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无负压供水方案设备设计

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　　摘要

　　Abstract

　　第一章绪论1

　　1.1 课题研究的目的和意义1

　　1.2 二次供水发展历史2

　　1.3国内外无负压供水研究现状4

　　1.4传统二次供水方式存在的问题5

　　1.5本课题的研究内容6

　　1.6本课题预计达到的目标6

　　1.7完成课题的方案和主要措施6

　　第二章无负压供水方案简介7

　　2.1方案的工作原理7

　　2.2方案的工作流程7

　　2.3 方案的适用范围8

　　2.4 方案的核心技术——无负压技术8

　　第三章设备的参数计算及设计10

　　3.1 稳流罐允许进水量的计算10

　　3.2 稳流罐调节容积计算12

　　3.3 稳流罐总容积的计算13

　　3.3 实例计算13

3.3.1工程概况13

　　　　3.3.2计算最大出水量14

　　　　3.3.3 确定水表特性系数14

3.3.4计算水泵扬程15

3.3.5水泵的选型15

3.3.6稳流罐容积的核算15

3.3.7 真空抑制器的设计16

　　总结17

无负压供水方案设备设计　　　　　　　　　　　　　　

摘要：近年来，随着科技的进步，二次供水设备作为一种新兴的二次供水产品，在节能和环保方面有独特的优势，无负压供水系统将市政供水管网和用户合并成为一个整体，在充分利用市政管网余压的情况下，进行变频无负压供水，即节水节电又可以防止二次污染。论文分析了无负压供水系统的组成、工作原理、工作流程、适用范围及其核心技术，即无负压技术。并对一高层住宅楼进行了实际的数据计算，根据所计算的数据设计选择不同型号的水泵和确定稳流罐的容积，并对稳流罐、真空抑制器等主要结构进行设计。

关键词：无负压、二次供水、节能、流量、扬程。

No negative pressure water equipment design program　　　

Abstract: In recent years, with advances in technology, secondary water supply equipment as anew secondary water supply products, energy saving and environmental protection has unique advantages, no negative pressure water supply system will be municipal water supply network and user merged into a whole, in the case of full use of the residual pressure in the municipal pipe network, no negative pressure frequency conversion water supply, water saving that can also prevent secondary pollution. This paper analyzes the composition of non-negative pressure water supply system, working principle, workflow, scope and its core technologies, namely non-vacuum techniques. And a high-rise residential building were actual data calculations, select different types of pumps and determine the steady flow tank volume calculated based on data design, and the main structure of the steady flow tank, vacuum suppressors design.

Keywords: No negative pressure、 Secondary water supply、Energy、Flow、Head

第一章绪论

1.1 课题研究的目的和意义

　　　水是自然界一切生命赖以生存的不可替代的物质，又是社会发展不可缺少的重要资源。目前，世界上 80 个国家或占全球 40%的人口严重缺水。据预测，今后 30 年内全球55%以上的人口将面临水荒。就我国而言，水资源不足尤其是人均占有量低已经成为我国的基本国情。而近年来，随着经济的快速增长，城市化建设的不断加快，人口的不断增加，土地需求日益紧张，高层建筑层出不穷。为满足建筑内部用水点对水量、水压和水质的要求，必须对自来水进行二次加压，因此，选择一种既能节水节能，又能保障供水安全的供水方式，这对降低建筑耗能、提高供水安全可靠性具有重要的意义。

　　　建筑内部给水系统是将城镇供水管网或自备水源的水引入室内，经配水管送至生活、生产和消防用水设备，并满足用水点对水量、水压和水质要求的冷水供应系统。从上世纪末开始，随着城市规模的不断扩大，城市建筑业得到突飞猛进的发展，10 层和10 层以上的住宅或建筑高度超过 24 米的其他民用建筑等高层建筑越来越多，使得城市的总用水量中，建筑内部用水占据的比例逐年增加，二次供水得到了更为广泛的应用。目前，我国城市自来水管网的压力在非用水高峰时，一般在 0.2MPa~0.35Mpa，此压力2值只能满足低层和多层建筑的供水需求，所以为了弥补市政供水管网压力的不足，高层建筑内部供水系统须使用二次加压设施以满足需求。

现有通常的供水方式都是将自来水放入蓄水池，然后由水泵将水从水池抽至屋顶的高位水箱，再由高位水箱向用户供水。这种供水方式存在严重的能量浪费问题：第一，将原本有压力能的水放到水池中变成了无压力能和势能的水，使得二次加压供水时需要更多的能量；第二，由于用水量是随时间变化的，大多数水泵并未在高效区运行，水泵低效率运行会浪费更多的电能。另外这种供水方式还存在严重的水质二次污染问题，据调查，各地二次供水主要水质指标都存在不同程度的超标。例如，深圳市对 274 个二次供水贮水池水质进行调查，合格率更低，经水池后余氯合格率不大于 30％，大体积水池的合格率只有 10.6％。兰州市目前使用二次供水的人口占全市总人口的近 70%，全市二次供水单位约 1200 家，二次供水设施约 1400 多个。2010 年，通过对兰州市 356 家单位的二次供水水质的调查发现，水样检测合格率为 68.35%，其中，游离性余氯合格率最低，仅为 57.31%，其次是细菌总数和总大肠菌群，合格率均低于 60%。迄今为止，发现至少有 10 余种传染病可以通过水传播，如伤寒、痢疾、霍乱等，一些病毒引起的病症也可以通过水进行传播。另外，水污染导致微量元素过多，容易引起身体器官的功能改变，严重的甚至会引起中毒。例如，l 998 年湖南省地税局办公楼工作人员集体腹泻，后被证实问题就是出在二次供水的水质上，而且是由细菌总数超标以及大肠菌群所致。长春市某生活小区不断有居民发生消化道疾病，经查，原来是屋顶水箱多

1.4 传统二次供水方式存在的问题　　

　　　总结以往的供水经验和实际工程，二次供水存在以下几个问题：

　　　1．投资大。传统二次供水都要修建水池，有的还要设置水箱，这就需要一定的成本。修建水池和水箱需占用一定的建筑面积，在如今土地价格高涨的今天，这又是个投资负担。此外，水池和水箱一般都有一些水质处理设施，从而加大了设备总投资，而且使用中要定期清洗，也增加了日常开支。

　　　2．水质二次污染严重。据调查，大部分水池和水箱由于管理不善，和其结构本身的原因，里面的贮水水质没有符合饮用水标准，水质污染相当严重，这将直接危害到人们的身体健康，因此饮用水卫生问题已成为急需解决的大问题。

