Specifications Part 1 - Water Supply, Sewerage and Tube Well Works

14.11 By pass:By pass arrangements should be provided from the inlet chamber and ifrequired special arrangements should be made for pumping the sewage to thelower reach of sewer line. Alternatively a vacuum pump maybe provided at theoutlet to overcome maintenance problems arising out of dogging and silting ofsiphons. If it is possible a blow off may be installed at the low point to facilitateemergency maintenance operations.14.12 Storm water inlets:-14.12.1 There are device meant to admit the surface runoff to the sewers and form avery important part of the systems. Their location and design should thereforebe given careful considerations.14.12.2 Storm water inlets maybe categorized under three major groups viz. curb inlets,gutter inlets and combination inlets, each being either depressed or flushdepending upon their elevation with reference to the pavement surface.14.12.3 The actual structure of an inlet is usually made of brickwork. Normally cast-irongratings conforming to IS: 5961 shall be used In case there is no vehiculartraffic, fabricated steel gratings maybe used. The clear opening shall not bemore than 25mm. The connecting pipe from the street inlet to the main streetsewer should not be less than 200mm in dia. and should have sufficient slope.14.12.4 Maximum spacing of inlets would depend upon various conditions of roadsurface, size and type of inlet and rainfall. A maximum spacing of 30m isrecommended.14.13 Sewer ventilators:-In a modern, well designed sewerage system, there is no need to provideventilation on such elaborate scale considered necessary in the past,especially with the present day policy to omit intercepting traps in houseconnections.14.13.1 The ventilating columns/shafts are not necessary where intercepting traps arenot provided. It is necessary however, to make provision for the escape of air totake care of the exigencies of full flow and also to keep the sewage as fresh aspossible especially in outfall sewers. In case of storm sewers providingventilating manhole covers can do these.14.13.2 Provision -Ventilating columns/ shafts shall be provided at an internal of 180min all mains intercepting and outfall sewers, near the manholes.14.13.3 The connections of house drains to the sewer shall be allowed without the useof any intercepting trap and thus permitting ventilation of laterals and branchsewers via. house drains and their ventilating pipes.14.13.4 Construction-The ventilating shaft shall consist of vertical columns of R.C.C. orcast iron about 6 to 8 meter in height and about 100 to 150mm in diameterUrban Administration & Development Department Page 168