Abstract:
A dart launcher launches a dart by placing the dart within a launcher bore formed within a launcher body. The launcher body also defines a central bore coupled inline with a tubing string and in fluid communication with the launcher bore. The launcher bore is formed at an angle to the central bore. A release assembly is coupled to the launcher body and includes a release rod protruding into the launcher bore to selectively release the dart. A visual indicator assembly is coupled to the launcher body downstream from the release assembly and includes a flapper protruding into the launcher bore. The release assembly is actuated by the dart rotating the flapper to rotate an arm from a non-released position to a released position.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates in general to drop balls, plugs, or darts used to operate well tool functions and, in particular, to a drop ball, plug, or dart launcher with a status indicator. 
         [0003]    2. Brief Description of Related Art 
         [0004]    Standard dart or ball launchers have a member that defines a central bore that may be coupled inline with a drill or tubing string. The launchers also include an angular bore that intersects the central bore at a shallow angle between the angular bore and the central bore. A dart or ball is dropped into the angular bore, and after opening a series of valves, the ball or dart is introduced into the central bore for further movement of the dart or ball down the borehole. There, the dart or ball will land at a predetermined location to block the borehole and allow hydraulic tool operations. In order to minimize the potential that the ball will snag or hang up as it moves from the angular bore to the central bore, the angle of the intersection between the two axes is as close to zero degrees as possible. This necessitates that the launcher must be very tall to smooth out the transition between the angular bore and the central bore. The height can make the launcher very difficult to access and operate. 
         [0005]    Other devices couple inline with the drill or tubing string and use a series of valves to launch the ball or dart. The dart or ball may become stuck or snagged at the valve openings, preventing successful release of the dart or drop ball. In addition, these types of devices require bypass passages within the valves so that fluids may flow around the darts and valves prior to launching the dart or ball. These passages restrict fluid flow through the running string and may become clogged. Clogging of these passages will, in turn, require stoppage of drilling operations in order to remove and reset the launcher for operation. Even when not blocked, these passages may restrict the flow of fluid downhole, causing further complications in drilling operations. 
         [0006]    Still other devices may couple inline with the drill or tubing string and use a series of balls to launch darts or plugs contained within the device. These devices rely on complex landing and sliding sleeve devices, to bypass the fluids around the landed balls and darts, again restricting fluid flow through the string. These devices also do not provide an indication that the proper dart or plug has been launched following landing of the ball. 
         [0007]    Generally, following launch of a ball, dart, or plug, operators wait for an increase in pressure within the tubing string to indicate that the ball, dart, or plug has properly released into the drill string and landed at the ball, dart, or plug seat. Operators may then proceed with operations such as cementing or running tool actuation. However, in some wells, particularly in deep subsea wells, the distances between the operating platform and the landing location are large enough that it may take over an hour for the dart to land at the seat. As a result, operators may proceed with operations following release of the ball, dart, or plug but before they have received any indication that the ball, dart, or plug has landed. In the event that the ball, dart, or plug becomes hung up or snagged in the launcher and does not release into the tubing string, the well may be significantly damaged, necessitating expensive and time consuming repair operations. Some launchers include an electrical system for indicating that the dart, ball, or plug has released, however these systems require complex components that are prone to failure and difficult to adapt to changing types and sizes of balls, darts, and plugs. Thus, there is a need for a launcher that launches the dart or ball from an inline coupling without restricting fluid flow through the central bore of the tubing and that may provide an indication of a successful launch of the ball, dart, or plug. 
       SUMMARY OF THE INVENTION 
       [0008]    These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by preferred embodiments of the present invention that provide a modular dart launcher with a status indicator and a method for using the same. 
