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Sanitary Drainage systemsSanitary Drainage systems

Lecture NotesLecture Notes

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Table of ContentsTable of Contents

ChapterChapter--1 Sanitary Drainage Fixture Units1 Sanitary Drainage Fixture Units Page 1Page 1--2121

ChapterChapter--2 Vent system2 Vent system Page 22Page 22-- 3939

ChapterChapter--3 Storm water & drainage systems3 Storm water & drainage systems Page 40Page 40--5151

ChapterChapter--4 Sizing the Underground Sewage Network for Buildings4 Sizing the Underground Sewage Network for Buildings Page 52Page 52--7474

ChapterChapter--5 Septic tank capacity5 Septic tank capacity Page 75Page 75--8787ChapterChapter--6 General example problem6 General example problem Page 88Page 88--9696

ChapterChapter--7 Sanitary Appliances & Arrangements7 Sanitary Appliances & Arrangements Page 97Page 97--103103

ChapterChapter--8 Applications8 Applications Page 104Page 104

ReferencesReferences Page 122Page 122


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Sanitary Drainage Fixture UnitsSanitary Drainage Fixture Units

The suggested values of DFU ( table 1 & 2) were designed forThe suggested values of DFU ( table 1 & 2) were designed forapplication in conjunction with the probability of simultaneousapplication in conjunction with the probability of simultaneoususe of fixtures so as to establish maximum permissibleuse of fixtures so as to establish maximum permissibledrainage loads, in terms of fixture units rather than indrainage loads, in terms of fixture units rather than innumbers of specific types of fixtures or gallons per minute ofnumbers of specific types of fixtures or gallons per minute ofdrainage flow, for each of the various parts of sanitarydrainage flow, for each of the various parts of sanitarydrainage systems.drainage systems.In general, the sanitary drainage fixture unit value assigned toIn general, the sanitary drainage fixture unit value assigned toa particular fixture is based on the average volume dischargeda particular fixture is based on the average volume dischargedand the average rate of discharge for the fixture. This valueand the average rate of discharge for the fixture. This value

is determined from the fixtures total discharge flow, inis determined from the fixtures total discharge flow, ingallons per minute, divided bygallons per minute, divided by 7.5,7.5, or, in other words, its totalor, in other words, its totaldischarge flow in cubic feet per minute.discharge flow in cubic feet per minute.

ChapChap--11

4Table 1Table 1


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5Table 1Table 1

Ref [2]Ref [2]

6

Table 2Table 2

Ref [2]Ref [2]


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8 F.UTotalDFU

44W.C.s (flash Tank),11.1/2- 22Bathtub1

33Floor drain *11.1/2- 21Bidet1

1.1/2- 21Lavatory1

DiameterDFUFixturesNumber

* Some references does not include F.D. in the calculation.

A shower head over a bathtub does not increase the F.U.

10

10

F.U

Total

DFU

44W.C.s (flashTank),

1

1.1/2-

2

2*2Bathtub2

33Floor drain *1

1.1/2-

2

1Bidet1

1.1/2-

2

1Lavatory1

Diameter

DFUFixturesNumber

ShowerShower


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7F.U

TotalDFU

44W.C.s

(flashTank),

1

1.1/2- 22Bathtub2

33Floordrain *

1

1.1/2- 21Lavatory1

DiameterFUFixturesNumber

Clean out SystemClean out System

12Drainage Stacks and BranchesDrainage Stacks and BranchesBased on the computed drainage stack flow capacity forBased on the computed drainage stack flow capacity forstacks flowingstacks flowing 7/24 full at terminal velocity7/24 full at terminal velocity, the, thecorresponding number of fixture units may be determinedcorresponding number of fixture units may be determinedfrom design load charts or tables (1,2 &3) so as to establishfrom design load charts or tables (1,2 &3) so as to establishthe total load which may be placed on a tall drainage stack.the total load which may be placed on a tall drainage stack.For example, the computed flow capacity for a 4For example, the computed flow capacity for a 4--in (10 cm)in (10 cm)stack flowing atstack flowing at 7/247/24 full is 143 gpm (9.02 L/s). From designfull is 143 gpm (9.02 L/s). From designload charts or tables, it may be found that this rate of flow isload charts or tables, it may be found that this rate of flow isequivalent toequivalent to 500 fixture units.500 fixture units. This is the total load that mayThis is the total load that maybe received from all branches on a 4be received from all branches on a 4--in (10 cm) tall stack.in (10 cm) tall stack.However, to avoid excessive interference between flowHowever, to avoid excessive interference between flowentering the stack and that coming down the stack, it isentering the stack and that coming down the stack, it isnecessary to limit the amount of flow, which may be, allowednecessary to limit the amount of flow, which may be, allowedto enter the stack at each of the branches.to enter the stack at each of the branches. Thus, in a buildingThus, in a buildingof just a few stories in height, the amount of flow enteringof just a few stories in height, the amount of flow entering

the stack through a branch may be greater than what would bethe stack through a branch may be greater than what would beermissible in a buildin of man stories.ermissible in a buildin of man stories.


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13Table 3Table 3 for sizingfor sizingdrainage stacksdrainage stacksprovides differentprovides differentpermissible loading forpermissible loading forstack of more thanstack of more than 33stories in heightstories in height..

