Sewer Appurtenances


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Sewer Appurtenances

  2. 2. SEWER APPURTENANCES Page 2 ACKNOWLEDGEMENT- I am very thankful to Prof. J.S Main for his constant support and valuable guidance. I am also thankful to my friends for valuable suggestions for the preparation of my seminar. Mr Sourabh M. Kulkarni. M. Tech (Environmental Engg). Roll No. 112020016.
  3. 3. SEWER APPURTENANCES Page 3 INDEX – Sr no. Description Page no Remark 1 Introduction 4 2 Lamphole 5 3 Manhole 6 4 Drop manhole 12 5 Oil & grease trap 14 6 Catch basin 15 7 Flushing tank 16 8 Ventilators 17 9 Cleanouts 17 10 Storm water inlet 18 11 Storm water regulator 19 12 Inverted siphon 21 13 Valves 23 14 References 24
  4. 4. SEWER APPURTENANCES Page 4 Introduction- In order to make the process of construction easy and to have efficient working and maintenance, the sewer system requires various additional other structures. These are called as sewer appurtenances. Sewer system requires various types of appurtenances for their proper functioning and maintenance, because simply sewers are laid, the sewage cannot flow in it continuously for longer time .After some time it will be chocked up and requires cleaning of sewers. If sewerage system is not properly maintained silt, ashes, grit, oil, fats, etc. will chock the sewer lines. Therefore, for proper operation and maintenance of sewerage system various devices are required. These are the appurtenances are as follows.  Manhole.  Catch basin.  Cleanouts.  Oil & grease trap.  Inlets.  Lampholes.  Drop manholes.  Flushing tanks.  Inverted siphons.  Sewer ventilators.  Storm water regulators.  Valves.
  5. 5. SEWER APPURTENANCES Page 5 LAMPHOLES - A lamphole is an opening or hole constructed in a sewer for the purpose of lowering a lamp inside. Description - The lamphole consist of vertical stoneware or concrete pipes which are connected to the sewer line through a tee junction. The pipes are surrounded by concrete make them stable. At the ground level, the manhole cover with frame is provided to take up the load of traffic. Purpose -  Under some circumtences, the lampholes may be also used as flushing device.  If the cover at the top of lamphole is perforated, the ventilation of sewers is achieved. such lamp hole is known as fresh air inlet. Location -  In narrow lanes change of gradient and slight curves where space is insufficient for the construction of manholes.  If the construction of manhole is difficult, a lamphole may be constructed in its place.  When the sewer length is straight for a considerable distance beyond the usual spacing between manholes, the provision of a lamphole is advisable.
  6. 6. SEWER APPURTENANCES Page 6 MANHOLES- A manhole is an opening constructed on the alignment of sewer for facilating a person access to the sewer for the purpose of inspection, testing, cleaning & removal of obstruction from the sewer line. Object - The following are the objects of the construction of manholes-  They permit inspection, cleaning, maintenance of sewer line. The obstructions in the sewage flow are collected in manholes and then they brought to the surface.  The manholes allow the joining the sewers or changing the direction or alignment or both.  A manhole sometimes receives the contribution of sewage from sewers of various sizes and coming from various directions.  If manholes covers are perforated, the manholes may allow the escape of undesirable gases and thus, ventilation of sewers can be achieved.  The manholes facillate the laying of sewers lines in convenient lengths. Location - Manholes should be built at every change of alignment, gradient and diameter. At the head of all sewers and branches and at every junction of two or more sewers. On sewers which are to be cleaned manually which cannot be entered for cleaning or inspection, the maximum distance between the two manholes should be 30 mt.
