PRV Use For Leakage Reduction
Contents
1. It is a common case where the supply pressure of the valve location may drop below the required downstream pressure To allow maximal pressure in the zone the valve should have a high Kv Cv factor provided by the manufacturer Generally one should notice that many valves on the market nowadays have a reduced water passage compared with the nominal size of the valve It is suggested to utilize only full bore valves and avoid using reduced bore ones Regulated pressure stability under low demand flow conditions As the aim of these valves is reducing the leakage rate it is expected that their minimal flow rate normally during the night would drop dramatically in some cases by over 50 of the initial MNF It is therefore essential that the PRV would regulate PRV Use For Leakage Reduction 5 without shuttering or vibrations through the entire range of expected flow rate conditions including low demand periods Note that in case the pressure is instable see figure 2 next page it may cause increased pipelines fatigue and the result may be_higher rupture frequency and larger loss volume than when no PRV is used A solution such as by pass PRV for low flow conditions is unacceptable for pressure management projects as it requires an increase instead of decrease achieved by modulation of the system pressure when the demand is low the bypass must be set to higher point in order to enter operation automatically Zone E 225A O2. C E Figure 5 Pressure setting of a fixed outlet PRV where Dh is the system friction losses Z is the CP elevation above the PRV and Pc is the minimal required pressure at the customer connection point Note that during low demand hours night flow the CP pressure will rise due to lower friction losses Where to use a fixed outlet PRV Where other application should be selected The PR application is designed for the use in Pressure Where demand flow changes result in significant pressure Management schemes where the target pressure in the variation in the target point due to pipeline friction losses zone the AZP or CP has insignificant variation as a consider using dual set point or fully modulated PRV result of varying demand Where a different or additional control functions are required such as PSV Flow control etc consult Dorot technical support department and or technical publications PRV Use For Leakage Reduction 7 Dual Set Point PRV This PRV type will regulate to one downstream set point pressure or another contingent upon the time of day or demand flow rate The high set point value will be selected in the same manner as selecting the set point of a standard fixed outlet PRV The lower setting point will be selected considering the lower system friction losses correlating to low demand situations With this valv
3. oo ooo oo o 6 Min Flow 11 4 m3 hr Flow Press Pressure bar Flow m3 hr Set point 1 yd 1 8 bar o f o 2222222020000000090009000 090 eocoecs oee a o oa en o 3 O 50809 2 3 0 9 2 SH O ab O an O amn Goa oc an O 0 Oan o o o 0 co 00 7 N 0 m 3 T D GN O m GO PS m O T Do uN o o Tr O co co co uo Ee G pe G ci o e lt O 0 iD ob ES Z O N G O G ao ao on on o G 0 0 0 O 0 D O O O D D O D O O 0 O D D O wo wo G B 6 6 G GDG 6 G 6 6 6 6 6 A G DD G G G G G GGG G G G G G G G G G G G G G sds DAA aaa N N CN N N ON N N CN AANA HN SN o KM SN KM M KM KM K KM KM KM KM KM KM M KM K R SN KM KM KM ci GGG oo oo Oo G 2 GG OO oO ooo oo fo oOo So Oo oO R R R S R R KR KR KR KR KR KR KR R R R R R S KKR KR K L a a e a e a e a A e e D d d d 11 I S 1 TTT H H H N A AA 0 H 0 coo La oa oo Figure 8 Dual Set point PRV reduces the pressure when the demand is low The normal flow into the zone in this case is reduced to 11 4 m3 hr Assuming 80 of the time the demand is low The average annual saving of using a Dual Set point PRV is estimated as 18000 m3 PRV Use For Leakage Reduction 9 Fully Modulated PRV The fully modulated PRV will regulate the downstream pressure to a varying set point so that the target point AZP or CP will remain minimal and stable regardless of friction losses varia
