Patent Abstract:
The disclosed embodiments relate to a fuel line valve for an aircraft, that includes a shell capable of rotation inside the valve body and connected to a driving shaft driven by an electric actuator. The valve further includes a torque generation means and position detection means. The torque generation means are connected to the shell and generate a torque that varies based on the position of said shell in the valve body on the driving shaft. The position detection means provide electric signals characterizing the positions of said driving shaft. The disclosed embodiments also relate to a method for diagnosing the operation of such a valve in order to detect a failure during the operation thereof, and to a device for implementing said method.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the National Stage of International Application No. PCT/FR2008/051276, filed on 08 Jul. 2008, which designated the United States of America, and which international application was published as Publication No. WO2009/016299, which claims priority from French Patent Application, No. FR 07 05053, filed on 12 Jul. 2007, both of which are incorporated by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    The aspects of the disclosed embodiments relate to a valve, the operation of which is provided by a remotely controlled actuator. More particularly, the disclosed embodiments relate to a device and to a method for detecting failures in the main constituent elements of a valve, such as a drive shaft or a motor of the valve, especially when the valve is used in an circuit which is important for safety reasons, such as an aircraft fuel circuit. 
         [0003]    Aircraft fuel circuits generally include fuel valves for performing functions such as cutting off the feed to the engines, opening for refueling or transferring fuel between independent tanks. 
         [0004]    As illustrated in  FIG. 1 , a fuel valve  1  comprises an actuator  11  driven by an electric motor  12  coupled to a reduction gear. The actuator  11  rotates a spherical ball  13  by means of a drive shaft  14  which penetrates into a fuel tank  15 . The spherical ball  13  is inserted into a valve body  16  and is mounted so as to rotate as one around an axis  132  inside said valve body. The spherical ball  13  has a through-opening  133  of axis  134 , approximately perpendicular to the axis  132 . The valve body  16  has two approximately cylindrical ends  161 , of diameter substantially smaller than the diameter of the spherical ball, to which ends fuel flow pipes  17  are fixed. The two ends  161  of axis  171  are substantially aligned, approximately perpendicular to the axis  132 . 
         [0005]    In such a fuel valve, there is no intermediate position in normal operation, the valve either being in an open position or in a closed position. 
         [0006]    When the valve is in an open position, to allow fuel to flow, the axis  134  of the opening  133  of the spherical ball  13  and the axis  171  of the flow pipes  17  are substantially coaxial. 
         [0007]    When the valve is in a closed position, to block the flow of fuel, the axis  134  of the opening  133  of the spherical ball  13  and the axis  171  of the flow pipes  17  are substantially perpendicular. 
         [0008]    The current methods for monitoring such valves consist in comparing the controlled position of the valve and the detected position of the valve by means of switches positioned in the actuator  11 . A fault in the monitoring devices is associated with the risk of one or more switches failing, for example due to electrical contact problems or to damage to the mechanism of the switch. In this case, the position of the valve cannot be determined and an error message, such as for example “unknown failure” is returned to a system for monitoring the aircraft. A maintenance operation is then necessary to close the valve in a known position and to replace the actuator  11 , which may entail taking the aircraft out of service and may require relatively long times for detecting and executing the failure. Another limitation lies in the fact that only the position of the actuator  11  is monitored, and not the actual position of the spherical ball  13  or that of the drive shaft  14 . This limitation leads to the possibility of hidden failures. Thus, it is possible for the position of the actuator  11  to be detected and sent to the flight deck although the spherical ball  13  is not in the corresponding position, for example following an undetected fault of the drive shaft  11 . Such hidden failures, among them the failure of the drive shaft  11 , are liable to affect the operational availability of an aircraft and it is necessary to program maintenance operations at regular intervals to check that the valves are operating correctly, which may prove to be penalizing for airlines. 
         [0009]    One solution consists in adding position sensors on the spherical ball  13 . However, the use of such sensors would involve introducing cables into the fuel tank, and this may lead to risks of short circuits. 
         [0010]    Patent applications US 2003/193310 and US 2005/156550 and Japanese patents JP 7280705 and JP 1121733 and Japanese patent application JP 19930349329 describe various devices using dedicated microprocessors coupled to position sensors placed either actually inside the motor or on or adjacent to the drive shaft  14 . Such solutions prove to be complex and have the drawback of increasing the number of sensors and in particular their associated power supplies close to the fuel tank. 
       SUMMARY 
       [0011]    The aspects of the disclosed embodiments provide a valve and a method of diagnosing the operation of a valve during its operation in order to detect a failure on said valve. 
         [0012]    An aircraft fuel circuit valve comprises a ball in a valve body that can be connected to fuel flow pipes, said ball being able to rotate about an axis in said valve body and secured to a first end of a drive shaft rotated by an electric actuator. The ball has a through-opening of axis approximately perpendicular to the axis of rotation and has two stable positions, at two ends of a range of rotation of said ball, such that:
       in a first position of the ball, called the open position, the axis of the opening is oriented so as to allow the fuel to flow in the pipes;   in a second position of the ball, called the closed position, the axis of the opening is oriented so as to prevent the fuel from flowing in the pipes.       
 