Included in the tableIncluded in the table,the maximum loads,the maximum loadspermitted on anypermitted on anyhorizontalhorizontal fixturefixturebranch of abranch of a short stackshort stack..

Table 3Table 3

14

Vertical forVertical for

each flooreach floorHorizontal perHorizontal per

floorfloor


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As a sample exampleAs a sample example : Calculate the total number of DFU , and: Calculate the total number of DFU , andsize the horizontal branch connecting the two adjacentsize the horizontal branch connecting the two adjacentbathrooms , knowing that, The total fixture unit of eachbathrooms , knowing that, The total fixture unit of eachbathroom consists of (water closet, bidet, lavatory andbathroom consists of (water closet, bidet, lavatory and

bathtub or shower) =bathtub or shower) = 8 FU8 FUssTotal fixture unit of two adjacent bath rooms connected toTotal fixture unit of two adjacent bath rooms connected tothe same horizontal branch pipe is :the same horizontal branch pipe is : 8 x 2 = 16 FU8 x 2 = 16 FUs.s.

As can be seen from table (3 ) for any horizontal branches ,As can be seen from table (3 ) for any horizontal branches ,the 3the 3 can handle up to 20DFU but , due to the presence ofcan handle up to 20DFU but , due to the presence ofthethe W.C.W.C.ss thethe 44 pipe diameter is selected which can handlepipe diameter is selected which can handleup to 160 DFU.up to 160 DFU.

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Table 4Table 4

Table 4Table 4 for sizingfor sizingdrainage stacks providesdrainage stacks providesdifferent permissibledifferent permissibleloading for stack ofloading for stack of 33stories or less in heightstories or less in heightand for stacks more thanand for stacks more than3 stories in height3 stories in height..Included in the table areIncluded in the table are

the maximum loadsthe maximum loadspermitted on anypermitted on anyhorizontal fixture branchhorizontal fixture branchof a short stack and atof a short stack and atanyany 1 story of stack more1 story of stack morethan 3 stories in heightthan 3 stories in height..

Ref [2]Ref [2]


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Slopes for horizontal drains are shown inSlopes for horizontal drains are shown in (Table 5) ,(Table 5) ,

Which are applicable for building underground sewersWhich are applicable for building underground sewersand drains as well as those running at the level of the ceilingand drains as well as those running at the level of the ceiling

of basements, service tunnels, etc. Readersof basements, service tunnels, etc. Readersshould note that the carrying capacity of horizontal drains isshould note that the carrying capacity of horizontal drains issubstantially lower than that for vertical pipes. Diameter of asubstantially lower than that for vertical pipes. Diameter of avertical stack may have to be increased when it runsvertical stack may have to be increased when it runshorizontally due to its reduced capacity in that position.horizontally due to its reduced capacity in that position.

18Table 5Table 5

For 4 Pipe diameter , having a slope of 1.04% , the Max. DFU is 180 ,

However if the slope is 4.2% , the DFU becomes 250


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Sanitary building drains are designed to flowSanitary building drains are designed to flow half full at peak loadhalf full at peak load. To. To

avoid backup of flow from the building drain into branches, eachavoid backup of flow from the building drain into branches, each

branch connection to the building drain should be made to its upbranch connection to the building drain should be made to its upper halfper half

or its airor its air--space portion. This may be achieved for 90 degrees branchspace portion. This may be achieved for 90 degrees branchconnections by means of a oneconnections by means of a one--sixth bend and a 45 degrees Y branch orsixth bend and a 45 degrees Y branch or

a longa long--sweep onesweep one--quarter bend and a Y branch. The Yquarter bend and a Y branch. The Y--branch fittingbranch fitting

may be rotated so that the branch is at 45 degrees angle above tmay be rotated so that the branch is at 45 degrees angle above thehe

horizontal when the onehorizontal when the one--sixth bend is to be used and at a vertical anglesixth bend is to be used and at a vertical angle

when the longwhen the long--sweep onesweep one--quarter bend is to be used. Less invertquarter bend is to be used. Less invert

elevation is lost with the oneelevation is lost with the one--sixth bend and Y combination (see Fig ).sixth bend and Y combination (see Fig ).

Connections to SanitaryConnections to Sanitary

Building DrainsBuilding Drains

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Figure 4Figure 4

Two pipe system S.S.Two pipe system S.S.

Vent pipeVent pipe

Vent pipeVent pipeVent pipeVent pipe


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Vent pipeVent pipe

One pipe system S.S.One pipe system S.S.

(Most popular )(Most popular )

Ref [2]Ref [2]

22

VentVent SystemSystem

ChapChap--22


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Sanitary drainage system of a building should be providedSanitary drainage system of a building should be providedwith an attendant system of vent piping designed so as towith an attendant system of vent piping designed so as topermit gases and odors in all parts of the drainage piping topermit gases and odors in all parts of the drainage piping to

circulate up through the system and escape into thecirculate up through the system and escape into theatmosphere above the building and to permit the admissionatmosphere above the building and to permit the admissionand emission of air in all parts of the system so thatand emission of air in all parts of the system so thatsiphonage, aspiration, or backsiphonage, aspiration, or back--pressure conditions will notpressure conditions will notcause an excessive loss of trap seal uncause an excessive loss of trap seal under ordinaryder ordinaryconditions of use. The sizing, arrangement, and installationconditions of use. The sizing, arrangement, and installationof attendant vent piping should be designed so as to limitof attendant vent piping should be designed so as to limitairair--pressure variations in all fixture drains to a differentialpressure variations in all fixture drains to a differentialnot exceeding 1 in (2.5 cm) of water column above or belownot exceeding 1 in (2.5 cm) of water column above or below

atmospheric pressure.atmospheric pressure.

