Sanitary-Plumbing

• Size of pipes depends on hydraulic design (total demand, maximum flow rate of discharge to prevent slow discharge) and pump performance.
• Allowance to be made for head loss, frictional loss due to internal roughness, loss at fittings, turbidity, surge and pumping facility.
• Pipes should not be oversized as slow flow may cause stagnation.

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• Water supply pipes should be made of material resistant to corrosion and non-reactive to the conveyed water and surrounding ground. It should not impart any taste or toxicity on the water.
• Use of single material for the whole system is preferable for easy joining.
• UPVC, copper, lined iron or steel are used for water supply. But UPVC pipes should not be used in exposed areas as it degrades under UV Ray.

Note: use of lead, lead alloy, unlined cast iron, unlined galvanized iron, bare mild steel are prohibited in Singapore.

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• In general: internal forces of design and transient pressure
• Underground pipes: backfill, ground water, soil settlement.
• Pipes over: self-load and load of water.

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• All pipes should follow shortest practical route without dead end.
• Mains preferably follow the gradient – a downward slope from air valve to wash outs.
• Several service pipes at the end of a “cul-de-sac” road can branch out from a small bore pipe.
• Branching from underground / concealed pipes is recommended to be in right angles and in straight lines to facilitate location for repairs.

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• No inter /cross connection of potable and non-potable water pipes or fittings (even though non-return or closed and sealed stop valves are used).
• Water supply should be at a higher level and separated from drainage pipes by a min distance of 300 mm. Same distance is applicable for pipes crossing each other.
• Service pipe should not be connected into any distributing pipe, pump delivery pipe or pump suction pipe. Else water may backflow from tank into the service pipe with consequent danger of contamination.

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• Backfilling material: free from debris, organic material, and sharp edged heavy elements. Should be able to be compacted and should not migrate from trench.
• Backfilling depth (as per figure):

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• Pipes exposed to outdoors should be painted externally to prevent corrosion.
• Pipe ducts or chases should have sufficient servicing space, and removable cover for easy access, but entry of vermin should be prohibited.
• UPVC pipes should not be exposed to direct sunlight.

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• Mains: anchor blocks provided at every bend, branch and dead end. Piling support may be required in case of soft soil.
• Service pipe: maximum spacing on vertical and horizontal direction depends on size and material of the pipe.
• Supports / hanger should be compatible (preferably of same material) with pipe to avoid deterioration. E.g. galvanized hanger and copper pipes are non-compatible.
• Supports should be strong enough to run the pipe with no deeps or high spots leading to air lock.

Faulty pipe installation – common causes of airlock

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• Removable cover.

• Removable cover, plaster or tile: pipe can be removed after opening the ends.

• Embedded in wall / floor & covered by finishes. Leaky pipes are capped off.

• To avoid stagnation, bigger pipes should be tapered at end to join smaller pipe (e.g. mains to service pipe) instead of tapped at right angle.

Reducer at joint pipes with different diameters

• Method of jointing should be strong, durable and must not cause internal roughness which may lead to slow discharge of flow. The acceptable jointing methods are:

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• At wall / floor penetrations, pipe should pass through a sleeve (dia. > 2 x pipe dia.) and the gap with flexible sealant.
• Articulated joints or flexible bushes allow free movements and hence prevent undue stresses.

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• Backflow is prevented by discharging at a higher level than the highest possible water level in a drains or watercourses.
• Provision of watertight sump and pumping equipment.
• Flush out points at the end of distributing pipes from storage tanks.
• Draining taps or draw-off taps (not underground) provided at the lowest point of the system containing float operated valves, tanks or vents etc.

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• Stop valves at suitable position to isolate any section so that repair in one part should not disturb the whole system.
• Valves should be accessible for easy maintenance and operation.

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• Air valves provided at summits, wash out and low points between summits.
• ‘Double acting’ air valves which have both large and small orifice. Air is released during normal operation through small orifice and at high pressure through big orifice during charging and draining of pipes.

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• Piping between hot water draw-off tap and hot water cylinder or secondary circulation pipe should be as short as possible. For a distance > 100 ft, secondary circulating system with hot water cylinder is needed.
• Heater should be installed close to all points of hot water usage.
• To prevent convection loss through vent pipes, the hot water pipe should run min 450mm horizontally before attaching to the vent pipe.

• Connection to the top of the hot water cylinder

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• Thermostat should be installed so that water is kept in the storage cylinder at 60°C. A higher temperature causes scalding and scale build-up if water is hard. A lower temperature promotes Legionella growth.
• Cylinder and piping should have non-combustible insulation.
• Vent / relief valve is a mandatory safety device against excessive temperature or pressure build up.
• A timer on storage units can be installed to reduce hot water production when requirement is less.

