DRAINAGE SYSTEMBy Asst. Professor S.KumarBudha College of Architecture

TERMINOLOGY

Soil pipe: A soil pipe is a pipe through which human excreta flows.

Waste Pipe: It is a pipe which carries only the waste water, such as that from a sink, bath, or shower. It does not carry

human excreta.

Vent pipe; it is a pipe which is provided for the purpose of the ventilation of the system. A vent is open at top and

bottom, to facilitate exit of foul gases. It is carried at least one meter higher than the roof level.

Rain water pipe: It is a pipe which carries only the rain water.

Anti-siphonage pipe: It is pipe which is installed in the house drainage to preserve the water seal of traps.

SIZES OF PIPES

Soil pipe: 100-150mm

Waste pipe: horizontal: 30-50mm

Waste pipe: vertical : 75mm

Rainwater pipe : 75-100mm

Vent pipe: 50mm

Anti siphoange pipe:

Connecting soil pipe: 50mm

Connecting waste pipe: 40mm

AIMS OF DRAINAGE SYSTEM

To maintain healthy conditions in the building.

To dispose off waste water as early and quickly as possible.

To avoid the entry of foul gases from the sewer or the septic tank.

To facilitate quick removal of foul matter.

To collect and remove waste matter systematically .

TRAPS

TRAPS A water seal trap is an integral part of gullies and WCs, being moulded in during manufacture.

Smaller fittings, i.e. sinks, basins, etc., must be fitted with a trap.

Foul air from the drain and sewer is prevented from penetrating buildings by applying a water trap to all sanitary appliances.

Designed to retain a small quantity of the waste water (from the discharge of fitting to which they are attached )as a barrier to prevent foul air entering the building.

The depth of a Trap Seal would depend upon the usage of a pipe.

The trap seal varies from 25 to 75 mm deep.

Sinks, baths and showers - 38 mm,

WCs and gullies - 50 mm

Good Traps should have following Qualities:

Traps should be self-cleaning.

Interiors surface should be smooth so that the flow is not obstructed which enables self cleansing.

Should provide enough water seal with large surface area.

An assess door should be provided for cleaning the trap.

It should be made of non- adsorbent material.

Depending upon the shapes the traps are classified as:P-Trap

Q-Trap

S-Trap

Nahni Trap

TRAPS

LOSS OF TRAP WATER SEAL

Loss of Trap Water SealIf a trap seal loss, smells from the sanitary appliances would enter the building.Therefore the water seal in the trap must be maintained under all circumstances.

Cause of water seal lossLeakageSelf siphonageInduced siphonageback pressureCapillary actionWavering outEvaporation Of Water From TrapsLeakageThe most obvious cause of water seal loss is leakage due to defective fittings or poor workmanship. Otherwise, it may be caused by poor system design and/or installation:

Self siphonage - as an appliance discharges, the water fillsthe waste pipe and creates a vacuum to draw out the seal.Causes are a waste pipe that is too long, too steep or toosmall in diameter.

Induced siphonage - the discharge from one appliancedraws out the seal in the trap of an adjacent appliance bycreating a vacuum in that appliance's branch pipe. Causesare the same as for self-siphonage, but most commonly ashared waste pipe that is undersized.

Capillary action - a piece of rag, string or hair caught on the trap outlet.

Back pressure - compression occurs due to resistanceto flow at the base of a stack. The positive pressuredisplaces water in the lowest trap. Causes are a too small radius bottom bend, anundersized stack or the lowest branch fitting too close tothe base of the stack.

Wavering out - gusts of wind blowing over thetop of the stack can cause a partial vacuum todisturb water seals.

Resealing and Anti-siphon TrapsWhere trap water seal loss is apparent, the problem maybe relievedby fitting either a resealing or an anti-siphon trap.Types of resealing trap:

McAlpine Resealing trap - this has a reserve chamber intowhich water is retained as siphonage occurs. After siphonage,the retained water descends to reseal the trap.