         [0009]    In accordance with an embodiment of the present invention, a wellbore drop member launcher is disclosed. The launcher includes a launcher body defining a central bore having a central bore axis, the launcher body having a lower end configured to attach to a string of pipe extending into a wellbore. The launcher body also defines a launcher bore having a launcher bore axis at an angle to the central bore axis, the launcher bore in fluid communication with the central bore. A release assembly is coupled to the launcher body and has a release rod protruding into the launcher bore to prevent movement of a drop member positioned within the launcher bore in a drop member hold position. The release assembly is configured to move the release rod to a drop member release position to selectively release the drop member positioned within the launcher bore. A visual indicator assembly is, coupled to the launcher body and is configured to provide a mechanically produced visual indication that the drop member has moved from the launcher bore to the central bore. 
         [0010]    In accordance with another embodiment of the present invention, a wellbore drop member launcher is disclosed. The launcher includes a launcher body defining a central bore having a central bore axis, the launcher body having a lower end configured to attach to a tubing string extending into a wellbore. The launcher body also defines a launcher bore having a launcher bore axis at an angle to the central bore axis. The launcher bore is in fluid communication with the central bore. A release assembly is coupled to the launcher body and has a release rod protruding into the launcher bore to prevent movement of a drop member positioned within the launcher bore into the tubing string. The release assembly is configured to move the release rod with a piston assembly from a drop member hold position to a drop member release position to selectively release the drop member. The piston assembly also biases the release rod to the drop member hold position. A pressure passage is defined by the release rod and is configured to equalize pressure between a compressible portion of the piston assembly and the launcher body, preventing premature drop member release. The pressure passage extends from an end of the release rod disposed within the launcher bore through a center of the release rod to an annular chamber within the piston assembly. An indicator housing is coupled to the launcher body proximate to an indicator bore that is defined by the launcher body and extends from an exterior of the launcher body to the launcher bore. An indicator rod extends through the indicator housing into the indicator bore. The indicator rod has a flapper formed near an end of the indicator rod and an arm secured to an opposite end of the indicator rod. The flapper and the arm are perpendicular to the indicator rod and parallel to each other. The flapper extends from the indicator bore into the launcher bore and the arm is visible to an operator. As the drop member passes the flapper it will rotate the flapper, indicator rod, and arm to indicate release of the drop member. 
         [0011]    In accordance with yet another embodiment of the present invention, a method for launching a drop member into a wellbore tubing string is disclosed. The method provides a launcher body having a central bore with a central bore axis and a launcher bore with a launcher bore axis at an angle to the central bore axis and in fluid communication with the central bore. The method places a drop member in the launcher bore and resting the drop member on a release rod of a release assembly coupled to the launcher body. The method couples a visual indicator assembly to the launcher body so that the visual indicator assembly is in communication with the launcher bore at a location downstream from the release assembly. The method couples the launcher body in line with the tubing string so that the central bore of the launcher body aligns with a body passage through the tubing string. The method then actuates the release assembly to allow the drop member to flow from the launcher body into the central bore where the drop member may move down the tubing string. The method actuates the visual indicator assembly with the drop member as the drop member moves from the launcher bore into the central bore. 
         [0012]    An advantage of a preferred embodiment is that it provides a dart launcher that may be used in high fluid pressures situations. In addition, the disclosed embodiments provide an apparatus and method to easily launch a ball, dart, or plug with minimal human intervention. Still further, the disclosed embodiments provide a modular apparatus that allows for variation in the size of the ball, dart, or plug launched. Sill further, the disclosed embodiment provides a visual indicator for an operator to confirm the successful launch of the ball, dart, or plug that does not rely on complicated electronics systems that may be prone to failure in harsh operating environments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, are attained, and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the appended drawings that form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the invention and are therefore not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
           [0014]      FIG. 1  is a perspective view of a dart launcher in accordance with an embodiment of the present invention. 
           [0015]      FIG. 2  is a sectional view of the dart launcher taken along ling  2 - 2  of  FIG. 1 . 
           [0016]      FIG. 3  is a sectional view of a release assembly of the dart launcher taken along line  3 - 3  of  FIG. 1 . 
           [0017]      FIG. 4  is an enlarged view of a portion of the dart launcher indicated at  FIG. 2 . 
           [0018]      FIG. 4A  is an enlarged view of a surface of the release assembly taken along line  4 A of  FIG. 3 . 
