GB2123983A - Pressure controllers - Google Patents

Abstract

A pressure controller (10) controls the pressure within a fluid (e.g. mains water) distribution system into which fluid flows via a valve. The controller (10) comprises means - e.g. pressure transducers (28, 30), a valve position monitor (38) and a microprocessor (36) - for ascertaining the flow rate of fluid through the valve into the system, means (38) for storing data characteristic of the system and indicative of a desired relationship between the inlet pressure to the system end the flow rate of fluid into the system, and control means - e.g. the microprocessor (36), an actuator and a motor (40) - responsive to the ascertained flow rate to vary the extent of opening (i.e. the position) of the valve, and thus the pressure drop across the valve, in the sense to make the inlet pressure to the system conform to said desired relationship. <IMAGE>

Description

SPECIFICATION Pressure controllers This invention relates to pressure controllers for controlling the pressure within fluid distribution systems.

There are a variety of types of fluid distribution system within which the pressure will vary from time to time, for instance due to different demands for fluid to be supplied by the system. One such type of system is a mains water distribution system. An adequate supply of water requires that a minimum pressure be maintained at all times in consumers' premises. The minimum pressure has to be maintained during peak demand periods (a few hours a year) at the most critical or sensitive point in a distribution system. Thus, if the system is so designed as always to provide the minimum pressure and the pressure within the system is not controlled or regulated, at all other times than during peak demand periods the pressure within the system will be higher. In fact, during low demand periods, the pressure can increase by a very large amount.Thus, since leakage from a mains water distribution system is directly related to pressure, if the pressure is not regulated there will be a lot of leakage during low demand periods.

The foregoing problem is known in the art and attempts have been made to overcome it by regulating the pressure within a water distribution system, ideally to keep the pressure within the system as neariy constant as possible at a level ensuring a sufficient pressure at all consumers' premises. One prior proposal uses a central computing installation installed, for example, at a central facility of a water supply company and connected to a large number of individual water distribution systems supplying waterto respective areas - by interconnecting links. In the case of a system or systems close to the computing installation, the link could be a simple wire connection. In the majority of the instances, however, the interconnecting link is a telephone line.

Equipment associated with each distribution system is interrogated in turn by the central computing installation. During each interrogation of each distri bution system, an input translator associated with the respective system reads data indicative of the pressure within the system and sends it via the link to the computing installation. The computing instal lation undertakes calculations and returns instructions to an output control means associated with the distribution system. Since the distribution systems require frequent updating, the interconnecting links need to be permanent connections, i.e. dedicated iines. The use of dedicated telephone lines for this purpose thus adds very considerably to both instal lation costs and annual operational costs.Further, the complexity of the programming requirements to operate such a system entail a high cost in both the equipment used in the central computing installation and in writing the computer program to operate the system. There is therefore a need for a control arrangement which does not require the use of an expensive, complex central computing installation and which does not require the use of dedicated telephone lines for its operation.

According to the present invention there is provided a pressure controller for controlling the pressure within a fluid distribution system into which fluid flows via a valve, the controller being installed or capable of being installed in the vicinity the valve and comprising: means for ascertaining the flow rate of fluid through the valve into the system, means for storing data characteristic of the system and indicative of a desired relationship between the inlet pressure to the system and the flow rate of fluid into the system, and control means responsive to the ascertained flow rate to vary the extent of opening (i.e. the position) of the valve, and thus the pressure drop across the valve, in a sense to make the inlet pressure to the system conform to said desired relationship.

Controllers in accordance with the invention can operate essentially on a "stand-alone" basis and can be disposed in the vicinity of associated valves leading to respective fluid distribution systems.

Thus, a plurality of or network of individual fluid distribution systems can be operated by a plurality of substantially independent controllers without the need for a central control computing installation and without the need for telephone links or other remote telemetry links.

Since each controller is provided with means for storing data characteristic of the system that is to be controlled, what is essentially a standard form of controller can readily be "tailored" to control a particular system by entering such data as is appropriate. Thus, a network of fluid distribution systems can be controlled by a plurality of basically similar controllers, each individually tailored to suit its particular associated system.

