Abstract:
The invention provides a valve assembly comprising a conduit with a bore  1   b  for passage of fluid therethrough. The valve assembly also comprises a sealing member that is movable within the conduit to open and close the bore. The seal assembly has a valve seat on which the sealing member seals when the bore is closed, and wherein the valve seat is movable within the conduit. The invention also provides a valve assembly comprising a sealing member, a first valve seat for the sealing member, and a second valve seat for the sealing member. The valve assemblies can be resettable. The invention further provides a flapper valve assembly wherein the flapper is pivotable through more than 90° and a bi-directional flapper valve assembly.

Description:
FIELD OF THE INVENTION 
     This invention relates to a valve assembly, particularly to a flapper valve assembly. 
     BACKGROUND 
     Flapper valves are widely used in fluid conduits that transfer fluids between an oil well reservoir and a wellhead. Flapper valves are typically one-way valves that are hinged at one side of the conduit so that in an open configuration they are disposed generally parallel to the conduit, out of the bore, but can pivot over to a closed position in which they occlude the bore of the conduit and lie across its axis. In the closed position, flapper valves typically seal against an annular seat on the inner bore of the conduit, and fluid pressure behind the flapper typically keeps the flapper tightly closed against the seat, as long as the pressure differential across the flapper persists. 
     The flapper can move back into its original open position if the pressure differential across the seat is removed or reversed, allowing fluids to flow in one direction, but retaining pressure in the other. 
     Conventional flapper valves necessarily hold pressure in only one direction, and permit fluid transmission in the other. 
     SUMMARY OF THE INVENTION 
     The invention provides a valve assembly having a conduit with a bore for passage of fluid, a sealing member that is movable within the conduit to open and close the bore, and wherein the seal assembly has a valve seat on which the sealing member seals when the bore is closed, and wherein the valve seat is movable within the conduit. 
     Typically, the valve seat is movable from a sealing configuration in which the sealing member engages with the valve seat to seal the bore, and an open configuration, in which the sealing member cannot engage the seat. 
     The seat is typically axially movable within the bore. 
     Typically, the sealing member has a first open configuration in which the bore of the valve assembly is open, and a second configuration in which the bore is closed, and fluid passage is restricted. Typically, there is also a third configuration of the sealing member where the bore is open. 
     The sealing member can be pivotally movable within the bore, and the seat can be movable axially relative to the pivot point of the sealing member. 
     According to the present invention there is also provided a valve assembly for a fluid conduit, the assembly comprising a sealing member, a first valve seat for the sealing member, and a second valve seat for the sealing member. 
     The sealing member can be a flapper. 
     At least one (and typically each) of the first and second valve seats can move relative to the flapper. The flapper can typically seal against one or other (or both) of the seats. 
     Typically, the flapper can move from a first open configuration to a closed configuration, and typically also can adopt a third (open) configuration. Typically, the flapper is hinged at one side and the hinge permits pivotal movement through more than 90° of rotation around the hinge. Typically, the hinge permits more than 180° of movement from the first open position (for example, up to 190° of movement), so that the third open position can be rotated through more than 90° with respect to the first open position. Typically, this figure is approximately 180°, although the exact degree of rotation does not matter; it is sufficient for the third open position of the flapper to be on the other side of the hinge than the first. 
     Typically, in a first configuration, the flapper can move in a first arc, and in the second configuration, the flapper can move in a second, different arc. 
     The flapper is typically biased by a spring device from the first open configuration towards the second and third configurations. Typically, the spring can be an extension spring, as this permits high spring forces, although in some embodiments the spring device can be a torsion spring. 
     The valve seats are typically movable axially within the conduit. The valve seats are typically mounted on the end faces of sleeves that slide within the bore of the conduit. The sleeves can be urged by spring devices to move them through the conduit. Electric (or other) motors can be used instead of springs. 
     The invention also provides a flapper valve assembly, wherein the flapper is pivotable through more than 90°. 
     The valve assembly can be resettable. The valve assembly can comprise a reset system the actuation of which can cause movement of the valve assembly from the closed to the open configuration. The reset system can be actuable to move at least one of the first and second valve seat to a predetermined position. 
     The valve assembly can be actuable by any of the following means: a timer; a radio frequency signal; a strain gauge; a pressure pulse; a chemical; and an electromagnetic induction. 
     Where the valve assembly incorporates a reset system, the reset system can be responsive to any of the following means: a timer; a radio frequency signal; a strain gauge; a pressure pulse; a chemical; and an electromagnetic induction for selective movement of the valve assembly into a predetermined configuration. 
