Water supply and Drainage in Building

7/27/2019 Water supply and Drainage in Building

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WATER SUPPLY AND DRAINAGE IN BUILDINGAbstract

Research on air and water flows in water supply and drainage systems for

buildings has led to a greater understanding of the aspects of design which

contribute to both enhanced public health and pragmatic water conservation

strategies. The study of airflows and the inevitable air pressure transients

generated by naturally occurring phenomena within building drainage systems,

has led to the development of unique surge alleviation devices in order toprotect fixture water trap seals, the main protection between the public sewer

and habitable space. This focus on pressure transient analysis has also

contributed to the development of a sonar like device for assessing the status

of water trap seals and curtailing the possibilities of infection spread via the

building drainage system. While these phenomena affect the safety of peoplefrom sewer borne pathogens, the supply of water still represents a significant

cost and challenge to supply authorities. The contribution of fixtures such as

WCs, baths and showers represent significant usage of potable water delivered

to a building; in the UK, WCs use 1/3 of the total potable water processed.

Numerical modelling of flows has assisted in formulating strategies for good

design practice, and is conducive to whole system modelling to ensure publichealth safety and water supply security is maintained, economically and

efficiently.

CONTENTS


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Introduction Water distribution system in building Methods of distribution Drainage system Installation of drains The requirements of a well designed system Venting Maintenance of house drainage system Conclusion Reference

Introduction


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Public water supply systems follow the sequence of

collection, conveyance, treatment, disinfection and distribution. Ultimately

water is distributed for various consumption purposes in a building through

internal water distribution.

The waste water is collected from the buildings and

taken to a treatment plant for treatment and disposal. In this seminar, only the

internal water supply and buildingdrainage are discussed.

The water distribution system in a building terminates at

various plumbing fixtures designed to receive water and discharge wastes. The

drainage system in buildings should not cause a nuisance or any hazard to

health.

Water distribution system in building

The layout of water distribution piping may be basicallya horizontal or vertical arrangement of limited height in which underground


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mains under pressure supply water to a fixture inlets. Systems, with piping

above the main or pressure tank, are called up feed systems.

Systems from public mains are supplied through a

service main. This starts at a top on the street mains known as a lateral. The sizeof laterals varies from 10 to 22.5 cm. a water meter is connected to the service

main. Service pipes are subjected to expansion and contraction and minor earth

movement. Hence service mains should be connected through a gooseneck or

expansion loop to avoid strain on joints.

Inside a building at the service valve, the building main

extends to each fixture ground in single storey buildings or to the foot of each

up feed riser in taller buildings. The service pipe may supply an up feed system

for as greater a height as the available pressure allows. In addition, it supplies a

sump from which pumps can draw for the elevated house tanks. A house tank

serves down feed risers to a number of flows. The washer and other valves with

stand pressures up to about 5 kg/ cm2 hence, the static head should be restricted

to 50 m of water. Thus, about 15 floors is the maximum height for a down feed

some


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METHODS OF DISTRIBUTION

Depending up onthe topography of the country any one ofthe following three methods may be adopted for the distribution of water

1) gravity system2) gravity and pumping system combined3)pumping system4)

Gravity systemIn this system the water is conveyed through pipes by

gravity only. The gravity system is the most reliable method of distribution. But

it is useful only when the source of water supply is situated at a higher level

than that of distribution area.

Gravity and pumping system combined

In this system the treated water is pumped and stored inan elevated distribution reservoir. The excess water during low consumption

remains in the elevated reservoir and it is supplied during the peak period. Thepumps are usually worked at constant rate and this rate of pumping is so

adjusted that the excess quantity of water stored in reservoir during low

consumption is nearly equal to the extra demand of eater during peak period.

Advantages In case of a fire, the motor pumps can be used to develop high pressure or

a fire demand can directly be satisfied from pump house after closing the

inlet valve for elevated reservoir. In this method, the pumps are generally worked at uniform rate. This method is economical. This method is fairly reliable in the sense that some quantity of water is

available from the elevated reservoir even during break down of pumps.

Pumping system


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In this system, the water is directly pumped in to the

mains leading to the consumers. The number of pumps required in this system

will depend on the demand of water.

Disadvantages

In case of power failure the entire water distribution system of locality isdisturbed.

It requires constant attendance because of the fact that the pumps are tobe kept in working conditions all the time and sudden failure of pumps

would lead to great hardship.

DRAINAGE

Drainage means the entire system of sewers, plant and

associated machinery, which is owned by or vested in a local authority, and

used for conveyance and treatment of sewage, the reclamation of water and the

disposal of effluents or by-products resulting from the treatment of sewage.