The control means may comprise drive means for opening or closing the valve and a microprocessor responsive to the ascertained flow rate, to the said stored data (preferably in the form of a look-up table) characteristic of the system, and also to stored data (also preferably in the form of a look-up table) characteristic of the valve, to compute a valve position that should provide a pressure drop making the system inlet pressure conform to said desired relationship.

The storage of data characteristic of a particular associated valve enables each controller to be "tailored" to a desired associated valve as well as to the associated distribution system.

The control means preferably operates to compute the valve position by determining a required system inlet pressure (and thus valve output pressure) that conforms with said desired relationship for the ascertained flow value, computing the valve pressure drop that will provide the desired inlet pressure, and computing from the stored data characteristic of the valve a valve position that will give the desired pressure drop and thus the required system inlet pressure.The stored data characteristic of the valve may be the relationship between the discharge coefficient and position of the valve, in which case the computing of the valve position may comprise computing a value of the discharge coefficient corresponding to the computed value of the desired pressure drop and the ascertained flow rate, and then looking up from the stored data characteristic of the valve a value of the valve position corresponding to the computed value of the discharge coefficient.

Preferably, the means for ascertaining the flow rate comprises transducers for measuring the pressure upstream and downstream of the valve and means for monitoring the valve position, the microprocessor being responsive to said pressures and to the stored data characteristic of the valve to compute therefrom the flow rate through the valve. (This facility takes advantage of the computing power of the microprocessor to enable the flow rate to be ascertained by measuring only pressure and position, no dynamic direct flow measurement technique being needed). If the stored data characteristic of the valve comprises the relationship between its discharge coefficient and its position, the flow rate can be computed by calculating the product of the discharge coefficient and the square root of the pressure drop.

The valve may be of conventional design and capable of adopting a closed position fully shutting off the flow. However, this is not essential. In some applications it may be sufficient that the valve simply has the capacity of providing a variable restriction to the flow and not necessarily cutting it off. Thus, the term "valve" as used herein is to be interpreted in such a broad sense.

The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which: Figure 1 shows part of a pressure controller embodying the present invention, the controller being shown connected to an underground mains water supply pipe having a valve therein; Figure 2 is a schematic circuit diagram of the controller of Figure 1; Figure 3 represents in graphical form the relationship between the discharge coefficient (Cv) and the position (V) of the valve, which relationship is stored in the form of a first look-up table in a memory of the controller;; Figure 4 is a graphical representation of a relationship between the inlet pressure (Pj) to the water distribution system and the flow rate (Q) of water into the system that has been ascertained will keep the pressure within the system at a desired value, this relationship being stored in the memory in the form of a second look-up table; Figure 5 is a graphical representation of data stored in a third look-up table in the memory, the relationship shown in Figure 5 being the inverse of that shown in Figure 3; and Figure 6 is a flow diagram of computing operations carried out by a microprocessor of the controller.

Figure 1 of the drawings shows a pressure controller 10 for controlling the pressure within a mains water distribution system (e.g. to a housing estate or the like). Water flows into the distribution system via a pipe 12, having a valve 14 fitted therein, in the direction of an arrow 16. In a manner described more fully hereinbelow, the controller 10 is operative to position the valve 14 as appropriate to ensure that the pressure at a critical or sensitive point in the distribution point is maintained at a minimum value, and that such pressure is maintained reasonably constant with changes in supply pressure whereby leakage in low demand periods (high supply pressure periods) is minimised.

The pressure controller 10 comprises a cabinet 18 standing on a base 20 that rests on the surface 22 of the ground, the pipe 12 and valve 14 being buried beneath the ground. An extension 24 of the valve 14 is connected to an actuator 26 within the controller cabinet 18 whereby the valve 14 can be moved in either an opening or closing direction by the controller 10. Respective pressure transducers 28,30 are fitted within the controller cabinet 18 and are connected by pipework 32 to the pipe 12 downstream and upstream, respectively, of the valve 14, to measure the pressure (PD) downstream of the valve and the pressure (Pu) upstream of the valve. As will be appreciated, the pressure (PD) downstream of the valve 14 will be equal to the inlet pressure (Pj) of the distribution system.

