Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D15/00—Control, e.g. regulation, of pumps, pumping installations or systems
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D15/00—Control, e.g. regulation, of pumps, pumping installations or systems
  • F04D15/0066—Control, e.g. regulation, of pumps, pumping installations or systems by changing the speed, e.g. of the driving engine
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
  • F04B49/00—Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00
  • F04B49/06—Control using electricity
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D15/00—Control, e.g. regulation, of pumps, pumping installations or systems
  • F04D15/0077—Safety measures
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D15/00—Control, e.g. regulation, of pumps, pumping installations or systems
  • F04D15/02—Stopping of pumps, or operating valves, on occurrence of unwanted conditions
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D15/00—Control, e.g. regulation, of pumps, pumping installations or systems
  • F04D15/02—Stopping of pumps, or operating valves, on occurrence of unwanted conditions
  • F04D15/0209—Stopping of pumps, or operating valves, on occurrence of unwanted conditions responsive to a condition of the working fluid
  • F04D15/0218—Stopping of pumps, or operating valves, on occurrence of unwanted conditions responsive to a condition of the working fluid the condition being a liquid level or a lack of liquid supply

Definitions

• the present invention relates generally to the field Of pumps, and more specifically .
• the present invention relates to pumps comprising variable frequency drive means.
• the present invention also relates to a method for operating ' such pumps.
• Pumps comprising variable frequency drive means, such as sewage pumps, drainage pumps and de-watering pumps as well as submersible pumps, for example, are commonly used- for pumping fluids in mining applications such as in mining shafts, wells, at construction sites, or at other applications.
• submersible pumps are submersed, wholly or partly, during long periods of time both when they are in operation and when in an off-state.
• a problem often encountered with pumps in general and with submersible pumps in particular, is so called snoring operation, which means that the pumps sucks partly liquid and partly air. This is due to the fact that the liquid level has fallen below the required level of the pump causing the pump to start sucking partly air.
• level sensors may, for example, be blocked or be subjected to a level shift due to a collision with subjects in the fluid such as a tree branch, and will thus in such a case deliver an erroneous signal.
• US 6,481,973 to Struthers present a pump system addressing a part of the abovementioned problem. Even though this pump system comprises variable frequency, drive means it makes use of another control method to detect if the liquid level falls below a preset level, as a complement to level switches. More precisely, this pump system detects if there is a sudden increase in the speed of the motor or a sudden drop of the motor torque. Said operation of the motor is monitored by a sensor connected to the AC output link extending from the variable frequency drive means to the motor.
• this pump system embraces great disadvantages.
• the system might not recognize the change as an indication of dry running of 'the pump.
• the pump system is not able to detect if the water level is high enough for pump operation upon start of the pump, since in this state there cannot be a sudden increase of the speed of the motor or a sudden drop of the motor torque. Thereby, ⁇ the pump will run for a considerable time until it is switched off due to overheating, and the pump runs the risk of getting seriously damaged.
• the pump operates in a dynamic environment and thus the pump should be able to operate in an efficient way in large range of head/pressure.
• the pump head corresponds to the height the pump, using a given power, is able to lift a given amount of liquid, for example, water, see Fig. 3 where a typical pump curve is indicated by the line 30..
• the degree of utilization of the power of the pump may be reduced at low flows (Q) .
• Q flows
• This entails that a large starting torque of the pump motor is required in order to initiate the rotating of the pump impeller. Often a maximum starting torque is even required in order to start the rotation and the motor has to be operated at a maximum torque during a significant period of time. This consumes large amo ⁇ nts of energy and also wears the pump impeller and the motor.
• variable frequency drive means Another known problem with pumps comprising conven- tional variable frequency drive means, is that the latter is usually mounted distant from the pump at a dry location above ground. More precisely, this necessitates a long power cable leading from the variable frequency drive means to the motor of the pump, which for conventional variable frequency drive means can result in severe problems with electromagnetic interference.
• the variable frequency drive means is mounted within the pump casing, more precisely on a plate connected to the motor.
• the operation of the variable frequency drive means in this case is adversely affected by the heat emitted . from the motor, which may lead to ' erroneous operation of the variable frequency drive means.