4. Various Technical Solutions Pressure amp Flow Data From Darnicle Hill 6 Modulator 15 Min Data 17 04 03 to 24 04 03 100 35 90 7 y 30 80 7 70 4 y om 60 7 A Peak Demand Pressure 52m a o o 250 Z 2 L B 40 7 Night Line 1 E 2 Pressure 32m a 30 40 20 HL AW AD a MM eae Ce a aie a eas pee ease ll AZNP point Critical point pressure Night Line Flow Rate 5 28 0 2 bar 0 6 bar 6 Lit sec 10 0 i i i i i 0 17 04 2003 18 04 2003 19 04 2003 20 04 2003 21 04 2003 22 04 2003 23 04 2003 24 04 2003 25 04 2003 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 Inlet Modulator Outlet pressure AZNP CPP Darnicel Hill Flow L sec Graph 1 Pressure and Flow results illustrating post commissioning of PRV and modulator Flows From the Darnicle Hill 30 6 PR HyMod 35 l 30 4 I 1 l 257 _ 2 H 2 15 I I 107 Old PRV Night Flow 12 L sed I Fixed outlet 30 6 PR 51 Night Flow 9 L sec S Modulating 30 6 PR HyMod i i Night Flow down to 6 L sec I apa 00 00 00 15 03 2003 00 00 00 20 03 2003 00 00 00 25 03 2003 00 00 00 30 03 2003 00 00 00 04 04 2003 00 00 00 09 04 2003 00 00 00 14 04 2003 00 00 00 19 04 2003 00 00 00 L
5. technical issues 1998 ISBN 1 84083 2 Pearson D Fantozzi M Soares D and Waldron T Searching for N2 How does Pressure Reduction Reduce Rupture Freguency IWA Halifax conference 3 Thornton J and Lambert A Managing Pressures to Reduce New Breaks Water21 Magazine December 2006 4 Dorot Automatic Control Valves August 2006 Pressure Management Solution Selection Guide 5 Dorot Automatic Control Valves February 2004 HyMod amp PRM FR Publications 6 Dorot Automatic Control Valves September 2002 Series 300 Design Manual 7 Dorot Automatic Control Valves January 1998 ConDor 2 13 User Manual 8 Technolog Module One Electronic Pressure Controller IOM 9 Fluid Controls Ltd Thames Water case study 2004 10 Gold Coast City Council web site http www goldcoast qld gov au t_gcw asp PID 5228
6. PRV Use For Leakage Reduction Various Technical Solutions Abstract The use of pressure reduction as a method for reducing water loss and labor cost in municipal water supply system is generally accepted in the industry However the real saving in various systems achieved through the usage of this method as well as the optimal selection of a control valve and control application are rarely known by all This paper presents some examples for the actual saving in background leakage Ruptures frequency and demand in municipal water systems It will also refer to the theoretical background leading for these results and explains the characteristics of different control valves their application and the optimal situations in which they should be utilized Keywords Pressure management Dynamic Pressure Reduction PRV Flow modulation Introduction Growing demand diminishing fresh water sources and increasing treatment costs gave in recent years a boost to extensive studies and research in the interest of water conservation and particularly leakage reduction These studies helped the development of two separate fields B Practices for measuring and assessing the volume and causes for the water losses and later defining the adequate technique for the reduction of lost water volume B Wide range of products that can be used for the measuring detecting and reduction of the losses Many text books and papers discuss the theoretical
7. PRV Use For Leakage Reduction Various Technical Solutions Case study Limassol harbour zone comparing fixed outlet to dual set point PRVs courtesy of Limassol water board Limassol District 123 10 00 200 00 9 00 180 00 8 00 160 00 7 00 n 140 00 Min Flow 13 6 m3 hr 120 00 Set point 3 4 bar 100 00 80 00 60 00 40 00 20 00 0 00 Flow Press Pressure bar Flow m3 hr o o o G GG G G G o oo 2a oe G 66 25 2 22 o o a a a a O OA o SH G G SH SCH SCH CH CH o uo GH O uo So mosg ND OO Ow Z 7 NID0m O w lt lt MD NO co w O co c Go rm cir aA GH c OG cc tb fc a o AN O N G S B Z G G Z 00 O o O D D D O D D D 0 D D D D D D D D D D co D B G G A66 BBB 6 5 a OO L I G G GG G GG GGG NN M M M MMM M MMM MM MM MM M M MM M M M GG G GG G GGG G 6 6666 O O GGG G G KR SR S S KR R S S KR R S SS R S S SR R R SR 22 mm G O QQ 000 O OOQ KL Z Z Z O 05 03 03 05 0 03 10 9 13 01806 6 6 6 60 O 6 Figure 7 Fixed outlet PRV set to supply enough pressure when docking ships are loading water The normal pressure in the zone is too high and as a result the minimal normal flow is high 13 6 m3 hr Limassol District 123 oc M wnaem mum oD o o 200 00 180 00 160 00 140 00 120 00 gt 100 00 80 00 60 00 40 00 20 00 0 00 o o o o Set point 2 48 PEN