ANTI SIPHONAGE PIPE: A pipe which is installed in the housedrainage to preserve the water seal of traps is known as anti siphonage pipe. It

maintains proper ventilation and does not allow the siphonic action to take

place.

CONSERVACY TANK: means any covered tank without overflow whichis used for the reception and temporary retention of sewage and which requiresemptying at intervals.

INSPECTION CHAMBER: means a chamber not deeper than 750 mmand of such dimensions that access may be obtained to a drain without causing a

person to enter into such chamber for the purpose of inspection.


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MAINHOLE: means a chamber of depth greater than 750 mm which allowsaccess to a drain.

ONE-PIPE SYSTEM: means a system of piping between sanitary fixturesand a drain in which both waste and soil water are permitted to flow down acommon stack.

RELIEF VENT: means a vent or ventilating pipe branching from a stackbelow the point of connection there to the lowest branch connection.

SANITARY FIXTURE: means that part of a drainage system which ispermanently connected to a water supply and which is used for the reception

and discharge of waste water.

SEPTIC TANK: means a tank designed to receive sewage and to retain it forsuch a time and in such a manner as to secure adequate decomposition of

organic solids by bacterial action.

SINGLE-STACK SYSTEM: means a system of piping between sanitaryfixtures and a drain, in which both waste and soil water are permitted to flowdown a common stack, and in which the stack and discharge pipes serve also as

vent pipes.

SINGLE-STACK (MODIFIED) SYSTEM: means a single stacksystem in which a relief vent is provided appurtenant to the discharge stack and

connected therewith below the lowest branch connection and at least at every

alternate floor by a cross vent.

SOIL PIPE: The term soil pipe is used to indicate the pipe which carriesdischarge from soil fittings such as urinals, water closets, etc. it should be ofgood materials and workmanship. The soil pips are kept of uniform diameter

and when they are carried above roof level, they will work as vent pipes also.


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STACK: means the main vertical discharge pipe or ventilating pipe connectedto a drainage system.

STORM WATER DRAIN: means a pipe or surface channel, which issituated on a site and is used to convey storm water to a sewer or a point of

discharge acceptable to the local authority.

TRAPPED GULLY: means a drain fitting, incorporating a trap into whichwaste water is discharged.

TWO PIPE SYSTEM: means a system of piping between sanitary fixturesand a drain, in which separate stacks are used for waste water and soil water and

each stack is vented and all traps are vented.

VERTICAL: in reference to a discharge pipe means any such pipe inclined at45 degrees or more to the horizontal.

WASTE FIXTURE: means any sanitary fixture which is used for thereception and discharge of waste water, and includes baths, drinking fountains,showers, baths, sinks, wash basins or wash tubs.

COWL: The top of vent pipes is provided with cowls. These are provided withslits or narrow openings.

FRESH AIR INLET: The last man hole which connects the house drainwith the public sewer is provided with an inlet of fresh air. This fresh air inletdilutes the sewage gasses.

VENT PIPE: The pipe installed for the purpose of ventilation is known as thevent pipe. It should be open at top and bottom and such openings should be at

suitable levels for the flow of foul gases. it is generally placed in the chamber or


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manhole from which sewage starts its flow sand it is carried at least about one

meter higher than the roof level.

WASTE PIPE: The term waste pipe is used to indicate the pipe which carriesdischarges from sanitary fittings such as bath rooms, kitchens, sinks, etc

TRAPS: A trap is a depressed or bent sanitary fitting which always remainsfull of water. It is technically termed to contain the water seal which is

measured as the vertical distance between crown and dip of a trap.

Function

The function of a trap in a drainage system is to prevent the

passage of foul air or gases through it. But at the same time it allows the sewageto flow through it thus the installation of a trap avoids the nuisance which will

be developed due to entry of bad smelling gasses in to the house.

Requirement of a good trap

1. It should be capable of being easily cleaned.2. It should be easily fixed with the drain.3. It should be of simple construction.4. It should possess self-cleansing property.5. The internal and external surfaces should be of smooth finish.

RAIN WATER PIPES

Down pipes should be discharged into channels, onto

concrete slabs or into pipes; where they are discharged into pipes, they should

be connected direct to the pipe and not through a catch pit.


