FLUID CONTROL APPARATUS AND METHOD

Abstract: The invention provides control apparatus for use with a fluid displacement device, for example a compressor, the control apparatus comprising means (24) to detect the temperature of fluid being displaced by the device and means (11) to control the device independence upon the sensor temperature. Preferably there is also means (22) to sense the pressure of the fluid being displaced by the device, a combination of temperature signals and pressure signals being utilised to control the device. The invention enables very sophisticated monitoring and control to be carried out, for example utilising pre-selected temperature and pressure bands.

Description: FLUID CONTROL APPARATUS AND METHOD The invention relates to control apparatus and to a control method, for use particularly, though not exclusively, with compressors. Many types of compressor are well known. Although the invention has wide applications, it was specifically developed for use in preventing damage to compressors used in the discharge of product, for example liquid or particulate product, from a road vehicle tanker. When a compressor is used to discharge a product, an undesirable, and potentially damaging, pressure build-up may result from a number of causes, including a blockage, over speed or other reason. An obvious solution to the problem is to utilise a pressure sensitive device which stops or slows the compressor if the pressure exceeds a predetermined limit. We have developed a more unusual and versatile solution to the problem. The invention provides control apparatus for use with a fluid displacement device, the control apparatus comprising means to detect the temperature of fluid being displaced by the device, and means to control the device in dependence upon the sensed temperature. Preferably there is also means to sense the pressure of the fluid being displaced by the device, a combination of temperature signals and pressure signals being utilised to control the device. Preferably the control means has means to preset at least one temperature control limit such that if fluid temperature rises above this limit, the apparatus operates to lower the working pressure. There may be a temperature control band extending between preset limits. Once the temperature has dropped below a preset limit, the control apparatus may continue to monitor the temperature for a predetermined period before increasing the working pressure again. The control apparatus may have means to preset at least one pressure limit, the control apparatus being arranged to drop the pressure if the pressure rises above this limit. There may be a pressure control band extending between preset limits. The control apparatus may be arranged to monitor pressure for a predetermined period. The apparatus may also be arranged to monitor the torque associated with a device being controlled by the apparatus. The apparatus may also be arranged to monitor the speed associated with a device being controlled by the apparatus. Although the invention has been specifically developed for use with a fluid displacement device in the form of a compressor, the control apparatus may also be used with other fluid displacement devices such as pumps and blowers. Preferably, the control apparatus has a pressure relief valve movable between a closed position in which pressure is contained, and a relief position in which fluid can vent to reduce pressure. Preferably, the pressure relief valve is solenoid operated. The control means may have means to receive an electric power supply, for example from a tanker vehicle. The power supply may be from 24 to 30 V DC. The control means may have means to receive an air supply, for example from a tanker vehicle. The air may be supplied at from 6 to 8 bar. The control means preferably has means to receive a temperature signal and a pressure signal. The control means preferably has a conduit to supply control air from the air supply to the pressure relief valve, under the control of the solenoid. The invention includes a method of controlling the pressure of a fluid comprising means to detect the temperature of the fluid and means to control the pressure of the fluid in dependence upon a sensed temperature. Preferably, the pressure of the fluid is also sensed, a combination of temperature signals and pressure signals being utilised for control purposes. The invention includes a displacement device having control apparatus according to the invention. The invention also includes a tanker vehicle having control apparatus according to the invention. By way of example, a specific embodiment of the invention will now be described, with reference to the accompanying drawings in which: Figure 1 illustrates an embodiment of control apparatus according to the invention, including a pressure relief valve shown in cross-section and associated control means; Figure 2 is an internal view of the control means; and Figure 3 is a graph illustrating how the apparatus and method according to the invention might operate under one particular set of circumstances. The basic components of the control apparatus are a pressure relief valve 10 and a control unit 11. The pressure relief valve 10 comprises a housing 12 in which there is slidingly