water & wastewater engineering water supply engineering lecture no. 4 water distribution system

WATER & WASTEWATER ENGINEERING Water Supply Engineering

Lecture No. 4

Water distribution system


E.T From R.S.F

G.T HLP 1- Pump station (HLP)2- Storage (ground-elevated)3- Pipe network


• Storage system:What is the purpose of storage system?With regard to water quantity1. Storage for change in quantity of water demand.2. Emergency storage (6-8 h)3. Fire demand 1/5 fire demand storage by elevated tank 4/5 fire demand storage by ground tank


With regard to water pressure1. For elevated tank near pump station:a) Fix the head on pumps, then they work at max. efficiency of

pump b) Prevent water hammer2. For elevated tank in middle town:Give better distribution for head pressure3. For elevated tank at distant point:Improve the head at distant pointImprove the head for extension

Water distribution system• Design of Elevated tank:

5

4 supply

b b a+b b empty b 3

a 2 1 2 3 4 5 demand

1

time


ال ) • الخط ميل من اكبر للمنحني supplyالمماس)

للخزان تفريغ يحدثال ) • الخط ميل اصغرمن للمنحني المماس

supply) للخزان ملئ يحدث

• Capacityc1= [(a+b)/1000]*pop*1.5C3 (fire) = 0.2* w.c/h *pop/10000


• Depth =6-10 m• D0 > 35m

Di = (2-3)m

capacity of one tank less than or = 2000 m3

c= n ∏/4 * (D0 - Di) depth


• Design of HLP• HP = γ × Qmax × Ht

75 × η1 × η2

Qmax = 1.8 Qav. + Qfire

Qav. = W.C* pop

Qfire = w.c /h* pop/10000

η1 =0.7

η2 = 0.9


• Basic requirements• Network types, accessories• network design

pipe equivelent method of selection Hardy cross method Computer analysis


• Basic requirements (minimum requirement)ذات الشبكة هذه تكون لكي ضمان عن عبارة هي

تشغيل كفاءةعالية

1 -well laid pipe

Served city

Water network covering the city


• Pipe materialسيتم التي المواسير انواع اختيار عملية هي

التعرف بعد ذلك و المواسير تصنيع في استخدامهاكل للتربة تؤخذ التي الجسات خصائص علي

متر 100حوالي .GCI GRPDCI STEELRC HDPEUPVC PP


2- Pressure of dischargeIt is the quantity of flow that we will need to

face our needs.يعادل ضغط توفر من االقل علي متر 25يجب .


3- Network typesA- tree system

صغير نطاق علي استخدامها يمكنالمحدودة االماكن .في P.S


عيوبه : منفي كسر اي حدوث عند المدينة عن المياه انقطاع

. الرئيسي الخطال الطحالب dead endوجود نمو علي يعمل مما

مشكلة حدوث الي باإلضافة النهايات عنداتجاه عكس المياه ارتداد نتيجة المائية المطرقة

. الطلمبات ريش كسر علي يعمل مما السريان


B- Grid iron loop)dead ends( ال ربط عملية )هي

بعضها مع السابق النوع في P.S

المدينة حول كوردون نعمل ان نحاولالي الكوردون هذا تقسيم يتم ثم ككل

صغيرة .اقسام


: مميزاتها منالمدينة • في المياه انقطاع مشكلة علي التغلب

. الرئيسي الخط في كسر حدوث عند كلهاال • وجود dead end عدم

عيوبها:عالية تكلفة ذو


• Main distribution system:

ᶲmin =300 mm for big cities = 250 mm for cities and big towns = 200 mm for towns = 150 mm for villages No. of valves = (n-1) where n is the number of main feederMinor system:

ᶲmin= 100 mmNo. of valves = (n-2) where n is the number of secondary

feeder


SoThe basic requirements of network:1- well laid pipe of durable material 2- sufficient capacity to meet max. demand at

any time.3- absence of dead ends Grid-iron 4-more than one feeder


• Network Accessories:E.T (we must choose the location of E.T so that to avoid many

problems such as water hummer)

sluice gate pressure relief valveValves non return valve or check valve float valve air relief valve wash out valve


1. Sluice valveIt is used to control the flow of water in distribution system during repairs and maintenanceAdv. Cheap in construction low resistance to the flow of water


• Pressure valveIt is used to relief high pressure in pipe line

automatically and which is caused by sudden closing of gate valve.