           [0019]      FIG. 5  is an enlarged view of the portion of the dart launcher indicated at  FIG. 2  following release of a dart. 
           [0020]      FIG. 5A  is an enlarged view of the surface of the release assembly taken along line  5 A of  FIG. 5 . 
           [0021]      FIG. 6  is a perspective view of a visual indicator assembly of the dart launcher. 
           [0022]      FIG. 6A  is a front view of the visual indicator assembly of  FIG. 6 . 
           [0023]      FIG. 7  is a sectional view of the visual indicator assembly taken along line  7 - 7  of  FIG. 2 . 
           [0024]      FIG. 8  is a sectional view of a portion of a spring plunger of the visual indicator assembly in pre-release position taken along line  8 - 8  of  FIG. 6 . 
           [0025]      FIG. 9  is a perspective view of the visual indicator assembly following release of the dart. 
           [0026]      FIG. 9A  is a front view of the visual indicator assembly of  FIG. 9 . 
           [0027]      FIG. 9B  is a sectional view of a portion of a spring plunger of the visual indicator assembly in a post-release position taken along line  9 B- 9 B of  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0028]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings which illustrate embodiments of the invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and the prime notation, if used, indicates similar elements in alternative embodiments or positions. 
         [0029]    In the following discussion, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details. Additionally, for the most part, details concerning drilling rig operation, well tool manufacture, well tool operation, well tool uses, and the like have been omitted inasmuch as such details are not considered necessary to obtain a complete understanding of the present invention, and are considered to be within the skills of persons skilled in the relevant art. 
         [0030]    Referring to  FIG. 1 , a dart launcher  11  is shown. Dart launcher  11  includes an upper tubular member or top pup  13  adapted to connect to a tubular member of a tubing or drill string. Fluid, such as drilling fluid, may circulate through dart launcher  11  from an external source coupled to top pup  13 . Dart launcher  11  also includes a lower tubular member or bottom pup  15  adapted to connect to a tubular member of a tubing or drill string. The tubing string may continue into a well to transport the fluid to a. subsurface location. A person skilled in the art will recognize that top pup  13  and bottom pup  15  have ends adapted to connect dart launcher  11  in line in a tubing string. In the illustrated embodiment, the ends of top pup  13  and bottom pup  15  comprise threaded connectors. In other exemplary embodiments, the ends of top pup  13  and bottom pup  15  may be any suitable connector type such that dart launcher  11  may couple inline to a tubing string. 
         [0031]    Dart launcher  11  also includes a launcher body  17 , a dart release assembly  19 , and a visual indicator assembly  21 . Top pup  13  and bottom pup  15  may secure to or couple to launcher body  17  on opposite ends of launcher body  17  so that top pup  13  and bottom pup  15  are coaxial with an axis  23  of a central bore  25  of launcher body  17  ( FIG. 2 ). In an exemplary embodiment, top pup  13  and bottom pup  15  secure to launcher body  17  through threaded connections. A person skilled in the art will understand that other connection types may be used. 
         [0032]    Referring to  FIG. 2 , a sectional view of launcher body  17  is shown. Launcher body  17  defines central bore  25  and a launcher bore  27  that intersects central bore  25 , allowing for fluid communication between central bore  25  and launcher bore  27 . Launcher bore  27  intersects central bore  25  at opening  35 . Opening  35  will be of a size and shape to allow a ball, plug, or dart  33  to pass from launcher bore  27  into central bore  25 . Launcher bore  27  has an axis  29 . Axis  29  my intersect axis  23  at an angle  31 . Angle  31  may comprise any suitable angle such that a drop member or dart  33  may pass from launcher bore  27  into central bore  25  for travel through a coupled tubing string. In the illustrated embodiment, central bore  25  and launcher bore  27  are formed from a single launcher body  17 . In other exemplary embodiments, central bore  25  and launcher bore  27  may be defined by separate bodies coupled or secured together. Dart release assembly  19  couples to launcher body  17  proximate to launcher bore  27  such that dart release assembly  19  may selectively allow passage of dart  33  from launcher bore  27  into central bore  25  through opening  35 . Visual indicator assembly  21  will couple or secure to launcher body  17  proximate to opening  35  such that as dart  33  passes from launcher bore  27  into central bore  25 , described in more detail below, visual indicator assembly  21  will indicate such passage. For illustrative purposes, visual indicator assembly  21  has been shown in the sectional view of  FIG. 2  to aid in the illustration of the relationship between visual indicator assembly  21  and dart release assembly  19 . 