         [0015]    According to thedisclosed embodiments, the valve comprises:
       torque generation means positioned at one end of a secondary shaft secured to the ball, said torque generation means generating a torque, which can vary according to the position of the ball in the valve body, on the drive shaft and capable of increasing a current drawn by the actuator; and   position detection means which are positioned at a second end of the drive shaft, opposite the first end, and capable of delivering signals characterizing positions of said drive shaft.       
 
         [0018]    Advantageously, the torque generation means and the position detection means are positioned so that, when the ball passes from an open position to a closed position, the torque increases before the closed position is detected and when the ball passes from a closed position to an open position the torque increases before the open position is detected. 
         [0019]    The torque generation means do not generate significant torque until closeness of the two ends of the rotation range is reached and generate a progressively increasing torque from close to each end up to the end in question. 
         [0020]    In one embodiment of thedisclosed embodiments, the torque generation means comprise:
       a disk, secured to the secondary shaft on the side of the free end, having at least one protruding element; and   two stop elements, positioned on the valve body,
 
arranged so that the at least one protruding element is in contact with a stop element when the ball is substantially before the open position and the at least one protruding element is in contact with the second stop element when the ball is substantially before the closed position.
       
 
         [0023]    In another embodiment of thedisclosed embodiments, the torque generation means comprise:
       a disk, secured to the secondary shaft on the side of the free end, comprising at least one protruding element; and   a stop element positioned on the valve body,
 
which are arranged so that the at least one protruding element is in contact with a first flank of said stop element when the ball is substantially before the open position and the at least one protruding element is in contact with a second flank of said stop element when the ball is substantially before the closed position.
       
 
         [0026]    Advantageously, the position detection means generate at least one signal characteristic of the open position and at least one signal characteristic of the closed position. 
         [0027]    In one embodiment of thedisclosed embodiments, the position detection means comprise:
       a cam, secured to the drive shaft on the side of the second end, having at least one protruding element; and   at least one position detector sensitive to the position of the protruding element and arranged at each end of the rotation range,
 
so that the at least one position detector changes state under the effect of the protruding element.
       