IntroductionIntroduction

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A vent system is a pipe in a drainage system used :

1. To provide a flow of air to and from a drainagesystem so as to ventilate it.

2. To provide a circulation of air within such asystem to eliminate trap siphonage and reduceback pressure and vacuum surge .

3. To insure the rapid and silent flow of waste


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Table 5Table 5 is used in sizing vents inis used in sizing vents inaccordance with drainageaccordance with drainagecapacity loadscapacity loads. Permissible. Permissiblelengths of vents are less thanlengths of vents are less thanthose computed by formulas (inthose computed by formulas (inwhich additional allowance needwhich additional allowance needto be made for the equivalentto be made for the equivalentlength of pipe fittings) that thelength of pipe fittings) that thestated length may be appliedstated length may be applieddirectly as permissible developeddirectly as permissible developedlength of pipe . This table islength of pipe . This table isapplied forapplied for vent stacks andvent stacks andbranch vent sizing.branch vent sizing.

Developed length of pipe =straight length of pipe + equivalentlength of fittings

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Ref [1]Ref [1]


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Ref [1]Ref [1]

28


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Ref [1]Ref [1]

30


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Traps.Traps. A fixture trap, illustrated inA fixture trap, illustrated inFig. , is a UFig. , is a U--shaped section of pipeshaped section of pipeof the necessary depth to retainof the necessary depth to retainsufficient liquid required by code. Allsufficient liquid required by code. Allfixtures and equipment directlyfixtures and equipment directlyconnected to the sanitary drainageconnected to the sanitary drainagesystem are required to have traps.system are required to have traps.All traps must beAll traps must be ventedvented in anin anapproved manner, except for specificapproved manner, except for specificconditions waived by local codeconditions waived by local code

requirements or authorities.requirements or authorities. Ref [3]Ref [3]


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Ref [3]Ref [3]

34

Ref [3]Ref [3]


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Ref [2]Ref [2]

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Ref [2]Ref [2]


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Ref [2]Ref [2]

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Ref [2]Ref [2]


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Ref [1]Ref [1]

40

Storm waterStorm water drainage systemdrainage system

&&Rain WaterRain Water pipespipes

ChapChap--33


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Roof drainage systemsRoof drainage systems

A roof drainage system is composed of stormA roof drainage system is composed of storm--water collection deviceswater collection devices

located in the roof and piping , connected to the collection devlocated in the roof and piping , connected to the collection devices,ices,which transforms the runoff out of the building to the ground.which transforms the runoff out of the building to the ground. SpacingSpacing

and location of the roof drains are dependent on a number of locand location of the roof drains are dependent on a number of localal

conditions and building characteristics. Consideration should beconditions and building characteristics. Consideration should be givengiven

to such criteria as the local climatic conditions, type of roof,to such criteria as the local climatic conditions, type of roof, slope ofslope of

roof, location of pipe chases, and available ceiling space to inroof, location of pipe chases, and available ceiling space to installstall

piping.piping.

42It has been found that a storm producing a rainfall intensityIt has been found that a storm producing a rainfall intensityof 75 mm/hr may occur for 5 minutes once in 4 years, Canof 75 mm/hr may occur for 5 minutes once in 4 years, Cancause a serious damage .cause a serious damage .The rate of runThe rate of run--from roof +balconiesfrom roof +balconiesis calculated as follows:is calculated as follows:

Where Q = The rate of runWhere Q = The rate of run--off from roof and balconies.off from roof and balconies.

A = effective area m2.A = effective area m2.P = impermeability factor which is 0.9 (concrete)P = impermeability factor which is 0.9 (concrete)For asphalt in good order is (0.875).For asphalt in good order is (0.875).

R = Rainfall intensity mm/hr, (R = Rainfall intensity mm/hr, ( 7575--100 mm/h100 mm/h ))For example:For example:Calculate the flow rate from a concrete roof having anCalculate the flow rate from a concrete roof having an

effective area of 50 m when the rainfall intensity is 75effective area of 50 m when the rainfall intensity is 75mm/hr.mm/hr.

]/[10003600

RPAQ

3sm

.sec/1]/[001.010003600

579.005Q 3 literisthatsm


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The following procedure should be used in designing a roof drainThe following procedure should be used in designing a roof drainageage

system:system:

((11)) Lay out the position of the roof drains, deck drains and rainwaLay out the position of the roof drains, deck drains and rainwaterter

leaders. Consideration should be given to placing an overflow drleaders. Consideration should be given to placing an overflow drainain

adjacent to each roof drain.adjacent to each roof drain.((22)) Determine the tributary area to each roof drain, deck drain, scDetermine the tributary area to each roof drain, deck drain, scupper,upper,

gutter, or rainwater leader. The tributary area is the surfacegutter, or rainwater leader. The tributary area is the surface area of roofarea of roof

that drains towards a specific drain. This tributary area shouldthat drains towards a specific drain. This tributary area should includeinclude

the effects of runoff from adjacent walls which drain onto the wthe effects of runoff from adjacent walls which drain onto the walls,alls, figfig

(R(R--1)1) indicates the wall area that should be added to roof area toindicates the wall area that should be added to roof area to

determine the total tributary area for each drain.determine the total tributary area for each drain.