8. e one can achieve better leakage reduction efficiency compared with the fixed outlet tyoe However the CP or AZP pressure may still be too high in cases were the demand flow is lower than the maximal but not low enough to change to low pressure setting Therefore the classical usage for dual set point PRV would be in locations where there is a distinct difference between the normal flow and the flow during low or high consumption such as in a case of a PRV supplying a zone with low normal demand that has single large industrial customer that cause a significant flow increase p Wt Cae Figure 6 Typical Dual Set point PRV installation Where to use a Dual Set point PRV Where other application should be selected The control application is designed for the use in Where varying demand flow result in insignificant target Pressure Management schemes where the zone is point pressure changes consider using fixed outlet PRV characterized by two distinct demand flow rates and the target pressure in the zone the AZP or CP has significant changes as a result of the friction at high flow Where a different or additional control functions are required such as PSV Flow control etc consult Dorot technical support department and or technical publications Where the demand changes are gradual it is suggested to use fully modulated PRV 8
9. ing fixed outlet PRV PED ane zone normally the AZP varies as a result Where demand flow changes are characterized by two of varying demand These changes are often associated f wilh Hich leakage index ahd fistire Requene distinct flow rates without much intermediate demand 9 9 p q y consider using dual set point PRV Where a different or additional control functions are reguired such as PSV Flow control etc consult Dorot technical support department and or technical publications PRV Use For Leakage Reduction 11 Case study London Thames Water A trial installation of a Dorot 150mm hydraulically modulated PRV system Source Fluid Controls UK Project objective To reintroduce appropriate pressure management to this water supply zone The challenge The existing flow meter and old PRV were surveyed for possible service and re use The valve was inspected found beyond economic repair The solution 1 Replace PRV with new 150mm 6 diaphragm type PRV 2 Pressure logging has identified a possibility of 20 25m pressure reduction using night time modulation A 150mm Dorot PRV was connected to a Fluid Controls hydraulic modulator with high pressure limitation pilot rail figure 10 E c Mm par Figure 10 Dorot 30 6 PRM HyMod installation Results As demonstrated in the charts below and in the next page The volumetric reduction is 0 23 Mid 12 PRV Use For Leakage Reduction
10. isec 24 04 2003 00 00 00 Graph 2 Flow results illustrating the drop in night flow pressure reduction during low demand hours and improvement of supply during high demand hours result of lower losses of the new PRV PRV Use For Leakage Reduction 13 Total Daily Flows From the Darnicle Hill 30 6 PR HyMod Modulator 70 i A j Old fixed outlet i y gt 1 gt t gt J 1 1 i 65 PRV Fixed Outlet PRV i Commissioning 20m modulation i 30 6 PR i 30 6 PR HyMod 11 30 6 PR HyMod 60 i 1 1 1 1 1 1 55 4 i i 1 1 1 R g 150 i i i 3 1454 i i 1 1 E i i Z 1404 i i a 1 1 1 S es l 1 i i i 30 i i i 1 1 j 1 1 i Average Daily Flow 1 i 1 Average Daily Flow 1 57 Ml d 1 34 Wd FL SS d ES FPF PS PS gt d gt SS Ss gt ESOS OSs POMS S PPPS OEE SS rk on SS LE oe E ee e ES o y GOS oes FOX ox K C oe S ae eee 0 0 Ss y SA A AS SS PIS EN ASAS SOS SIAP A se CW wes ER ae KS nh y CER PES eS E ee bn ws oe Se ES we PA AE SES ie y Ses Pe 6 Old Glenfield amp Kendey Stuck Total Daily Flow 6 Dorot PRV as Fixed Outlet 6 Dorot Hydraulic Modulator Under Modulation Graph 3 Daily Flow results illustrating volumetric savings 14 PRV Use For Leakage Reduction Various Technical Solutions References 1 Lambert A Mayers S and Trow S Managing Water Leakage Economic and