Referring now also to Figure 2 of the drawings, it will be seen that the transducers 28,30 can be represented as resistors, the voltages across which are proportional to the respective pressures. The resistors (transducers) 28,30 are connected to an analog-to-digital (AID) conversion means 34 that digitisesthe analog signals provided bythetrans- ducers so that they can be processed by a microprocessor 36. Also connected to the AID conversion means 34 is a potentiometer 38.Means (not shown) within the controller 10 generates a reference voltage that is applied across the potentiometer 38 and the potentiometer is associated with means driving the valve 14 such that a voltage proportional to the valve position (i.e. the extent of opening of the valve) is developed by the potentiometer and applied to the AID conversion means 34 for digitisation prior to application to the microprocessor 36.

Associated with the microprocessor 36 is a memory 38 that stores a program for operating the microprocessor 36 together with three data look-up tables I, II and Ill represented in graphical form in Figures 3 to 5, respectively, and described in more detail hereinbelow.

The microprocessor 36 is connected to control a motor 40 operating the valve 14 (via the extension 24) by an output control means 42 comprising the actuator 26 and, for example, one or more solid state relays. Appropriate signals from the microprocessor 36 are operative on the output control means 42 to cause the latter to energise the motor 40 to rotate in one direction or the other, as appropriate, to move the valve 14to a desired position.

The first (I) of the three look-up tables stored in the memory 38 is shown in graphical form in Figure 3.

The data constituting the look-up table I is characteristic of the particular valve 14 associated with the controller 10 and represents the relationship between the discharge coefficient (Cv) of the valve and the position (V) of the valve in terms of the percentage extent of opening thereof.

The data stored in the second look-up table (II) in the memory 38 is shown in graphical form in Figure 4 and is characteristic of the distribution system controlled by the controller 10. More specifically, Figure 4 represents a desired relationship between the inlet pressure (Pj) to the distribution system and the flow rate (Q) of water into the system that will ensure that the pressure within the system will remain at least approximately at a value sufficient to maintain at least a desired minimum pressure at all of the consumers' premises supplied by the system, even though the supply pressure may vary as the load on the system changes. In this way, the pressure within the system does not rise excessively when demand is low and thus a significant reduction in leakage from the system can be obtained.

The data contained in the third look-up table (III) in the memory 38 is represented in graphical form in Figure 5 and is again characteristic of the particular valve 14 associated with the controller, being in fact the inverse relationship to that shown in Figure 3.

The manner of operation of the controller 10, more specifically the sequence of operations performed by the microprocessor 36, will now be described with reference to the flow diagram constituting Figure 6 of the drawings.

At the start (block 52) of a measurement/computa tion cycle, the current value Puck, ) of the pressure upstream of the valve 14, the current value PD(1 ) of the pressure downstream of the valve 14 and the current position V of the valve 14 are read (blocks 54, 56 and 58, respectively). The upstream and downstream pressures are substracted (block 60) to compute the current pressure drop or difference AP(1) across the valve 14. That value of the discharge coefficient Cv of the valve 14 corresponding to its current position is looked up (block 62) from the first look-up table I (Figure 3).The current flow rate Q through the valve is then computed in accordance with the relationship shown in block 64, namely from the relationship that the flow rate Q is equal to the product of the current discharge coefficient and the square root of the current pressure drop.

Then (block 66) that value (PD(2) ) of the required system inlet pressure Pj corresponding to the computed value of the flow rate Q is looked up from the second look-up table II (Figure 4). As has been mentioned above, the inlet pressure Pj to the water distribution system is, of course, substantially equal to the pressure PD downstream of the valve 14.

As represented in block 68, the microprocessor 36 then computes the value of the required pressure drop (AP2) = Puck, - PD(2) ) across the valve 14that will produce the required pressure downstream of the valve 14, i.e. the desired inlet pressure PD(2) to the water distribution system. Next, as represented in block 70, that value (Cv(2) ) of the discharge coefficient of the valve 14 corresponding to the required pressure drop AP(2) across the valve 14 is computed in accordance with the relationship shown in block 70, namely that the desired discharge coefficient is equal to the measured flow rate Q divided by the square root of the computed pressure drop At2).

The next step in the program (block 72) is to look up from the third look-up table III (Figure 5) that value of the valve position V corresponding to the value of the discharge coefficient (Cv(2) ) just computed. Then (block 74), the output control means 42 is operative to move the valve 14 to its new position which, as has been explained, has been computed to be such as to cause the relationship shown in Figure 4 to be followed, whereby the pressure within the distribution system is kept generally constant. (The relationship represented in Figure 4 is shown to be a straight line purely for the sake of convenience. As will be appreciated by those skilled in the art, the optimum relationship might diverge from a straight line).

