Particular care should be taken to secure a firm foundation for man-holes, flush-tanks and lamp-holes, as their greater weight may cause a settlement which will break the pipes. Man-Holes.-Man-holes should be built with an eight-inch brick wall, as shown in Plates V, VI and VIII. They should be plastered outside and inside. The iron cover with which they are surmounted should weigh from 300 to 500 pounds. The style shown in Plate IX has given good satisfaction when made to weigh 350 pounds. It has the following advantages: The least possible surface is exposed to traffic. The impact of passing wheels comes well within the base. The interior downward projecting rim prevents any loosened brick from falling into the sewer. It is usual to hang a dust-pan below the perforations in the cover to catch the street detritus which may work through them. With good grades, however, there will be no danger of stoppage from this source when they are omitted. The method of forming the bottom of man-holes to preserve the proper cross-sectional form of the flow is shown in section. The method of connecting a sewer of small diameter with a larger one is also shown. Unless particular care is taken in forming these curves, solid matters will be stranded in the manholes and become offensive. Iron steps may be built in the wall, ladder used in ascending and descending. convenient, but are liable to collect street above. or a light, portable The steps are most detritus falling from Flush-Tanks.-Flush-tanks should be built with an eightinch brick wall, and plastered inside and outside with cement mortar. The upper courses of both man-holes and flush-tanks are exposed to the action of alternating frost and moisture in an unusual degree, and to the constant impact of vehicles, and with the best of material a four inch wall is not sufficiently durable. The interior of the flush-tank should be connected directly with the sewer, independently of its discharge, by a pipe of large diameter, as shown in the Plates following. This will induce a current of air flowing along the crown of the sewer from the lower levels to pass into the tank and out through the perforations in its cover. No other protection against frost is needed. This is also a material aid in the ventilation of the sewers. flush tanks should be supplied with a dust-pan. All The various types of flush-tanks will be more fully discussed in the chapter on flushing and ventilation. Lamp-Holes.-Lamp-holes should have a concrete bed under them to prevent settlement. They should be carried up as the trench is filled, and care must be taken to keep the sections vertical. Care must be taken in locating man-holes, flush-tanks and lamp-holes to avoid gutters, crossings and other objectionable locations. Upon leaving the work for the night, the ends of the pipe should be well cemented up as a protection against possible rain storms. House Sewers.-Experience with sewers of the Separate System demonstrates that stoppages in the house sewers are MAN-HOLE—BRICK SEWER. much more frequent than in the laterals; and the point in the house sewers which are particularly liable to obstruction is at the junction with the street sewer. Particular care should, therefore, be taken in the construction at this point. The Y branch should be properly elevated so as to bring the invert of the house sewer above the ordinary flow line of the street sewer, as shown in Plate X. The curve should have a sharp grade and particular care should be taken to have the spigots put squarely into the sockets and the gasket well placed. No cutting and trimming of the pipe should be allowed, as it is impossible to make smooth joints of terra cotta pipe in this way. Curved pipe always warps unevenly in the kiln, and from an ordinary stock there will be no difficulty in selecting a curve suitable for any reasonable case. Three or four of these, slightly varying in radius should always be at hand. A very common defect is to allow the centre or belly of the curve to drop down and open the joints before they are hardened, or to do the refilling in such a manner that the subsequent settlement of the trench breaks the joints or pipe. This can be avoided by thoroughly ramming the earth up to the horizontal diameter of the curve as it is laid and water-tamping or ramming in layers above this. House drains can be very nicely laid in favorable ground with an ordinary carpenter's level placed on each pipe as laid, one end of the level being supplied with a graduated slide and set-screw, by which is set off the fall corresponding to one length of pipe. |