GB2424966A - Method and apparatus for controlling fluid flow. - Google Patents

Abstract

A method/ apparatus for controlling fluid flow in a pipe network. The method comprises steps of: measuring fluid pressure and flow rate at a location in the pipe network, whereby a flow meter is disposed down stream of a fluid pressure measuring means; calculating a hydraulic impedance value defined by pressure : flow rate (ratio); comparing the calculated impedance value with a pre-determined impedance value; and adjusting fluid flow in the pipe network in order to control the hydraulic impedance towards the pre-determined impedance value. Alternatively there may be a pressure sensing means disposed either side of the flow meter to account for fluid flow in both directions. Preferably the flow meter is of the types selected from a venture tube, orifice plate, a flow probe, a magnetic flow meter and/or an ultrasonic flow meter. Preferably the pipe network is for potable water.

Description

METHOD AND APPARATUS FOR MONITORING FLUID FLOW

The invention relates to methods and apparatus for monitoring and controlling fluid flow through a fluid distribution network such as a potable water supply network and to a method for designing or improving a fluid distribution network.

Background of the Invention

Water supply and distribution systems for delivering potable water to the end user typically include a pumped source of water, a reservoir and a sophisticated arrangement of intersecting pipes. The fluid is introduced under positive pressure into the closed pipe system to deliver water to the customer and to maintain adequate levels in any connected reservoir (or storage tank). The system typically has flow and pressure measurement devices installed at the input/output points of the pipe system whose measured values are transmitted back to a SCADA (Supervisory Control and Data Acquisition) system to allow control and monitoring of the positive-pressure potable water source inputs.

In recent years, many water utilities as part of their active leakage detection and monitoring strategies, have created district metered areas (DMAs). DMAs are boxed-in' areas of the distribution network with one or more supply points each : *s containing a flow and pressure measuring device. The measured values of these devices are transmitted back to a central computer system for data storage and S...

historical analysis of totalised flows and perceived leakage levels. The DMAs have S...

*..: added to the complexity of the supply and distribution system leading to a decrease * in the network's responsiveness and creating an increase in its thirst' for more fluid * throughout the diurnal cycle; i.e. increased distribution input (DI) levels and minimum night flows (MNF).

Flow control devices installed on the network may be either gravitypressure based or positive-pressure based. Gravity-pressure based flow control devices rely on the force of gravity for fluid flow. These devices may include a reservoir that interfaces with the supply and distribution network. The reservoir may be filled by a dedicated water supply source and then allowed to gravitate directly into the distribution system. The level of the reservoir is monitored and additional water is supplied as required to maintain an adequate head of pressure into the distribution network. Customers residing on elevated ground levels andlor upper floors of tall buildings are the first to suffer from low pressures during peak flow periods.

In certain situations the amount of pressure provided by gravity-pressure based flow control devices may be insufficient. In other situations, greater force and precision of flow rates are required. In these situations positive-pressure based flow control devices are necessary. Positive-pressure based flow control devices exert a mechanical force on the fluid to establish fluid flow. One commonly used positive- pressure based flow control device is a pump that when operated forces fluid through the pipe system increasing the input pressures. On initial start-up, these devices create a transient pressure wave that travels through the pipe system setting up numerous harmonic reflections when it comes into contact with any solid object blocking or restricting its free passage. This sequence of events, coupled with end user activity (i.e. rapid opening and closing of taps, valves, etc), is instrumental in setting up transient unsteady and oscillatory flows throughout the pipe system that, in turn, leads to higher than necessary flows and pressures being employed to maintain satisfactory customer service levels.

* :1:. Another type of positive-pressure based flow control device is the infusion' valve.

s 20 Generally, this is a boundary valve between two different pipe systems that allows potable water to flow from the higher-pressure system to the lower-pressure system S... . when opened, the flow rate being proportional to the amount the valve is open and S..

* the pressure differential across the valve. In most cases, the lowerpressure system : . . rarely attains the higher-pressure system's operating pressure and therefore the flow *..