• one object of the present invention is to provide an improved pump, a pump system including such a pump, a computer program, a control device for such a pump and methods ⁇ for controlling such a pump and pump systems in an efficient way with respect to pump capacity at varying pump head.
• Another object of the present invention is to provide an improved pump, a pump system including such a pump, a computer program, a control . device for such a pump and methods for controlling such a pump and pump systems in an efficient way with respect to energy consumption.
• Another object of the present invention is to pro- vide an improved pump, a pump system including such a . pump, a computer program, a control device for such a pump and methods for controlling such a pump and pump systems in an efficient way with respect to durability of the pump. It is a further object of the present invention to provide an improved 1 pump, pump system including such a pump, a computer program, a control device for such a pump and a method for controlling such a pump and pump systems in a manner that reduces the wear of the pump and extends the pump life.
• pump speed is defined as the numbers of revolutions per time unit of the pump.
• a method for operating a pump comprising a motor and variable frequency drive means, the latter being arranged to control the operation of the motor by being connected to said motor and to a feeder cable of the pump, the variable frequency drive means comprising a rectifier, an inverter and a DC link extending therebetween, furthermore the pump is operatively connected to a control device.
• the method comprises the steps of: - obtaining values of operating parameters of the pump indicating pump conditions, by means of sensing means, which is comprised in said variable frequency drive means and which is operatively connected to said DC link, - communicating said values of operating parameters from the variable frequency drive means to the control device,
• a pump arranged to be operated in accordance with the abovementioned method.
• a computer program product loadable into a memory of a digital computer device including software code portions for performing the method of according to the first aspect of the present invention when the computer program product is run on the computer device.
• a pump system comprising a pump according to the second aspect of the invention.
• the present invention is based on the ⁇ idea of obtaining values of operating parameters of the pump substantially continuously from the variable frequency drive means, which operating parameters indicate pump conditions and which are measured in an easy and inexpensive way and at the same time with high accuracy; and controlling the variable frequency drive means based on the obtained values of operating parameters, wherein the ope- ration of the motor is adjusted in accordance with said pump conditions .
• the pump is operated in an efficient way with respect to output capacity at varying flows, energy consumption and durability of the pump.
• the wear of the pump parts such as the impeller and the seals is reduced, the pump life can be extended. Due to the fact that all information required for the- control of the pump and pump motor and variable frequency drive means is obtained from the variable frequency means, no external sensors are required.
• the operating parameters may be: the DC link voltage of the variable frequency drive means, the DC link current of the variable frequency drive means, the speed of the motor, or the like.
• the power of the motor, the torque of the motor, or other suitable quantities may be determined.
• the event of dry running of the pump is determined based of the obtained values of operating parameters, e.g. the power of the motor at different motor speeds are compared with a predetermined reference value. If it is determined that the power of the motor is lower than the predetermined reference level, the operation of the pump motor is stopped during a period of time having a predetermined length.
• the motor is restarted when the predetermined period of time has expired and the same check is performed once again until the predetermined condition is fulfilled.
• the snoring operation problem which, as discussed above, causes extra wear of the pump, and in particular of the impeller, may cause the pump motor to overheat and also leads to unnecessary energy consump- tion, is dealt with and an efficient way of operating a ⁇ pump comprising variable frequency drive means in respect of energy consumption and durability can thereby be obtained.
• the pump life can be extended owing to the fact that the wear of pump parts such as the im- peller, seals and suction cover is significantly reduced.
• the power of the motor is maintained at a substantially constant level.
• the obtained operating parameter value is compared 'with a predetermined reference level of the operating parameter; if the operating parameter value is lower than the predetermined reference level, the speed of the motor required to obtain the predetermined power level is calculated; and the pump is ran at the calculated speed.
• the calculated speed is compared with a preset maximum allowed speed of the pump; and if the calculated speed is higher than the preset maximum speed of the pump, the pump is ran at 'the preset maximum speed.
• the pump head/pressure can be increased by 20% to 30% by means of the method according to said second aspect.
• the pump will reach a higher pump head at lower flows than a conventional pump.
• an efficient way of operating a pump comprising variable frequency drive means in respect of pump capacity at varying pump head is obtained.