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• Size depends on many parameters, such as demand, supply, probability of pump failure, time to repair, ratio of peak hours to average flow rate, provision of alternative supply or storage etc.
• Demand is met by two or more tanks coupled in series instead of one large tank. This is required for isolation during maintenance.
• Capable to handle load of water, transient load, earth pressure, water table, seismic load or wind load (as applicable) without showing signs of crack, stress or deformation.

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• Above ground: least possibility of contamination.

• Semi buried.

• Buried: highest possibility of contamination.

• Body: water tight, corrosion resistant material. Such as reinforced or pre-stressed concrete, steel, glass fibre reinforced plastics.
• Coating: surface treatments, waterproof coating, or lining which may either be bonded to or independent from the supporting structure. This is to resist water seepage and weathering. But such finishes should not affect hygienic quality of the stored water.
• Structure: of adequate strength and free from deformation.

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• Min 600mm space all around tank.
• Min possible number of opening to each compartment. And it should be fitted with cover / trapdoor.
• Permanent type climbing ladder for easy inspection & cleaning of interior.
• Fitted with corrosion resistant mosquito proof netting for vent / over flow pipe and material strainer.

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• A min air gap above maximum water level is maintained.
• In large storage tanks, mechanical ventilation is recommended.
• The vent passes through the roof slab. It is connected at a sleeve and bent to prevent ingress of dirt or dust.

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• Pumps are designed to meet the pressure requirement. Head loss, frictional loss and loss at bends should also be considered.
• Variable speed drive (VSD) to handle both maximum and variable demand.
• Minimum 2 pumps should work interchangeably as duty & standby pumps.
• Sewage pumps should be able to handle long and fibrous material. If required pre-treatment (e.g. crushing) is provided.

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• Housed in a room with adequate ventilation, lighting and protected access.
• Space around the machines for easy inspection and maintenance.
• Mounted at a height of 150 mm on an insulated padding.

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• Appliances should be made of impervious, non-crazing, corrosion resistant material approved by Product Listing Scheme, e.g. vitreous china, stainless steel, acrylic etc.
• All fixing and fastening should be corrosion resistant strong, durable and supplied by manufacturer. Else stainless steel or copper is used.
• Grating and cover made of stainless steel or GRP (glass reinforced plastic).

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• For waste sanitary appliance (sink, basin, bath, shower tray etc), direct supply is allowed but with an air gap of min 150 mm above flood level rim of the fixture to prevent backflow.
• For soil sanitary appliance (WC, bidet, urinal etc), no direct water inlet, but only through flushing cistern or flash valve.

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• For soil sanitary appliance at least one trap with a min water seal of 50 mm should be created before connecting to discharge pipe.
• Waste fitting trap connected to waste pipe above the water seal of floor trap.
• Overflow paths for basin or tubs prevent any water retention after the fixture is drained.

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• Provided in adequate number and diameter. Positioned as near as possible to the tap point or shower point.
• Floor to be graded and sloped towards the trap. Else whole toilet gets wet.
• Floor waste should be as short as possible and connect to the discharge via floor trap at a level above the trap seal.
• Should have a grating and tight-fitting cover of suitable size. .Else garbage or other solid waste enters into the sewerage system.

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• Fixtures are placed at adequate distance from wall and other fixtures to allow easy servicing.
• If a dwarf wall supports the bath, an access opening / panel is provided in the wall to reach the waste pipe under the bath.

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• System design includes type of venting which depends on building height:
• < 6 storey: single stack.
• 7- 30 storey: secondary ventilated stack.
• > 30 storey: fully ventilated.

• Vent dia. ≥ 1/2 dia. of pipe or 50mm whichever s greater.
• Individual vent pipes are connected in upward direction to the main vent stack at a point above the spillover level of the concerned sanitary appliance or floor trap.
• Vent stack should terminate at same height as discharge stack or connect into it at min 150mm above spillover level of the topmost appliance or floor trap.
• Cross venting between the vent and discharge stack at every ten storeys is recommended.

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• Size depends on drainage load or amount of fall placed by fixtures.
• Embedded pipes should have min dia. of 50mm.
• Min dia. of discharge stack and branch drain line is 100mm.
• Max length of branch drain is 10m.
• Dia. or material of a drainpipe should remain same for the entire length. Usually U PVC, duct iron, cast iron or vitrified clay are used.