* : . : 25 is proportional to the pressure differential. This leads to the higher-pressure system having to be pumped at a higher rate to overcome any losses through such flow control devices. Pressure reducing valves (PRV) operate in a similar manner, closing as the downstream pressure attains a predetermined set limit.

During the operation of water supply and distribution systems, events may occur that interfere with the proper administration of the fluid to the customer and/or reservoir, such as a restriction caused by a closed or partially closed valve. It is desirable to detect these conditions as soon as possible so that they can be remedied. A commonly used technique for detecting such conditions and for evaluating the operating status of the pipe network is to monitor the pressure of the downstream portion of the fluid delivery system. The downstream portion of the delivery system is typically thought of as the portion between a fluid supply, such as a pump or a higher-pressure source main, and supply or distribution system. An increase in the downstream pressure may be caused by a restriction. Flow control devices monitor the downstream pressure of the supply routes by altering the flow rates through the bulk water supply system and measuring the corresponding change in downstream pressure andlor reservoir levels. The changes in downstream pressures and/or reservoir levels are used by an operator to judge whether a fluid input increase or decrease is required.

However, the existing monitoring systems are far from ideal and do not provide a complete picture of the behaviour of potable water in distribution networks and the manner in which changes to the network and the partitioning of the network in DMAs can affect fluid flow through the network.

One reason why many of the systems and methods for monitoring and controlling * : : the flow of water in a potable water distribution system are not of optimal * 20 efficiency is that they are based on an assumption that the water in the network is incompressible. Whereas water per se is not compressible, potable water is a * highly complex fluid comprising water and gas molecules in solution and a number *** * of hydraulic text books suggest that ordinary water contains 2-4% air by volume - : * see' Fluid Principles', Alan Vardy ISBN: 0-07-707205-7}. The air present in the * * 25 water, together with trapped air in the network and unsteady oscillatory flow profiles found in a typical water distribution network, means that in reality the potable water behaves as though it is does have a degree of compressibility.

A further problem is that the methods currently used for monitoring fluid flow through a potable water distribution network can create a misleading impression as to the amount of water lost through leakage from the system, with the result that much unnecessary effort and expenditure may be incurred in an attempt to resolve problems that are more to do with network design and configuration than actual leakage.

Summary of the Invention

The invention provides methods and apparatus for overcoming or alleviating the problems set out above. More particularly, the invention provides a method and apparatus for measuring the performance parameters of a positive-pressure water supply and distribution system and using the measured parameters for connecting and controlling the fluid flow through the system.

The present inventor has recognised that there is an analogy between the behaviour of water distribution networks and the laws governing the behaviour of electrical circuits containing resistors and capacitors and that the concepts of resistance (impedance) and capacitance, and related parameters are useful in analysing and controlling the behaviour of fluid distribution networks.

Although the analogy between the laws of electrical resistance and capacitance and the behaviour of fluids has previously been recognised (see for example Mechanics of Fluids', A.C.Walshaw & D.A.Jobson ISBN: 0582-44495-0 and Principles of Measurement Systems', John P. Bentley ISBN: 0-13-043028-5), such concepts * have not been applied hitherto (so far as the inventor is aware) to the behaviour of potable water distribution systems or similar fluid networks. S...

By analogy with Ohm's law and the laws governing capacitance in electrical : circuits, the following relationships can be derived in regard to the behaviour of fluids.

Impedance = (Absolute Pressure)! (Vol. Flow Rate) = Hydraulic (Fluidic) Impedance {Z] Capacitance = Volume! (Absolute Pressure) = Hydraulic (Fluidic) Capacitance [C] Inertance = (Absolute Pressure)! {d (flow rate) !dt} = Fluidic Inertance [L] Response = Hydraulic (Fluidic) Capacitance x Fluidic Impedance Fluidic Time Constant [t] Note: Absolute (i.e. gauge + atmospheric) Pressure is measured in Pascals.

The foregoing parameters, which are explained in more detail below, can be used in the analysis and monitoring of distribution network of pipes having a positive- pressure based system for inducing fluid flow and a monitoring system for measuring the downstream hydraulic impedance (resistance) of the fluid system based on changes in pressure and flow rate. From the downstream hydraulic impedance values and pressure measurements, the effective fluidic capacitance and inertance can be deduced and their effects subsequently controlled.

