use of overflows or regulators is a relic of the time when storm-water sewers formed the general type of sewers, and is really a makeshift, to adjust the undesirable conditions thus formed to the modern necessities for purification. Except for Eng. Rec., Vol. 22, p. 41.

1

the need of purification, or for the construction of long, intercepting sewers to relieve excessive local pollution, no such devices would be needed. Nor would they be needed if house sewage had been kept out of the storm sewers. It is not likely that in

LONGITUDINAL SECTION

TRANSVERSE SECTION

PLAN

Fig. 149

the future the construction of combined sewers will be permitted by the state sanitary authorities, so that the devices here described will be limited in their application to old sewers built on the combined plan, the proportional number of which must steadily decrease.

CHAPTER XII.

BELL MOUTHS.

WHEN sewers are over three feet in diameter it is not necessary to make bends entirely within the manhole walls, since workmen can readily enter such sewers and remove obstructions by hand. Also the junction of two large sewers need not be made within the manhole, but the sewer walls can be brought to an intersection. When the angle between the axes of the intersecting sewers is greater than about 30 degrees, the walls are brought into each other, the weight of the arches, with their loadings, being safely carried down through the walls of one of the two sewers to the foundation. For this construction a template of the line of intersection of the inside walls should be made, and the brickwork carefully laid up to this on the main sewer, the other being afterward tied on along this line. When the angle is less than about 30 degrees, the arch thrust cannot be taken up, and a construction known as a bell mouth must be resorted to. In this (and the same construction applies when one sewer is brought into the other in a curve), the side walls nearest each other are stopped where the springing lines intersect, and a vertical wall is built across in the triangular spaces above. Then from the outside walls at the springing lines a large cover arch is thrown from outside to outside, the former small arches being omitted. This large arch is then gradually reduced in span in the form of a trumpet until it coincides with the arch of the main sewer below the junction. The object of this construction is to avoid a reëntrant intersection of the two arches which would be entirely unsupported and unstable. The section on KK in Fig. 141 shows the conditions, the intersection of the arches. evidently introducing unbalanced and unsupported vertical

[subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][ocr errors][merged small][merged small]

forces. The dotted lines in that figure show the relative position of the enveloping arch which would be used in a bell-mouth construction.

The plan of the intersecting sewers should show a connect

Curve of

Invert Intersection

IHG FE

D C

B

A

ing curve even if the angle between the two lines is as small as 25 or 30 degrees. An ideal intersection will bring the central threads of the surface flow in the two sewers together tangentially, so that the connecting curve is always desirable. Such an intersection, however, makes the quoin, or wedge-shaped

[blocks in formation]
[graphic]

Fig. 150

« AnteriorContinuar »