　　　3．能量浪费严重。传统的二次供水是将自来水放入水池中，再从水池抽水至用水点，但是市政管网中的水具有一定的能量，也就是说这部分能量没有得到充分利用。

　　　4．水资源浪费严重。大多数水池采用混凝土结构，因此存在不同程度的渗水、跑水、漏水、蒸发等问题，造成水资源浪费。此外，水池、水箱要进行定期的清洗，这就又成一部分浪费。

1.5 本课题的研究内容　　

　　　无负压供水设备由智能型变频控制柜、稳流罐、真空抑制器、水泵机组、仪表阀门及管路、基座等组成。本次课题研究的主要内容是供水方案的设备设计，其中包括稳流罐的设计，真空抑制器的设计，水泵的选型已经设备的整体结构设计。

1.6 本课题预计达到的目标

　　　能够顺利完成课题所需要完成的任务，设备达到无水池，不用消毒，体积小，占地少，安装方便的要求。设备应具有无负压供水能力，整套设备全封闭无污染。

1.7 完成课题的方案和主要措施

1、同老师讨论合适的方案和机体结构，讨论其可行性。

2、在图书馆和网上查找相关资料。

3、从网上实体照片中形成设备的基本模型。

4、按照老师布置的任务按时完成计划，画出装配图及主要零件图。

5、主要参数的计算和设备的选型。

6、设计说明书的编写。

7、后期工作。　　　　　　　　　　　第二章无负压供水方案简介

.1 方案的工作原理

1．市政管网自来水进入调节罐，罐内的空气从负压消除器内排出，待水充满后，负压消除器自动关闭。当市政管网的压力满足用水点的要求时，即管网压力大于或等于设定压力时，设备通过旁通阀门直接向用户供水。

　　　2．当市政供水管网压力不能满足用水点要求时，供水系统利用压力传感器(或压力控制器、电接点压表)发出启泵信号，水泵进入运行状态，向用户持续供水。

　　　3．在用水高峰期，供水管网压力下降，当降至低于设定压力时，压力传感器发信号给控制柜，升高变频器频率，使水泵机组转速增加，出水量和压力也随之上升，直至用水点实际压力等于设定压力。

　　　4．在用水低谷期，供水管网压力上升，当高于设定压力时，压力传感器发信号给控制柜，降低变频器频率，使水泵机组转速降低，直至供水管网实际压力等于设定压力。若用水量变小甚至无流量时，水泵处于空转状态，则水泵机组自动停止工作，自来水通过旁通管直接供给用户。

　　　5．若市政管网流量大于或等于水泵的进水量，负压消除器使得稳流补偿器与外界隔绝，系统正常供水。若市政管网流量小于水泵流量时，空气由负压消除器进入稳流补偿器，消除了市政管网的负压，保证市政管网的正常供水，同时罐内的水作为补充水源仍正常供水，待用水高峰期过后，系统恢复正常状态。

　　　6．当市政供水管网停水时，利用稳流补偿器内的部分存水，水泵仍可继续工作一段时间，当稳流补偿器内水位下降至一定水位时，自动停机以保护水泵；来水后随着水位的上升而自动开机。

　　　7．停电时，水泵不工作，自来水通过旁通管直接到达低层用户，保证低层部分用户的用水，来电时水泵机组自动开机，恢复所有用户的正常供水。

2.2 方案的工作流程

　　　无负压供水技术综合利用负压处理技术、变频调速技术和全自动智能化控制技术，实现从市政管网直接加压向用户持续和稳定地供水，达到用户用水要求，其工作流程如图2-2所示：

图2-2 无负压供水方案工作流程图　　　　　　　　

2.3 方案的适应范围

　　　无负压供水系统适用于市政供水管网压力不足地区的二次加压供水，包括：新建、改建或扩建的住宅小区、办公楼、宾馆、学校等民用建筑的生活给水工程，工矿企业的生活、生产用水，各种循环用水系统，原有传统二次供水的改造工程，低层供水压力不能满足要求的消防用水等。

　　　无负压供水系统不适用的场所：市政管网可利用水头过低的区域；供水可靠性要求高的地区；市政管网供水流量和压力波动大的区域；用户用水量非常集中的区域；可能会对公共供水管网造成有毒污染的相关行业(医院、医药、化工、核工业等)。　

2.4 方案的核心技术 —— 无负压技术

　　　无负压供水技术中所提到的无负压中负压的概念，并非物理学所指负压概念，即低于常压（通常为一个大气压）的压力状态。这里的负压是在此基础上的演绎而来的说法，是指以各地区规定的最低市政管网服务压力值为界限，低于这一压力即为负压。无负压供水系统必须要保证直接抽水时市政管网的压力不低于最低服务压力值，同时由此产生的压降也要控制在一定的范围内，符合当地管理部门的有关规定。

　　　负压消除器，也叫真空抑制器，是该设备的核心，它和稳流补偿器联合工作以消除管网中的负压，从而避免对周围用户的影响，保证市政管网与设备安全可靠地供水。其原理如下：它根据稳流补偿器内的水量、水压、液位、真空度等信号，进行实时反馈、处理和控制，在满水时关闭阀门，在容器内产生负压会水位下降时打开阀门，从而调节稳流补偿器吸气和排气，保证内部压力平衡，同时消除容器内的负压。该装置的控制方式主要有水力机械式、电动式（利用电接点真空表或容器内水位接点控制电磁阀的启闭）。　　　　　　　　　　　　　参考文献　　　

［1］姚福来.?无负压供水设备的现状与发展态势[J].建设科技,2005,(22)

［2］濮良贵. 纪名刚. 机械设计[M]. 北京:高等教育出版社，2006.

［3］尤百琴.?新型供水设备问世[J].船艇,1992,(0).

［4］邵军.?无负压变频恒压供水[J].大众科学(科学研究与实践),2007,(08).