Accordingly, in a first aspect, the invention provides a method for monitoring and controlling fluid flow within a pipe network; the method comprising (i) measuring the fluid pressure and flow rate at a given location in the network; (ii) calculating a hydraulic impedance value at the given location using the equation: pressure/volume flow rate = hydraulic impedance (iii) comparing the hydraulic impedance value with a pre-determined required * * value, and (iv) adjusting fluid flow and fluid pressure within the network to bring the hydraulic impedance value towards the pre-determined required value; wherein the measurement of the flow rate is made using a flow meter positioned S...

*. down stream with respect to a means for measuring the fluid pressure at the given location. * S * . * *

* . Particular and preferred aspects and embodiments of the invention are as set out in the claims appended hereto.

In a very simple network, it may be necessary only to determine the hydraulic impedance at a single location on the network. More usually, however, the hydraulic impedance will be determined at a plurality of locations on the network.

The pressure measuring means and the flow meter at each location are typically linked to a central processor (e.g. computer) which is programmed to carry out calculations of the hydraulic impedance at each location. The central processor can in turn be linked to actuators for opening and controlling valves to control fluid flow around the network. In this way, the hydraulic impedance at a given location can be adjusted towards a pre-defined required value by opening or closing one or more control valves. Since each network will have different response characteristics and ground levels the pre-defined impedance values will be determined by field trial, and to a degree, experimentation, to determine the optimal performance parameters for all prevailing conditions and throughout the diurnal cycle.

The means for measuring fluid pressure can take the form of piezoresistive sensing elements, piezoelectric sensing elements, capacitive pressure sensors, etc. A variety of different flow meters may be used to measure the flow rate and such flow meters can be positioned inside a pipe at the given location or outside the pipe.

Examples of common types of flow meters include Venturi tube flow meters, orifice plate flow meters, flow probes, magnetic flow meters and ultrasonic flow meters. Flow meters, such as ultrasonic and magnetic flow meters, which do not present an obstruction (or disturbance) to the flow of fluid through the pipe, are preferred. * a. * * a

In regions of the pipe network where fluid flow is uni-directional, only a single a...

fluid pressure measuring means may be required at a given location, together with a a...

single flow meter. However, where fluid flow is bi-directional, a pair of fluid * * pressure measuring means may be provided, one either side of the flow meter. A : * pair of fluid pressure measuring means may also be employed, one either side of a *..* . . . . . flow meter, when the flow meter is one which is located inside a pipe and hence a: 25 offers resistance (disturbance) to the flow of fluid through the pipe.

The invention also provides a network equipped with means for carrying out the method described above.

Accordingly, in another aspect, the invention provides a fluid network comprising one or more pipes and/or pipe elements through which fluid may pass, one or more control elements (e.g. valves) for controlling movement of fluid around the network, and means for measuring in at least one location on the network the hydraulic impedance at the said location, the means for measuring fluid impedance comprising a fluid pressure measuring device and a flow meter at the said location, the flow meter being positioned downstream with respect to the fluid pressure measuring device, the fluid pressure measuring device and the flow meter being linked to a processor programmed to calculate the hydraulic impedance at the given location from measurements of the fluid pressure and fluid flow by means of the equation: pressure volume flow rate = hydraulic impedance and one or more actuators for actuating one or more control elements to alter the fluid flow within the network to change the fluid impedance at the said location.

Examples of control elements include valves such as actuated needle, gate, butterfly, pressure reducing (PRy), pressure sustaining (PSV) valves, etc. The invention also provides apparatus for use in the foregoing methods and networks of the invention. Thus, in a further aspect, the invention provides apparatus for use in a method of monitoring and controlling fluid flow within a pipe network as herein before defined, the apparatus comprising means for measuring in :. : : at least one location on the network the hydraulic impedance at the said location, I...