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MATERIAL AND GRADIENTS

The following material should be used for the different pipes:

A.Underground drain pipes-vetrified clay pipes (VCP) except beneathbuildings where they are of cast iron. PVC, glass fibre or other types

or pipe may only be used with approved

B. Surface pipes:

1. Soil stacks and vent pipes - cast iron pipe (CIP) or PVC.

2. Waste pipes - cast iron or galvanized mild steel pipes (GMSP) or

PVC.

3. Anti siphon pipes - galvanized mild steel pipes or PVC.

INSTALLATION OF DRAINS

Drainage Installation means an installation vested in the

owner of a site which is situated on such site and which is intended forthe reception, conveyance, storage or treatment of sewage and includes

sanitary fixtures, traps, discharge piped, drains, ventilating pipes, septic

tanks, conservancy tanks, sewage treatment works, or mechanical

appliances associated therewith.

Drain means that part of a drainage installation which

conveys the sewage from a building to a connecting sewer or to a common drain

or to any other means of sewage disposed on the site concerned, but shall not

include

A. any discharge pipe;

B. that portion of a discharge stack which is below ground level; or

C. the bend at the foot of a discharge stack, whether such bend is exposed

or not.

Where any drain is constructed adjacent to or under or through a

structural part of any building, adequate measures must be taken to ensure that

the trench in which such drain is laid in no way impairs the stability of suchbuilding or the stability of any other building or interferes with or affects any

existing services.

A.Any drain shall be of such strength, having regard to the manner in whichit is bedded or supported, so that the maximum loads and forces to which


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it may normally be subjected will be sustained by it and it shall where

necessary be protected against damage.

B.The requirements contained in paragraph shall be deemed to be satisfiedif either of the following is complied with:

(i)The minimum cover over the outside of the drain is not less than 300

mm or

(ii) Precast or cast-in-situ concrete slabs are placed over the drain,

isolated from the crown of the pipe by a soil cushion not less than 100

mm thick and such slabs are wide enough and strong enough to prevent

excessive superimposed loads being transferred directly to the pipes.

Any drain shall;-

A. Be laid in a straight line between any points where changes of

direction or gradients occur.

B. Be laid with approved flexible joints which will permit joint

movement to take place throughout the life of the drainage installation.

C. Withstand root penetration and not deteriorate when in contact with

sewage or water, and will not cause any obstruction in the interior of such

drain.

D. Be laid at a minimum gradient of 1:60 for 100 and 1:100 for 150

pipes. However the Project Manager may in his discretion permit

gradients less than those specified above.

E. Where the gradient exceeds 1:5 it must be provided with anchor blocks

which must securely fix such drain in place.

Where any portion of a drain passes under any building such portion shall:

A .Be of Cast Iron

B. Be laid without change of direction or gradient.C. Not be provided inside such building with any means of access forcleaning.

Where any portion of a drain passed through a building such portion shall be:

A. Cast Iron

B. Supported throughout its length without restricting thermal movement

and such support must be securely attached to the building.

C. So placed that any junction, bend or any point of access into it isreadily accessible.


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Where any drain has a branch drain connected to it, such connection shall:-

A. be by means of a junction fitting which shall not be a saddle junction.

B. Enable the flow from such branch drain to enter the drain obliquely inthe direction of flow so that the included angle between the axes of thetwo drains does not exceed 45.

Where drains are to be laid in heaving, unstable or filled in ground, the Project

Manager must be consulted.

PIPES BENEATH BUILDINGS

Where it is necessary for a drain to pass beneath a building it

must be of cast iron and be without change of direction or gradient. It must not

carry any imposed load and provisions should be made for relieving arches onother supports where drains pass beneath the walls.

MINIMUM DEPTH OF DRAIN PIPES

To protect drains with a covering of less than 300mm they

must be encased in concrete.


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SEPTIC AND CONSERVANCY TANKS

Where sewage disposal is by means of septic tanks or

conservancy tanks, type drawing of the tanks may be obtained from the ProjectManager. The sizes of the septic tanks are based on the number of contributors

to the tanks and these sizes are shown on the type drawings Septic and

conservancy tanks must be located at least 3m from any building. French drains,

soakage pits or agricultural drains at least 5m from any building. Care should be

taken that underground water supplies are not polluted; where effluent flows

away from any underground water supply the distance should be at least 50m. Ifeffluent flows towards an underground water supply, the distance should be

considerably greater and will depend on such conditions as depth of water

supply, water table and soil or rock formations.

GROUPING

Where possible all toilet facilities should be grouped in abuilding, both horizontally and vertically and low outlet fittings such as baths

and showers should be placed as close as possible to outside or duct walls, to

facilitate drainage.