［5］张凤英.?论无负压供水设备的优点[J].安装,2006,(02)

［6］会议论文?北京地区无负压加压供水设备的管理现状及存在问题?2010’建筑二次供水技术推广与管理经验交流会 – 2010

［7］会议论文?NFWG无负压变频供水设备?中国水协设备材料委第二届二次供水设备选型与应用技术交流研讨会 – 2009

［8］会议论文?浅谈箱式无负压供水设备?2010’建筑二次供水技术推广与管理经验交流会 – 2010

内容简介：: (12) United States Patent US007201180B2 (10) Patent N0.: US 7,201,180 B2 Ephrat et a1. (45) Date of Patent: Apr. 10, 2007 (54) WATER SUPPLY SYSTEM 4,364,408 A 12/1982 Griswold 4,562,552 A 12/1985 Miyaoka (75) Inventors: Uri Ephrat, Givat Ela (IL); Abraham 5,460,196 A * 10/1995 Yonnet . . 137/12 Gleichman, MaAlot Tarshiha (IL) 5,660,198 A * 8/1997 McClaran . . . . 137/12 6,112,137 A * 8/2000 McCarty et al. . . 700/301 (73) Assignee: Optimus Water Technologies Ltd., MaAlot Tarshiha (IL) ( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 355 days. (21) Appl. No.: 10/498,834 (22) PCT Filed: Dec. 19, 2002 (86) PCT No.: PCT/IL02/01023 371 (O0) (2), (4) Date: Jun. 14, 2004 (87) PCT Pub. No.: WO03/057998 PCT Pub. Date: Jul. 17, 2003 (65) Prior Publication Data US 2005/0016593 A1 Jan. 27, 2005 (30) Foreign Application Priority Data Jan. 8, 2002 (IL) . . 147506 (51) Int. Cl. G05D 16/20 (2006.01) (52) US. Cl. . . 137/14; 137/487.5; 137/488; 251/29; 251/30.01 (58) Field of Classi?cation Search . . 137/ 14, 137/12, 487.5, 488; 251/29, 30.01 See application ?le for complete search history. (56) References Cited U.S. PATENT DOCUMENTS 4,200,911 A * 4/1980 Matsumoto . . 700/28 24 FOREIGN PATENT DOCUMENTS EP 1 126 089 A2 8/2001 JP 11256624 A * 9/1999 JP 2001280597 A * 10/2001 OTHER PUBLICATIONS Christine Chan, Development of an Intelligent Control System for a Municipal Water Distribution Network, 1999 IEEE Canadian Conference on Electrical and Computer Engineering. * cited by examiner Primary ExamineriRamesh Krishnamurthy (74) Attorney, Agent, or F irmiThe Nath LaW Group; Jerald L. Meyer; Derek Richmond (57) ABSTRACT A Water supply system comprising a supply line and a network of consumers, one of Which being a monitored consumer Who receives the least amount of pressure, a pressure regulation system comprising a pressure reducing valve (PRV) associated With a pilot valve preset to a nominal output pressure and a pressure control system comprising a diiferential control valve (DCV). A pickup unit is provided for measuring a How parameter indicative of the pressure at the monitored consumer and emitting a pressure signal to a controller generating in turn a control signal responsive to the pressure signal to activate an actuator of the DCV thereby governing the How rate through the DCV, so as to obtain desired pressure at the monitored consumer, regard less of altering ?oW rate through the PRV. 21 Claims, 9 Drawing Sheets U.S. Patent Apr. 10, 2007 Sheet 1 0f 9 US 7,201,180 B2 cor _.0_u_ 8 OJ Nml/ AHA 2: n L / / I1 mm mm NM vm $3 $0 Y. 2 “a 8 Fa Ham mama _ , u m a a a a a n ” m 8 / ., . , _ “ .q t L 1 A8 A3 A8 “ a U ml _ _ _ n _ 8 W 5 om U.S. Patent Apr. 10, 2007 Sheet 2 0f 9 US 7,201,180 B2 N E g a mm mm S S bl AM Goa _l _ a wm 8) w2/ Nm/ om mm mm L8 om CI .MN 2 B 0 00 1. 1 m m 7, S U 4 5 1 4 4 1. U.S. Patent Apr. 10, 2007 Sheet 3 0f 9 132 164 134 170 FIG. 3A US 7,201,180 B2 /9O 0 154 132 U.S. Patent Apr. 10, 2007 Sheet 4 0f 9 134 164 172 169 170 4 7 4| 178 176 FIG. 3B U.S. Patent Apr. 10, 2007 Sheet 6 0f 9 US 7,201,180 B2 200 190 204 196 198 194 FIG. 4 U.S. Patent Apr. 10, 2007 Sheet 7 0f 9 US 7,201,180 B2 FIG. 5 U.S. Patent Apr. 10, 2007 Sheet 8 0f 9 US 7,201,180 B2 .GE www EN p U.S. Patent Apr. 10, 2007 Sheet 9 0f 9 US 7,201,180 B2 386 2. 380 378 337 335 333 341 321 339 FIG. 7 331 374 327 US 7,201,180 B2 1 WATER SUPPLY SYSTEM FIELD OF THE INVENTION The present invention is generally in the ?eld of Water How and pressure control. More particularly the invention is concerned With a control system for a netWork of Water supply. The invention is also concerned With a device used With the system and With a Water control method. BACKGROUND OF THE INVENTION A Water supply system, eg a municipal Water system, typically comprises a main supply line fed from a source of Water (Water reservoir, Well, lake, etc.) and pumping means for propelling the Water through a netWork of pipes so it can reach various consumers doWnstream. Typically, there are also provided various pressure regu lating and control means along the pipes netWork in order to monitor the Water How and to reduce pressure of Water to such a level that Will, on the one hand, ensure proper functioning of various systems Which are pressure activated, e.g. irrigation systems valving means, etc. and, on the other hand, Will not damage any end equipment of the consumers by excessive pressure, e.g. burst of pipes, damage of solar heaters, and other domestic equipment connected to the Water netWork (dishwashers, Washing machines, etc.). Excessive pressure may also be harmful for industrial facili ties receiving Water from the netWork. Hereinafter in the speci?cation and claims the term “pipe netWor ” refers to the piping and installations extending from the Water source to the consumers. The consumers of a Water supply system may be for example domestic consumers, industrial facilities, public and municipal facilities, agricultural consumers, etc., all of Which being referred to herein in the speci?cation and claims collectively as a “network of consumers”. Among the netWork of consumers there is at least one consumer at a location Where the measured pressure is loWer than the pressure measured at the other consumer sites. Such a consumer may be for example a remote one Whereby pressure loss occurs oWing to How through a long and branching pipeline (friction and head loss), or a consumer at an elevated location (high building or on a mountain) etc. Hereinafter in the speci?cation and claims, the one or more consumer at Which loWest pressure is measured is referred to as a “monitored consumer” (also knoWn as a “critical consumer”). Water consumption in a municipal Water supply system varies throughout the day. Increased consumption is typi cally measured at the morning hours (betWeen about 6 and 9 am.) and again in the evening hours (betWeen about 7 and 9 pm.) HoWever, these peaks are subject to changes, eg at Weekends, upon setting of DST, season changes, major events such as an important sports match, etc. It is the concern of the Water supplying authority, for example a municipality or a Water supplying company, that the monitored consumer receives Water at a minimal pres sure, say for example, about 21/2 atmospheres so as to ensure proper functioning of various pressure activated equipment and to enjoy reasonable pressure at a domestic Water facili ties, e.g. taps, shoWers, etc. Increasing the pressure at the monitored consumer Will necessarily entail a much more signi?cant pressure increase at consumers upstream, even as much as harmful over pressure. For one thing, over pressure demands more poWerful pumping units and is more costly. Second, it requires a pipe 20 25 30 35 40 45 50 55 60 65 2 netWork that can Withstand such overpressure. Then there is a problem of over pressure Which can cause damage to the consumers as already mentioned above. Even more so, non-signi?cant leaks in the pipe netWork, e.g. minor holes or poor connections of piping elements, become proportionally signi?cant upon pressure increase and may be the reason for some signi?cant loss of fresh Water Which goes astray. Reports shoW that rates of loss of fresh Water by leaks reach as much as