((33)) Determine the routing and slope of the stormDetermine the routing and slope of the storm--water conductors. First,water conductors. First,

determine the points from which, and to which, the conductors mudetermine the points from which, and to which, the conductors must best be

installed. Then determine the space available for installing theinstalled. Then determine the space available for installing the stormstorm--water conductors. Finally, the routing and slope of the stormwater conductors. Finally, the routing and slope of the storm--waterwater

conductors.conductors.

Roof Drainage Design Procedure

44

Fig (RFig (R--1)1)

Ref [2]Ref [2]


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45((44)) Determine the rainfall rate to be used in sizing of the roof draDetermine the rainfall rate to be used in sizing of the roof drainageinage

system. The rainfall rate (also known as the rainfall intensity)system. The rainfall rate (also known as the rainfall intensity) is a termis a term

that relates the quantity of rainfall to a unit of time. Such rathat relates the quantity of rainfall to a unit of time. Such rainfall ratesinfall rates

are usually expressed in inches per hour or centimeters per hourare usually expressed in inches per hour or centimeters per hour..

((55)) Determine the flow rate (volume per unit time) of equipment suchDetermine the flow rate (volume per unit time) of equipment such asas

pumps, ejectors, airpumps, ejectors, air--conditioning equipment, and similar equipmentconditioning equipment, and similar equipment

which discharge into the roof drainage piping. Then convert theswhich discharge into the roof drainage piping. Then convert these flowe flowrates into equivalent roof area. Flow rate is a term expressingrates into equivalent roof area. Flow rate is a term expressing a volumea volume

of water over a period of time such as cubic feet per second (cuof water over a period of time such as cubic feet per second (cubicbic

meters per hour), and gallons per minute (liters per second). Thmeters per hour), and gallons per minute (liters per second). Thee

following equations determine the roof area which will produce rfollowing equations determine the roof area which will produce runoff atunoff at

a flow rate equal to the flow rate of the equipment:a flow rate equal to the flow rate of the equipment:

Equivalent roof area = 96/R * flow rate of the equipmenEquivalent roof area = 96/R * flow rate of the equipment ftt ft

Equivalent roof area = 359/R * flow rate of the equipmeEquivalent roof area = 359/R * flow rate of the equipment mnt m

where R is the rainfall rate used in the design of the roof drwhere R is the rainfall rate used in the design of the roof drainageainage

system in inches per hour (centimeters per hour). The flow ratesystem in inches per hour (centimeters per hour). The flow rate of theof theequipment is expressed in gallons per minute (liters per second)equipment is expressed in gallons per minute (liters per second)..

46

((66)) Calculate the total roof area drained by each segment of the rooCalculate the total roof area drained by each segment of the rooff

drainage system. This calculation should include all roof areasdrainage system. This calculation should include all roof areas

calculated in step (2) and the equivalent roof area calculated icalculated in step (2) and the equivalent roof area calculated in step (5).n step (5).

Express the total area in square feet (square meters).Express the total area in square feet (square meters).

((77)) Determine the size of the roof drains and stormDetermine the size of the roof drains and storm--water conductors orwater conductors or

the gutters and rainwater leaders. Sizes can be determined usingthe gutters and rainwater leaders. Sizes can be determined using tabletable 11

through tablethrough table 22.. These tables list the maximum roofThese tables list the maximum roof

area in square feet (square meters) which can be handled byarea in square feet (square meters) which can be handled bystormstorm--water drainage piping of different sizes and slopeswater drainage piping of different sizes and slopesfor various rainfall rates.for various rainfall rates.An example of Roof rain water distribution is shown in figureAn example of Roof rain water distribution is shown in figure(R(R--2)2)

Area supplied by a drain pipe == (Area of the balcony) +(area of the adjacent wall)

+ Part of the roof area.+ Part of the roof area.


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AREA OF ROOF PART = 65 M2

Roof Drain

BALCON OF AREA = 10 m2

WALL AREA = 15 M2

BALCON OF AREA = 10 m2

WALL AREA = 15 M2

Figure ( RFigure ( R--3)3)

52

Sizing the UndergroundSizing the Underground

Sewage Network for BuildingsSewage Network for Buildings

ChapChap--44


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Type of undergroundType of undergroundDrainage ForDrainage For

buildingsbuildings

Separated SewerSeparated Sewer& rain water& rain water

systemsystemFig (UFig (U--1)1)

CombinedCombinedSewer + Rain waterSewer + Rain water

Fig( UFig( U--2)2)

54

Separate System of drainageSeparate System of drainage

Drainage below ground connectionDrainage below ground connection

Fig ( UFig ( U--1)1)

Ref [3]Ref [3]


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Combined Rain + Sewer drainCombined Rain + Sewer drainFig ( UFig ( U--2)2)Ref [3]Ref [3]

56

In the case of combined systemIn the case of combined system(( Sewer +Rain waterSewer +Rain water), rainwater), rainwatermust be connected to the foulmust be connected to the foulwater drain through a back inletwater drain through a back inletgully, to prevent the smellgully, to prevent the smell

as shown in Fig. (Uas shown in Fig. (U--3).3). In the caseIn the caseof separate systemof separate system(( Rain water onlyRain water only), it is not), it is notnecessary to provide a trap beforenecessary to provide a trap beforethe rainwater pipe .It is connectedthe rainwater pipe .It is connectedto the surface water drain, andto the surface water drain, andtherefore a rainwater shoe, astherefore a rainwater shoe, asshown in Fig. (Ushown in Fig. (U--4), may be used.4), may be used.