11. issues of the leakage causing and ways to asses and manage the water supply system But very little attention was given for the actual selection of hydraulic control devices that can deal with such problems The aim of this document is to guide technicians and engineers puzzled by a wide selection of technical solutions in selecting the adequate product for a specific case of hydraulic conditions of their network Theoretical background A first essential step for any leakage control scheme is gaining a fair understanding of the sources for leakage and other real losses in the system The most common Real Losses sources are m Pipe ruptures 7 Leakage from fittings joints and small pores in the distributing pipes 1 2 PRV Use For Leakage Reduction Various Technical Solutions m Tanks and reservoirs overflow 7 Leakage from Storage tanks Factors that influence the water loss volume and costs m Infrastructure condition Quality of materials ground condition water quality and workmanship Improving the infrastructure condition usually requires large capital investments 7 Awareness time AT the average time between the start of the leak until the water company becomes aware of it The total volume of water lost from a single leak is the time delay from emergence to fixture multiplied by the average leak flow rate If a methodology for monitoring the system condition is applied large rupture would usually be characte
12. ld PRV Low flow o perra aT 4 Minute Intervals instability Flow logged at 15 Minute Intervals Inlet Pressure Outlet Pressure Flow 0 T Fo 18 TMTHIR TINI 15 T NP 15 TNT 45 T NP 15 UT MT 18 T 2NT6 15 7 0 MR 15 TI 2NT6 15 71 NTE 16 T INTE 00 00 02 24 04 48 07 12 09 36 12 00 14 24 16 48 19 12 21 36 00 00 Figure 2 Low flow instability as logged in a sample zone unknown PRV Figure 3 LTP Low flow throttling plug in a Dorot Series 300 PRV is enabling standard low flow stability combined with low pressure losses at high flow rates Dorot database 6 PRV Use For Leakage Reduction Various Technical Solutions Control Application Selection Fixed Set Point PRV A fixed outlet PRV is the standard pressure reducing valve that regulates a high varying upstream pressure to a lower fixed and stable downstream pressure regardless of variations in demand flow Figure 4 Typical fixed set point PRV Dorot Series 300 publication The fixed outlet PRV s set point will be adjusted so that the pressure at the C P critical point most distant and elevated demand point in the pressure zone will be higher than the minimal value as required by the local regulations This in view of head losses created by elevation differences and system losses at maximal demand ph Pset p 2 a LA
13. ption e 71 reduction in water main breaks and e 75 reduction in water service breaks On the basis of these savings Gold Coast Water began implementing a full scale Pressure and Leakage Management Program across the city which is expected to save up to 10 15ML of water every day or about 10 of the city s daily water consumption PRV Selection A selected PRV for a pressure management project should have the performance that matches the specific operation conditions of the network Reliability The valve should contain minimal number of internal high friction sealing points as those tend to wear over the course of time One should also avoid narrow unfiltered internal passages in the internal mechanism of the main valve Maintainability The valve should be inspected and maintained through the years The costs of maintaining a PRV may be equal and often exceeding the cost of a new valve It is highly important to select a valve that can in relative simplicity be maintained without removing from the pipeline In most locations the valve is installed in a narrow underground pit Using globe valves should be preferred over the usage of Y pattern oblique pattern mechanism valves as they are extremely difficult to assemble and disassemble when located underground Pressure loss One should bear in mind that the same valve meant to supply maximal perhaps future demand as well as exceptional flow such as a fire event