* .. 20 the means for measuring fluid impedance comprising a fluid pressure measuring device and an ultrasonic flow meter at the said location, wherein the fluid pressure * measuring device and the flow meter are linked to a processor programmed to S. calculate the hydraulic impedance at the given location from measurements of the : * : fluid pressure and fluid flow by means of the equation: *: * 25 pressure volume flow rate = hydraulic impedance the processor being connected to (or connectable to) one or more actuators for actuating one or more control elements to alter the fluid flow within the network to change the fluid impedance at the said location.

The apparatus comprises a central processor together with communication links connecting the central processor to the means for measuring fluid pressure and the flow meter at each location on the network. Communication between the central processor and the flow meter and pressure measuring means may be of the hard wired variety or may be wireless (e.g. radio communication), or a combination of hard wired and wireless. The apparatus may further comprise one or more actuators operatively linked to the central processor, the actuators being configured to actuate one or more control valves or other fluid control means for adjusting fluid flow The parameters of hydraulic resistance or impedance, hydraulic capacitance and the fluidic time constant as defined herein may also be used in the design and modification of fluid distribution networks.

Accordingly, in another aspect, the invention provides a method for modifying a fluid distribution network, the method comprising (i) measuring the fluid pressure and flow rate at one or more locations in an existing portion of the network; (ii) calculating a hydraulic impedance value at each location using the equation: pressure/volume flow rate = hydraulic impedance (iii) calculating from the hydraulic impedance, using the computational process set out in Figure 3, the fluidic capacitance and the fluidic time constant for the existing :.:. portion of the network; S...

* 20 (iv) calculating the effect on flow rate of changing the connectivity of one or more elements in the existing portion of the network from parallel connectivity to series * connectivity or vice versa, wherein the calculation is carried out using the

S

equations: :::. (a) for series to parallel change:- * . 25 { [Q (parallel) - Q (series)] / [Q (series)] } x Flow rate (series) = Change in Flow rate (iNFlow) where Q is the capacitance charge and is equal to C x P where C is the capacitance of a network element and P is the fluid pressure; Flow rate (parallel) = Flow + Flow rate (series) (b) for parallel to series change (and by deduction):- { [Q (parallel) - Q (series)] / [Q (parallel)] } x Flow rate (parallel) = Change in Flow rate (Flow) Flow rate (series) = Flow rate (parallel) - iiFlow and (v) modifying the fluid distribution network so as to reduce or minimise or maintain or increase or maximise any one or more of the impedance, fluidic capacitance and the fluidic time constant to achieve a desired change in flow rate; wherein the measurement of the flow rate is made using a flow meter positioned down stream with respect to a means for measuring the fluid pressure at the given location.

The inventor has found by experimentation that the above calculations provide a very good prediction of the change in fluid flow that can be expected by modifying the capacitance charge (internal energy) levels of a network. The calculations are useful in determining the change in DI and MNF levels for reporting purposes and/or to support any business case for asset investments, and, for determining the change in network storage levels when operating the network as an overnight storage device.

The fluid distribution network can be modified by adjustment of strategically * : . placed control valves to ensure that the reservoir remains connected in series with as much of the distribution network as possible, the distribution network and DMAs are arranged to improve fluid transfer between source input(s) and the reservoir (i.e. **** * low resistance/impedance values), good connectivity between trunk mains and distribution system is maintained at all times (i.e. hydraulic gradient across the : : * network is as flat as possible under all prevailing conditions) by balancing the * * 25 impedance of the supply/trunk mains and adjusting DMA configurations to minimise the number of dead-end (water accumulator - high capacitance value) networks and adjusting the source inputs to prevent over subscription of fluid. This method of control will minimise the fluid storage properties of the network leading to minimal fluid flow throughout the diurnal cycle.

The converse of this is, of course, to use the pipe network as a storage device by increasing the capacitance value of the network by closing strategically positioned actuated valves. The latter may prove useful during the peak demand periods (i.e. summer) to increase the storage levels of the network (i.e. numerous parallel water accumulators) over night then switch the network, in a controlled manner, back to a series connected system (i.e. minimal storage). A water company may find this a more cost effective solution than building a new or increased size reservoir to support a supply area.

The invention will now be illustrated by reference to the following specific embodiments illustrated in the accompanying drawings.