  7. 7. SEWER APPURTENANCES Page 7 Square manhole cover Rectangular manhole cover Constructional details - The manholes are constructed directly over the centre line of the sewer. They are circular & rectangular in shape. Manholes should be of such size as will allow necessary cleaning & inspection of manholes. A) Rectangular manholes- These are the manholes of sizes like 1) For the depth of manholes less than 0.90mtr, 900x800mm. 2) For the depth of manholes 0.90 up to 2.5 mtr, 1200x900mm. B) Arch type manhole - For the depth of 2.5 & above arch type of manhole can be provided and the internal sizes of chambers between brick faces shall be 1400x900mm.the width of manhole chamber on bends and junction of pipes with dia. greater than 450mm, should be suitably increased to 900mm or more so that benching width on either side of channel is at least 200mm. C) Circular manholes- The circular manholes may be constructed as a alternative to rectangular as well as arch type manholes. These are the manholes are provided for all the depth starting from 0.90 m. circular manholes are straight down in lower portion and slanting in top portion so as to narrow down the top opening equal to dia. of manhole cover. Depending upon the depth of manhole the diameter of manhole changes. The internal diameter of circular manholes may be kept as following depths.  For depth above 0.90m and up to 1.65m, 900mm diameter.  For depth above 1.65m and up to 2.30m, 1200mm diameter.  For depth above 2.30m and up to 9.0m, 1500mm diameter.  For depth above 9m and up to 14m, 1800mm diameter.
  8. 8. SEWER APPURTENANCES Page 8 Circular manhole cover If the sewers are constructed in tunnel the manhole should be located at the access of working shafts and the manhole chamber must be constructed of a size to suit the working shaft or vice-versa. The openings for entry into the manhole (without cover) should be of such minimum dimensions as to allow workman with a cleaning equipments to access into the manhole without any difficulty. A circular opening is generally preferred. A minimum clear opening of 60cm is recommended. Suitable steps usually of cast iron shall be provided at entry. Access shaft for large sewers – Access shaft shall be circular in shape and shall have a minimum internal dia. of 750mm. Where the depth of shaft exceeds 3m suitable dimensions shall be provided to facilitate cleaning and maintenance. Access shaft where built of brickwork should be controlled on three sides it to the size of the opening in the cover frame, and to provide easy access on the forth side to step irons or ladder in determining sizes, the dimension of maintenance equipment likely to be used in the sewers shall be kept in view. Where the dia. of sewer is increased, the crown of the entering and leaving pipes shall be fixed at the same level and necessary slope is given in the invert of the manhole chamber. A slab, generally of plain cement concrete at least 150mm thick should be provided at the base to support the walls of the manholes and to prevent the entry of ground water. The thickness of the base also shall be suitably increased up to 300mm for manholes on large dia. with reinforcement. in case of large manholes ,the flow in the sewer should be carried in U shaped smooth channel constructed integrally with the concrete base of manhole. The side of the channel should be equal to the dia. of largest sewer pipe. The side walls of the manhole are usually constructed of cement brick work 250mm thick and corbelled suitably to accommodate the frame of the manhole cover.
  9. 9. SEWER APPURTENANCES Page 9 The inside & outside of the brickwork should be plastered with cement mortar 1:3 (1 cement & 3 corse sand) and inside should be finished with the coat of cement. Covers & frames - The size of manhole covers should be such that there should be clear opening of not less than 560mm dia. for manholes exceeding 0.90m depth. The frames of manhole shall be firmly embedded to correct alignment and level in plain concrete on the top of masonry. After completion of work the manhole cover should be sealed with grease. Types of manhole -  Straight-Through manholes - The simplest type of manhole is that built on straight run of sewer with no side junctions. Where there is change in the size of sewer, the soffit or crown level of the two sewers should be the same, except where special conditions require otherwise.  Junction manholes- A manhole should be built at every junction of two or more sewers and the curved portions of the inverts of tributary sewers should be formed within the manhole. To achieve this with the best economy of the space, the chamber may be built of shape other than rectangular. The soffit of the smaller sewer at a junction should be not lower than that of the larger sewer in order to avoid the surcharging of the former when the latter is running full.  Side entrance manhole – In larger sewers or where it is difficult to obtain direct access to the sewers from ground level, owing to existing service, gas, water etc. the success shaft should be constructed in the nearest convenient position off line of sewer and connected to the manhole chamber by a lateral passage.