         [0033]    Referring to  FIG. 3 , a side sectional view of dart release assembly  19  is shown. Dart release assembly  19  includes a release housing  37  and a pressure chamber  39 . Pressure chamber  39  may be a hydraulic pressure chamber, pneumatic pressure chamber, or the like. Pressure chamber  39  is coupled to an end of release housing  37  by any suitable means. In an exemplary embodiment, pressure chamber  39  is bolted to release housing  37 . Pressure chamber  39  includes a piston  41  extending from an interior of pressure chamber  39  into an actuator bore  43  of release housing  37 . Piston  41  has a piston head  45  that seals to the interior surfaces of pressure chamber  39  to divide pressure chamber  39  into two sections. Each section of pressure chamber  39  is in communication with a pressure source through ports  47 ,  49 . The pressure source may be a hydraulic pressure source that supplies hydraulic pressure through ports  47 ,  49 . In other embodiments, the pressure source may be a pneumatic pressure source that supplies pneumatic pressure through ports  47 ,  49 . In the exemplary embodiment, port  47  comprises a dart release port, and port  49  comprises a vent. Pressure may be supplied to port  47  to assert a force on piston head  45  to move piston  41  from a dart hold position, where dart  33  ( FIG. 2 ) is prevented from moving into central bore  25 , to a dart release position, where dart  33  ( FIG. 5 ) is allowed to move into central bore  25 . Pressure within pressure chamber  39  will vent through port  49  when pressure is supplied through port  47  to move piston  41  from the dart hold to the dart release position. In other embodiments, pressure may be supplied to port  49  to assert a force on piston head  45  to move piston  41  from the dart release position to the dart hold position, shown in  FIG. 3 . 
         [0034]    A shaft of piston  41  passes through a spring  51  disposed within actuator bore  43 . An end of the shaft of piston  41  will couple to a spring perch  53  disposed within actuator bore  43  opposite pressure chamber  39  in the dart hold position. Spring perch  53  may move through actuator bore  43  with piston  41  in response to application of pressure to pressure chamber  39 . Spring  51  will be positioned to bias spring perch  51  to the dart hold position of  FIG. 3 . Actuator bore  43  will include an indicator window  55  extending a portion of a length of actuator bore  43 . An indicator screw  57  will pass through indicator window  55  and couple to spring perch  53  such that a head of indicator screw  57  will remain disposed within indicator window  55 . As spring perch  53  moves through actuator bore  43  indicator screw  57  will move from an end of window  55  to an opposite end of window  55 . In an exemplary embodiment, indicator screw moves from an area spaced from pressure chamber  39  to an area proximate to pressure chamber  39 . 