Brief Description of the Drawin2s

Figure 1 illustrates a first-order response curve for a unit step in pressure [or capacitance charge (internal energy)].

Figure 2 illustrates various arrangements for taking pressure and flow measurements from which impedance can be calculated.

Figure 3 illustrates the computational process for measuring the hydraulic * *. impedance, fluidic capacitance and fluidic inertance from pressure and flow :::.: measurements. S...

Figure 4 illustrates a fluid control system that automatically controls even * 20 distribution of fluid flows and pressures under all prevailing operating conditions *..

: . * Detailed Description of the Invention * S..

* :* : The flow of water in a network can be likened to the flow of electricity in an electrical circuit and the laws and relationships governing electrical circuit parameters such as resistance and capacitance have a direct analogy in the behaviour of water networks - see for example Mechanics of Fluids', A.C.Walshaw & D.A.Jobson ISBN: 0- 582-44495-0, and Fluid Transients in Systems', E.Benjamin Wylie & Victor L.Streeter ISBN: 0-13-934423-3.

In an electrical circuit, the relationship between voltage (V), resistance (R) and current (I) is given by Ohm's law (V = I x R) and is a linear relationship.

By analogy, in a fluid network, the resistance to the flow of fluid through an element of the network (which can be defined as the hydraulic impedance (Z)) can be likened to the resistance in an electrical circuit and the relationship between fluid pressure (P) (analogous to voltage), flow rate (F) (analogous to current) and hydraulic impedance can be expressed as P = F x Z, and is a quadratic relationship.

The laws governing the calculation of resistances in series and in parallel in electrical circuits also find analogy in calculation of hydraulic impedances in a fluid network. Thus, in an electrical circuit, the total resistance of two resistors in series and in parallel is given by the equations: Rtotai = R1 + R2 resistors in series liRtotai = hR1 + hR2 resistors in parallel Analogously, the total hydraulic impedances for two network elements arranged in series and in parallel can be given by the expressions: Ztotai = Z1 + Z2 network elements in series liZtotai = liZ1 + liZ2 network elements in parallel * : :* The equations governing the behaviour of capacitors also have analogy in fluid I.IS * *. networks. In an electrical network, a capacitor stores charge. In a fluid network, the pipes, reservoirs and other elements of the network store energised fluid and can be regarded as being analogous to capacitors. However, in a fluid system, capacitance 1.

is distributed throughout the pipe network but for analytical purposes can be lumped' together. S. I

In an electrical circuit, the amount of charge stored in a capacitor is given by the equation Q = C x V where Q is the charge in Coulombs, C is the capacitance in Farads and V is the voltage.

The laws governing the total capacity of capacitors linked in series and in parallel are the inverse of the relationships governing resistance and are given by the equations: Ctotai = C1 + C2 capacitors in parallel l/Ctotai 1/C1 + 1/C2 capacitors in series In a fluid network, by analogy, the "fluidic charge" (Q) (i.e. internal energy) can be expressed as Q C x P where C is the fluidic capacitance and P is the fluid pressure. The total capacitance of network elements arranged in series and in parallel may also be calculated using the equations for capacitors in series and parallel set out above. However, in a hydraulic system, if the fluid is flowing, the capacitance value of the pipe element is 1/C' and is in series with the downstream demand point. If there is no fluid flow the capacitance value of the pipe element is C' and is a parallel coimected component. Therefore, a network with many dead- end pipes suffers from the effects of the capacitance randomly switching between 1/C' and C' values. The invention effectively controls this natural phenomenon in order to minimise the DI and MNF levels.

In electrical circuits, the rate at which a capacitor charges or discharges can be expressed in terms of a time constant (t) which is equal to the resistance (R) multiplied by the capacitance (C) i.e. t = R x C. A large time constant means that a capacitor charges slowly and vice versa.

: .. In a fluid network, a time constant (t) for a given region of the network can be calculated from the equation r = Z x C. The time constant is a useful parameter in $*4 analysing the performance of a fluid network. For example, it can be used to determine the response time of a network and hence determine whether the pipe system is adequate to serve the level of customer demand in the area. It is also * important in the determination of the capacitance value, which is quadratic in nature : and is distributed throughout the pipe network and therefore difficult to measure.