Grevak Resealing trap - contains an anti-siphonage pipethrough which airflows to break any siphonic action.

Resealing and Anti-siphon TrapsWhere trap water seal loss is apparent, the problem maybe relieved by fitting either a resealing or an anti-siphon trap.Types of resealing trap:

McAlpine Resealing trap - this has a reserve chamber intowhich water is retained as siphonage occurs. After siphonage,the retained water descends to reseal the trap.

Grevak Resealing trap - contains an anti-siphonage pipethrough which airflows to break any siphonic action.

Econa Resealing trap - contains a cylinder on the outlet intowhich waterflows during siphonic action. After siphonage the water in thecylinder replenishes the trap.

Anti-siphon trap - as siphonage commences, a valve on theoutletcrown opens allowing air to enter. This maintains normalpressureduring water discharge, preventing loss of water seal.

SANITARY PIPEWORK

TWO PIPE SYSTEM

The waste stack received the discharge ablutionary fitments and conveyed this to the ground level where it was delivered above the water seal in a trapped gully connected to the drainage system.

The soil stack receives the discharge from soil appliances and delivered it direct to the underground drainage system.

The waste and soil water did not combine until they reached the below ground drainage system.

ONE PIPE SYSTEM In the system all soil and waste water discharge into one

common pipe and all branch ventilating pipes into one main ventilating pipe.

This system largely replaces the two pipe system and lent itself very well to use in multi storey developments.

It is far more economical than the two pipe system.

Fully Vented One-pipe System

The fully vented one-pipe system is used in buildings where thereare a large number of sanitary appliances in ranges, e.g. factories,schools, offices and hospitals.

The trap on each appliance is fitted with an anti-siphon or ventpipe.

This must be connected within 300 mm of the crown of the trap.

Individual vent pipes combine in a common vent for the range,which is inclined until it meets the vertical vent stack.

This vent stack may be carried to outside air or it may connect tothe discharge stack at a point above the spillover level of the highestappliance.

The base of the vent stack should be connected to the dischargestack close to the bottom rest bend to relieve any compression at thispoint.

SINGLE STACK SYSTEMThe single stack system was developed as a means of simplifying the extensivepipework .

The concept is to group appliances around the stack with a separate branch pipeserving each.

Branch pipe lengths and falls are constrained.Lengths and falls of waste pipes are carefully selected to prevent loss of trap waterseals.

Initially the system was limited to five storeys, but applications have provedsuccessful in high rise buildings of over 20 storeys.

Branch vent pipes are not required unless the system is modified.

To prevent loss of trap water seals:-Water seals on the waste traps must be 75mm (50 mm bath and shower).Branch pipe slope or fall:Sink and bath -18 to 90 mm/mBasin -20 to 120 mm/mWC - 9 mm/m.

The stack should be vertical below the highest sanitary appliance branch.If an offset is unavoidable, there should be no connection within 750 mm of theoffset.

The branch bath waste connection must be at least 200 mm below the centre ofthe WC branch to avoid crossflow. This may require a 50 mm nom. dia. parallel pipeto offset the bath waste pipe, or an 'S' trap WC to offset its connection.

The vent part of the stack may reduce to 75 mm nom. dia. when it is abovethe highest branch.

Reduces the cost of soil and waste systems.

Modified single stack system

The ventilated stack system is used in buildings where close grouping of sanitary appliances occurs - typical of lavatories in commercial premises.Appliances may be fitted with resealing or anti-siphon traps .

The appliances need to be sufficiently close together and limited in number not to be individually vented.

Branch waste pipes can be ventilated.

Larger than standard diameter waste pipes may be fitted.

To prevent the loss of trap water sealsWC branch pipe min. 100 mm bore and the angle θ = 90.5° to 95°.

To prevent the loss of trap water seals basin main waste pipe min. 50 mm bore and the angle θ = 91° to 92.5°.