and sealingly mounted a valve member having a head 13 and a shank 14. The housing 12 is connected by bolts 15 to a valve seat plate 16 having an aperture 17 therein. The valve head 13 can be urged against the valve seat 16, to seal the aperture 17, by the application of pressure to an inlet 18 via a conduit 19. In use, the valve seat plate 16 is bolted to a component 20 at a location where the aperture 17 will be subject to the working pressure of the compressor to be controlled. The conduit 19 leads to the control unit 11. The control unit is also connected by a conduit 21 to a bore in the component 20 and the conduit 21 is connected to a pressure transducer 22 (see figure 2) to enable the compressor pressure to be monitored. This pressure is illustrated on a digital display 23. The control unit 11 is also capable of sensing the temperature of the compressed air via a lead 24. The temperature is displayed on a bar graph 25. Also connected to the control unit 11 is a power supply 26 from a tanker vehicle (not shown) at 24 to 30 V DC. The same tanker vehicle provides an air supply 27 at 6 to 8 bar. Within the control unit 11 the air supply conduit 27 and pressure supply conduit 19 are connected to a solenoid valve 28. The solenoid valve also has a vent 29. During normal operation, the solenoid valve 28 connects the air supply 27 to the conduit 19 so that air pressure forces the valve member 14 into the closed position shown in Figure 1. In this configuration, the vent 29 is closed by the solenoid valve. However the solenoid valve is movable to a second position in which the air supply 27 is closed and pressure vents from the valve via the conduit 19, solenoid valve, and solenoid vent 29. In this configuration, compressor pressure causes the valve head 13 to lift off the valve seat 16, relieving compressor pressure. The control unit 11 has also a SET button 30, an up SET POINT button 31 , a down SET POINT button 32, and lamps 33, 34 to warn an operator of a signal fault or a control fault respectively. Figure 3 illustrates graphically how the apparatus might operate under a particular set of circumstances. Temperature is measured in degrees centigrade on the left vertical axis 35. Pressure is measured in bar on the right vertical axis 36. Time is measured on the horizontal axis 37. Line 38 shows how pressure varies with time. Line 39 shows how temperature varies with time. The operator sets acceptable pressure limits at points 40 and 41. Acceptable temperature limits are set at points 42 and 43. At start up, pressure and temperature rise steadily to approach the working limits. The pressure control zone 44 illustrates an area in which some degree of pressure control is required, possibly because of a temporary blockage. When the problem occurs, pressure starts to rise again, and when the pressure passes the upper limit 41, this actuates the solenoid which allows the valve member 13 to lift and vent pressure. This control is exercised until pressure drops below the limit 40, and then normal working is resumed. Reference numeral 45 indicates a temperature control zone over which temperature control is exerted, because of an unexpected rise in temperature, for example caused by a faulty fan. As soon as the lower temperature limit 42 is breached, the solenoid is actuated to reduce pressure. Pressure is dropped in steps of 0.1 bar until the temperature falls below the lower limit 42. Even then, the temperature is monitored over the period 46 to make sure that there is no recurrence before normal-operationis resumed. The limits 40, 41 , 42 and 43 are set using the buttons 31 and 32. The apparatus provides very sophisticated and sensitive control, which means that discharge from a tanker vehicle does not have to be continually monitored by an operator. If relief of pressure fails to rectify a situation, the control fault lamp is illuminated and a signal is sent to shut down the vehicle engine. The control unit can be arranged to log pressure, temperature and output states at regular intervals, for example one minute, during a period of operation, for example the most recent 16 hours of operation. The control unit can also store cumulative operation time for the compressor. The data is preferably stored in a non-volatile form available for download from a PC programme via a custom communication interface unit. The temperature display 25 may be arranged to flash as a single bar to indicate when limit 42 has been reached, display two flashing bars when limit 43 has been reached, and display three flashing bars to indicate that the temperature has reached a critical level and that engine shut-down is imminent. When pressure reaches the upper limit 41, the pressure indication on display 23 will flash. A solenoid will then withdraw pressure from conduit 19 until the pressure falls to the level 40. At this point, the solenoid will restore the output signal. If pressure does not return the lower level 40 within a pre-set time period, a warning _ outpTJt ~ sighal-will " be turned on to be used to sound a warning horn and/or flash the vehicle lights. If after a further period, the lower pressure time limit has still not been achieved, then the engine will be shut down. In a sophisticated mode of operation, the control