  10. 10. SEWER APPURTENANCES Page 10 House drainage – Gully traps - A gully trap is usually made of stoneware and cast-iron grating is provided at its top. The gully trap is provided inside a masonry chamber. A water seal about 60 to 70mm is provided in gully trap. The gully traps forms the starting point of horizontal flow of sewage. It is usually situated near the external face of the wall and kept slightly higher or even in line with ground level. The gully trap leads the sewage either to the sewer or to inspection chamber or to manhole. A well designed gully trap may serve two or three connections from the nahani trap. But it is advisable to provide separate gully trap for sullage and soil waste. The top of the gully trap is provided with a cover cast iron which can be taken out easily for cleaning purpose. Inspection chamber - The trap has a water seal of about 100mm and it is provided in the last manhole house drainage system. It thus conveys sewage from house to the public sewer. The main idea of providing the intercepting sewer trap is to prevent the entry of sewer gases from public sewer line to house drainage. Hazards of manhole work - The element of the sewer maintenance ignored very often and which requires careful attention and protective measures is the manhole work. The staff should be trained for comparatively easy act of removing a manhole cover, not only to avoid smeshed toes and fingers, but also to prevent more serious back injuries. In addition, the approaching drivers on
  11. 11. SEWER APPURTENANCES Page 11 the road should be warned from a distance about the manhole work in progress by the installation of suitable signals or lights. The most serious hazard of manhole work are however flammable gas and oxygen deficiency. The staff should be thoroughly trained to carry out simple tests on every manhole before entry for oxygen deficiency, combustible, carbon monoxide or hydrogen sulphide. If however an emergency demands to enter a gas-filled manhole or one where oxygen may be lacking, the worker should wear a self contained air breathing mask and a safety harness with lifetime. The extra two other employees should be stationed at the manhole opening because one individual cannot life an unconscious person out of a manhole. Manhole safety -  Use safety harness & life line before entering into the sewer line. The two persons should stand at the top and they should give the signals to the person in manholes.  Test for the hazardous gases before entering into the manhole.  The manhole should be opened before one hour of the work. The care should be taken that it should be fenced to prevent any person, children in to the manholes. The dummy covers should be provided.  Use the mask when man have to into the sewer line.  No material should be kept near to the manhole as it can fall into the manhole which cause the accident.  Test the ladders of manhole before entering into the manholes.  The lighting material should be fire proof.  Lower all the tools into the manhole through buckets only.
  12. 12. SEWER APPURTENANCES Page 12 Drop manhole - When a sewer connects with another sewer, where the difference in level between water lines of main line and the invert level of branch line is more than 600mm or a drop of more than 600mm is required to be given in the same sewer line and it is uneconomical and impracticable to arrange the connection with in 600mm, a drop connection shall be provided for which a manhole may be built incorporating a vertical or near vertical drop pipe from the higher sewer to lower sewer. This pipe may be outside the shaft and encased in concrete or supported on brackets inside the shafts. which should be suitably enlarged. If the drop pipe is outside the shaft the continuation of sewers should be built through the shaft wall to form a rodding and inspection eye. Which should be provided with a half blank flange. If the drop pipe is inside the shaft, it should be in cast iron and it would be advantageous to provide adequate means for rodding and water cushion of 150mm depth should also be provided. The diameter of the back drop should be atleast as large as that of incoming pipe. The drop pipe should terminate at its lower end with a plain or duck foot turned so as to discharge its flow at 45 degrees or less to the direction of the flow in main sewer and the pipe unless of cast iron, should be surrounded with 150mm of concrete. In case of sewers over 450mm in diameter the drop in level may be accomplished by one of the following methods- a) A cascade- This is a steep ramp composed of steps over which the flow is broken up and retarded. A pipe connecting the two levels is often concreted under the steps to allow small flows to pass without trickling over the steps. The cascade steps may be made of heavy duty bricks of class I quality cement concrete with granolithic finish or dressed granite. b) A ramp- A ramp may be formed by increasing the grade of the last length of the upper sewer to about 45 degree or by constructing a steeply graded channel or culvert leading from the high level to the low level. In order to break up the flow down the ramp and minimise the turbulence in the main sewer. The floor of culvert ramp should be obstructed by raised transverse ribs of either brick or concrete at 1.15 m intervals and a stilling pool provided at the bottom of the ramp. c) By drops in previous successive manholes - Instead of providing the total drop required at the junction manhole , the same may be achieved by giving smaller drops in successive manholes preceding the junction manhole. Thus, for example, if a total drop of 2.4 m is required to be given, 0.6 m drop may be given in each of the previous three manholes and the last 0.6m may be given at the junction manhole.