about 15 to 40% of a suppliers ?oW delivery. A variety of Water pressure and control systems are knoWn. A basic arrangement comprises a pressure reducing valve (PRV) Which functions to reduce pressure betWeen an inlet and an outlet thereof, regardless of How changes through the device or change of pressure upstream. Several such PRVs are typically ?tted along a pipe netWork, eg at branchings to suburbs, adjacent major consuming facilities, buildings, etc. A typical PRV comprises an inlet port being in How communication With an outlet port via a How passage governed by a pressure control chamber. When the pressure control chamber is pressuriZed, the How passage is restricted to thereby restrict ?oW betWeen the inlet and the outlet port so as to obtain essentially constant outlet pressure. Pressure Within the control chamber is governed by various ?oW control means Which eventually serve for the purpose of controlling the Water ?oW rate through the control chamber. In accordance With one prior art embodiment there is provided a so-called hydraulic valve, Wherein the pressure chamber is charged by a restriction ori?ce having a constant inlet flow rate Ql connected upstream of the PRV and is discharged by a pilot valve having a set nominal outlet ?oW Q2 connected doWnstream of said PRV. When O1 is greater than Q2 the pressure Within the pressurized control chamber increases to thereby restrict (or close) the How passage betWeen the inlet port and the outlet port of the PRV to thereby restrict the outlet ?oW Q01” of the PRV, entailing a corresponding drop in out let pressure Pout of the PRV. In accordance With a different arrangement, rather than the restriction ori?ce and the pilot valve, there are provided solenoids (optionally proportional solenoids) connected to electric controllers, Whereby Water inlet ?oW Q1 and outlet ?oW Q2 are controlled to thereby govern pressure Within the control chamber. In accordance With still a different embodiment a bias chamber is ?tted onto a plunger of the pilot valve for hydraulically activating an internal diaphragm of the pilot valve. Said bias chamber is connected to an upstream Water supply Whereby a plunger of the pilot valve is displaceable to restrict the outlet ?oW Q2 of the pilot valve. Still another control system is concerned With ?tting a bias chamber onto an adjusting member of a pilot valve supply Whereby the adjusting member of the pilot valve is displaceable so as to restrict the outlet ?oW Q2 of the pilot valve. In accordance With an embodiment of the above solution, there is provided a bias chamber integrally ?tted With the pilot valve. Nevertheless, control solenoids are still required for restricting the inlet ?oW Q1 and the outlet ?oW Q2. Each of the above control systems have at least one of several de?ciencies and draWbacks as folloWs: i. Malfunctioning of one or both the solenoids renders the PRV inactive. This may result in one of tWo undesired extreme positions, the ?rst being complete cut-off of the Water supply and the second being providing the consumers With a pressure Which is equal to high US 7,201,180 B2 3 pressure upstream (as the PRV does not ful?l its function) whereby the Water supplier is exposed to malfunctioning liability oWing to damages caused to consumers. ii. Every recognizable pressure or ?oW change entails activation of the solenoids Whereby an associated poWer source is rapidly exhausted; iii. Increased openings/closing of the solenoids and valve components may render the system vulnerable to mal function. iv. Usage of solenoids requires ?ltration of the Water at a high level (typically as much as microns). Thus increased maintenance is expected. v. An important factor is the option to install the control system in retro?t. In most cases individual ?ttings and installations are required Which render the installation not cost effective. vi. At loW ?oW rates the system enters a so called hunting state Where the system is unsuccessful in reaching a steady state. vii. The bias chamber is a sensitive element requiring ?ne adjustments and being susceptible to dirt. viii. The systems does not offer any bypassing arrange ments, Whereby malfunctioning of such a system may result in that the consumer Will receive excessively high pressure, Which may cause damage. It is thus an objection of the present invention to provide a Water supply control system capable of providing essen tially desired pressure at the monitored consumer regardless changes in consumption, i.e. ?oW rate through the system. A Water supply system in accordance With the invention pro vides for essentially constant pressure measured at the monitored consumer regardless of its location and head loss in the piping netWork and also regardless of sudden changes in consumption or periodic such changes. In accordance With another aspect of the present invention there is provided a differential control valve useful in obtaining a constant ?oW rate in spite of pressure changes in the line by eliminating such pressure alterations. Still a further object of the present invention is to provide a method for controlling pressure at a Water supply system so as to provide desired pressure at a monitored consumer. SUMMARY OF THE INVENTION The present invention calls for a Water supply system comprising a netWork of consumers and a pressure regulat ing system Which in spite of alternating ?oW rate through the system maintains the pressure at the monitored consumer at a desired pressure level. In accordance With one aspect of the invention there is provided a Water supply system comprising a supply line and a netWork of consumers, one of Which being a moni tored consumer Who receives the least amount of pressure, a pressure regulation system comprising a pressure reducing valve (PRV) associated With a pilot valve preset to a nominal output pressure; and a pressure control system comprising a differential control valve (DCV); a pickup unit for measur ing a ?oW parameter indicative of the pressure at the monitored consumer and emitting a pressure signal to a controller; said controller generating a control signal respon sive to the pressure signal to activate an actuator of the DCV thereby governing the ?oW rate through the DCV, so as to obtain desired pressure at the monitored consumer, regard less of altering ?oW rate through the PRV. In accordance With one embodiment, the ?oW parameter is ?oW rate measured adjacent the PRV and converted into 20 25 30 35 40 45 50 55 60 65 4 a pressure signal representative of the pressure at the moni tored consumer, based on conversion calculations. And in accordance With another embodiment the ?oW parameter is pressure measured at the monitored consumer. Where the ?oW parameter is ?oW rate, there is typically provided a pressure pickup for reading pressure at an outlet line of the DCV to generate a local pressure signal, Whereby said local pressure signal and the pressure signal are com pared at the controller. In accordance With still another embodiment, the Water supply system further comprises a bypass gate for overriding the DCV in case malfunction of the DCV and/or of the controller is detected (including any control parameters eg softWare problems, control signal errors etc.). In accordance With a different aspect of the present invention, there is provided a differential control valve useful in a pressure control system in accordance With the present invention. The