     The invention also provides a bi-directional flapper valve assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described by way of example, and with reference to the accompanying drawings, in which: 
         FIG. 1  is a side-sectional view of a valve assembly in a first (open) configuration; 
         FIG. 2  is a close up view of a flapper of the valve assembly of  FIG. 1 , shown in the first (open) configuration; 
         FIG. 3  is a perspective view of the  FIG. 2  flapper; 
         FIG. 4  shows a motor sub portion of the  FIG. 1  valve assembly in the first configuration; 
         FIG. 5  is a side-sectional view of the  FIG. 3  flapper transitioning between the first (open) and a second (closed) position; 
         FIG. 6  is a side-sectional view of the  FIG. 4  flapper in the second (closed) position; 
         FIG. 7  is a perspective view of the  FIG. 5  flapper in the second (closed) position; 
         FIG. 8  is a side-sectional view of the flapper in a third (open) position; 
         FIG. 9  is a perspective view of the  FIG. 7  flapper in the third (open) configuration; 
         FIG. 10  is a side-sectional view of a motor sub of the valve assembly in the third (open) configuration; 
         FIG. 11  is an end view of the valve assembly shown in the earlier figures; and 
         FIG. 12  is a side sectional view of a housing of the  FIG. 1  valve assembly. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings,  FIG. 1  shows a side-sectional view of a valve assembly. The valve assembly has an outer casing formed by a tubular housing  1 , which is set in a string below an upper sub  2 . The respective ends of the housing  1  and upper sub  2  can have conventional end connectors (e.g. box/pin etc) in order to make up the valve assembly into a tubing string such as a production tubing string for the recovery of production fluids from hydrocarbon reservoirs. The housing  1  has an annular bore to contain the various inner components, and to act as a conduit for the flow of fluids through the housing  1  and upper sub  2 . 
     The housing  1  has different internal diameters along its length, as best shown in  FIG. 12 . At the lower end of the housing  1 , the lower bore  1   a  has a narrow inner diameter for connection to tubing string below the housing. The inner diameter increases stepwise at a first annular, shoulder  1   s  to form a middle bore  1   b , and again at a second annular shoulder  1   s ′ to form an upper bore  1   c . The upper bore  1   c  accommodates a pocketed spacer  3  set between the second annular shoulder  1   s ′ and the upper sub  2 . The pocketed spacer  3  incorporates the flapper mechanism within it, and can optionally be sealed in the upper bore  1   c  by or O-rings, or the like. 
     The pocketed spacer  3  has an inner bore  3   b  that is coaxial with the middle bore  1   b  of the housing between the first and second annular shoulders  1   s  and  1   s ′. The bore  3   b  of the pocketed spacer  3  has the same inner diameter as the middle bore  1   b , so when the pocketed spacer  3  is in place within the housing  1 , the bore  3   b  in the pocketed spacer  3  effectively constitutes a continuous extension of the middle bore  1   b . This combined bore accommodates a lower flow tube  20  and a upper flow tube  22 . The outer diameter of the flow tubes  20  and  22  are a sealing fit within the bore  3   b  of the pocketed spacer  3  and within the middle bore  1   b  of the housing, but the flow tubes  20 ,  22  are too wide to pass the shoulder  1   s , or to enter the narrow bore  2   b  of the upper sub  2 . The flow tubes are, however, dimensioned to be slidable within the bores  1   b  and  3   b.    
     The narrower bore  2   b  of the upper flow sub  2  prevents the upper flow tube  22  from moving up after it has shouldered out on the upper sub  2 . Likewise, the annular shoulder  1   s  at the lower end of the housing is narrower than the lower flow tube  20 , and thereby restrains its downward movement within the bore  1   b  of the housing  1 . Optionally the flow tubes  20 ,  22  can be sealed within the bores  1   b / 3   b  by O-ring seals etc, although in some embodiments this is not necessary. 
     The bore  3   b  of the pocketed spacer  3  is a fluid conduit for production fluids flowing from a reservoir below the housing, and a flapper  30  is provided to close the bore  3   b  of the pocketed spacer  3 , and to control the flow. It is often required to set a packer or to pressure test the conduit prior to other operations commencing and the valve assembly described is useful for providing the barrier to conduct these operations, and then being removed to permit two-way flow once the testing or packer setting operations have been completed. 