• a detection whether the pump is clogged is performed; and if it is detected that the pump is clogged, the pump is ran reversely at a predetermined speed during a period of time having a predetermined length.
• the pump is stopped and started in the normal direction. Moreover, the step of running the pump impeller reversely, stopping it and change the operating direction is repeated until it is detected, that the ⁇ clog- ging condition has ceased.
• the problem of clogging or jam of the intake .and/or pumping house which may be caused by particles in the fluid that sediment at the intake and at the impeller and build silt having a relatively thick or solid consistency, is dealt with. Owing to the fact that pump runs backwards and forward again in a repeated manner, the clogging can be removed in an efficient way. Thereby the starting reliability can be increased.
• this embodiment provides for an efficient way of operating a pump comprising variable frequency drive means in respect of energy consumption and durability since the wear of, especially, the pump impeller is reduced. Moreover, since the clogging con- dition can be removed in an efficient way the energy consumption of the pump can also be reduced.
• the method according to the present invention are suitable to realize or implement as a computer program or a computer readable medium, preferably within the contents of a control device or a processing means of a pump or a pump system.
• The' features that characterize the invention, both as to structure and to method of operation, together with further objects and advantages thereof, will be better understood from the following description read in conjunction with the accompanying drawings. It is to be expres.sly understood that the drawings is for the purpose of illustration and description and is not intended as a definition of -the limits of the invention.
• Fig. 1 schematically shows an embodiment of a pump according to the present invention
• Fig. 2 schematically shows an embodiment of a pump system according to the present invention
• Fig. 3 shows a pump curves for a conventional pump and a pump operated in accordance with the present invention
• Fig. 4 shows the principles of a method of an embodiment 5 according to the present invention
• Fig. 5 shows the principles of a method of another embodiment according to the present invention.
• FIG. 6 shows the principles of a method of yet another embodiment according to the present invention
• FIG. 7 schematically shows a further embodiment- of a pump and a control device for such a pump according to the present invention
• FIG. 8 schematically shows another embodiment of a pump and a control device for such a pump ' according to 15 the present invention.
• FIG. 9 schematically shows yet another embodiment of a pump and pump system according to the present invention.
• the submersible pump 1 of Fig. 1 comprises a
• variable-speed unit 2 preferably variable frequency drive means (VFD unit) connected via a connection cable 3 to a power source (not shown) delivering, for example, a single phase voltage or a three phase voltage.
• VFD unit variable frequency drive means
• the pump 1 according to the present invention is able to receive a power supply within the range from approximately 90 V to approximately 250 V.
• the inventive pump 1 may be used both in countries/regions having a standard power supply of approximately 110 V and in countries/regions having a standard power supply of approximately 230 V.
• prior art pumps are designed to be supplied with electricity having a frequency of 50 Hz or 60 Hz, which are known standards for different countries and/or diffe- ⁇ rent regions in a country.
• the inventive pump is designed to be used in many different countries, i.e. the input frequency may be at least within the range of 50-60 Hz, but in reality the inventive pump may cope with which ever frequency available.
• a given pump may be used connected to many different power mains, i.e. a given pump is a globally usable pump ready to be put into ope- ration.
• the VFD unit 2 comprises an electromagnet interference filter 4 (EMI filter) arranged at the connection cable 3 in order to filter out electromagnet interference at the input.
• the connection cable 3 is connected to a feeder cable of the pump 1.
• the EMI filter 4 is connected to a rectifiex 5, which in turn is connected via a DC link 10, including a capacitor 6, to a transducer or inverter 7.
• the inverter 7 converts the DC current to a three-phase current, which is supplied to a pump motor 9 via a connection 8.
• the function and components and parts of a VFD unit 2 is well-known for the man skilled within the art and hence they will not be described in further detail herein.
• VFD unit 2 is mounted ther- n ⁇ ally shielded from the motor 9 and at the same time mounted in a thermally conductive arrangement with the . • pumped fluid, such that the temperature of the VFD unit 2 is kept at a low level during operation, which eliminates a source of error.
• a control device 11 is arranged operatively connected to the pump 1 and in communication with the VFD unit 2 via a communication bus (not shown) and controls or drives the pump 1, e.g. to increase or decrease the speed of the motor 9 in order to pump a larger or a smaller amount of liquid, for example, water.
