2. Introduction
● These are structures or devices in a sewerage system
● Constructed at suitable intervals along sewer line
● They assist in operation and functioning and maintenance of the sewerage
system
5. Location
● Every change of alignment
● Every change in gradient
● Every change in size (dia)
● At every junction
● At regular interval (in case of straight alignment)
7. Construction of Manhole
Manhole Cover
● Made of cast iron, it rests over the frame
● Clear cover of opening not less than 50 cm
● Top level is kept same as level of pavement
Access Shaft
● Upper portion of manhole which gives access to working chamber
● Dimensions less than that of working chamber
● Rectangular: 0.6m* 0.75m
● Circular: 0.6 to 0.75m in dia
● Steps made in it to access working chamber
● Made of bricks
8. Working chamber
● Lower portion of manhole
● Provides workspace
● Size: circular 1.2m dia
● Rectangular: 0.9m * 1.2m
● Made of brick masonry or cement concrete
● Bottom portion is called benching, made of cement concrete
10. Drop Manhole
● Constructed to connect a high level branch sewer to a low level main sewer
● Elevation difference more than 0.6m
● Made to avoid splashing sewage on working chamber
● Plug opened while inspecting and cleaning
15. Catch Basin (Catch Pits)
● For retention of debris in storm water
● If this not present, debris is carried to the sewer
● Helps in settlement of sand, grit, debris from storm drainage
● Settled matter are cleaned periodically
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19. Flushing Tanks
● Provided when there are high chances of blockage
● Blockage occurs when self cleansing velocity is too small or when pipe doesnt
have enough slope
● Also placed at dead end points of sewer
● These hold water temporarily
The water in flushing tank is thrown into sewer for flushing purpose so that the
blockage is removed
21. Manually Operating
● Consists of a concrete chamber connected to water supply
● Outflow pipe is present, which has a valve so that water can be discharged to
the sewer for flushing
● Gate valve is opened or closed manually
25. ● If sand has to also be removed, dead space kept at bottom of the chamber for
sand to be deposited
26. Inverted Siphons
● It is a sewer section obstructed lower than the adjacent sewer sections
● Runs full under gravity with pressure greater than atmospheric
● Differs from a true siphon
● Here, it runs with flow line below HGL and therefore under pressure, above
atmospheric
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28. Sewer outlet
● A masonry head structure, made at the bank of streams to discharge into river
● Last point of sewer line
29. Ventilating Shaft
● A vertical column made of cast iron or steel pipes
● At top of shaft, a copper wire cage or cowl is provided
● Prevents accumulation of gases like ammonia, methane, h2s, co2, etc
● Height must be greater than height of nearby buildings
● Provided every 200-300m