     The pocketed spacer has a first pocket p 1  and a second pocket p 2  disposed on one side of the bore  3   b . The pockets p 1  and p 2  are axially disposed below and above an annular hinge ringer  5  that is set in an annular recess in the pocketed spacer  3 . The pockets p 1  and p 2  are typically symmetrical to one another, and are each sized to accommodate the flapper  30  when it is folded parallel to the axis of the bore  3   b.    
     When the assembly is in the configuration shown in  FIG. 1 , the flapper  30  is in the first (open) configuration, and is tucked away out of the bore  3   b , in the first pocket p 1  on the pocketed spacer  3 , parallel to the axis of the bore  3   b . The first pocket p 1  is typically located above the second pocket p 2 . 
     The flapper  30  is pivotally mounted on a pivot pin  6  passing through a lever  7  on one side of the flapper  30 . The pin  6  is anchored on the annular hinge ringer  5 . The annular hinge ringer  5  is located at the mid point between the two pockets p 1  and p 2 , so that the flapper  30  can move into either pocket p 1 , p 2 , by pivoting around the pin  6 . 
     An elbow link  8  is pivotally attached to a second pin extending through the lever  7 , and a linkage arm  10  connects the elbow link  8  to a locking pin  11  located in a narrow axial bore  14  set above the flapper  30  in the pocketed spacer  3 . The narrow axial bore  14  in which the locking pin  11  is located houses an extension spring  13  held in tension between the locking pin  11  and a spring anchor  12  fixed in the lower end of the bore  14  adjacent to the upper sub  2 . The tension in the spring  13  pulls the linkage arm  10  up towards the upper sub  2 . This tension is transmitted to the flapper  30  via the link member  8  and the lever  7 , which urges the flapper  30  to move clockwise in the figures around the pivot pin  6 , out of the first pocket p 1  and into the bore  3   b . However, the flapper  30  can only pivot out of the pocket p 1  when it is unlatched from the spacer  3 , and when the bore is not obstructed by a flow tube. Thus, when the lower flow tube  20  occludes the bore  3   b , it prevents the flapper  30  from rotating out of the pocket p 1 . 
     As shown in  FIGS. 1 to 4 , in the first (open) configuration, the lower flow tube  20  occupies a position straddling both of the pockets p 1  and p 2  in the pocketed spacer  3 . As shown in  FIG. 11 , the flapper  30  has a concave profile on each face, which matches the outer profiles of the flow tubes  20 ,  22 . Thus while the lower flow tube  20  is disposed across the pocket p 1 , the flapper  30  is constrained within the pocket and cannot occlude the bore  3   b . In certain embodiments, the flapper  30  can be constrained within either pocket (or in another position) by a latch means (not shown) independently of the flow tubes, to prevent the spring  14  from moving the flapper  30  until the latch is released. 
     The lower flow tube  20  can be moved axially within the bore  3   b  by means of an electric motor  40  ( FIG. 4 ) which rotates a worm gear  41  that meshes with external striations on an annular nut  42  surrounding the lower flow tube  20  and held between thrust bearings  43  on the outer surface of the lower flow tube  20 . The threads on the inner diameter of the threaded nut  42  mesh with corresponding threads on the outer diameter of the lower flow tube  20 , so that as the electric motor  40  rotates the worm gear  41 , the threaded nut  42  held axially between the thrust bearings  43  rotates around its axis, causing relative axial movement of the lower flow tube  20  within the bore  1   b . Thus, the lower flow tube  20  can be moved axially in either direction, in accordance with the direction of rotation of the electric motor  40 . 
     In some embodiments, the motor  40 , worm gear  41  and threads on the threaded nut  42  are chosen so that the lower flow tube  20  only moves a small distance for each rotation of the nut  42 . This enables very precise axial movements of the lower flow tube  20 , so that its exact position within the housing  1  can be known in accordance with the readings from (or signals to) the electric motor  40 . The motor can be programmed to execute a certain number of rotations of the motor (corresponding to a precise axial translocation of the flow tube  20 ) when it receives a signal to do so. The motor can be programmed to execute a pattern of movements corresponding to several different axial positions of the flow tube  20 . 
     In some embodiments, the striated nut  42  can be replaced by a ball screw. 