• the VFD unit 2 comprises sensing means 16, which is operatively connected to said DC link 10 and which is arranged to obtain values of operating parameters of the pump 1 indicating pump conditions.
• the VFD unit 2 is arranged to communicate to the control device 11 said values of operating parameters, which, according to a preferred embodiment of the present invention, may be: the DC link voltage, the DC link current, the speed of the motor, or the like. By means of these operating parameters the power of the pump 1 or of the motor 9, the torque of the motor 9-, or other suitable quantities may be determined.
• the control device 11 is arranged to determine if a predetermined condition is . . fulfilled based on said obtained values of operating parameters and to communicate instructions to the VFD unit 2, based on the fulfillment of said predetermined condition, in order to control the operation of the motor 9 in accordance with said pump conditions.
• the control device 11 is, in turn, controlled by processing means 12, which includes storing means 13.
• the storing means 13 may include a random access memory (RAM) and/or a non-volatile memory such as read-only memory
• the storing means 13 comprises a computer program 14 comprising instructions for bringing a computer or a microprocessor, such as the process- sing means 12, to cause method steps in accordance with the present invention.
• storing means may include various types of physical devices for temporary and/or . persistent storage of data which includes solid state, magnetic, optical and combination devices.
• the storing means may be implemented using one or more physical devices such as DRAM, PROMS, EPROMS, EEPROMS, flash memory, and the like.
• control device 11 is arranged in communication via an interface unit (not shown) with an operator unit 22 including input means in the form of a keyboard 24, which allows the operator to input, for example, control ' commands, and a display means or screen 26 for presenting information related operation of the pump, for example, time history of the operating parameters, or status information of the pump.
• the operator unit 22 is a personal computer.
• the communication link between the pump 1 and the operator unit 22 can be a wireless link or a hard wired link.
• the operator unit 22 can, in turn, be connected to a communications network, such as the Internet. By means of the operator unit 22, the operator is capable of monitoring the operation of the pump as well as different operating parameters associated to the operation thereof via the display 26.
• the display is a touch sensitive screen and in this case a number of soft-keys • can be arranged on the screen in order to present different commands at different presented interfaces on the display 26.
• the operator unit may comprise storing means (not shown) , which, in turn, may include a random access memory (RAM) and/of a non-volatile memory such as read-only memory
• storing means may include various types of physical devices for temporary and/or persistent storage of data which includes solid state, magnetic, optical and combination devices.
• the storing means may be implemented using one or more ' physical devices such as DRAM, PROMS, EPROMS, EEPROMS, flash memory/ and the like.
• Running data of the pump 1, such as operating parameters like running time, number of starts , energy consumption, and alarm data, as well as service record can be obtained and stored in a logging file in the storing means 13.
• the logging file can be presented for an operator by means of the operator unit 22.
• the logging file can be downloaded to the operator unit 22 for, e.g. storage.
• control device 11 can be realized by means of a processor including, inter alia, programmable instructions for executing the methods according to the present invention.
• the control device is implemented in the form of a micro-chip or the like data carrier comprising software adapted to execute the functions described above and hereinafter.
• Figs. 7-9 alternative embodiments of the present invention are shown. Like or similar parts and/or devices in Figs. 1, 2 and 7-9 are being denoted with the same reference numerals.
• the control device 11 which may be encapsulated in a hermetically sealed housing, is arranged on an outer surface of the pump housing.
• the control device 11 can be attached or fixed at the housing in a number of ways.
• the device 11 can be fixed by means of screws.
• the control device 11 is in form of a plug-in unit adapted to be inserted in a control device receiving recess 15.
• the control device 11 is arranged in the control panel 22.
• Fig. 4 the general principles of "the method for operating a pump according to a first aspect of the present invention will be described.
• This first aspect of the method according to invention deals with the snoring operation problem or the dry running operation problem, which, as discussed above, entails increased wear of pump part such as the impeller and the seals, may cause the pump motor to overheat and also leads to- that unnecessary energy is consumed.