Connections of the rain water DrainConnections of the rain water Drain

Fig. (UFig. (U--3).3).

Fig. (UFig. (U--4).4).


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Garage Gully trapGarage Gully trap

The public Health Act 1936The public Health Act 1936section 34 defines certainsection 34 defines certainprohibited discharges into drainsprohibited discharges into drainsor sewers asor sewers as1. anything that may injure a drain1. anything that may injure a drainor sewer or interfere with the freeor sewer or interfere with the free

flow or treatment and disposalflow or treatment and disposalprocesses,processes,2. hot liquids with a temperature2. hot liquids with a temperatureexceeding 43.3 C,exceeding 43.3 C,3. petroleum spirit and calcium3. petroleum spirit and calciumcarbide.carbide.This means that the floor washingsThis means that the floor washingsof large garages, petrol stationsof large garages, petrol stationsand indeed small garages should beand indeed small garages should beprovided with some means ofprovided with some means ofintercepting petrol before itintercepting petrol before it

enters the drain or sewer. For theenters the drain or sewer. For thefloor washings of a small garage, itfloor washings of a small garage, itis sufficient to provide a garageis sufficient to provide a garagegully as shown in Fig. (Ugully as shown in Fig. (U--5).5).

Garage DrainageGarage Drainage


Ref [3]Ref [3]

58Grease Traps (Fig,UGrease Traps (Fig,U--6)6)Special gullies for the collection ofSpecial gullies for the collection ofgrease are not required for houses,grease are not required for houses,but for canteen kitchens where thebut for canteen kitchens where thewaste water from the sinks andwaste water from the sinks anddishwashers contains a considerabledishwashers contains a considerableamount of grease they are essential.amount of grease they are essential.When grease is hot or contained inWhen grease is hot or contained inhot water, it is in the form of anhot water, it is in the form of anemulsion, and if it is allowed to flowemulsion, and if it is allowed to flow

into the drain it will cool and adhereinto the drain it will cool and adhereto the sides of the pipes. Theto the sides of the pipes. Theprinciple of operation of the greaseprinciple of operation of the greasetrap is that of cooling down thetrap is that of cooling down thegrease in a large volume of water,grease in a large volume of water,which will generally be cool,which will generally be cool,so that the grease is solidified andso that the grease is solidified andfloats on the surface. At periodicfloats on the surface. At periodicintervals, the tray is lifted out of theintervals, the tray is lifted out of thetrap, which at the same timetrap, which at the same time

collects the grease.collects the grease.


Grease TrapsGrease Traps

Ref [3]Ref [3]


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59Flow under gravity conditions ( Manning Formula )Flow under gravity conditions ( Manning Formula )

Manning , after carrying out a series of experiments ,Manning , after carrying out a series of experiments ,deduced the following equation which is the most commonlydeduced the following equation which is the most commonlyused for open channel flow and for water, sewer flowsused for open channel flow and for water, sewer flowsfreely in pipes and conduits when both ends are open tofreely in pipes and conduits when both ends are open to

atmospheric pressure .atmospheric pressure .Calculations :Calculations :

).(.486.1

2

1

3

2

unitsSUSRn

V

2/13/2486.1SR

nAQ

WhereWhere

Q= flow rate ft3/sec.Q= flow rate ft3/sec.

A = Wetted area ft2, (half pipe cross sectional area)A = Wetted area ft2, (half pipe cross sectional area)N= roughness of surface from table( ).N= roughness of surface from table( ).

R = Hydraulics radius (Area/wetted perimeter).R = Hydraulics radius (Area/wetted perimeter).

S= Slope 0.5S= Slope 0.5 --1 % from1 % from ChezyChezy formulaformula

60TheThe determination of the hydraulics radiusdetermination of the hydraulics radius R for flow not running fullR for flow not running fullwas explained before (chapwas explained before (chap--10 Dr. Hammoud lecture notes).10 Dr. Hammoud lecture notes).In an open channel , the slope S can be determined as follows :In an open channel , the slope S can be determined as follows :Since the flow velocity is the same and the depth pressure doesSince the flow velocity is the same and the depth pressure does notnotchange , the general energy equation becomes :change , the general energy equation becomes :

We can express this equation on a unit of length basis by dividiWe can express this equation on a unit of length basis by dividi ng bothng bothsides by the length of the channel under consideration . Changesides by the length of the channel under consideration . Change inin

elevation divided by change in distance yields the slope :elevation divided by change in distance yields the slope :

( ft / ft ) or dimensionl( ft / ft ) or dimensionlessess

From the above formula , it is clear that the flow down is causeFrom the above formula , it is clear that the flow down is caused byd bythe difference in potential energy or gravity . On the other hanthe difference in potential energy or gravity . On the other hand thed thevariable n known as Manning s , is a measure of the roughness ofvariable n known as Manning s , is a measure of the roughness of thethechannel . Table (Uchannel . Table (U--1) lists the values of n for some of the more commo1) lists the values of n for some of the more commomaterials .materials .