differential control valve comprises: a housing ?tted With a static inlet, a dynamic inlet and a valve outlet; a control chamber sealingly partitioned by a ?exible diaphragm dividing the chamber into an a ?rst chamber communicating With the static inlet, and a second chamber communicating With the valve outlet and With a controlled ?oW passage serving to effect communication betWeen said second chamber and said dynamic inlet; a spring loaded obturating member articulated With the diaphragm and being axially displaceable Within the con trolled ?oW passage responsive to differential pressure dis placement of the ?exible diaphragm; and a controlled actuator for axially displacing the obtu rating member thereby to govern ?oW through the controlled ?oW passage responsive to differential pressure over the ?exible diaphragm and an opposing force imparted by the actuator and the spring. In accordance With one particular embodiment of the differential control valve the obturating member is a needle type sealing member ?tted for sealing engagement With a corresponding sealing seat of the ?oW passage; said sealing member and sealing seat being essentially equally tapered and Where cross-sectional ?oW area betWeen the sealing seat and the sealing member is proportional With respect to axial displacement of the sealing member. The invention is further concerned With a method for controlling pressure at Water supply system comprising a supply line and a netWork of consumers, one of Which being a monitored consumer Who receives the least amount of pressure; a pressure regulation system comprising a pressure reducing valve (PRV) ?tted With a pilot valve preset to a nominal output pressure, a pressure control system compris ing a differential control valve (DCV) connected in series to said pilot valve, a ?oW parameter pickup unit and a con troller; the method comprising the folloWing steps: (i) measuring a ?oW parameter indicative of the pressure at the monitored consumer and emitting a pressure signal to the controller; (ii) generating a control signal by the controller, said control signal being responsive to the pressure signal; (iii) activating an actuator of the DCV by the control signal, thereby governing the ?oW rate through the DCV so as to control ?oW rate through the pilot valve and to obtain desired pressure at the monitored con sumer, regardless of altering ?oW rate through the PRV. Where the ?oW parameter is ?oW rate, the method com prises the additional steps of: US 7,201,180 B2 5 (iv) measuring the ?oW rate adjacent the PRV and trans mitting a ?oW rate signal to the controller; (V) converting the ?oW rate signal into a pressure signal representative of the pressure at the monitored con sumer, based on conversion calculations; (vi) measuring the local pressure at an outlet line of the DCV and generating a corresponding local pressure signal; (vii) comparing the local pressure signal and the pressure signal and generating a corresponding control signal (viii) returning to step (iii). It is advantageous that the Water supply system be ?tted With a bypass gate overriding the DCV such that at the event of malfunction of the system, the bypass opens to thereby provide outlet pressure Pomat an outlet of the PRV corre sponding With the nominal output pressure set at the pilot valve. The invention is also concerned With a Water supply system Which is capable of handling also signi?cantly loW ?oW rates thus avoiding so-called “hunting”, namely a situation at Which a typical Water supply system cannot stabiliZe its pressure parameters at loW ?oW rates. Accordingly, there is provided a Water supply system comprising a line connected to at least one consumer, a pressure regulation system comprising a high ?oW rate path and a parallely installed bypassing loW ?oW rate path; said high ?oW rate path comprising a high ?oW pressure regu lating valve (HFPRV) having a high nominal ?oW output and associated With a pilot valve preset to a ?rst nominal output pressure; and a pressure control system comprising a controller, a differential control valve (DCV), a pickup unit for measuring ?oW rate through the system; said loW ?oW rate path comprising a loW ?oW pressure reducing valve (LFPRV) having a loW ?oW nominal output and associated With a pilot valve preset to a second nominal output pres sure; Wherein said pickup unit emits a ?oW parameter signal to the controller Which generates a responsive control signal to activate an actuator of the DCV to thereby govern the ?oW rate through the DCV; Whereby When the ?oW parameter signal declines beloW a preset value, said DCV closes entailing in closing of the HFPRV and simulations opening of the LFPRV; and When the ?oW parameter exceeds said preset value the LFPRV closes and the HFPRV opens. Where the ?oW parameter is ?oW rate measured before or after the HFPRV, but before or after the branching of the loW ?oW control circuit, respectively, the DCV comprises: a housing ?tted With a static inlet and a dynamic inlet both being in ?oW communication With an outlet of the pilot valve preset to a high nominal output pressure, and a valve outlet being in ?oW communication to an outlet of the HFPRV; a control chamber sealingly partitioned by a ?exible diaphragm dividing the chamber into an a ?rst chamber communicating With the static inlet, and a second chamber communicating With the valve outlet and With a controlled ?oW passage serving to e?fect communication betWeen said second chamber and said dynamic inlet; a spring loaded obturating member articulated With the diaphragm and being axially displaceable Within the con trolled ?oW passage responsive to differential pressure dis placement of the ?exible diaphragm; and an actuator controlled by the controller, for axially dis placing the obturating member thereby to govern ?oW through the controlled ?oW passage responsive to di?eren tial pressure over the ?exible diaphragm and an opposing force imparted by the spring and the actuator. 20 25 30 35 40 45 50 55 60 65 6 BRIEF DESCRIPTION OF THE DRAWINGS In order to understand the invention and to see hoW it may be carried out in practice, some preferred embodiments Will noW be described, by Way of non-limiting example only, With reference to the accompanying draWings, in Which: FIG. 1 is a schematic representation of a Water supply system in accordance With an embodiment of the present invention; FIG. 2 is a schematic representation shoWing in someWhat more detail a control system of the Water supply system illustrated in FIG. 1; FIGS. 3A to 3C illustrate a differential control valve used in a ?oW control system in accordance With the present invention, Wherein: FIG. 3A illustrates the valve in a closed position; FIG. 3B illustrates the valve in a partially open position; and FIG. 3C illustrates the valve in a completely open posi tion; FIG. 4 illustrates an embodiment of a differential control valve in accordance With the present invention, the valve in its closed position; FIG. 5 is a schematic representation of a Water supply system in accordance With a different embodiment of the present invention; FIG. 6 is a schematic representation of the control system used in a Water supply system in accordance With the embodiment of FIG. 5; and FIG. 7 is a schematic representation of a control system for preventing hunting, in association With a Water supply system in accordance With the present invention. DETAILED