• the first aspect of the invention provides for a an efficient way of operating a pump 1 comprising a VFD unit 2, as described with reference " to any one of Figs. 1-2 and 7-9 in respect of energy consumption, pump life, and durability.
• the operation of the pump is ini- tiated, i.e. the pump is started.
• steps 42 and 44 it is determined if a predetermined condition is fulfilled.
• the pump is operated at a first speed level for a predetermined period of time and at a second speed level for a predetermined period of time.
• said first speed level and said second speed level are low speed levels.
• the power of the motor 9 is determined and thereafter, at step 44, it is checked whether the relation between the speed of the motor 9 and the power of the motor is approximately a cubic function (if the power of the motor is proportional to the cube of the speed of the motor) using the two speed levels and the resulting power from each one of them.
• the pump can be ran in normal operation and -if the rela- tion is not a cubic function it is an indication that the pump 1 pumps air and it is determined that the liquid level is too low and the pump cannot be ran ' at the desired speed level. This determination is performed in the control device 11, e.g. in the processing means 12. It shall be pointed out that the relationship between the speed level and the resulting power not necessarily has to be cubic, other exponents may be appropriate for other mixtures of fluids, i.e. liquids and gases.
• step 44 If, in step 44, it is determined that the liquid level is not sufficient, the algorithm proceeds to step
• control device 11 sends instructions to the VFD unit 2 to stop/pause the operation of the pump during a predetermined time period, e.g. a number of minutes, maybe about 2 minutes.
• a predetermined time period e.g. a number of minutes, maybe about 2 minutes.
• step 44 determines that the liquid level is sufficient
• the algorithm pro- ceeds to step 48, where the speed of the pump 1 is increased to a desired ⁇ speed.
• the pump 1 is now operated in a normal manner.
• step 50 it is checked whether the liquid level still is sufficient, i.e. whether the pump 1 sucks air partly or mainly or if it is pumping liquid, by determining if a second predetermined condition is fulfilled. This is performed on a substantially continuous basis.
• a value of a suitable operating parameter is obtained by the sensing means 16 of the VFD unit 2, which value is communicated to the control device 11.
• the DC link voltage, the DC link current, or the like can be used directly or can be used to determine, for example, the torque of the motor 9 or preferably the power of the motor 9.
• a sudden drop of the power of the motor 9 during operation indicates that the pump 1 pumps air instead of liquid.
• the second condition is a comparison between the power of the motor 9, for example, and a predetermined reference level, which may be stored in the storing means 13, and if the power of the motor is lower than the predetermined reference level, it is determined that the liquid level is too low.
• the predetermined level may be about 70% of the maximum power of the motor for the present speed of the. motor 9.
• a step comparable to step 42 may be performed at a regular basis between step 48 and step 50, in order to determine if liquid is present at the inlet of the pump 1.
• step 48 If it is determined that the liquid level at the inlet of the pump is sufficient, i.e. the power of the motor 9 is higher than the predetermined level, the algorithm returns to step 48. On the other hand, if it is determined that the fluid level at the inlet of the pump is too low, i.e. the power of the motor is lower than the predetermined level, the algorithm instead proceeds to step 52, where the operation of the pump is stopped. Subsequently, the algorithm proceeds to step 46, where the operation of the pump is kept stopped during a predetermined period of time. When this pause period has expired, the algorithm proceeds to step 42.
• This second aspect of the method according to invention deals with the problem of maintaining the power of the pump at a substantially constant level over a large range of flows.
• the pump head/ pressure can be increased by 20% to 30% by means of the method according to the second aspect.
• the power of the pump is kept at a substantially constant level at varying pump head by adjusting the speed of the motor. Due to the fact that the pump is operated more efficient at low flows a smaller pump can be used to pump a given amount of liquid, and the wear of the pump can also be reduced.
• the inventive pump is an universally usable pump which is designed to be used in many different applications having varying demands .
• a high pump capacity may be achieved for a given pump for varying pump head by adjusting the speed of the motor.
• the second aspect of the invention provides for a an efficient way of operating a pump comprising a VFD unit 2 as described with reference to any one of Figs. 1-2 and 7-9 in respect of energy consumption and durability.
• the operation of the pump 1 is initiated, i.e. the pump 1 is started.