 
         [0030]    In another embodiment of thedisclosed embodiments, the position detection means comprise at least two position detectors at each end of the rotation range, which are positioned so that when the ball passes from an open position to a closed position, the first position detector delivers the signal characteristic of the position of said drive shaft before the second position detector and when the ball passes from a closed position to an open position, the first position detector delivers the signal characteristic of the position of said drive shaft before the second position detector. 
         [0031]    The disclosed embodiments also relate to a method of diagnosing the operation of a fuel circuit valve during operation, in which consistency of a control signal, sent to the actuator in order to make the ball pivot, with the signals generated by the torque generation means and the position detection means, is checked, or an inconsistency is detected. 
         [0032]    The disclosed embodiments also relate to a device for implementing the method. Said device comprises:
       control means, capable of controlling the rotation of the electric actuator and of recording the signals generated by the torque generation means and the position detection means;   power supply means, capable of delivering a necessary electric current to the actuator;   current control means, capable of measuring the intensity of the current and of analyzing the current drawn by the actuator; and   maintenance means, capable of generating a warning message in the event of the valve failing.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]    The disclosed embodiments will be described in detail with reference to the figures, which show: 
           [0038]      FIG. 1 , already mentioned, a sectional view of a fuel valve according to the prior art; 
           [0039]      FIG. 2 , a sectional view of a fuel valve according to thedisclosed embodiments; 
           [0040]      FIG. 3 , a top view of torque generation means associated with the fuel valve; 
           [0041]      FIG. 4 , an exploded view of the torque generation means associated with the fuel valve; 
           [0042]      FIG. 5 , a view of the position detection means associated with the fuel valve; and 
           [0043]      FIG. 6 , a schematic illustrating a failure detection device which includes the fuel valve according to thedisclosed embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0044]    A fuel valve  1  of an aircraft fuel circuit according to thedisclosed embodiments, as illustrated in  FIG. 2 , includes an actuator  11  driven by at least one electric motor  12  coupled to a reduction gear. The motor-driven actuator  11  rotates a drive shaft  14 , which penetrates into a fuel tank via a damp-proof passage in one wall of the tank. The drive shaft  14 , at a first end  143 , drives a spherical ball  13 . 
         [0045]    The spherical ball  13  is secured to a secondary shaft  131  and is inserted into a fuel valve body  16  with the secondary shaft  131  protruding to the outside of said valve body. The spherical ball  13  and the secondary shaft  131  are mounted so as to rotate as one about an axis  132  inside the valve body  16 . 
         [0046]    The aspects of the disclosed embodiments will be described in the case of a spherical ball  13 , although this choice is not limiting—in practice the ball may have any other shape provided that it has a surface of revolution about the axis  132 , such as for example a cylindrical shape. 
         [0047]    The valve body  16  has two approximately cylindrical open ends  161 , of diameter substantially smaller than the diameter of the spherical ball  13 , to which ends fuel flow pipes  17  are fixed. The two ends  161  of axis  171  are substantially aligned, approximately perpendicular to the axis  132 . 
         [0048]    The spherical ball  13  has a through-opening  133 , of axis  134  approximately perpendicular to the axis  132 . To allow or prevent fuel from flowing between the two flow pipes  17 , the opening  133  in the spherical ball  13  is positioned relative to said flow pipes  17  by rotating the spherical ball  13  about the axis  132 , between two stable positions:
       a first position, called an open position, to allow fuel to flow, in which the axis  134  of the opening  133  of the spherical ball  13  and the axis  171  of the flow pipes  17  are substantially coaxial; and   a second position, called the closed position, for blocking the flow of fuel, in which the axis  134  of the opening  133  of the spherical ball  13  and the axis  171  of the flow pipes  17  are substantially perpendicular.       
 