DESCRIPTION OF THE INVENTION Attention is ?rst directed to FIG. 1 of the draWings, illustrating by Way of a schematic representation, a Water supply system in accordance With the present invention Which represents a branching portion of a typical municipal Water supplying system. The system comprises a netWork of pipes originating at a source of water, eg lake, Water reservoir, Well, etc. (not shoWn). Water may be propelled through the pipe netWork 20 by means of one or more pumping units 24 or other suitable means, as knoWn per se, e.g. gravity, etc. The Water ?oWing through the pipe netWork is pumped at essentially high pressure until it reaches to branching sections at each neighborhood or block Where a pressure reducing valve (PRV) 26 is ?tted for reducing pressure of the Water as Will become apparent hereinafter With more detail also to the control system generally des ignated 30 illustrated in someWhat more detail in FIG. 2. It is a concern of the Water supplying company (typically municipality, etc.) that all the consumers along a supply line receive at least a certain nominal pressure to thereby ensure proper operation and functioning of various pressure acti vated equipment, eg sprinklers, valve and ?ltering means, etc. as Well as to enjoy reasonable pressure and domestic Water facilities, eg tap shoWers, etc. On the other hand, it is a signi?cant concern of the Water supplying company that the pressure at the consumers does not exceed a certain nominal pressure so as not to be liable to damages caused by over pressure, e.g. bursting of pipes (typically occurring in solar collectors), signi?cant leaks, etc. A main pipeline 32 extending from PRV 26 branches off into pipes 34 leading to a netWork of consumers comprising several houses 36 and a municipal or domestic faucet 38 and US 7,201,180 B2 7 a signi?cantly remote consumer designated 40 positioned on top of a hill and connected to the main pipe 32 by pipe line 42. Under normal conditions, the pressure monitored at this latter consumer 40 is loWest, oWing to the long pipeline reaching thereto (friction and head loss through coupling and branching elements) and oWing to head loss in vieW of altitude differences. The consumer 40 is referred to as a monitored consumer (at times also referred to as a critical consumer). Further discussion is directed to the control system gen erally designated 30, With further reference being made also to FIG. 2. The PRV 26 comprises an inlet 50 coupled to an upstream main pipe section 20 and an outlet 52 coupled to a doWnstream main pipe line 32. A ?oW passage 56 is formed Within the PRV betWeen the inlet 50 and outlet 52 sealable by a valve member 58 sealingly engageable over a valve seating 62. The PRV further comprises a control chamber 64 formed With a ?exible diaphragm 66 axially supporting the valve member 58. The arrangement is such that pressuriZing the pressure chamber 64 causes diaphragm 66 to deform doWnWardly, entailing corresponding displacement of valve member 58 toWards valve seating 62, thus restricting or completely closing the ?oW passage 56. DepressuriZing pressure cham ber 64 results in axial displacement of valve member 58 to disengage from the valve seating 62 so as to reopen the ?oW passage 62. The pressure Within the control chamber 64 is governed by the amount of Water introduced or drained from the chamber 64. A control bypass line 72 is connected to the PRV upstream at 74 being in ?oW communication With an inlet pressure PinWhiCh corresponds With the upstream pres sure. Fitted on the control bypass line 72 there is a ?lter unit 78 and a ?oW restriction ori?ce 80 having a constant ?oW rate. Extending into the control chamber 64 is a pressure control line 82. Further ?tted on the control bypass line 72 there is a pilot valve 86 having a nominal outlet pressure, manually adjustable by screW-type governor 88. Extending doWnstream of pilot valve 86 and connected to pipe section 87 there is a differential control valve (DCV) 90 having an outlet coupled to outlet 52 of the PRV 26. The DCV comprises an electrically operated actuator 92. The construction of DCV 90 Will be explained in more detail With reference to FIGS. 3 and 5. The DCV is coupled to the PRV at 96 by pipe section 94 being in ?oW communication With a doWnstream portion of main pipe 32 at pressure Pom. As can be seen in FIG. 1, a pressure pickup unit 100 is ?tted at the site of the monitored consumer 40, said pickup unit 100 comprising a transmitter for transmitting a pressure signal PS receivable by a controller 108. It is appreciated that rather than transmitting the pressure signal PS by Wireless communication means, this may be carried out by other means, eg Wired telecommunications (e.g. telephone lines, electric lines, optical signaling etc.). The control loop closes upon issuing a control signal CS Which is responsive to the pressure signal PS and Which activates the actuator 92 of the DCV, as Will be explained hereinafter in more detail. A Water supply system Which is not supported by a closed-loop control system Would normally have several pressure drops during the day, as a result of increased consumption typically measured at the morning hours (be tWeen about 6 and 9 am.) and again in the evening hours (betWeen about 7 and 9 p.m.). HoWever, these peaks are subject to changes, eg at Weekends, upon setting of DST, season changes, major events such as an important sports match, etc. Each time such a pressure drop is measured, the 5 20 25 30 35 40 45 50 55 60 65 8 monitored consumer 40 Will experience a rather signi?cant drop in pressure Which may have in?uence on functioning of some household equipment or even e?ect quality of life. On the other hand, in order to compensate for loss of pressure during critical hours, the system may be programmed such as to avoid pressure drop beloW a predetermined minimum nominal pressure at said monitored consumer. The outcome of such an arrangement is that at the so-called dead hours of the day, i.e., those hours Which Water consumption is kept to a minimum (eg after midnight and before daWn) consump tion is very loW and thus minor leaks at the piping, eg at connections and couplings, eg 109 in FIG. 1, or leaks in domestic or public taps, e.g. faucet 38 Will become signi? cant leaks. The Water supply system in accordance With the present invention, as illustrated by one example in FIG. 1, over comes this problem by continuously monitoring the pressure at the monitored consumer 40 Where the minimal nominal pressure is determined. Apressure signal corresponding With the pressure measured at the pressure pickup unit 100 is transmitted and picked up by aerial 113 of the controller 108. Responsive to the pressure signal PS, the controller gener ates a control signal CS to the actuator 92 of the DCV 90 to thereby open or close a ?oW path through the DCV 90 such that the PRV 26 is continuously adjusted to provide the desired pressure at the monitored consumer 40, regardless of altering ?oW rate oWing to changes of consumption. The controller 108 is preprogrammed or programmable so as to control the actuator 92 Within preselected ranges of operation so as to not exhaust poWer source (typically batteries) and to reduce Ware of the system occurring by excessive use. Accordingly, it is advantageous that the controller 108 be programmed so as to generate a control signal CS corresponding With a range of