Five basins or more / length of the main waste pipe exceeds 4.5 m a 25 mm bore vent pipe connected to main waste pipe at a point between the two basins farthest from the stack.Urinals (bowls):5 maximum

50 mm pipe Branch pipe as short as possibleGradient between 18 and 90 mm/m.

SEPTIC TANK

SEPTIC TANKBrick or Concrete Septic Tank A septic tank is used where main drainage is not available .

A septic tank is self-cleansing and will only require annual desludging.

It is a private sewage disposal plant, which is quite common for buildings in rural areas.

The tank is a watertight chamber in which the sewage is liquefied by anaerobic bacterialactivity. This type of bacteria lives in the absence of oxygen which is ensured by a sealed cover and the natural occurrence of a surface scum or crust.

Traditionally built tanks are divided into two compartments with an overall length of three times the breadth.Final processing of sewage is achieved by conveying it through subsoil drainage pipes or a biological filter. Capacity of septic tank is determined from the formula: C = (180 x P) + 2000 where: C = capacity in litresP = no. of persons servedE.g. 10 persons; C = (180 x 10) + 2000 = 3800 litres (3.8 m3).

SEPTIC TANK

Klargester Settlement/Septic TankThe Klargester settlement tank is a simple, reliable and cost-effective sewage disposal system manufactured from glass reinforced plastics for location in a site prepared excavation.

The tanks are produced in capacities ranging from 2700 to 100 000 litres, to suit a variety ofapplications from individual houses to modest developments including factories and commercial premises.

The sewage flows through three compartments (1,2,3) on illustration where it is liquefied by anaerobic bacterial activity. In similarity with traditionally built tanks, sludge settlement at the base of the unit must be removed annually. This is achieved by pushing away the floating ball to give extraction tube access into the lowest chamber.

Processed sewage may be dispersed by subsoil irrigation or a biological filter.

SOAKWAYS

SoakawaysWhere a surface water sewer is not available, it may be possible to dispose of rainwater into a soakaway. A soakaway will only be effective in porous soils and above the water table.Water must not be allowed to flow under a building.soakaways should be positioned at least 3 m away (most local authorities require 5 m). A filled soakaway is inexpensive to construct, but it will have limited capacity. Unfilled or hollow soakaways can be built of precast concrete or masonry.

Soakaway capacity can be determined by applying a rainfall intensity of at least 50 mm per hour to the following formula:C =( A x R)/3where C = capacity in m3A = area to be drained in m2R = rainfall in metres per hour.E.g. a drained area of 150 SQMC =(150 x 0.050 )/3 = 2.5 CuM

DRAINAGE LAYOUT

Combined and Separate Systems Drainage Systems :- The type of drainage system selected for a building will be determined by the local water authority's established sewer

arrangements. These will be installed with regard to foul water processing and the possibility of disposing surface water via a sewer into a local water course or directly into a soakaway.

The layout of foul drains depends on whether foul water and rainwater are discharged to a common drain system or to separate drain systems, which in turn depends on whether there is one sewer carrying both foul and rainwater or separate sewer for foul and rainwater.

Combined system :

This uses a single drain to convey both foul water from sanitary appliances and rainwater from roofs and other surfaces to a shared sewer.

The system is economical to install, but the processing costs at the sewage treatment plant are high.

Separate system :

This has foul water from the sanitary appliances conveyed in a foul water drain to a foul water sewer.

The rainwater from roofs and other surfaces is conveyed in a surface water drain into a surface water sewer or a soakaway.

This system is relatively expensive to install, particularly if the ground has poor drainage qualities and soakawayscannot be used. However, the benefit is reduced volume and treatment costs at the processing plant.

Combined and Separate Systems Drainage Systems

A Rain water gully or trapped gully used where there is a combined sewerthat takes both foul water discharges and rain water from roofs and paved areas.

Rain water shoe is used where there is a separate drain and sewer systemfor foul water discharges and rain water from roofs and paved areas.