  13. 13. SEWER APPURTENANCES Page 13 Scrapper or service type manholes- All sewers above 450mm in diameter should have one manhole at intervals of 110 to 120 m of scrapper type. The manhole should have clear opening of 1200 x 900mm at the top to facilate lowering of buckets.
  14. 14. SEWER APPURTENANCES Page 14 OIL AND GREASE TRAP - These are the traps or chambers which are provided on the sewer line to exclude grease and oil from sewage before it enters the sewer line. Principle- The principle on which grease and oil traps work is simple. The grease and oil are the light in weight float on the surface of sewers. Hence, if outlet draws the sewage from lower level, the oil & grease are excluded. Thus, the outlet level is near the bottom of the chamber & inlet level is near the top of the chamber. If sand is desired to be excluded from the sewage, the space should be kept at bottom of chamber for sand to be deposited. Location- The oil & grease traps are to be located near the source contributing grease & oil to sewage. They are thus located at places like automobile garage, grease & oil producing industries, kitchens of hotels. The following are reasons for excluding grease and oil from the sewage.  If the grease & oil are allowed to enter the sewer, they stick to sides of sewer and consequently the capacity of sewers are reduced.  The presence of grease & oil in the sewage also adds to the possibilities of explosion in sewers.  The presence of grease & oil in the sewers is also objectionable from view point of treatment of sewage.  The suspended matter which would otherwise have been conveyed also sticks to the side of sewers due to sticky nature of oil & grease. Cleaning- The oil & grease traps should be carefully inspected & properly cleaned at regular intervals. If it is not done they will not functioned properly & there will not be a free flow of sewage.
  15. 15. SEWER APPURTENANCES Page 15 CATCH BASIN - A catch basin or catch pit is a structure in the form of a chamber which is provided along the sewer line to admit or allow the clear rain water free from silt, grit, debris etc. into the combined water. These are the small masonary chambers (75 to 90 cm in dia. And 75 to 90 cm in deep) which are constructed below the street inlets to prevent the flow of grit sand, debris, etc. in the sewer lines. When storm water enters these basin the grit, sand settles in the bed and storm water free from all these enters the sewers. The outlet pipe of catch basin is fixed about 60 cm above the bottom of catch basin. The catch basins collect the solids from storm water. These solids are to be removed at frequent intervals for the proper functioning of the catch basins, otherwise they will block the passage of storm water to the sewers resulting in flooding of streets creating nuisance. Purpose -  To prevent the entry of silt, grit, debris, etc. contained in the rain water.  To prevent the sewer gas. Maintenance - The catch basins provided a temporary storage of impurities contained in the rain water. Hence, it requires a periodical cleaning. Otherwise the organic matter decomposes and gives out bad smell. It also then forms a breeding place for mosquitoes and causes annoyance to the person passing or living nearby. Use – The catch basins are adopted for the combined sewerage system. But at present the trend is to lay sewers with such a gradient that self-cleaning velocity is achieved and to construct paved streets which contribute little debris or grit. Hence, it is not required to provide the catch basins in the modern separate sewarage system.