The system then reverts to a quiescent state and, after a predetermined delay (block 76), which may if desired be variable (for instance between 5 seconds and 2 hours), the whole procedure is repeated. That is to say, the measurement, computation and valve position adjustment procedure just described are periodically repeated at a desired frequency.

It is possible that, at least in some instances, users of the controller may wish to log one or more of the upstream and downstream pressure readings and the computed flow rate. If so, the controller could be provided with means to record same. The recorded data could be accessed in a variety of ways. For instance, the controller could be provided with an interface so that the record could be interrogated by telemetry, for instance by calling up the controller when required by means of a telephone line. It should be noted that, should such a facility be provided, the controller does not require a dedicated line for its operation, as in the prior art arrangement discussed above. Firstly, the line is not required for the operation of the controller - which remains "stand-alone" - but to read out data stored during the course of its operation.Secondly, a dedicated line is not needed because the logged data can be accessed casually, as convenient, for example by means of the public switched telephone network.

CLAIMS (Filed on 30 Jun 83) 1. A pressure controller for controlling the pressure within a fluid distribution system into which fluid flows via a valve, the controller being installed or capable of being installed in the vicinity of the valve and comprising: means for ascertaining the flow rate of fluid through the valve into the system, means for storing data characteristic of the system and indicative of a desired relationship between the inlet pressure to the system and the flow rate of fluid into the system, and control means responsive to the ascertained flow rate to vary the extent of opening (i.e. the position) of the valve, and thus the pressure drop across the valve, in a sense to make the inlet pressure to the system conform to said desired relationship.

2. A pressure controller according to claim 1, wherein the control means comprises drive means for opening or closing the valve and a microprocessor responsive to the ascertained flow rate, to the said stored data characteristic of the system, and

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. The data stored in the second look-up table (II) in the memory 38 is shown in graphical form in Figure 4 and is characteristic of the distribution system controlled by the controller 10. More specifically, Figure 4 represents a desired relationship between the inlet pressure (Pj) to the distribution system and the flow rate (Q) of water into the system that will ensure that the pressure within the system will remain at least approximately at a value sufficient to maintain at least a desired minimum pressure at all of the consumers' premises supplied by the system, even though the supply pressure may vary as the load on the system changes. In this way, the pressure within the system does not rise excessively when demand is low and thus a significant reduction in leakage from the system can be obtained. The data contained in the third look-up table (III) in the memory 38 is represented in graphical form in Figure 5 and is again characteristic of the particular valve 14 associated with the controller, being in fact the inverse relationship to that shown in Figure 3. The manner of operation of the controller 10, more specifically the sequence of operations performed by the microprocessor 36, will now be described with reference to the flow diagram constituting Figure 6 of the drawings. At the start (block 52) of a measurement/computa tion cycle, the current value Puck, ) of the pressure upstream of the valve 14, the current value PD(1 ) of the pressure downstream of the valve 14 and the current position V of the valve 14 are read (blocks 54, 56 and 58, respectively). The upstream and downstream pressures are substracted (block 60) to compute the current pressure drop or difference AP(1) across the valve 14. That value of the discharge coefficient Cv of the valve 14 corresponding to its current position is looked up (block 62) from the first look-up table I (Figure 3).The current flow rate Q through the valve is then computed in accordance with the relationship shown in block 64, namely from the relationship that the flow rate Q is equal to the product of the current discharge coefficient and the square root of the current pressure drop. Then (block 66) that value (PD(2) ) of the required system inlet pressure Pj corresponding to the computed value of the flow rate Q is looked up from the second look-up table II (Figure 4). As has been mentioned above, the inlet pressure Pj to the water distribution system is, of course, substantially equal to the pressure PD downstream of the valve 14. As represented in block 68, the microprocessor 36 then computes the value of the required pressure drop (AP2) = Puck, - PD(2) ) across the valve 14that will produce the required pressure downstream of the valve 14, i.e. the desired inlet pressure PD(2) to the water distribution system. Next, as represented in block 70, that value (Cv(2) ) of the discharge coefficient of the valve 14 corresponding to the required pressure drop AP(2) across the valve 14 is computed in accordance with the relationship shown in block 70, namely that the desired discharge coefficient is equal to the measured flow rate Q divided by the square root of the computed pressure drop At2). The next step in the program (block 72) is to look up from the third look-up table III (Figure 5) that value of the valve position V corresponding to the value of the discharge coefficient (Cv(2) ) just computed. Then (block 74), the output control means 42 is operative to move the valve 14 to its new position which, as has been explained, has been computed to be such as to cause the relationship shown in Figure 4 to be followed, whereby the pressure within the distribution system is kept generally constant. (The relationship represented in Figure 4 is shown to be a straight line purely for the sake of convenience. As will be appreciated by those skilled in the art, the optimum relationship might diverge from a straight line). The system then reverts to a quiescent state and, after a predetermined delay (block 76), which may if desired be variable (for instance between 5 seconds and 2 hours), the whole procedure is repeated. That is to say, the measurement, computation and valve position adjustment procedure just described are periodically repeated at a desired frequency. It is possible that, at least in some instances, users of the controller may wish to log one or more of the upstream and downstream pressure readings and the computed flow rate. If so, the controller could be provided with means to record same. The recorded data could be accessed in a variety of ways. For instance, the controller could be provided with an interface so that the record could be interrogated by telemetry, for instance by calling up the controller when required by means of a telephone line. It should be noted that, should such a facility be provided, the controller does not require a dedicated line for its operation, as in the prior art arrangement discussed above. Firstly, the line is not required for the operation of the controller - which remains "stand-alone" - but to read out data stored during the course of its operation.Secondly, a dedicated line is not needed because the logged data can be accessed casually, as convenient, for example by means of the public switched telephone network. CLAIMS (Filed on 30 Jun 83)