P V

gZ h

P V

gZL

1 1

2

12 2

2

22 2. .

Z Z hL1 2

S Z Z L h LL( ) / ( / )1 2


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The following procedure should be used in designing a theThe following procedure should be used in designing a theunderground sewer pipe system:underground sewer pipe system:

(1)(1) Lay out should be drawnLay out should be drawn(2)(2) The total DFU connected to the sewer pipe should beThe total DFU connected to the sewer pipe should be

calculate.calculate.

(3)(3) From load tablesFrom load tables cconvert the DFU to gpm or L/s,onvert the DFU to gpm or L/s,(4)(4) Select the value Select the value nn based on the pipe material. based on the pipe material.(5)(5) Select a value of Select a value of SS , recommended underground slope, recommended underground slope

S=0.5S=0.5--1 % .1 % .(6)(6) Use Manning formula to determine the pipe diameter.Use Manning formula to determine the pipe diameter.

Note :Note :

PVC pipe is used where n = 0.01 , flow Running half full &PVC pipe is used where n = 0.01 , flow Running half full &

recommended slope is 1% .recommended slope is 1% .

62

Values of Mannings nValues of Mannings n

Table (UTable (U--1)1)


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63ExampleExample

S.I. unitS.I. unit

Water at the rate of 0.1 mWater at the rate of 0.1 m33 /s flows through a 1 m pipe diameter vitrified/s flows through a 1 m pipe diameter vitrifiedsewer when the sewer pipe issewer when the sewer pipe is halfhalf-- fullfull . Find the slope of the water , if. Find the slope of the water , ifMannings n is 0.013 .Mannings n is 0.013 .

Solution :Solution :Given discharge ,Given discharge ,Q = 0.1 mQ = 0.1 m33 /s/s

Diameter of pipe D = 1 mDiameter of pipe D = 1 mArea of flow , A = ( 3.14/8) (0.5)Area of flow , A = ( 3.14/8) (0.5)22 =0.2777 m2=0.2777 m2

Wet Perimeter P = 3.14Wet Perimeter P = 3.14 DD/2 = 3.14/2= 1.57m/2 = 3.14/2= 1.57m

Hydraulic radiusHydraulic radius

Manning s constant n = 0.013Manning s constant n = 0.013

Find the slope S:Find the slope S:

S = ( 0.1 / 8.477 )S = ( 0.1 / 8.477 )22 = 1 /7186= 1 /7186

RA

P

DmH

0 393

1 57 40 25

.

..

1.0.)25.0(013.0

2777.0..

12

1

3

2

2

1

3

2

SSRAn

Q

64


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65

66


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67

ManholesManholes

Usually constructed ofUsually constructed ofbrickwork,brickwork, precastprecast concrete orconcrete orplastic. Shallow manholes,plastic. Shallow manholes,

which sometimes calledwhich sometimes calledinspection chamber built in 113inspection chamber built in 113mm of brickwork, providing thatmm of brickwork, providing thatthey are not in a road orthey are not in a road orwaterlogged ground.waterlogged ground.Fig. (UFig. (U--7) shows a detail of brick7) shows a detail of brickmanhole whereas Fig. (Umanhole whereas Fig. (U--8)8)shows A detail of ashows A detail of a precastprecastconcrete manhole.concrete manhole.

Fig. (UFig. (U--7)7)Ref [3]Ref [3]

68

Fig. (UFig. (U--8)8)


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69

Dimensions of Brick ManholesDimensions of Brick Manholes

Cover sizes for depths up to 2.7 m are 600 mm. x 600Cover sizes for depths up to 2.7 m are 600 mm. x 600mm, and for depths up to 3.3 m aremm, and for depths up to 3.3 m are900 mm x 600 mm. For depths above 3.3 man access900 mm x 600 mm. For depths above 3.3 man access

shaft may be constructed above the main chamber.shaft may be constructed above the main chamber.

70

Precast ConcretePrecast ConcreteManholeManhole


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73

Figure (R ) Junctions between drains and sewers. Note: 1,2,3 and 4 are alternative

positions of the inspection chambers.

Fig ( UFig ( U--10)10)

74

Ref [1]Ref [1]


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75

Septic TankSeptic Tankcalculationcalculation

ChapChap--55

76The Septic tank capacity is calculated as follows:The Septic tank capacity is calculated as follows:

The type of building & the number of persons is firstThe type of building & the number of persons is firstcalculated and then multiply by the average wastecalculated and then multiply by the average waste--water( tablewater( tableSS--1& S1& S--2) per person a day . {2) per person a day . {Rain water is not included}Rain water is not included}

For example :For example :

Suppose we decide to determine the septic tank capacity for aSuppose we decide to determine the septic tank capacity for aluxury home having 10 persons . From table (Sluxury home having 10 persons . From table (S--1) the daily1) the daily

waste water per person is between 75waste water per person is between 75--150 gpm /person/day .150 gpm /person/day .If we select 110 gpm as an average value Then the daily wasteIf we select 110 gpm as an average value Then the daily wastewater flow is: 110 gpm x 10= 1100 gpm /day . The volume of thewater flow is: 110 gpm x 10= 1100 gpm /day . The volume of theseptic tank should be sized for at least 10septic tank should be sized for at least 10--15 days (if no city15 days (if no citysewer net work is available ) & for 2 days [if a city sewer netsewer net work is available ) & for 2 days [if a city sewer network is available + pump (electricity cutwork is available + pump (electricity cut --off)].off)].