  16. 16. SEWER APPURTENANCES Page 16 FLUSHING TANKS - A flushing tank is a device or an arrangement which is made to hold and then to through water into the sewer for the purpose of flushing it. Where it is not possible to obtain self cleaning velocities due to flatness of gradient espically at the top ends of branch sewers which receive very little flow.It is essential that some form of flushing device be incorporated in the system. This can be done by making grooves at intervals of 45 to 50 m in main drains in which wooden planks are inserted and water allowed to head up and which will rush on with great velocity when planks are removed. Alternately, an overhead tank is built from which a connections are made through pipes and flushing hydratants to rush water to the sewers. The flushing can be conveniently accomplished by the use of a fire hydradant or tanker & hose. The flushing manholes are provided, they are located generally at the head of the sewers. Sufficient velocity shall be imparted in the sewer to wash away the deposited solids. There are two types- 1. Hand operated flushing tank. 2. Automatic flushing tank. The automatic systems which are operated by mechanical units get often corroded by the sewer gases and do not generally functions satisfactory and hence not recommended. In case of hard chokage of in sewers, care should be taken to ensure that there is no possibility of backflow of sewage into the water supply mains. Quality of waters- The water required for the working of flushing tanks are untreated. There is no need of treated water. Approximate water to be needed for the flushing given below- Slope 200mm 250mm 300mm 0.050 2300 lits. 2500 lits. 3000 lits. 0.075 1500 1800 2300 0.0100 1300 1500 2000 0.0200 500 800 1000 0.0300 400 500 700
  17. 17. SEWER APPURTENANCES Page 17 VENTILATORS IN SEWERS - Various gases are produced in the sewers due to decomposition of organic materials of sewage. These gases are foul in nature, cause harm to human health and corrode the sewers reducing their life. The gases so produced are highly explosive and in high concentration may cause fatal accidents to the maintenance people on duty due to their explosive and poisonous characters. Due to the above difficulties, ventilation is provided to the sewers lines at every 80-100 meters which will provide fresh air to the workers working in the manholes. It may be of RCC or cast iron 15 to 23 cm in diameter with a cowl provided at the top. The ventilating shaft is generally connected to the manholes by 15 cm in diameter pipe. In open areas, the manhole covers may provided with vent pipes, but in crowed areas they should be air tight and connected with ventilating shaft. In modern, well designed sewerage system, there is no need to provide ventilation on such elaborate scale considered necessary in the past specially with the present day to omit intercepting traps in house connections. The ventilating columns are not necessary where intercepting traps are not provided. It is necessary however to make provision for the escape of air to take care of the exigencies of full flow and also to keep the sewage as fresh as possible espically in outfall sewers. In storm water this can be done by providing ventilating manhole covers. CLEAN OUTS - A clean out is an inclined pipe which is connected to the underground sewer. The other end of the clean out pipe is brought up to ground level & cover is placed at ground level. A clean out is generally provided at the upper ends of lateral sewers in place of manholes. Working - The working of a clean out is simple. The cover is taken out and the water is forced through clean out pipe to the lateral sewers to remove the obstacles in the sewer lines. If the obstructions are large enough, a flexible rod may be inserted through the clean out pipe and pushed backward and forwarded to remove such obstacles.
  18. 18. SEWER APPURTENANCES Page 18 STORM WATER INLETS – Street inlets- An inlet is an opening through which storm water and surface wash flowing along the streets are admitted and conveyed to the storm water sewer by means of pipe. Location- The inlets are located or placed by the sides of roads at a distance of about 30 to 60 m. The inlets are so located that the storm water is collected in a short period and there is no flooding or accumulation of huge quantity of storm water on the roads. The inlets are connected to nearby manholes by pipe line. The clear opening should not be more than 25mm. The dia. of connecting pipe to street to main street sewer should not be less than 200mm. Types- The inlet is simply a concrete box. It may have gratings or openings in vertical direction or horizontal direction. The former is known as vertical inlet or curb inlet and the latter is known a Gutter or horizontal inlet. Openings- The inlet leads the storm water directly to the sewer and hence, its design should be made in such a way that the least opportunity is given for the storm water to stop. The openings of
  19. 19. SEWER APPURTENANCES Page 19 inlet therefore should be of such pattern that the chances of clogging are brought down to minimum possible extent. The objects that are cause most of the troubles at the openings of an inlet are sticks, waste papers, leaves etc. the cleanliness of footpaths and streets is therefore most essential for the successful and efficient functioning of inlets. STORM WATER REGULATORS - The structures constructed to divert part of sewage in case of combined sewers are known as the storm water regulators and they come into operation when discharge exceed certain value. Object- The main object of providing a storm water regulator is to divert the excess storm water to natural stream or river. The excess sewage will be mainly composed of storm water and it will therefore be not foul in nature. It will further result in the decrease in load on the treatment units or pumping stations. The following are the three types of storm water regulators- 1) Leaping weir. 2) Overflow weir. 3) Siphon spillway. Leaping weir- The term leaping weir is used to indicate the gap or opening in the invert of a combined sewer. The intercepting sewer runs at right angles to the combined sewers. When the discharge is small, the sewage falls directly into the intercepting sewer through the opening. But when a discharge exceeds a certain limit, the excess sewage laps or jumps across the weir and it is carried to natural stream or river. The leaping weir has no moving parts. A grating may be provided at the gap level to prevent the entry of small stones, debris etc. into the intercepting sewer.