It is used to prevent water hammer• float valveUsed in reservoirs (automatically)


• Non return valve or check valveIt is an automatic valve which allow water to flow

in one directionIt is used at elevated tanks, pumping stationsAir relief valveIt is used in long pipe lines, air accumulates at high

points and will interfere with flow of water and increase velocity and friction

This valve allow air to escape to atmosphere


• Wash out valvesIt is provided at lowest point and dead ends to

drain out waste water or sediment that may be collected

This valve must be in a chamber


• Hydrants1. Fire hydrant (on minor only)They are provided at all street crossing and

turning at distance 60-90 m2. Irrigation hydrantLike fire hydrant


• Design of pipes networksFour parameters must be computed for any pipe of

the network for purpose of complete analysis, they are:

1. Slope of HGL along the pipe“S” It is the head lost per unit length of pipe 2.Velocity of flow inside the pipe ‘V’ m/s3. Diameter of the pipe ᶲ mm4. Rate of discharge in the pipe Q l/sec


Hazen & Williams formulaV= 0.355 C D0.63 S0.54

V = The mean velocity (m/sec)C= Hazen & Williams friction factorD= internal diameter (m)S = HGL


• Methods of distribution system analysis:1. Equivalent pipe method2. Method of sections3. The circle method4. Hardy-cross method5. Computer analysis


1. Equivalent pipea. Pipes in series H

Q Q1 Q2 Q3

D1,L1 D2,L2 D3,L3

Q = Q1 = Q2 = Q3H= H1 + H2 +H3


• TO DETERMINE THE EQ. PIPEAssume Leq Then find Seq = H (cm) / Leq (m) *100From chart get Deq. ORAssume Deq.From chart get Seq., Then find Leq. = H (cm)/ Seq( cm/100m)*100 = m


b. Pipes in parallel

Q1,L1,D1 H Q Q2,L2,D2 Q3,L3,D3Q=Q1+Q2+Q3H=H1=H2=H3

Water distribution system2. Method of sectionsكفاءة و الحسابات من للتاكد ذلك و الشبكة اقطار حساب بعد تستخدم الطريقة هذه

الشبكة: التصميم خطوات

بكل 1. المخدومة المسافة حساب طريق عن تقريبا ماسورة لكل القطر حسابماسورة

ال 2. محصلة اتجاه علي عمودي يكون بحيث مقطع اخذ الشبكة flowيتم في

من 3. اقل االقطار اهمال مع المواسير عد يتم مقطع المدن” 6لكل في

ال 4. حساب باخذ Qيتم ذلك و قطعهم تم الذين من ماسورة لكلC= 100 , HL = 2m/Km

حساب. 5 Q1يتمQ1=SUMM OF FLOW IN CUT PIPES

حساب Q2يتمQ2= WATER DEMAND FOR THE DOWNSTREAM AREAS OF THE CITY

Q2= DOMESTIC DEMAND + FIRE DEMAND


• Domestic demand= pop*Qav./(24*60*60) = L/secPop = area of D.S the section *pop denisty = / عدد * ) القطاع خلف المربعات عدد الكلي السكان عدد

) الكلي المربعات

Water distribution system• Fire demand

pop Fire demand L/SEC

1000 55000 1010000 1520000 2030000 2550000 30100000 40200000 50


• Ground reservoirPurpose of ground reservoir1. Cover the contact time for disinfection [cl2(0.5-

1hr)]2. Cover the emergency requirements3. Cover the difference between Qmax daily &Qmax

monthly4. Cover 80 % fire demand


The reservoir is laid under ground 1. To keep the temperature of water2. To decrease the construction requirements3. Not to high the constructions before the reservoirImportance of the internal walls4. To stir the water from the inlet to the outlet to be

sure of the disinfection process to kill the bacteria in a certain time

5. To decrease the area of the slab to be designed as one way slab


• Importance of the air ventTo ventilate the waterHelp in emptying the reservoirHelp in filling the reservoirgive alarm in case of stopping the float valve


• Design criteriaCapacityC1=(1/2-1)hr * Qmm disinfectionC2= Qmm* T(4-10)hr emergencyC3= (Qm.d – Qmm*1d) difference between

max consumption & max productionC4= 0.8*120*pop/10000 80 % fireCd =the max of C1,C2,C3 + C4= hLBd

Water distribution system• d= 3-5 m• Area > 2000 m2

L= K*5m = (1.2-1.5)B > 50 m n < 2 (n الخزانات ( عددNotesFire demandFire hydrant flow = 60 m3/hrFire duration = 2 hrs10000 C 120 m3 fire = 120*pop/10000 (m3) if given fire demand =6000 m3

C4 = 0.8*6000 m3

emergency = 25 % of the summer flow (Qmm)

C2 = 0.25 Qmm

water & wastewater engineering water supply engineering lecture no. 4 water distribution system

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