         [0035]    Release housing  37  defines actuator bore  43  and a rod bore  59 . Rod bore  59  and actuator bore  43  are separated by a chamber wall  61  having a port for communication between actuator bore  43  and rod bore  59 . Spring perch  53  may include a protrusion extending into the port of chamber wall  61  such that a release rod  63  may couple to spring perch  53 . As shown in  FIG. 4 , a seal  60  may be positioned within chamber wall  61  to seal to release rod  63 . Referring to  FIG. 3 , a surface of spring perch  53  may contact chamber wall  61  in the dart hold position, limiting movement of spring perch  53  away from pressure chamber  39 . Release rod  63  extends from rod bore  59  to an exterior of release housing  37 . Release rod  63  couples to spring perch  53  such that as spring perch  53  moves with piston  61 , release rod  63  will move in response. Release rod  63  includes a flange portion  65  that seals with a seal  66  ( FIG. 4 ) to rod bore  59 . Flange portion  65  may be spaced from an end of release rod  63  coupled to spring perch  53  to define an annular passage  69  between flange portion  65  and chamber wall  61  in the dart hold position of  FIGS. 3 and 4 . Release rod  63  will include a pressure passage  67  extending through a length of release rod  63  and in fluid communication with annular passage  69 . Launcher bore  27  will be in fluid communication with annular passage  69  through pressure passage  67  such that a hydraulic pressure of launcher bore  27  will be substantially equivalent to the hydraulic pressure within annular passage  69 . Release housing  37  further includes a flange  71  formed on an end of release housing  37  opposite pressure chamber  39 . Flange  71  provides a mating contact to couple dart release assembly  19  to launcher body  17 . In the illustrated embodiment, flange  71  is bolted to launcher body  17 . 
         [0036]    Referring to  FIG. 4 , dart release assembly  19  is shown coupled to launcher body  17  and in the dart hold position of  FIG. 3 . As shown, an end of release rod  63  will extend from an end of releasing housing  37  and pass through a release rod bore  73  formed in a wall of launcher body  17 . Release rod  63  will seal to release rod bore  73  with a seal  74  positioned within release rod bore  73 . Release rod  63  will extend a sufficient distance into launcher bore  27  to prevent passage of dart  33  from launcher bore  27  into central bore  25 . A person skilled in the art will recognize that release rod  63  extends into launcher bore  27  a sufficient length to allow for variation in the size of dart  33 . Thus, dart launcher  11  may be used in various types of operations to release or launch multiple types of darts  33 . 
         [0037]    As shown in  FIG. 4A , indicator screw  57  will be positioned in an end of window  55  proximate to launcher body  17 . Referring to  FIG. 5 , pressure has been supplied to port  47 , causing piston  41  to move to the dart release position. In response, spring perch  53  has moved toward pressure chamber  39 , compressing spring  51 . Release rod  63  will be pulled into rod bore  59  until flange portion  65  contacts chamber wall  61  opposite actuator bore  43 . This will pull release rod  63  completely from launcher bore  27 , allowing dart  33  to move freely from launcher bore  27  into central bore  25  for further movement through a tubing string coupled to bottom pup  15  ( FIG. 1 ). As shown in  FIG. 5A , when spring perch  53  moves from the dart hold position to the dart release position, indicator screw  57  will move through indicator window  55  from a position proximate to launcher body  17  ( FIG. 4A ) to a position proximate to pressure chamber  39  ( FIG. 5A ). 
         [0038]    Referring to  FIG. 6 , visual indicator assembly  21  is shown. Visual indicator assembly  21  includes an indicator housing  75 , and an indicator rod  77 . Indicator rod  77  has an interior end  76  and an exterior end  78 . Indicator rod  77  will pass through an indicator housing bore  79  ( FIG. 7 ) extending through indicator housing  75 . Indicator housing  75  will define a flange  81  adapted to secure visual indicator assembly  21  to launcher body  17 . In the illustrated embodiment, flange  81  defines a plurality of bores through which a plurality of bolts are passed to thread into corresponding threaded bores of launcher body  17 . A flapper  83  is formed near interior end  76  of indicator rod  77 . Flapper  83  will be orthogonal to indicator rod  77 . Indicator rod  77  will have a length greater than a length of indicator housing  75  such that, when indicator rod  77  is passed through indicator housing  75 , interior end  76  having flapper  83  will protrude from indicator housing  75  into launcher body  17  as shown in  FIG. 7 . Exterior end  78  of indicator rod  77  will protrude from an opposite side of indicator housing  75 . An arm  85  will be secured to indicator rod  77  on exterior end  78 . In the illustrated embodiment, arm  85  is orthogonal to indicator rod  77  and extends from indicator rod  77  parallel to flapper  83 . 