pressure signals PS so as to respond only to signi?cant pressure changes for example, a control signal CS Would be generated by the controller 108 only When the pressure signal departs from a certain range of value. Each time a control signal CS is emitted by controller 108, the actuator 92 of DCV 90 changes a ?oW passage in the DCV to thereby control the amount of Water ?oWing through pipe section 94, ie the extent to Which the pressure chamber 64 of PRV 26 is pressurized, eventually controlling the outlet pressure Pout of PRV 26. Further attention is noW directed to FIGS. 3A to 3C of the draWings concerned With a particular design of the differ ential control valve (DCV) 90 Which is a needle-type valve. The differential control valve comprises a housing 132 having a static inlet port 136 (Which in the con?guration of the control system illustrated in FIG. 2 is coupled to pipe section 87) and a dynamic inlet 134 (Which in the con?gu ration of a control system of FIG. 2 is also coupled to pipe section 87). Housing 132 is further formed With a valve outlet 140 (Which in the con?guration of the control system of FIG. 2 is coupled to pipe section 94 extending to the outlet port of PRV 26). Formed Within the DCV 90 there is a control chamber 144 sealingly partitioned by a ?exible diaphragm 146 Which divides the control chamber into an upper, ?rst chamber 148 being in ?oW communication With the static inlet 134, and a loWer, second chamber 150 being in ?oW communication With the outlet port 140. A ?oW passage 154 is formed With a sealing surface 156. The ?oW passage 154 communicates betWeen the dynamic inlet 134 and the second chamber 150, and in fact serves to effect communication betWeen the dynamic inlet 136 and the outlet 140. An obturating member 160 is articulated at 162 US 7,201,180 B2 to diaphragm 146 and comprises a tapering sealing portion 164 corresponding With the tapering sealing seat 156 (best seen in FIG. 3C). An O-ring 166 is provided for complete sealing. The obturating member 160 is axially displaceable Within the How passage betWeen a completely closed position and open positions in Which ?oW communication is effected betWeen the dynamic inlet 134 and the outlet 140. The obturating member 160 is normally biased toWards sealing engagement (closing) of the How passage 154 by means of an actuating mechanism 169 comprising a coiled spring member 170 bearing at one end against a support plate 172 ?tted at an end of the obturating member 160 and at its opposed end against an axially displaceable plate member 174 ?tted on a threaded rod 176 supported by bearing 178 and rotatable by means of actuator 92. The arrangement is such that the rotation of rod 176 entails axial displacement of plate member 174 to thereby increase or decrease axial force of spring 174, resulting in axial displacement of support plate 172 and respectively of obturating member 160 toWards opening or closing ?oW passage 154. It is hoWever appreciated that both inlet ports, namely static inlet 136 and dynamic inlet 134 are coupled to the same Water supply line and are thus equally pressured. Accordingly, the ?rst chamber 148 and the second chamber 150 are equally pressured resulting in that the diaphragm 156 is in a neutral position apart from axial pressure applied by the actuating mechanism 169. Pressure Within the second chamber 150 With the force applied by spring 170 converted into pressure, is essentially equal to the pressure in the ?rst chamber 148. The outcome of this arrangement is that the dynamic pressure is differentiated and the actual opening of the How path is governed by the axial pressure applied by the actuating mechanism 169, namely by the force of spring 170 and the axial displacement imparted by the actuator 92. Whoever, it should be appreciated that the obturating member 160 may be axially displaced by means other than the actuating mechanism 169, eg by a hydraulic actuating mechanism., etc. In the position of FIG. 3A, the DCV 90 is in its so called closed position Wherein sealing portion 164 of the obturating member 160 sealingly engages seat 156 to effectively close the How passage 154. In FIG. 3B, the DCV 90 is illustrated in a partially opened position Wherein the How passage 154 is opened to some extent to effect communication betWeen the dynamic inlet 134 and the outlet 140, via the second chamber 150. It is appreciated that the corresponding taper ing surfaces 156 and 164 give rise to a sufficiently Wide ?oW passage Which is less susceptible to blockage by sand, dirt, etc. In the position of FIG. 3C, the DCV 90 is illustrated in a completely open position Wherein the plate member 174 is completely retracted and essentially no force is applied by spring 170 to thereby e?fect maximal ?oW betWeen the dynamic inlet 134 and the outlet 140. Further attention is directed to FIG. 4 of the draWings Which illustrates a DCV in accordance With an embodiment of the present invention generally designated 190 Which is essentially similar in principle to the DCV 90 illustrated in FIGS. 3Ai3C, the main difference residing in the construc tion of the inlet ports. As seen in FIG. 4, the housing 194 comprises a main inlet 196 splitting into a dynamic inlet 198 and a static inlet 200 communicating With the main inlet 196 via duct 204 integral With the housing 194. Other compo nents and construction of the DCV 190 are similar to those disclosed in connection With the DCV 90 illustrated in FIGS. 3Ai3C and the rear is directed to the description referring to these ?gures. 20 25 30 35 40 45 50 55 60 65 10 Further attention is noW directed to FIGS. 5 and 6 illustrating a Water supply system in accordance With an embodiment of the present invention. The present embodi ment differs from the previous embodiment illustrated With reference to FIGS. 1 and 2, in particular as far as concerned With the control system generally designated 220. Accord ingly, elements in the embodiment of FIGS. 5 and 6 Which are similar With those of the embodiment depicted in FIGS. 1 and 2 are designated same reference numbers With a prime () indication. In the present example Water is provided to a suburb of a toWn supplying Water to a plurality of houses 225, some industrial facilities 227 and public facilities 229 eg an office building and a skyscraper 230 constituting the so called monitored consumer Wherein the pressure measured is loW est. Unlike in the embodiment of FIG. 1, a How meter 240 is ?tted on a supply line 242 extending from the PRV 26 for measuring a How parameter Which in the present case is a How rate signal FRS Which signal is then transferred to controller 250. The How rate signal is converted at the controller 250 into a corresponding pressure signal repre sentative of the pres sure residing at the monitored consumer 230. This is obtained by conversion calculations Which based on experience and measurements convert a How rate signal into a pressure signal. Responsive to the FRS (and to the pressure signal PS corresponding thereto) a control signal CS is generated at the controller 250 Which control signal CS is then directed to actuator 92 of a DCV 90 to thereby activate the actuating mechanism of the DCV 90 as explained hereinbefore With reference to FIGS. 3Ai3C. In addition, a pressure sensor 258 is ?tted on line section 94 extending betWeen an outlet 140 of the DCV 90 and the outlet 52 of the PRV 26. The pressure sensed by pressure meter 258 