By using the relationship:- Fluidic Capacitance (C) Time Constant (t) / Fluidic Resistance And, as both the Time Constant (t) and Fluidic Resistance can be measured from the flow and pressure measurement elements the Fluidic Capacitance value can be computed throughout the diurnal cycle.

Figure 1 is a first-order response curve illustrating the response of a unit step in pressure [or capacitance charge (internal energy)].

For the Response of a first-order element to a unit step {f (t) = 1 - exp (-tlt)} :- t='r, f(t)= 1 -e1 = 0.63 t=2t, f(t) = 1- e2 = 0.87 t=3t,f(t)= I -e=0.95 t4t, f (t) = 1 - e4 = 0.98 t=5'r, f (t) = 1 - e5 = 0.99 As an example of use of the first-order equation, consider the absolute pressure of a measurement point on a distribution network. Initially the absolute pressure of the point in the early evening is 15 metres (absolute). If it suddenly rises to 30 metres (absolute), then this represents a step change tP of height 15 metres. The corresponding change in measurement is given by EP = 15(1 - e) and the actual pressure P of the transducer at time t is given by: P (t) = 15 + 15(1 - et) Thus at time t = t, P 15 + (15 * 0.63) = 24.45 metres (absolute). By measuring the time taken for P to rise to 24.45 metres (absolute) the time constant r of the element can be found. * . * I*I

A large time constant is indicative of poor connectivity between a supply point and *.II fluid demand point (i.e. DMA). ***

S

Thus, by measuring the time constant and hence determining the responsiveness of * the network to the change in a parameter such as pressure (internal energy), the network designer/operator can deduce whether a network configuration is overloaded and if there is a need to increase the supply capability to a given network (i.e. more input connections, larger pipes, etc) andlor to make the network supplied from a given input configuration smaller (i.e. reduce the demand and capacitance levels). It also helps to assess whether the capacitance value of a measured network will reach an adequate charge level within the window of opportunity (when fluid input levels are greater than demand levels) during each diurnal cycle.

The downstream time constant can be measured at all points of a network wherever there is a flow and pressure measurement in close proximity to each other and using the response curve of figure 1 as described below. For a multiple supplied area (i.e. multi-feed DMA) the overall time constant would be equivalent to the longest (highest value) downstream time constant for that particular area. High value time constants are indicative of high resistance and capacitance downstream elements which may require remedial action should they fall outside the window of opportunity period of the diurnal cycle.

In recent years, many water utility companies have installed numerous flowmeters and pressure measuring devices on their supply and distribution systems. In many cases, these devices are used to measure the totalised daily flows and minimum night flows (MNF) for the configured DMAs, the choice of technology employed being very much based on cost and ease of instalment. Few, if any, have taken into account the effects the differenttechnologies have on the downstream hydraulic * impedance (resistance) or, indeed, the fact that the fluid is highly complex and :.: contains a variable liquid-gas mixture. Although, any technology flow- measuring SS*I S device will provide a reasonable fluid flow measurement it is, however, better to * : * 20 use a technology that places no constriction or disturbance of the fluid flow.

* ** S Ultrasonic and magnetic flow meters use sensors which are clamped to the outside of the pipe, i.e. do not intrude into the pipe, and this makes them particularly useful for multiphase uni and bi-directional flows and not adding to the hydraulic : impedance of the dynamic fluid system. Good quality, reliable and accurate pressure measurement is equally important and needs to be carried out at the correct position on the pipe system in relation to the flowmeter to give an accurate downstream resistance indication. Pressure transducers should be levelled' to enable accurate AOD pressures to be computed. Where other technology devices and configurations are employed their effect on the hydraulic impedance and hence their accuracy should be taken into account when analysing results.

Figure 2 illustrates some typical flow meter and pressure transducer configurations in accordance with the invention.

Figure 2(a) shows a portion of a water supply mains pipe and a branch pipe with control valve. Measurement of fluid impedance at the junction is carried out using a pressure gauge located at the mouth of the branch pipe and a flow meter located downstream on the other side of the valve.