         [0039]    Referring to  FIG. 7 , indicator rod  77  also includes an indicator flange  87  formed between interior end  76  and exterior end  78 . Indicator flange  87  will define an outward facing shoulder  89  adapted to contact an inwardly facing shoulder  91  formed on an interior end of indicator housing  75 . Contact between outward facing shoulder  89  and inwardly facing shoulder  91  will limit movement of indicator rod  77  in an outward direction. A seal  90  will be positioned in indicator housing bore  79  to seal indicator rod  77  to indicator housing bore  79  between outward facing shoulder  89  of indicator flange  87  and exterior end  78  of indicator rod  77 . 
         [0040]    Indicator housing  75  will secure to launcher body  17  so that indicator rod  77  will extend into an indicator bore  93 . A seal  94  will be positioned within indicator housing  75  to seal an outer diameter of indicator housing  75  to indicator bore  93 . Indicator bore  93  extends from an exterior surface of launcher body  17  to launcher bore  27 . A keyhole  95  may be formed in an interior end of indicator bore  93 . Interior end  76  of indicator rod  77  inserts into keyhole  95  so that indicator rod  77  may rotate on an axis  97 . Flapper  83  will be spaced along axis  97  from interior end  76  so that interior end  76  may fully seat within keyhole  95 . When indicator rod  77  is positioned within indicator bore  93  and seated within keyhole  95 , flapper  83  will extend into launcher bore  27 . In the illustrated embodiment, flapper  83  will extend from indicator rod  77  such that axis  29  of launcher bore  27  may pass through an outer end of flapper  83 . In other embodiments, the outer end of flapper  83  may be proximate to axis  29  of launcher bore  27 , but axis  29  may not pass through the outer end of flapper  83 . 
         [0041]    As shown in  FIG. 6 , visual indicator assembly  21  also includes a spring plunger  99  positioned within a spring plunger bore  101  formed in indicator housing  75 . Referring to  FIG. 8 , spring plunger bore  101  extends from an exterior of indicator housing  75  to indicator housing bore  79 . Spring plunger  99  will be disposed within spring plunger bore  101 . Spring plunger  99  includes a plunger housing  103 , a plunger  105 , and a spring member  107 . Plunger housing  103  secures within spring plunger bore  101  against a downward facing shoulder  109 . Plunger housing  103  has an open end proximate to indicator housing bore  79  into which plunger  105  inserts. Spring member  107  will be disposed between an internal shoulder  111  of indicator housing  103  and an end  113  of plunger  105  proximate to an exterior of indicator housing  75 . Plunger  105  includes an end  115  opposite end  113  and proximate to indicator housing bore  79 . Plunger  105  includes a flange  117  between end  113  and exterior end  115 . Flange  117  defines a shoulder  119  facing indicator housing bore  79 . Exterior end  115  protrudes from flange  117  toward indicator housing bore  79 . During operation of visual indicator assembly  21 , spring member  107  will bias plunger  105  to the position illustrated in  FIG. 8 , where shoulder  119  will contact an oppositely facing shoulder  121  to limit movement of plunger  105 . As shown, exterior end  115  may seat within a pre-launch detent  123  formed on an exterior surface of indicator rod  77 . When exterior end  115  seats within pre-launch detent  123  rotation of indicator rod  77  will be stopped. When not in the position shown in  FIG. 8 , exterior end  115  may be in contact with an exterior surface of indicator rod  77 , but shoulder  119  will be spaced from oppositely facing shoulder  121 , allowing for exterior end  115  to move into pre-launch detent  123  when indicator rod  77  is rotated. 