transmitting a general local pressure signal PS Which is compared With the converted pressure signal obtained by the How rate signal FRS so as to close the control loop and thereby provide a more accurate control loop. The arrangement in accordance With the embodiment of FIG. 5 is such that upon increase of How rate sensed by the How meter 240, a corresponding ?oW rate signal FRS is transmitted to controller 250 Whereby a corresponding pres sure signal is obtained, in response to Which a control signal CS is generated by controller 250 so as to actuate the actuator 92 of the DCV 90 to thereby drain the pressure chamber of the PRV 26 to thereby increase ?oW through the PRV and provide the increased demand, e. g. in peak hours as explained hereinabove. HoWever, When the How rate sensed at the How meter 240 decreases, a corresponding control signal CS is transmitted by controller 250 to the actuator 92 of DCV 90 to thereby close the How passage thereof Whereby the pressure cham ber of the PRV 26 is pressured to thereby e?fect restriction of the How passage of the PRV 26. The embodiment of FIG. 6 illustrates a control system generally designated 260 Which comprises the same ele ments as in the control system 30 of FIG. 2 and thus like elements are designated With same reference numbers dis tinguished by a double prime indication. The control system 260 of FIG. 6 comprises an additional bypass gate 264 overriding the DCV 90 With an electrically operated gate 268, typically being a solenoid connected by a control line 270 to the controller 108. The arrangement is such that When the system senses a faulty position eg a broken spring of the DCV or an error in the controller 108, a capacitor 274 ?tted in the controller US 7,201,180 B2 11 108 is discharged to activate the solenoid 268, whereby bypass gate 264 opens so as to override the DCV 90. Upon opening of the override gate 264 the DCV 90 becomes inactive Whereby the pilot valve 86 is directly connected to outlet 96 of PRV 26. It is obvious that a bypass gate 264 as illustrated in FIG. 6 may as Well be applied on to a control system of the type disclosed With reference to FIG. 5. Furthermore, it is appre ciated that rather than activating solenoid 268 by discharg ing capacitor 274, an override control signal ORCS may be generated by the controller 108 each time some sort of faulty state is sensed. For example, in case of a communi cation problem Where any of the signals is not received or transmitted by the controller, a poWer failure, a mechanical problem concerned With the DCV (e.g. breakage of spring), softWare problems, etc. Even more so, rather then a solenoid activated gate, other means may be utiliZed for opening the gate, such as, for example, hydraulics or pneumatics. Turning noW to FIG. 7, there is illustrated a control system in accordance With a variation of the invention, generally designated 300. In the embodiment of FIG. 7, elements Which correspond With elements referred to in FIG. 2 are given same reference numbers shifted by 200. The control system 300 is in particular suited for handling situations referred to in the art as hunting Where the How through supply line 332 is signi?cantly loW and Where the PRV 326 is not capable of providing stabiliZed outlet pres sure. This occurs in particular since the PRV 326 is designed for handling high ?oW rates and Where insigni?cant dis placement of the valve member 358 With respect to the valve seat 62 , renders the device unstable. This situation is overcome by providing a control system 300 as illustrated in FIG. 7 comprising a high ?oW control circuit 319 and a loW ?oW control circuit 321. High ?oW control circuit 319 comprises a high ?oW pressure regulating valve HFPRV 326 ?tted With a control system similar to that disclosed in connection With FIG. 2, i.e. comprising a ?lter unit 378, a How restriction ori?ce 380, a pressure control line 382, a pilot valve 386 and a DCV 390. Controller 408 is provided for governing actuator 392 of DCV 390 and further receives a How rate signal FR sensed by a How meter 325 ?tted for measuring the total ?oW through the system. The How meter 325 may be ?tted either before or after the HFPRV 326, but before or after the branching of the loW ?oW control circuit 321, respectively. The loW ?oW pressure control circuit LFPRV designated 321 is in fact a pipe system overriding the high ?oW pressure regulating valve HFPRV 326 by a tube section 327 extend ing from an upstream inlet pipe 320 and an outlet pipe section 329 connected doWnstream to main supply line 332. A loW ?oW pressure regulating valve LFPRV 331 is ?tted along the bypass ?tted With the loW pressure control circuit 321 comprising similar elements, namely a ?ltering unit 333, a How restriction ori?ce 335 and a pilot valve 337 connected doWnstream of the LFPRV 331 at 339. Extending betWeen the How restriction ori?ce 335 and the pilot valve 337 is a pressure control line 341 connected to the pressure chamber 347 of the LFPRV 331, similar to the arrangement of the high ?oW pressure control circuit 319 and to the control system generally designated 30 of FIG. 2. The arrangement in accordance With the embodiment of FIG. 7 is such that the How rate is continuously monitored by How meter 325 issuing a How rate signal PR to the controller 408. Upon detecting that the How rate has dropped beloW a minimal threshold, the controller 408 generates a control signal CS to the actuator 392 of the DCV 390 to thereby compress the coiled spring of the DCV thereby 20 25 30 35 40 45 50 55 60 65 12 closing ?oW through the DCV 390. As a result, Water no longer ?oWs through pilot valve 386 Whereby the control chamber 364 of HFPRV 326 is highly pressured to thereby close the How passage of the HFPRV 326 by valve member 358. As already mentioned, the How meter 335 may be positioned at any location suitable for measuring the total ?oW through the system. As a result, pressure drops at the outlet 339 of LFPRV 331, beloW the preset pressure at the pilot valve 337, Whereby the How passage therethrough opens to facilitate Water ?oW through the bypass at loW ?oW rate. The control system 300 returns to its high ?oW rate circuit, When the How meter 325 generates a How rate signal corresponding With a high ?oW rate signal (preceding a predetermined threshold) to the controller 408 Which in turn generates a control signal to actuator 392 of DCV 390 to thereby open its ?oW passage, resulting in opening of the HFPRV 326 and simultaneously closing the LFPRV 331. The invention claimed is: 1. A Water supply system comprising a supply line and a netWork of consumers, one of Which being a monitored consumer Who receives the least amount of pressure, a pressure regulation system comprising a pressure reducing valve (PRV) associated With a pilot valve preset to a nominal output pressure; and a pressure control system comprising a differential control valve (DCV) connected in series to said pilot valve; a pickup unit for measuring a How parameter indicative of the pressure at the monitored consumer and emitting a pressure signal to a controller; said controller generating a control signal responsive to the pressure signal to activate an actuator of the DCV thereby governing the How rate through the DCV, so as to obtain desired pressure at the monitored consumer, regardless of altering ?oW rate through the PRV. 2. A Wa

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