1. A pressure controller for controlling the pressure within a fluid distribution system into which fluid flows via a valve, the controller being installed or capable of being installed in the vicinity of the valve and comprising: means for ascertaining the flow rate of fluid through the valve into the system, means for storing data characteristic of the system and indicative of a desired relationship between the inlet pressure to the system and the flow rate of fluid into the system, and control means responsive to the ascertained flow rate to vary the extent of opening (i.e. the position) of the valve, and thus the pressure drop across the valve, in a sense to make the inlet pressure to the system conform to said desired relationship.

2. A pressure controller according to claim 1, wherein the control means comprises drive means for opening or closing the valve and a microprocessor responsive to the ascertained flow rate, to the said stored data characteristic of the system, and

also to stored data characteristic of the valve, to compute a valve position that should provide a pressure drop making the system inlet pressure conform to said desired relationship.

3. A pressure controller according to claim 2, wherein the stored data characteristic of the system is in the form of a look-up table.

4. A pressure controller according to claim 2 or claim 3, wherein the stored data characteristic of the valve is in the form of a look-up table.

5. A pressure controller according to claim 2, claim 3 or claim 4, wherein the control means is operative to compute the valve position by determining a required system inlet pressure (and thus valve output pressure) that conforms with said desired relationship for the ascertained flow value, computing the valve pressure drop that will provide the desired inlet pressure, and computing from the stored data characteristic of the valve a valve position that will give the desired pressure drop and thus the required system inlet pressure.

6. A pressure controller according to claim 5, wherein the stored data characteristic of the valve is the relationship between the discharge coefficient and the position of the valve.

7. A pressure controller according to claim 6, wherein the control means is operative to compute the valve position by computing a value of the discharge coefficient corresponding to the computed value of the desired pressure drop and the ascertained flow rate, and then looking up from the stored data characteristic of the valve a value of the valve position corresponding to the computed value of the discharge coefficient.

8. A pressure controller according to any one of claims 2 to 7, wherein the means for ascertaining the flow rate comprises transducers for measuring the pressure upstream and downstream of the valve and means for monitoring the valve position, the microprocessor being responsive to said pressures and to the stored data characteristic of the valve to compute therefrom the flow rate through the valve.

9. A pressure controller according to claim 8, wherein the microprocessor is operative to compute the flow rate by calculating the product of the discharge coefficient and the square root of the pressure drop.

10. A pressure controller substantially as herein described with reference to the accompanying drawings.