Figure 2(b) illustrates a more complex arrangement in which a PRV (pressure reducing valve) is positioned downstream of the valve, and a second pressure gauge is located downstream of the PRy. The fluidic impedance Z at this location is calculated by pressure/volume flow rate = hydraulic impedance at both locations, one showing the downstream impedance as a result of the PRV and the other showing the impedance of the control valve and PRV configuration.

Figure 2(c) illustrates a straight length of pipe containing a pair of pressure gauges either side of a flow meter. Such an arrangement may be used when flow in the pipe is bi-directional or when the flow meter is one that resides within the pipe (and : hence provides an obstacle to fluid flow). The second or downstream pressure * gauge can be used to calculate any additional impedance introduced by the flow meter. ****

S S...

*:. 20 Figure 2(d) illustrates an arrangement for determining the fluid impedance at a * reduction in the pipe bore. In this arrangement, the pressure gauge is located in the : wider bore portion of the pipe and the flow meter is located so as to measure flow * in the reduced diameter portion.

Pressure and fluid flow data collected over a defined period of time can be used to calculate the hydraulic impedance, fluidic capacitance and fluidic inertance. Figure 3 illustrates the computational process for measuring and calculating these parameters.

The computed values enable the performance efficiency of the fluid transfer through the pipe and network connectivity to be measured and monitored. Any changes to the pipe connectivity (i.e. opening and/or closing of valves, throttling, etc.) will cause the values to change in accordance to standard Ohm's Law rules for series and parallel-connected elements as described above. The most efficient pipe networks are those with minimised values of Z, C, Q (internal energy) and t under all operating conditions.

High values of hydraulic impedance (Z) may indicate restricted supply routes or poor connectivity; thus providing early indications of network connectivity issues requiring remedial action. DMA connectivity to the supply system can be monitored in this way using Ohm's Law to compute an overall impedance value.

Similarly, high values of C and Q indicate inefficient networks containing too many dead-end pipes that are behaving as fluid accumulators. DMA designs can be a major contributor to this effect and monitoring C and Q values provides an early indication of the need for design reviews and remedial work. Similar effects can be observed on multi sourced systems when two or more inputs to a pipe system are activated.

In a network provided with pressure gauges and flow meters at key locations, flow * ** meters and pressure transducers can transmit their measured values instantaneously or at frequent intervals to a central processor or computer which is programmed to S... . . calculate the impedance at each location. The computed hydraulic impedance * . 20 values can be employed to operate control valves to maintain an even and efficient *. distribution of flows and pressures through the fluid network.

: * : * On multi source and bulk supply pipe systems, it is necessary to monitor the downstream hydraulic impedance of each supply route and use these values to set the position of strategically located control valves. To balance the distribution of fluid flows and pressures throughout the fluid supply system under all prevailing operating conditions, the position of each valve is automatically adjusted. Figure 4 illustrates schematically a fluid control system that automatically controls even distribution of fluid flows and pressures under all prevailing operating conditions Without any type of control, i.e. an open pipe system, fluid flow will naturally follow the least line of resistance through the pipe system causing flow and pressure imbalances. Such systems require greater pumping pressures and hence fluid input requirements in order to satisfy customer service levels. (Higher DI and MNF).

Using downstream impedance measurement at M3 and M4, the positions of control valves CVI and CV2 can be automatically adjusted to ensure an even balance of flow and pressure through the fluid supply system under all prevailing operating conditions. This results in lower pumping pressures being required to satisfy the customer service levels and hence reduced fluid requirements. (Lower DI and MNF).

The benefits of the methods and apparatus of the invention are many and include: * Visibility of the essential network design parameters * Visibility of the daily network performance and operating efficiency * Visibility of DMA connectivity issues * Greater understanding of the network fluid transfer characteristics * Automatic computer monitoring of low performing networks * Visibility of the true effects of network valve changes * Early indication of problem areas requiring remedial action : * ** * Improved fluid transfer efficiency : : :.: * Reduced operating costs (energy, process and maintenance) **** * Reduced DI and MNF *...