     The axial position of the upper flow tube  22  within the bore of the pocketed spacer is typically restrained by a collet  15  which is captive in an annular groove  3   g  on the inside of the pocketed spacer  3 , and which extends into the bore in which the upper flow tube  22  is housed. The collet  15  has inherent resilience, and is normally biased radially inwards. Thus in the absence of any other forces, it contracts the outer surface of the upper flow tube  22 . The outer surface of the upper flow tube  22  has three grooves  23 ,  24  and  25  to receive the collet  15 . The upper groove  25  has mutually parallel sides that are perpendicular to the axis of the bore  3   b , so that when the collet  15  is in the upper groove  25 , it prevents relative movement between the collet  15  and the flow tube  22 . The lower two grooves  23  and  24  each have one lower side that is perpendicular to the axis of the bore  3   b , and one upper side that is ramped. Thus, when the collet  15  is in the lower grooves, the flow tube  22  cannot move up relative to the collet  15 , because the perpendicular lower side of each groove  23 ,  24  shoulders out on the collet  15 . However, axial downward movement of the flow tube  22  relative to the collet is permitted, because the collet can slide up the ramped upper side of each groove  23 ,  24  and expand radially out of the groove  3   g.    
     The annular groove  3   g  housing the collet  15  connects the bore  3   b  housing the upper flow tube  22  with the axial passage  14  housing the spring  13  and the locking pin  11 . The locking pin  11  has a step between a narrow diameter portion  11   a  at its lower end, and a large diameter portion  11   b  at its upper end. When the large diameter portion  11   b  at the upper end of the locking pin is situated over the annular groove  3   g  containing the collet  15 , it prevents radial expansion of the collet  15 , and keeps it pressed radially inwards into one of the grooves  23 ,  24  on the outer surface of the upper flow tube  22 . The collet  15  cannot travel up the ramped sides of the grooves  23 ,  24  because it cannot expand radially out of the groove  3   g , and so when the large diameter portion of the locking pin  11   b  is axially aligned with the groove  3   g , the collet cannot expand radially, and axial movement of the upper flow tube  22  within the bore  3   b  is thereby prevented. When the narrow diameter portion  11   a  of the locking pin  11  is located over the collet  15  and groove  3   g , the collet is able to radially expand within the annular groove  3   g , and thus the collet  15  can radially expand and slide up the ramped sides of the grooves  23 ,  24 , and the upper flow tube  22  can move axially downwards within the bore  3   b.    
     The upper flow tube  22  is biased downwards by a spring (not shown) disposed between the upper end of the lower flow tube  20  and the lower end of the upper sub  2 . The spring is strong, and is sufficient to drive the flow tube  22  downwards, and thereby radially expand the collet  15  by means of the ramped sides of the grooves  23 ,  24  on the outside of the upper flow tube  22 . 
     In use, the valve assembly is run into the hole in the open configuration shown in  FIGS. 1 to 4 . The upper flow tube  22  is locked against axial movement by the collet  15  being radially compressed within the grooves  3   g  and  23 . The large diameter portion  11   b  of the locking pin  11  is axially aligned with the collet  15 , preventing its expansion, and thereby locking the upper flow tube  22  down and keeping the spring above it in compression. The lower flow tube  20  is at its uppermost position driven axially up against the upper flow tube  22 , and keeping the flapper  30  in the pocket p 1 , preventing its rotation around the pivot pin  6 . Thus, fluid is free to flow through the continuous bore  3   b  in either direction. 
     The valve assembly can be used in this way for circulating fluid in a conventional tool string. 
     When the flapper valve assembly is to be closed to occlude the bore  3   b , for example during packer setting or pressure-testing operations, the motor  40  is activated and the nut  42  spins on its axis for the desired number of revolutions to move the lower flow tube  20  axially downwards within the bore  3   b  until the upper end of the lower flow tube  20  is level with the hinge ringer  5 , between the pockets p 1  and p 2 . A latch member (not shown) typically keeps the flapper  30  in the pocket p 1 , and thus prevents movement of the locking pin  11  within the axial channel  14 , and thereby prevents axial movement of the upper flow tube  22 , by means of the collet  15 . 
     Once the lower flow tube  20  has moved downwards away from the upper pocket p 1  in which the flapper  30  is housed, the latch is released and the flapper  30  is then free to move down across the bore  3   b . The tension applied to the flapper  30  by means of the spring  13 , transmitted through the locking pin  11 , linkage arm  10 , elbow link  8  and lever  7  then starts to move the flapper  30  pivotally around the pivot pin  6  as shown in  FIG. 5 .  FIG. 5  is a partial sectional view with the lower flow tube  20  omitted for clarity. Normally the lower flow tube  20  would be in the position shown in  FIG. 6 . 