         [0042]    As shown in  FIG. 9B , indicator rod  77  includes a post-launch detent  123 ′. Pre-launch detent  123  will be circumferentially spaced from post-launch detent  123 ′. When flapper  83  extends into launcher bore  27  as shown in  FIGS. 2 ,  6 , and  7 , exterior end  115  of plunger  105  will extend into pre-launch detent  123  as shown in  FIG. 8 . In this manner, spring plunger  99  will prevent rotation of indicator rod  77  prior to launch of dart  33  so that visual indicator assembly  21  will not incorrectly indicate a launch of dart  33 . When dart  33  is launched, dart  33  will overcome the spring force of spring member  107 , allowing for rotation of indicator rod  77  and moving flapper  83  to the position of  FIG. 9 . Exterior end  115  of plunger  105  will then extend into post-launch detent  123 ′ ( FIG. 9B ), which is circumferentially spaced from pre-launch detent  123 , to prevent additional rotation of indicator rod  77 . 
         [0043]    During operation of dart launcher  11 , dart release assembly  19  will be in the position shown in  FIGS. 2 ,  3 ,  4 , and  4 A; visual indicator assembly  21  will be in the position illustrated in  FIGS. 2 ,  6 ,  6 A, and  7 . Referring to  FIG. 2 , dart  33  will be placed into launcher bore  27  and an end of dart  33  will rest on release rod  63  ( FIG. 4 ). As shown in  FIG. 2 , a plug  125  will be placed within launcher bore  27  behind dart  33  to limit entry of undesired objects into launcher bore  27  and prevent release of fluid from launcher bore  27 . As shown in  FIGS. 2 ,  6 ,  6 A, and  7 , flapper  83  will extend into launcher bore  27  perpendicular to axis  29  of launcher bore  27  so that a flat portion of flapper  83  may contact an object moving through launcher bore  27 . Similarly, arm  85  will be perpendicular to launcher bore  27 . Pressure passage  67  will equalize pressure between annular passage  69  and launcher bore  27  to prevent hydraulic pressure in launcher bore  27  from acting on release rod  63  to cause premature release. Plunger  115  of  FIG. 8  will be positioned within pre-launch detent  123 . 
         [0044]    When release of dart  33  is desired, pressure will be supplied to port  47  to act on piston head  45 . This will result in movement of piston  41  from the position shown in  FIG. 3  to a position where piston head  45  is proximate to port  49 . As shown in  FIG. 5 , this will result in movement of release rod  63  from launcher bore  27  to allow dart  33  to move from launcher bore  27  into central bore  25 . Indicator screw  57  will move from the position proximate to launcher body  17  as shown in  FIG. 4A  to the position spaced further from launcher body  17  as shown in  FIG. 5A . 
         [0045]    As dart  33  moves through launcher bore  27 , it will contact flapper  83  as shown in  FIG. 7 . Flapper  83  will minimally resist movement of dart  33 ; thus, dart  33  will cause flapper  83 , and consequently indicator rod  77  to rotate as dart  33  moves past visual indicator assembly  21 . As indicator rod  77  rotates, plunger  105  will release from pre-launch detent  123  and bring post-launch detent  123 ′ proximate to plunger  105 , allowing exterior end  115  of plunger  105  to move into post-launch detent  123 ′ as shown in  FIG. 9B . This will arrest rotation of indicator rod  77  in the position shown in  FIGS. 9 and 9A . As shown, arm  85  will undergo a ninety degree rotation so that arm  83  will be generally parallel to launcher bore  27  as shown in  FIG. 5 . This ninety degree rotation will indicate to an operator that dart  33  has successfully moved from launcher bore  27  into central bore  25  for further movement down a coupled drill string. 
         [0046]    Accordingly, the disclosed embodiments provide numerous advantages. For example, the disclosed embodiments provide a dart launcher capable of launching darts, balls, or plugs of different sizes. In addition, the disclosed embodiments provide a pressure balancing system to prevent premature release of the dart that may be caused by hydraulic pressure within the launcher bore. The disclosed embodiments also allow for maintenance of circulation pressure within the coupled tubing string while dropping the dart. Still further, the disclosed embodiments provide a visual indicator of a successful dart launch, that requires no external energy source, can be seen from a distance, and is easy to assemble. 
         [0047]    It is understood that the present invention may take many forms and embodiments. Accordingly, several variations may be made in the foregoing without departing from the spirit or scope of the invention. Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered obvious and desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.