The vent pipe size for the septic tank is shown in table (SThe vent pipe size for the septic tank is shown in table (S--3)3)

Practically for ordinary buildings a value of 200LPractically for ordinary buildings a value of 200L--250250L/Person/day is satisfactory.L/Person/day is satisfactory.


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77

SS--11

78

SS--22


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79

SS--33

80

1/3 L1/3 L 2/3 L2/3 L

SS--44

Length and structure of a septic tankLength and structure of a septic tank

Ref [1]Ref [1]


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81

Septic Tank CapacitySeptic Tank CapacitySS--55

Ref [1]Ref [1]

82

SS--66

Ref [1]Ref [1]


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83

84WaterWater --Drainage Pumping (Fig.)Drainage Pumping (Fig.)

Wherever possible, drains should be laid soWherever possible, drains should be laid sothat the liquid flows by gravity to thethat the liquid flows by gravity to thesewer, or other point of disposal. In somesewer, or other point of disposal. In somecases, however, the water pipe or point ofcases, however, the water pipe or point ofdisposal is above the drain, and pumping isdisposal is above the drain, and pumping istherefore required. For the pumping oftherefore required. For the pumping ofsurface water, a pumping installation assurface water, a pumping installation as

shown in Fig. ( Sshown in Fig. ( S--7) may be used.7) may be used.For larger installations, two pumps shouldFor larger installations, two pumps shouldbe installed, so that one of the pumps maybe installed, so that one of the pumps maybe used for Standbe used for Stand by purposes.by purposes.This type of installation is used forThis type of installation is used forbasements and boiler rooms tobasements and boiler rooms todeal with seepage of water, floor washingdeal with seepage of water, floor washingor the draining down of the boilers andor the draining down of the boilers andheating pipe work,heating pipe work,

Fig. ( SFig. ( S--7)7)

Ref [3]Ref [3]


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85Sump pumps (For waste waterSump pumps (For waste water

drainage):drainage):

The sewer pipes are located below theThe sewer pipes are located below thecity network; in this case, acity network; in this case, a

submersible pump will be used wheresubmersible pump will be used wherethe motor and the pump section arethe motor and the pump section aresubmersed in the liquid. Usually, twosubmersed in the liquid. Usually, twoparallel sump pumps accompanied withparallel sump pumps accompanied withautomatic switches are used.automatic switches are used.

Figure (SFigure (S--8) shows the operation8) shows the operationprinciple of the pumps set .When theprinciple of the pumps set .When theliquid reaches a certain level, pump (Noliquid reaches a certain level, pump (No1) will start first, next to the second1) will start first, next to the secondlevel, pump (No 2) starts according tolevel, pump (No 2) starts according to

the position of the level switches. Forthe position of the level switches. Forfurther safety, the system isfurther safety, the system isaccompanied with an alarm signalaccompanied with an alarm signal.. Fig. ( SFig. ( S--8)8)

86

Fig. ( SFig. ( S--9)9)


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89

Example 3. Determine the diameter of the main waste and soilstack for a five-storey Motel, having 6 W.C.s (flash valve),8 bathtub, 3 urinals wall lip and 2 Lavatories (1.1/2)on eachfloor connected to one single S.S. riser.From Table 1 ,2 & 3

Each floor6 W.c.s, 6 = 36 DFU , 8 Bathtub 33 = 24 DFU3 urinals 44= 12 DFU , 2 Lav 2 = 4 DFUTotal = 76 DFU in each floor .

From table (4) horizontal fixture branch for the 76 DFU ,the4 is selected because it can handle up to 160 DFU. The sametable shows that the vertical S.S diameter can be 4 since itcan handle up to 90DFU per floor which is sufficient for the

76 DFU that connected in at each T-Y connection.

90

Per floor76 DFU

4366W.C.s(flashvalve),

6

1.1/242Lavatory2

2.1/2124urinals wall lip

3

2243Bathtub8

Diameter

TotalDFU

DFUFixturesNumber

The Total for five floors =76The Total for five floors =76xx 5=5= 380380 DFUDFU


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93

Table 5Table 5

From table(5) four values ofFrom table(5) four values ofDFU is available for the 4DFU is available for the 4 S.SS.Sthat is, 43, 140, 320 & 540that is, 43, 140, 320 & 540DFU . Our values isDFU . Our values is 380 which380 which

is between 320 & 540 DFUis between 320 & 540 DFUThe higher value is selectedThe higher value is selected(540 DFU ).(540 DFU ).The pipe diameter of the ventThe pipe diameter of the ventpipe handling 540 DFU at a 50pipe handling 540 DFU at a 50--150 ft effective height is150 ft effective height isbetween 2.1/2between 2.1/2 & 3& 3. The. Thehigher value is selected (3inch)higher value is selected (3inch)

Refer to the followingRefer to the followingschematic drawingschematic drawing

Size the vent pipeSize the vent pipe

94

Building drain or sewer connection pipeFor 5" pipe ( maximum) 480 DFU @1/4 in per ft

5" SS.