         [0051]    The fuel valve  1  further includes torque generation means  18 , as illustrated in  FIGS. 3 and 4 . 
         [0052]    The shaft  131  has, at one end  135  accessible from outside the valve body  16 , a face  136  on which a disk  181  is mounted, the disk preferably having substantially the same diameter as the face of the shaft  131 . Said disk includes at least one protruding element  183  on an outer peripheral surface  182 . 
         [0053]    Preferably, the at least one protruding element  183  is an excrescence on the disk  181  which together form one and the same part. 
         [0054]    In one embodiment, the at least one protruding element  183  is formed by a frustoconical element secured to the outer peripheral surface of the disk via the large base. 
         [0055]    Advantageously, the disk  181  is made of an elastomer material, said material having to be chosen from materials that are rigid and fuel-resistant. 
         [0056]    Preferably, the disk  181  includes, over all or part of the outer peripheral surface  182 , a foil, covering said outer peripheral surface so as to provide a wear-resistant surface. Preferably, the foil is made of a metallic material. 
         [0057]    The disk  181  is kept secured to the secondary shaft  131  by means of a cover plate  185 . To prevent any relative movement between said disk and said secondary shaft, the cover plate  185  includes blocking means  186 , such as for example a blocking groove or an anti-rotation device. 
         [0058]    The cover plate  185  and the disk  181  are fixed to the secondary shaft by means of a fixing element  187 . In the example shown in  FIG. 4 , the fixing element is a bolt associated with a washer  188 . Said bolt passes through the cover plate  185  and the disk  181 , to engage in a thread  137  associated with said bolt, machined in the shaft  131 . 
         [0059]    Two stop means  189  are fixed to the valve body  16  by means of fixing elements, such as for example a screw. 
         [0060]    The at least one protruding element  183  comes into contact, for a given angular position of the disk  181 , with a first stop element  189  and comes into contact, for another given angular position of the disk  181 , with a second stop element  189 . 
         [0061]    The two stop elements  189  are arranged in such a way that, when the spherical ball  13  is in the open position, the at least one protruding element  183  of the disk  181  is in contact with a first stop element  189  and when the spherical ball  13  is in the closed position, the second protruding element  183  is in contact with the second stop element  189 . 
         [0062]    In one embodiment, illustrated in  FIGS. 3 and 4 , in order to place the stop elements  189  in positions as far apart as possible relative to the axis  132 , the disk  181  has two protruding elements angularly offset so as to obtain the same result. 
         [0063]    Preferably, the stop elements  189  are made of a strong material such as a steel. 
         [0064]    In one embodiment, the stop elements  189  are formed by cylinders, one of the bases of which is secured to the valve body  16 . 
         [0065]    The disk  181  is representative of the position of the spherical ball  13  to which it is secured to the drive shaft  14 . 
         [0066]    When the secondary shaft  131  secured to the spherical ball  13  is rotated in a certain direction, either to open or to close said spherical ball, by the at least one motor  12 , the disk  181  is simultaneously rotated until the at least one protruding element  183  comes into contact with a stop element  189 . This results in a resistance manifested by an increase in the torque on the drive shaft  14 . 
         [0067]    A rotation range of the spherical ball  13  is thus delimited at each of the ends by an increase in the torque, measurable from an increase in the current level drawn by the at least one motor  12 . 
         [0068]    Preferably, the value of increase in the torque is sufficient to create a clear and repeatable current inrush, but care is taken to limit the drive torque to a reasonable value so as not to introduce fatigue problems at the teeth of the actuator reduction gear. 
         [0069]    Advantageously, the change in torque may be controlled by adjusting the level of deformation of the protruding elements  183  of the disk  181 . This deformation adjustment is for example performed by modifying the diameter of the disk  181  or by modifying the spacing between the stop elements  189  and the secondary shaft  131  secured to the spherical ball  13 . 
         [0070]    In another embodiment (not shown), a single stop element  189  is fixed to the valve body  16  and at least one protruding element  183  comes into contact with a first flank of the stop element  189  for a given angular position of the disk  181  and with a second flank of the stop element  189  for another given angular position of the disk  181 . 
         [0071]    The fuel valve  1  also includes position detection means  19  placed inside the actuator  11 , as shown in  FIG. 5 . Said position detection means comprise a cam  191  secured to the drive shaft  14  at a second end  141  located on the side of the actuator  11 , and therefore outside the fuel tank. 
         [0072]    The cam  191  has, on an outer peripheral surface  192 , at least one protruding element  193  which actuates, for a given angular position of the cam  191 , an angular position detector  195  and which actuates for another given angular position of the cam  191  another angular position detector  195 . 
         [0073]    The two position detectors  195  and the cam  191  are arranged in such a way that one of the position detectors  195  is actuated when the spherical ball  13  is in the open position and the other position detector  195  is actuated when the spherical ball  13  is in the closed position. 