14. rized by a very short AT compared with small leaks that may be left un noticed for years Therefore there is a need for methods and solutions for minimizing the rate of the losses through these small leakage points Flow Large pipe burst Flow Background leakage point No awareness or too small to justify the cost of fixing t Awareness Time __ End of event Reaction time fixing Loss Volume Ox t Figure 1 Comparing two water loss types in a network where the system is monitored and well maintained The loss volume through many background leakage points may become much larger than the volume lost due to large pipe breaks m Average Zone Pressure AZP has significant influence on both leakage flow rate and creation of new leakage points and rupture occurrence rate The ratio between pressure reduction and leakage rate change is calculated by Oi Qo x Pi Po Where N1 factor is 0 5 lt N1 lt 2 5 and the average value for large systems is N1 1 15 This shows a very strong link between system pressure and leakage flow rate A second correlation that should be noted is the one between the system s pressure and the rupture frequency described by the index N2 Bi Bo x P1 Po System age and conditions influance N2 deviations but average values for N2 are 2 47 for large mains and 2 36 for distribution lines PRV Use For Leakage Reduction 3 Table 1 show
15. s some sample case studies presenting the very strong link between AZP and rupture frequency Table 1 Percentage reduction in new break numbers before and after pressure management A clear conclusion from the above data is that pressure reduction reduces the leakage flow rate even at locations where the leak is left undetected or unfixed as well as reduction in the occurrences of new pipe breaks Number of Assessed o Average i Water Utility or FREE initial Aii i ee W Country Syst Managed maximum reduction Seni Fem Sectors in pressure meximum in new SES Study metres Pressure breaks 5 Bubane_ 1 100 sw 2 M3 60 m er 150 vetrala Soacoast to bae a gy O Yara vay 4 100 30 28 M Bahamas erea r CK Herzegovina e a n mn Peete IM 2 s i 1 2355 M _ bas EA E 1 8 aes ee So BEI CYFN E li SH q L 485 M YR emesos 7 ws 32 Pa s 40 M Bristol Water A ee England Bristol water 55 S 77 United Utilities 32 m S tay Torino Hume tr ee 4 E LO 3 99 2 Om Total or Average 110 4 PRV Use For Leakage Reduction Various Technical Solutions Case study Gold Coast Source Gold Coast City Council web site A trial on the Gold Coast involving 12 000 properties in four residential areas showed significant water saving benefits e 20 reduction in average daily water consum
16. tions due to demand flow rates The set point modulates according to either The flow values at the valve location Time of day Actual pressure value at the target point and sent via telemetry system to the PRV This type of operation enables a maximal optimization of leakage reduction with best level of customer service as the zone pressure is kept stable regardless of demand variations Fully modulated PRVs are usually controlled by a specialized controller that logs the pressures and flow rate and modifies the set point of the pilot valve on the control system of a standard PRV Figure 9 Dorot Electronically modulated PRV installed in Gold Coast pressure management project Gold Coast Pressure and Leakage FAQs document 10 PRV Use For Leakage Reduction Various Technical Solutions Another unique type of fully modulated PRV is the Dorot HyMod system which is a completely hydraulically modulated PRV This valve does not require the electronic controllers batteries or telemetry connections The system will modulate the downstream pressure following automatically the local hydraulic conditions and the user adjusted pressure flow profile Where to use a fully modulated PRV Where other application should be selected The fully modulated application is designed for the use in Where demand flow changes result in insignificant target Pressure Management schemes where the target point pressure changes consider us
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