For 4" pipe ( maximum) 160 DFUAny Horizontal short fixture branch

4" SS.

2" V.pipe

Total @ 1 story or 1 branch intervalFor 4" pipe ( maximum) 90 DFU

3" V.S.

Roof

2" V.pipe

76 DFU each floor5 x76 =380 DFU less than 500

4" SS.

Vertical 4" S.S. is enough

For 4 S.S.For 4 S.S.pipe the max.pipe the max.

FU is 500FU is 500


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95

Now it is required to size the underground pipe diameter,Now it is required to size the underground pipe diameter,S=1%S=1% ,flow half full,,flow half full, L= 100 mL= 100 m ..

As mentioned previously the total DFU = 380As mentioned previously the total DFU = 380,the corresponding flow rate is 105 gpm =,the corresponding flow rate is 105 gpm =6.63 L/s6.63 L/s (from load table for flash tank) =(from load table for flash tank) =

0.01 m0.01 m33/s ./s . The value of n =0.01The value of n =0.01

01.0..1

2

1

3

2

SRAn

Q

001.0)01.0(

01.001.05.02/1

3

2

S

QnRA

D= 0.15 m (6)D= 0.15 m (6) This is the minimumThis is the minimum

diameter for the out flow of the building.diameter for the out flow of the building.

96


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97

Sanitary Appliances &Sanitary Appliances &

ArrangementsArrangements

ChapChap--77

98

Types of SanitaryTypes of SanitaryAppliance WCAppliance WC

TwoTwo--trap Siphonic WCtrap Siphonic WC

panpan

Single Siphonic WC (mostSingle Siphonic WC (most

popular)popular)

Ref [3]Ref [3]


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99

UrinalsUrinals--typestypes

Ref [3]Ref [3]

100


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101

BathsBaths

There is a large variety of bath shapesThere is a large variety of bath shapesRef [3]Ref [3]

102

There is a large variety of kitchen shapesThere is a large variety of kitchen shapes

Kitchen sinkKitchen sink

Ref [3]Ref [3]


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103Kitchen sinkKitchen sink

Ref [3]Ref [3]

104

Fixture ConnectionFixture Connection

&&

Pipe sizingPipe sizing

ApplicationsApplications

ChapChap--88

From Reference [4]From Reference [4]


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105

106


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107

108


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109

110


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111

Ref [4]Ref [4]

112

Ref [4]Ref [4]


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113

114

Ref [4]Ref [4]


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115

116


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117

Ref [4]Ref [4]

118

22

22


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119

120

washer

25

fridge

dish

875

washer

dish

fridge

1425

575

338

1175

338 500

950

n

H.W.H.W.

Draw & size the drain pipesDraw & size the drain pipes

The location of the Sewer Stack are shownThe location of the Sewer Stack are shown


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121

Example 1Example 1.. Find the internal diameters of the soil stack forFind the internal diameters of the soil stack for

an eightan eight--storey office, having fivestorey office, having fiveWC.sWC.s, and five basins on, and five basins oneach floor, assuming public use of fittings.each floor, assuming public use of fittings.

Example 2Example 2 Find the internal diameter (If the soil and wasteFind the internal diameter (If the soil and wastestack for a four storey office having fourstack for a four storey office having fourW.c.sW.c.s, and four, and fourbasins on each floor, assuming public use of fittings.basins on each floor, assuming public use of fittings.

H.WH.W..

122

Example 3Example 3.. Find the internal diameters of the Rain waterFind the internal diameters of the Rain waterriser pipe serving eightriser pipe serving eight--balconies 10 mbalconies 10 m22 each .each .

Example 4Example 4.. Find the septic tank capacity for Motel servingFind the septic tank capacity for Motel serving100 persons ( no sewer net work). Size the pump , and the100 persons ( no sewer net work). Size the pump , and thecorresponding vent pipe. Knowing that the septic tank mustcorresponding vent pipe. Knowing that the septic tank mustbe recovered weekly.be recovered weekly.

ProjectProject.. The drawingThe drawingentitledentitledtahertaher consist of 7 floorsconsist of 7 floorsbuilding . It required to:building . It required to:

1)1) Draw & size sewerage layout for each bathroom include theDraw & size sewerage layout for each bathroom include thelocation and the size of the vent pipe.location and the size of the vent pipe.

2)2) Draw & size the drainage riserDraw & size the drainage riser..3)3) Draw & size the rain water pipesDraw & size the rain water pipes4)4) Draw and size the underground septic tankDraw and size the underground septic tank


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ReferencesReferences

11-- Mechanical & electrical equipment for buildingsMechanical & electrical equipment for buildings bybyStein/Reynolds, Ninth edition ,John Wiley, 2000.Stein/Reynolds, Ninth edition ,John Wiley, 2000.

22--Practical Plumbing Engineering , CyrilPractical Plumbing Engineering , CyrilM.Harris,ASPE,1998.M.Harris,ASPE,1998.

33-- Building Services & equipment , F. Hall, ThirdBuilding Services & equipment , F. Hall, Thirdedition, 1994.edition, 1994.

44-- Upland engineering , Mechanical consulting office,Upland engineering , Mechanical consulting office,

Dr. Ali hammoud.Dr. Ali hammoud.

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