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• Pipes should not run above bedrooms, living, dining or kitchen areas.
• Floor trap connecting waste appliances should be fitted with net to prevent mosquito breeding or entry of solid dirt.
• Provision for water seal ≥ 50 mm at sanitary appliances and floor traps.
• Min. bends or kinks in any branch/main drain-line and min. penetration through structure.
• Piping to be confined and supported properly for noise reduction.
• Size and uniform gradient ensure adequate flow and ventilation. Usually fall per feet are 0.25”, 0.125”and 0.0625” for pipe dia. 2.5”, 3- 6” and > 8” respectively.

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• Only vent pipe, vent stack or waste pipe can be embedded in structures.
• Shafts with discharge pipe should be big enough and have access opening.
• Position of access covers and cleaning eyes should allow cleaning along the direction of the flow at the following points:
• Connections to below ground drains.
• Changes in direction of stacks or horizontal runs.
• End of branch receiving multiple appliances and above the spill-over level of the lowest appliance on that branch.
• Joints or junctions of discharge pipes / stacks and other fittings.

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• Pipes / pipe sleeves should be cast with the floor slab rather than leaving an opening in the slab for the pipes.
• Method and material for jointing depend on pipe materials, size and system (spigot or socket) of pipes are as follows:
• CI: proprietary gasketted joint, lead caulking, proprietary cold caulking.
• Steel: proprietary cold joint, bolted flange & gasket. Welding is not allowed for GI pipes.
• Plastic (ABS, MUPVC, and UPVC): solvent cement, compression fittings, ring seals or similar push fit friction seals.
• Plastic (PE, PP): compression fittings, fusion welding, ring seals or similar push fit friction seals.

Note: If prefabricated products are available, site fabrication should be avoided.

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• A min dimension of 3m x 3m to accommodate the pumps, dewatering sump pump, valves, pipe work etc. along with working space.
• Securely covered with lockable doors or covers.
• Made of corrosion resistant material suitable for the pumped media (e.g. stainless steel). The tank should be mounted on a concrete plinth.

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• Away from driveway – preferably within a room solely used to house the sewage pumping facility.
• Away from potable water storage tank and electrical transformer or switchgear.
• Measures shall be provided all round the pit to prevent water flowing into it

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• The access opening should be directly above and extend over the whole of the tank and pump.
• No structural element or services should hinder access.
• Access ladders of Aluminium alloy or GRP should be provided to the pit.

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• Forced ventilation is recommended for safe working environment.
• Vent pipe of min 75mm dia. should be connected to the main vent stack
• Adequate lighting, water tap and lifting equipment should be provided..

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• Dewatering submersible sump pump should be fitted with reflux and isolating valves. It should pump into the ejector / diverter discharge pipe.
• For solid diverter, incoming pipe invert should be at a min height of 1.8m from floor to ensure that it is always higher than the outlet / bypass pipe.
• Air release pipes with isolating valves and air release valves to be provided for the separating chamber and the two-way valves for the diverter tank.
• Perforated strainer plate and cone baffle of the solid diverter should be made of stainless steel. Strainer plate should be of the removable type.

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• Sewer:
• Vitrified clay.
• Ductile iron / cast iron with internal lining of high alumina cement (HAC) or sulphate resisting cement and external layer of metallic zinc covered by a finishing of a bituminous coating.
• Thick-walled RCC with internal sacrificial layer of 38mm.
• RCC lined with a PVC or HDPE of min thickness of 1.5mm and fixed by mechanical keys.
• Man hole (MH) & inspection chamber (IC):
• Pre-cast circular units or chamber rings. For a depth > 10.5m, special RCC chambers are constructed.
• Underside of all intermediate platforms and roof slabs of MH/ IC should be lined with PVC or HDPE.
• The channels and the benching in the manholes shall be smoothly rendered to reduce turbulence in the sewage flow.
• Grade of cover as per location, e.g. heavy duty type in unloading bay.

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• Pipes to be connected by approved flexible joint and made water tight.
• Connection to manhole is at soffit levels.
• Connection of a bigger sewer to an existing smaller sewer is at invert levels of the manhole.

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• Gradient should maintain self-cleansing velocity (min 0.9 m/sec) and not to exceed scouring velocity (2.4 m/sec). Sewers turn septic under low flow condition.
• Incoming sewers should not eject at a speed higher than 1.2m/sec. To prevent that following special precautions are taken based on the level difference between incoming and outgoing sewers.

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• The branch drain-line should be connected obliquely in the same direction of flow as the main drain-line within an IC with its invert above the horizontal diameter of the main channel.
• IC to be located at all bends, junctions, at changes to the direction of flow or gradient or pipe diameter or materials.
• Max distance between two ICs and two MHs are 50m and 120m respectively.
• The last IC and MH should be connected via pipe of min dia. of 200mm.