         [0074]    In one embodiment, illustrated in  FIG. 5 , in order to place the position detectors  195  in positions as far apart as possible relative to the axis  132 , the cam  191  has two angularly offset protruding elements so as to obtain the same result. 
         [0075]    Preferably, the protruding elements  193  are excrescences on the cam  191 , forming one and the same part. 
         [0076]    In one embodiment, the protruding elements  193  are formed by frustoconical elements, which are secured to the outer peripheral surface  192  of the cam  191  via the large base. 
         [0077]    In one embodiment, the position detectors  195  are contact sensors, such as for example switches, a control lever  196  of which comes into contact with one of the two protruding elements  193  of the cam  191 . 
         [0078]    In another embodiment, the position detectors  195  are contactless sensors, such as for example Hall effect sensors. 
         [0079]    The position detectors  195  make it possible to indicate the position of the actuator  11  of the carburetor valve  1 . 
         [0080]    Advantageously, the position detection means  19  include second position detectors  197  located close to each position detector  195 . 
         [0081]    The role of the second position detectors  197  is twofold. Firstly, when the position detectors  195  are defective, said second position detectors act as an additional means for returning a signal characteristic of the position of the actuator  11 . Secondly, when the drive shaft  14  is defective, the second position detectors  197  are used as a means of signaling that the actuator has exceeded the rotation range. 
         [0082]    In another embodiment, the second position detectors  197  are contactless sensors such as, for example, Hall effect sensors. Because they are contactless, the second position detectors  197  are more reliable. 
         [0083]    Advantageously, the fuel valve is integrated into a failure detection device  20 , illustrated schematically in  FIG. 6 . Said device includes control means  21  capable of controlling the at least one motor by power supply means  22 . 
         [0084]    The rotational movement of the spherical ball  13  is initiated in response to a command generated by the control means  21 , as a function of signals received from other systems (not shown) and/or by means of a control member that can be actuated by the crew, such as for example a switch  23  positioned in the aircraft flight deck. 
         [0085]    When a command is generated, the control means  21  transmit a signal to the power supply means  22  via a data bus  24 , and said power supply means deliver, from an electrical distribution network  25 , a supply electric current to the at least one motor  12  via supply cables  29 . 
         [0086]    By activating the at least one motor  12 , the actuator  11  is rotated through approximately one quarter of a turn in the controlled direction of the drive shaft  14  which, in turn, drives the spherical ball  13 , in order to switch from the open position to the closed position or vice versa. 
         [0087]    The power supply means  22  further include current control means  26  which enable the intensity of the current to be measured and the current drawn by the at least one motor to be analyzed. 
         [0088]    When a current inrush detected by the current control means  26  is interpreted as an increase in the torque generated by the torque generation means  18 , a first signal, called a presignal for stopping the at least one motor, is generated. 
         [0089]    Under normal operating conditions, when the control means  21  position the spherical ball  13  either in the open position or in the closed position, a current is delivered to the at least one motor  12  located near the actuator  11 . Said actuator rotates the drive shaft  14  which, in turn, rotates the spherical ball  13  secured to the torque generation means  18 . The spherical ball  13  pivots until the at least one protruding element  183  of the disk  181  comes into contact with a stop element  189 . This contact incurs a resistance that opposes the rotation of the spherical ball and leads to an increase in the torque on the drive shaft  14 , manifested by inrush current drawn by the at least one motor  12 . When the current inrush is detected, the control means  21  generate the presignal for stopping the at least one motor. The at least one motor  12 , which remains powered, still drives the drive shaft  14  until the at least one protruding element  193  of the cam  191  of the position detection means  19  actuates a position detector  195 . A second signal, called the signal for cutting off the power to the at least one motor  12 , is then sent to the control means  21  which cut off the supply to the at least one motor  12 , this having the effect of stopping the drive shaft  14  and the spherical ball  13  from rotating either in the open position or in the closed position, depending on the command generated by the control means  21 . 
         [0090]    By analyzing the normal operation of the fuel valve  1 , it follows that the signals relating to a current inrush, interpreted as an increase in the torque generated by the torque generation means  18 , and relating to a state of the position detectors, which is generated by the position detection means  19 , respond to a precise logic scheme described above.
       The main failures of such a fuel valve  1  are the following:   a blockage of the spherical ball  13 ;   a rupture of the drive shaft  14 ; and   a malfunction of the actuator  11 , these having effects on said signals such that the logic scheme associated with correct operation of the fuel valve  1  is no longer respected.       
 