• the pump is ran at a desired speed level.
• An operating parameter of the pump is monitored substantially continuously and values corresponding to the operating parameter are obtained by the sensing means 16 of the VFD unit 2, which value is communicated to the control device 11.
• the DC link voltage, the DC link current, or the like can be used directly or can be used to determine, for example, the torque of the motor 9 or preferably the power of the motor 9.
• the power of the motor 9 is compared with a predetermined reference level at step 64, e.g.
• step 64 it is determined that the power level of the motor is higher than the predetermined reference level, the algorithm returns to step 62, and the operation of the pump is maintained at said desired speed level.
• step 66 the speed required to reach the predetermined power level of the motor is calculated in the processing means 12.
• step 68 the calculated speed is compared with a preset maximum speed.
• step 70 the control device 11 communicates instructions to the VFD unit 2 to run the motor 9 at the preset maximum speed, and the algorithm returns to step 64. If it is found that the calculated speed is lower than the preset maximum speed, the algorithm proceeds to step 72 " and the control device 11 communicates instructions to the VFD unit 2 to run the motor 9 at the calculated speed. Thereafter, the algorithm proceeds to step 64 where the procedure is continued.
• This third aspect of the method according to invention deals with the problem of clogging or jam of the intake and/or the impeller of th.e pump 1, which may be caused by particles in the fluid that sediment at the intake and in the impeller and build silt having a relatively thick or solid consistency.
• a large starting torque of the pump motor is required in order to initiate the rotating of the pump impeller. This consumes large amounts of energy and also wears the pump impeller and the motor.
• the third aspect of the invention provides for a an efficient way of operating a pump comprising a VFD unit 2 as described with reference to any one of Figs. 1-2 and 7-9 in respect of energy consumption, durability and starting reliability.
• the operation of the pump 1 is initiated, i.e. the pump 1 is started.
• the pump is ran at a desired speed level.
• a check is performed whether the pump is clogged/jammed. This can as an example be performed in the following two ways.
• One way is to measure an operating parameter of the pump and compare it with a predetermined reference level, for example, determine the power of the motor 9 and comparing it with a predetermined reference level of the power of the motor 9, for example, the rated power of the motor 9. If the measured power of the motor is higher than this predetermined reference level, it is an indication of a clogged/jammed condition.
• the second way is to monitor an alarm function of the variable frequency drive means 2 and an alarm indicating DC link over-current is used as an indication of a clogged/jammed condition.
• step 84 If it, in step 84, is determined that the pump 1 is not clogged, the algorithm returns to step 82, where the operation of the pump 1 is maintained. On the other hand, if it is determined that the pump 1 is clogged, the algorithm proceeds to step 86, where the control device 11 communicates instructions to the VFD unit 2 to drive the impeller reversely at a first speed during a prede- • termined period of time. After the predetermined period of time the pump 1 is stopped and then ran in a forward rotating direction again. Preferably, such a cycle lasts about 1-10 seconds. Then, at step 88, it is checked whether the clogging state has ceased, as is performed at step 84 above. If not, the procedure returns to step 86.
• step 82 In order to prevent clogging during normal operation of the pump 1, the following procedure can be performed at regular intervals : running the pump 1 reversely at a predetermined speed during a period of time having a predetermined length, stopping the pump 1 after said period and running the pump 1 at its normal rotation direction. Thereby, the operational reliability of the pump can be improved still more.
• the lines shown at reference numbers 30 and 32 are examples of liquid flow and head ratio for a certain pump 1, which is supplied with a 3 phase voltage having a frequency of 60 Hz from the VFD unit 2.
• 60 Hz is the standard frequency in some countries in the power mains, but by means of the VFD unit 2, this level may be increased considerably, e.g. up to 150 Hz, and by doing so said lines 30, 32 will be more or less offset in an direction upwards in the chart of fig. 3, and a certain pump may be used for very fluctuating applications and conditions.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Control Of Non-Positive-Displacement Pumps (AREA)
• Control Of Positive-Displacement Pumps (AREA)

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• 2005
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• 2006
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  • 2007-09-25 IL IL186295A patent/IL186295A/en not_active IP Right Cessation
• 2008
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