POSITIONING

WC's and urinals must be placed against outside or duct walls

or in the case of urinals, the drainage points may end against such walls. Urinals

must be adequately screened from passages, windows etc. A wash-hand basin

must be available at all WC's. Walls must be of one brick thickness where morethan 3 wash hand basins or bowl urinals are to be hung and also where the wall

holding any of these fittings is longer than 3m


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The requirements of a well designed system

Put simply, the main requirement of a well designed system

is that it should operate without the user being aware of its existence. However,this is a tall order and there is therefore a need to more fully specify some

requirements which can lead to the invisible system. The following

requirements are essential in achieving a safe, usable and reliable drainage

system;

The system should remove all waste as quickly as possible

Long horizontal pipe runs must be self-cleansing

There must be minimal loss of water trap seal to ensure there is a barrier

for the ingress of sewer gasesOther requirements which are less critical are

Minimal noise from the system

Minimal Odor from the appliance side (WC design)

Ease of maintenance

Code regulations were essentially designed in order to

ensure that installations meet these requirements, and to protect inhabitants

against any possible health risks from contact withcontaminated fecal material.

In developed industrialized countries the majority of installations meet thesestandards and the health risks from drainage systems are still very low. As with

most fields of engineering, sanitary equipment and techniques have benefited

from scientific and engineering research which has improved understanding of

system operation and helped develop new innovate and cost-effective ways of

achieving the goal of safe, reliable drainage systems with no increase in healthrisk.


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Venting

Usually vent piping is installed to accommodate air flow only. Sometimes largepipes are used as fixture branches and vents. A pipe which functions in this

manner is called a wet vent

Whenever fixtures from more than one floor drain in to a

single soil or waste stack, vents from the fixtures must connect to a vent stack

installed next to the soil or waste stack. It must terminate through the roof or be

connected to the vent extension at the top of the soil or waste stack its base must

connect to the base of the soil or waste stack

Vent terminals through the roof should be three meter away

from windows or other openings and must be 1.5 m above occupied roof decks.

Otherwise vent terminals should be 60 cm above openings or at least 15cm

above a roof. Venting or horizontal drain lines require a vertical connection of a

vent pipe more than 450 from the vertical. The size of vents and vent stacks

depends on the size of the line vented, the fixture unit load, and the developed

length of the vent. No vent can be smaller than 3.1 cm and it can be less than

one - half the diameter of the pipe vented.


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MAINTENANCE OF HOUSE DRAINARE SYSTEMThe house drainage system should be properly maintained and cleaned at

regular intervals for its efficient working.

1. Entry of undesired element.The users of house drainage system should take extreme precautions to

avoid the entry of undesired in the system. Such substances include grit,

sand, decayed fruits, prices of cloth, leaves, etc.

2.

Flushing.In order to maintain the house drainage system in proper working order, it

is advisable to flush it once or twice in a day.

3. Inspection.The various units of house drainage system should be inspected at regular

intervals and the obstructions, if any, should be removed. Similarly the

damaged pipes should be replaced.

4. Quality of materials.The materials used in the house drainage system should be of betterquality.

5. Use of disinfectants.To maintain good sanitary condition in the building, the disinfectants

should be freely used in lavatory blocks, bath rooms, etc.

6. Workmanship.The laying of drains and fixing of pipes should be carried out by licensed

or authorized plumbers only in systematic way.


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Conclusions

This report has considered the implications for venting

in building drainage systems. The discussion has concentrated on the

fundamental fluid mechanics which so readily describe the unsteady flows

resulting from plumbing fixture discharges. The description of the workings of a

drainage and vent system in these terms is not new, many early innovators were

well aware of this, however, many codes and regulation worldwide seem to

avoid the engineering imperative of a description based on fluid mechanics in

favor of a prescriptive legalistic approach based on the evolution of the industry

rather than the science. The fundamentals of system friction and pressuretransient generation and propagation are central to understanding why ventingis required in the first place. Possible solutions for alleviating pressure transients

were discussed, including the well respected view that in certain circumstances

systems operate perfectly well without venting.

In each vertical waste water pipe longer than 3,5m A vent pipe the same

size as the drain pipe which it ventilates must be provided.

The various units of house drainage system should be inspected atregular intervals and the obstructions, if any, should be removed.

Similarly the damaged pipes should be replaced. The materials used in

the house drainage system should be of better quality.


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Reference

Water supply and sanitary engineering

-RANGWALA

Building technology and valuation

(technical teachers training institute,Madras)

Water supply and waste water engineering

-B S N RAJU

Google.com

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