     Optionally, embodiments can be constructed without a latch to keep the flapper  30  in the upper pocket p 1  until the lower flow tube  20  has reached the hinge ringer  5 . In such embodiments, the force applied by the spring  13  to the flapper  30  to rotate it around the pivot pin  6  can be fairly weak, and the friction and inertial forces involved mean that the lower flow tube  20  has almost reached the hinge ringer  5  as shown in  FIG. 6  by the time the flapper  30  starts to rotate around the hinge pin  6  into the bore  3   b  of the pocketed spacer. 
     As the spring  13  contracts, the large diameter portion  11   b  of the locking pin  11  is pulled upwards in the axial channel  14  as the flapper  30  rotates around the pivot pin  6 . Just as the flapper  30  reaches the position shown in  FIG. 6  where the flapper  30  is disposed across the axis of the bore  3   b , the large diameter portion  11   b  of the locking pin  11  clears the annular groove  3   g  containing the collet  15 , leaving the collet  15  free to expand radially out of the groove  3   g . At that point, the spring (not shown) urging the upper flow tube  22  downwards in the bore  3   b  drives the radial expansion of the collet  15  by means of the ramped side of the groove  23  on the outer surface of the upper flow tube  22  so that the upper flow tube  22  moves rapidly downwards to collide with the upper face of the flapper  30  in its closed position as shown in  FIG. 6 . A seal on the lower face of the upper flow tube  22  mates with a matching annular seal face on the upper side of the flapper  30 , and at the point of collision, the collet  15  held in the groove  3   g  is axially aligned with the second groove  24  on the outer surface of the upper flow tube  22 . Groove  24  is asymmetric in a similar manner to groove  23 , and has one lower perpendicular side, and one upper ramped side. As the lower perpendicular side of the groove  24  passes the collet  15 , the collet is able to recoil radially inwards into the groove  24 , and has enough inherent resilience to do so without external forces being applied to it. At that point, the lower sealing surface on the end of the upper flow tube  22  is sealed against the upper seal face of the flapper  30 . The upper flow tube  22  is pressed against the flapper  30  by the spring above it. 
     The seal between the upper surface of the upper flow tube  22  and the lower seal face of the flapper  30  is not tight at this point, and there is a certain amount of axial “slop” within the system because of the tolerance of the groove  24  and the collet  15 . In order to remove the slop and seal the bore  3   b , the electric motor  40  is then signalled to initiate axial movement of the lower flow tube  20  back up the bore  3   b  in order to compress its upper seals on its end face against a corresponding annular seal face on the lower surface of the flapper  30 . The motor  40  can be driven in reverse until the flapper  30  is tightly sealed between the seal faces of the upper and lower flow tubes. The lower flow tube  20  is typically sealed within the bore of the housing  1  and/or pocketed spacer  3 , and optionally the upper flow tube  22  can be sealed in the same way, thereby preventing fluid communication across the flapper  30  while it is in the closed position shown in  FIG. 6 . 
     The flapper  30  is now resistant to pressure differentials in either direction. This permits pressure testing or packer setting operations to be carried out. 
     In some embodiments, the upper flow tube  22  can be initially retained in its upper position shown in  FIG. 1  while the lower flow tube  20  is lowered to enable operation of the flapper  30  against the static seat provided by the lower flow tube  20  in a conventional manner. Thus the flapper  30  could be freed to pivot around the pivot pin  6  in and out of the upper pocket p 1  with the lower flow tube  20  in the  FIG. 6  position, so that fluids flowing up the lower flow tube  20  could pass the flapper  30  in a conventional manner, but fluids flowing in the opposite direction would set up a pressure differential and close the lower seal face of the flapper  30  against the lower flow tube  20 . 
     Alternatively, the upper flow tube  22  can be moved to the position shown in  FIG. 6 , and latched there, with its lower end axially aligned with the annular hinge ringer  5 , and the lower flow tube  20  can be moved down the bore and also latched by separate latching means, so that the flapper  30  can then pivot around the pivot pin  6  in and out of the lower pocket p 2  and seat against the seal face on the upper flow tube  22  in the  FIG. 6  position, so that fluids flowing down the upper flow tube  22  could pass the flapper  30  in a conventional manner, but fluids flowing in the opposite direction would set up a pressure differential and close the upper seal face of the flapper  30  against the upper flow tube  22 . Typically, the flapper  30  can be latched in the closed position until the lower flow tube  20  has cleared the lower pocket p 2 . 