*..: 20 * Real time automated closed-loop fluid management system * * * Enables fluid supply and distribution systems to be managed more : * effectively S...

* :* * * Invention is applicable to any process industry where positivepressure closed pipe systems are employed for the deployment of fluids and gases.

Eciuivalents It will readily be apparent that numerous modifications and alterations may be made to the specific embodiments of the invention described above without departing from the principles underlying the invention. All such modifications and alterations are intended to be embraced by this application.

Claims (15)

1. A method for monitoring and controlling fluid flow within a pipe network; the method comprising (i) measuring the fluid pressure and flow rate at a given location in the network; (ii) calculating a hydraulic impedance value at the given location using the equation: pressure/volume flow rate = hydraulic impedance (iii) comparing the hydraulic impedance value with a pre-determined required value, and (iv) adjusting fluid flow and fluid pressure within the network to bring the hydraulic impedance value towards the pre-determined required value; wherein the measurement of the flow rate is made using a flow meter positioned down stream with respect to a means for measuring the fluid pressure at the given location.

2. A method according to claim 1 wherein the flow meter and the means for * measuring the fluid pressure at a given location are located within 5 metres :.: of each other (for example within 4 metres or within

3 metres or within 2 * S..

* metres or within 1 metre of each other). S...

* 20 3. A method according to any one of the preceding claims wherein the S..

hydraulic impedance is determined at a plurality of locations on the : * * network. S...

4. A method according to any one of the preceding claims wherein the fluid pressure measuring means and the flow meter at each location are linked to a central processor programmed to carry out a calculation of the hydraulic impedance.

5. A method according to any one of the preceding claims wherein the hydraulic impedance at the or each given location is adjusted towards a pre- defined required value by opening or closing one or more control valves.

6. A method according to any one of the preceding claims wherein the flow rate in at least one given location is measured using an ultrasonic or magnetic flow meter.

7. A method according to any one of the preceding claims wherein a valve is positioned between the means for measuring the fluid pressure and the flow meter.

8. A method according to any one of the preceding claims wherein fluid flow at a given location is bi-directional and a pair of fluid pressure measuring means is provided, one either side of the flow meter.

9. A fluid network comprising one or more pipes and/or pipe elements through which fluid may pass, one or more control elements (e.g. valves) for controlling movement of fluid around the network, and means for measuring in at least one location on the network the hydraulic impedance at the said location, the means for measuring fluid impedance comprising a fluid pressure measuring device and a flow meter at the said location, the flow meter being positioned downstream with respect to the fluid pressure .: measuring device, wherein the fluid pressure measuring device and the flow *: : : :* meter are linked to a processor programmed to calculate the hydraulic * impedance at the given location from measurements of the fluid pressure and fluid flow by means of the equation:

SS

pressure - volume flow rate hydraulic impedance : * . and one or more actuators for actuating one or more control elements to S...

* * alter the fluid flow within the network to change the fluid impedance at the said location.

10. A fluid network according to claim 9 wherein means are provided for measuring the fluid impedance at a plurality of locations on the network.

11. A fluid network according to claim 9 or claim 10 wherein the processor is remote from each location at which the hydraulic impedance is measured.

12. A fluid network according to claim 11 wherein the flow meter is selected from a venturi tube flow meter, an orifice plate flow meter, a flow probe, a magnetic flow meter and an ultrasonic flow meter.

13. A fluid network according to claim 12 wherein the flow meter in at least one location is an ultrasonic or magnetic flow meter.

14. A fluid network according to any one of claims 9 to 13 wherein the processor contains data defining a desired value or range of values for fluid impedance at each location on the network from which the processor receives measurements of fluid pressure and fluid flow rate, and wherein the processor is programmed to compare an actual hydraulic impedance value at each location with the desired value or range of values for that location.

15. A fluid network according to claim 14 wherein the processor is linked to one or more actuators for actuating one or more control elements and wherein when the actual impedance value at a location does not match a desired value or range of values, the processor prompts one or more actuators to alter the fluid flow within the network to change the fluid * : impedance towards a value matching the desired value or range of values. S... * . * *1**

S *155

S *.I * . * S S S... S. S S 5 5 S 55