         [0095]    Thus, any detected inconsistency, on the basis of the signals generated by the torque generation means  18  and the position detection means  19 , is recorded by the control means  21  and a failure message is generated and then transmitted by the control means  21  to monitoring means  27  via the data bus  24 . 
         [0096]    In one embodiment, all the data necessary for the maintenance personnel to identify the failure, including for example which element is failing and the time available to make the repair, which mainly depend on the criticality of the fuel valve  1 , are stored in a maintenance means  28 . 
       Failure of the Position Detectors  195   
       [0097]    The failure detection device according to the disclosed embodiments may for example detect a failure of the position detectors  195  by means of the second position detectors  197 . 
         [0098]    When the current inrush is detected, the first signal is triggered and the drive shaft  14  continues to rotate. If the position detectors  195  are defective and therefore do not transmit signals to the control means  21 , the drive shaft  14  continues its rotation through an additional fraction of a degree until the at least one protruding element  193  of the cam  191  of the position detection means  19  is detected by the second position detectors  197 . In this situation, said second position detectors replace said first position detectors and transmit a signal to the control means  21  which cut off the supply to the at least one motor  12 . Said control means transmit a maintenance message, for example of the “defective switch” type to the maintenance means  28  so that operations to replace the defective position detectors  195  may take place. Knowing that the position detectors  195  have failed in this way does not mean that the aircraft has to be immediately taken out of service. The fuel valve  1  may thus remain in service since the spherical ball  13  rotates properly and the second position detectors  197  temporarily replace the position detectors  195 . 
       Motor Failure 
       [0099]    In another failure situation, when, as a result of a command issued by the control means  21 , no current is drawn by the at least one motor  12 , the supply to said at least one motor is interrupted. This failure is interpreted as a failure of the at least one motor  12  and a maintenance operation is programmed so as to replace the defective motor-driven actuator  11 . The maintenance operation is programmed, to be carried out sooner or later depending on the criticality of the fuel valve. 
         [0000]    Failure of the Bearings and/or the Reduction Gear 
         [0100]    In another failure situation, when cyclic anomalies are detected by the current monitoring means  26 , if said anomalies appear repeatedly at each rotation of the drive shaft  14 , these anomalies are interpreted as the sign of incipient failures in the bearings and/or in the reduction gear, for example damage to a gear wheel of the reduction gear. 
       Failure in the Drive Shaft 
       [0101]    In another failure situation, where no current inrush is detected and when the position detection means  19  transmit a power supply cut-off signal, the inconsistency is interpreted as an anomaly in the drive shaft  14 . 
         [0102]    The absence of feedback torque, manifested by the absence of current inrush in the current monitoring means  26 , makes it possible to give the control means  21  an indication that the actuator  11  has pivoted as controlled by the control means  21 , but that the spherical ball  13  has remained in its previous precontrolled position. 
         [0103]    Since the spherical ball  13  does not rotate, the at least one protruding element  183  of the disk  181  of the torque generation means  18  is not engaged in the stop elements  189 , and therefore no resistance to the movement is detected when the actuator  11  approaches the position controlled by the control means  21 . When the feedback torque is absent, the power supply cut-off signal is not detected by the control means  21  and the drive shaft  14  continues to pivot until the at least one protruding element  193  of the cam  191  of the detection means  19  actuates with one of the two position detectors  195 . Under these conditions, the actuation of the position detectors  195  is considered as a complementary first signal and the power supply to the at least one motor  12  is cut off as soon as the at least one protruding element  193  is detected by the second position detectors  197 . A message is then sent by the control means  21  to the maintenance means  28  to prevent the loss of movement of the spherical ball  13  and to program an immediate maintenance operation. In this way, the crew is immediately aware of the nature of the failure and the clear rupture of the drive shaft  14  necessarily means that the valve has to be replaced before the next flight. 
       Valve Blockage 
       [0104]    In another failure situation, when the control means  21  record a high current inrush but do not receive any indication about the position of the drive shaft  14  via the position detection means  19 , an anomaly, such as the spherical ball  13  being jammed or iced up when ice is present in the fuel flow pipes  17 , may be envisaged. Under such conditions, it is obvious that the at least one motor  12  applies a torque but the drive shaft  14  does not pivot. To discriminate between the failures and identify the presence of ice from other failure conditions, one means consists in including, in the control means  21 , an algorithm capable of recording, in a non-volatile memory, the events detected as affecting the bearings or the reduction gear or other physical parts of the valve. Thus, if subsequently it is confirmed that there are no mechanical failures, the most probable cause of the valve blockage is the presence of ice in the flow pipes  17 . 
         [0105]    Among the methods for resolving the doubt regarding the presence of ice as the cause of valve blockage, attempts to make the spherical ball  13  undergo alternating movements are advantageously initiated. Said attempts confirm the presence of ice if said spherical ball remains inactive. Another solution consists in testing the valve when the temperature of the fuel reaches a temperature sufficient for water no longer to be in the ice state. If such actions are conclusive, the incident is reported in the memory of the maintenance means  28  and a message is sent so as to initiate a maintenance operation, such as that of checking that the water has been removed from the tank in question.

Technology Classification (CPC): 8