unit stores the operating pressure which prevails when temperature reaches the lower limit 42. The control unit then uses this as the upper pressure limit, instead of limit 41. The pressure control loop then continues as described above, with the displays indicating the severity of the problem. Failure to control the problem causes the engine to be shut off when the upper temperature limit 43 is reached. However, if normal operating temperature is restored for a minimum period, the memory location is cleared and the upper pressure limit reverts to 41. Using an algorithm to operate the control unit in this way allows the driver of the vehicle to continue to operate as close to his normal pressure as possible during an acceptable fault condition. The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). The invention extend to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims: CLAIMS 1. Control apparatus for use with a fluid displacement device, the control apparatus comprising means to detect the temperature of fluid being displaced by the device, and means to control the device in dependence upon the sensed temperature. 2. Control apparatus as claimed in Claim 1 , in which there is also means to sense the pressure of the fluid being displaced by the device, a combination of temperature signals and pressure signals being utilised to control the device. 3. Control apparatus as claimed in Claim 2, having means to preset at least one temperature control limit such that if fluid temperature rises above this limit, the apparatus operates to lower the working pressure. 4. Control apparatus as claimed in Claim 3, in which there is a temperature control band extending between preset limits. 5. Control apparatus as claimed in Claim 4, in which the control apparatus is such that, once the temperature has dropped below a preset limit, the control apparatus continues to monitor the temperature for a predetermined period before increasing the working pressure again. 6. Control apparatus as claimed in any one of Claims 2 to 5, having means to preset at least one pressure limit, the control apparatus being arranged to drop the-pressure if the pressure-rises above this limitr- 7. Control apparatus as claimed in Claim 7, in which there is a pressure control band extending between preset limits. 8. Control apparatus as claimed in any one of Claims 2 to 7, arranged to monitor pressure for a predetermined period. 9. Control apparatus as claimed in any one of the preceding claims, arranged to monitor the torque associated with a device being controlled by the apparatus. 10. Control apparatus as claimed in any one of the preceding claims, also arranged to monitor the speed associated with a device being controlled by the apparatus. 11. Control apparatus as claimed in any one of the preceding claims, in which the fluid displacement device is a compressor. 12. Control apparatus as claimed in any one of Claims 1 to 10, in which the fluid displacement device is a pump. 13. Control apparatus as claimed in any one of Claims 1 to 10, in which the fluid displacement device is a blower. 14. Control apparatus as claimed in any one of the preceding claims, having a pressure relief valve movable between a closed position in which pressure is contained, and a relief position in which fluid can vent to reduce pressure. 15. Control apparatus as claimed in Claim 14, in which the pressure relief valve is solenoid operated. 16. Control apparatus as claimed in any one of the preceding claims, having means to receive an electric power supply, for example from a tanker vehicle. 17. Control apparatus as claimed in Claim 16, in which the power supply is from 24 to 30 V DC. 18. Control apparatus as claimed in any one of the preceding claims, having means to receive an air supply, for example from a tanker vehicle. 19. Control apparatus as claimed in Claim 18, in which the air is supplied at from 6 to 8 bar. 20. Control apparatus as claimed in any one of the preceding claims, having means to receive a temperature signal and a pressure signal. 21. Control apparatus as claimed in any one of the preceding claims, having a conduit to supply control air from an air supply to a pressure relief valve, under the control of a solenoid. 22. Control apparatus constructed and arranged substantially as herein described, with reference to the accompanying drawings. 23. A displacement device having control apparatus as claimed in any one of the preceding claims. 24. A tanker vehicle having control apparatus as claimed in any one of Claims 1 to 22. 25. A method of controlling the pressure of a fluid comprising detecting the — temperature-of-the-fluid-and-controlling -the-pressure of the fluid in dependence upon a sensed temperature. 26. A method as claimed in Claim 25, in which the pressure of the fluid is also sensed, a combination of temperature signals and pressure signals being utilised for control purposes. 7. A method of controlling the pressure of a fluid, substantially as herein described with reference to the accompanying drawings.

Inventors: KELLY ALEXANDER, KELLY, ALEXANDER
Applicants: DRUM INTERNAT LTD, KELLY ALEXANDER, DRUM INTERNATIONAL LIMITED, KELLY, ALEXANDER
Application year: 2001
Main classification: G05D27
IPC codes: F04B49, F04C28, G05D16