  20. 20. SEWER APPURTENANCES Page 20 Overflow weir- In this type of arrangement, the excess sewage is allowed to overflow in the channel made in the manhole. When the quantity of sewage exceeds the capacity of the combined sewer, it overflows and falls into the channels and it is conveyed to the storm water sewer. In order to prevent the escape of floating matter from the combined sewer channel, the adjustable plates, are sometimes provided. Siphon spillway-  This arrangement of diverting excess sewage from the combined sewer is the most effective because of following-  It works on the principle of siphon action and it operates automatically. The rise of sewage in combined sewer is thus controlled in a better way.  It is automatic in functioning and this is the most effective in all other methods.  This arrangement has no moving parts and thus low maintenance. However it is likely to be clogged due to narrow passages.
  21. 21. SEWER APPURTENANCES Page 21 INVERTED SIPHON – An inverted siphon is a sewer section which is constructed lower than the adjacent sewer sections and which runs full under gravity with pressure greater than the atmosphere. It is however to be noted that the term inverted siphon as such is misnamed as it is not a siphon. It will be more appropriate to refer it as a depressed sewer or a sag pipe. To ensure the self cleaning velocities for wide variations in flow the two or more pipes not less than dia. 200mm are provided so that up to the average flow the pipe is used and when the flow exceeds the average the balance flow is taken by second or subsequent pipes. The siphon should not have any sharp bends as it should be cleaned by self cleaning velocity. Velocity- It is necessary to have the self cleaning velocity 1.0 mps for minimum flow to avoid the deposition in the line. Inlet and outlet chamber- The inlet and outlet chambers should allow the sufficient room for entry and maintenance of siphon. The outlet chamber is so designed so that to prevent the backflow of sewage into the pipes which are not used at a time of minimum flow. Hydraulic calculations- As the inverted siphon is pipe under pressure, a difference in the level at the inlet and outlet is the head under which the siphon operates. This head should be sufficient to cover the entry, exit and frictional losses in the pipes. The hazen Williams formula can be used to calculate the head loss. Size and arrangement of pipes- In the multiple pipe siphon,the inlet should be such that the pipes come into action successively as the flow increases. This may be achieved by providing lateral weirs with heights kept in accordance with the depth of flow at which one or more siphon pipes functions. The fig shows the general arrangement of siphons. In two pipe siphon, the first pipe should take 1.25 to 1.5 times the average flow and second should take the balance of the flow. Purpose- The main purpose of installation of inverted siphons is to carry the sewer line below obstructions such as ground depression, streams, rivers, railway etc.
  22. 22. SEWER APPURTENANCES Page 22 Float actuated gates and valves - Control of the flow in sewers can be regulated by means of automatic mechanical regulators. These are these are actuated by the water level in the sump interconnected to the sewers. These regulators involve moving parts which are actuated by the varying depths of flow in the sewers. They required periodic maintenances and inspection. Flap gates and Flood gates - Flap gates or backwater gates are installed at or near sewer outlets to prevent backflow of water during the or at high stages in the receiving stream. Such gates should be designed so that the flap should open at a very small head differential. With a properly operated flap gate it is possible to continue to pump a quantity equivalent to the sanitary sewage flow from the combined sewer to the treatment plant even though flood conditions prevail in the stream at the sewer outlet. Many flap or back water gates are rectangular and may consist of wooden planks .circular or rectangular metallic gates are commercially available. Flat gates may be of various metals or alloys as require. Flap gates are usually hinged by a link type arrangement that makes it possible for the gate shutter to get seated more firmly. Hinge pins, linkage and links should be of corrosion resistance material. The maintenance of the flap gates requires regular inspection and removal of debris from the pipe and outlet chamber. Lubrication of hinge pins and cleaning also it requires.
  23. 23. SEWER APPURTENANCES Page 23 REFERENCES-  Manual on sewerage and sewage treatment. Second edition.  Water supply and sanitary engineering By-G.S Birdie and J.S.Birde.  Water supply and sanitary engineering By- Rangwala