     Optionally, the collet  15  can be held above the perpendicular side of the groove  24  and kept from expansion by the large diameter portion  11   b  of the locking pin  11  as previously described to prevent the axial movement of the upper flow tube  22  within the bore  3   b , so that the upper flow tube  22  can remain with its upper seal face in axial alignment with the hinge ringer  5  as shown in  FIG. 6  and  FIG. 7 , and the flapper  30  can seat against the upper flow tube  22 , and flap downwards into the lower pocket p 2 . Fluid flowing down the bore  3   b  can then pass the flapper  30  in the normal way, but fluid flowing up the bore  3   b  sets up a pressure differential across the seal between the upper face of the flapper and the end seals on the upper flow tube  22 , which closes the flapper against the seat on the upper flow tube  22  and prevents fluid passage in that direction. If desired the upper flow tube  22  can be latched in position to operate the flapper  30  in this direction for a period of time. 
     However, in most cases, the seal provided by the flapper  30  being squeezed between the two flow tubes as shown in  FIG. 6  is sufficient to permit pressure testing or packer setting, and once these operations are completed, the operator will want to remove the seal completely and resume two-way circulation of fluids within the bore  3   b . Two-way fluid communication can thus be restored across the flapper  30  after one-way operation in both directions. 
     When two way flow through the housing is to be re-established, the lower flow tube  20  is moved axially downwards in the same manner using the electric motor  40  to permit downward movement of the flapper  30  around the pivot pin  6  as shown in  FIG. 8 . 
     Once the lower flow tube  20  has moved clear of the lower pocket p 2 , the upper flow tube  22  can be unlatched to move axially within the bore  3   g . This can be achieved with by separate latches, or by manipulating the tension of the spring  13  to contract further to pivot the flapper  30  around the pivot pin  6 , causing the flapper  30  to enter the lower pocket p 2 , out of the bore  3   b , and causing the large diameter portion  11   b  of the locking pin  11  to clear the groove  3   g , thereby allowing the collet  15  to expand radially and release the upper flow tube  22  for axial movement in the bore  3   b.    
     The spring between the upper sub  2  and the upper flow tube  22  then urges the upper flow tube  22  downwards, causing radial expansion of the collet  15  by the ramped side of the groove  24  as previously described. 
     The disengagement of the locking pin  11  from the collet  15  thus enables the axial movement of the upper flow tube  22  past the hinge ringer  5 , under the flapper  30  and into sealing contact with the lower face of the lower flow tube  20 . At that point, the collet  15  then snaps into the plain annular groove  25  above the groove  24 , thereby locking the upper flow tube  22  against axial movement in either direction. At that point, the electric motor can then be driven again in reverse to move the lower flow tube  20  up in order to press the end seals of the flow tubes together and establish a two-way conduit for flow of fluid through the bore  1   b  of the housing. This also takes up any axial slop in the system. 
     The concave profile on the upper and lower surfaces of the flapper  30  accommodates the outer surfaces of the flow tubes. In certain embodiments, the flapper can be latched in position within either pocket, or within the closed position. 
     The flapper  30  and flow tubes  20 ,  22  can be resettable downhole. The valve assembly can be programmed to cause selective movement of the flapper  30  and flow tubes  20 ,  22  to a predetermined reset configuration. 
     Signalling mechanisms used to initiate the electric motor can be of any suitable kind, for example, RFID tags can be dropped through the bore in order to initiate pre-programmed activities of the electric motor, or electric control lines can extend from surface. Pressure pulses in the bore or hydraulic lines can also be used for signalling, or any other conventional signalling pathway currently used for the activation of downhole tools. Other means of actuating the motor can involve the use of a strain gauge, specific chemicals or electromagnetic induction. The motor can typically be powered by onboard batteries housed within the pocketed spacer, or electric power can be supplied from cables within the string. If desired, the motor can be a hydraulic motor and other variations can be incorporated without adhering to the particular embodiments described herein. 
     The seals between the flapper and the flow tubes can be carried on the flow tubes or the flapper. The seals can be metal-to-metal or conventional resilient seals. The precise form of seal is not critical. In some embodiments, it may be preferable to provide one seal on a flow tube, and the other seal in the flapper, depending on the orientation of the flapper. 
     Clearly, the flapper can operate in either direction, and possible embodiments are not limited to those described herein. 
     Modifications and improvements can be incorporated without departing from the scope of the invention.