Patent Publication Number: US-9404342-B2

Title: Top mounted choke for percussion tool

Description:
RELATED APPLICATIONS 
     The present application is related to U.S. patent application Ser. No. 14/079,323, entitled “Double Wall Flow Tube For Percussion Tool” and filed on Nov. 13, 2013, and U.S. patent application Ser. No. 14/079,362, entitled “Coating Of The Piston For A Rotating Percussion System In Downhole Drilling” and filed on Nov. 13, 2013, both of which are hereby incorporated by reference herein. 
     BACKGROUND 
     This invention relates generally to percussion tools used in downhole drilling. More particularly, this invention relates to an apparatus and method for controlling air flow within percussion tools, such as rotary bits, shear bits, and lighter hammer bits, used in downhole drilling. 
     Rotary drilling tools, such as rock bits, can benefit from percussive energy to improve drilling rate, or rate of penetration (ROP), and improve hole straightness. However, this percussive energy should be controlled. If the percussive energy is too little, the drilling tool will not create and/or propagate fractures in the rock. If the percussive energy is too much, the drilling tool life is unacceptably reduced due to bearing spalling, steel fatigue cracking, and/or other life reducing causes. Hence, to be an effective tool, the drilling tool should be efficient with low drill system pressure, but also should be able to limit percussive force at high drill system pressure. 
     A choke is commonly used to control the amount of air directed to the piston, which generates, or applies, the percussive force. The remaining amount of air that is not used, or not needed, to be directed to the piston flows into a bypass, or piston passageway, which is described in further detail below in conjunction with  FIGS. 1A and 1B . In general, chokes having a larger internal diameter, which is less restrictive to the air flow, are used when air volume is high and less air should be directed to the piston or the required percussive force for the intended application is low. Thus, the excessive air that is not used flows through the choke via this larger internal diameter. Conversely, chokes having a smaller internal diameter, which is more restrictive to the air flow, are used when air volume is small and more air should be directed to the piston or the required percussive force for the intended application is high. Again, any excessive air that is not used flows through the choke via this smaller internal diameter. 
     The location and positioning of the choke is determined by the design of the percussion tool&#39;s internal air flow paths. Generally, this location for the choke is deep inside the percussion tool and not readily accessible without disassembly of the percussion tool. The disassembly of the percussion tool is cumbersome and time intensive, resulting in excessive lost drilling time and increased operational costs. Typically, the percussion tool is disassembled from the drill string or other downhole tool, sent to a shop, and further disassembled to gain access to the choke. The choke may need maintenance due to blockage or due to needing to change out the choke with a different internal diameter choke, for example. There is a need to develop a percussion tool with a choke which can be quickly replaced and/or adjusted without disassembly of the percussion tool. 
       FIG. 1A  is a longitudinal cross-sectional view of a portion of a conventional downhole percussion tool  10  in accordance with the prior art.  FIG. 1B  is a longitudinal cross-sectional view of a remaining portion of the conventional downhole percussion tool  10  of  FIG. 1A  whereby  FIG. 1A  is intended to be joined to  FIG. 1B  along common line a-a in accordance with the prior art. The conventional downhole percussion tool  10  is described in detail in U.S. Pat. No. 7,377,338, which issued to Bassinger on May 27, 2008, and is incorporated by reference herein in its entirety. Thus, the conventional downhole percussion tool  10  is briefly described herein for the sake of describing airflow therein and the positioning of the choke  74 , or orifice plug. Referring to  FIGS. 1A and 1B , the conventional downhole percussion tool  10  includes a tool cylinder or housing  12 , a rear adapter or sub  24 , a check valve  36 , a piston  44 , a drive sub  106 , and an integrated claw bit  92 . Although an integrated claw bit is illustrated within  FIG. 1B , a bit sub (not shown) capable of receiving a claw bit, or other bit type such as a rotary or fixed cutter bit, can be used in lieu of the integrated claw bit  92 . Once the conventional downhole percussion tool  10  is assembled, a top pressure fluid chamber  78 , an annular chamber  97 , and a bottom pressure fluid chamber  88  are formed. 
     The sub  24  includes a sub passage  30  extending longitudinally therein. The check valve  36  is coupled at an end of the sub passage  30  and is positioned within the housing  12  once the sub  24  is threadedly coupled to an end of the housing  12 . The check valve  36  allows for pressurized fluid to flow from the sub passage  30  into the housing  12 ; however, the check valve  36  prevents pressurized fluid from flowing from the housing  12  to the sub passage  30 . 
     Similarly, the drive sub  106  is threadedly coupled to an opposing end of the housing  12 . The integrated claw bit  92  is movably coupled within the drive sub  106  at the opposing end of the housing  12 . The integrated claw bit  92  includes a bit passage  118  extending longitudinally therein and is in communication with one or more secondary bit passages  120 , which are in communication with an environment external to the bit  92 . The integrated claw bit  92  is capable of moving in at least an axial direction and may be capable of moving in a rotational manner as well. When the integrated claw bit  92  is in contact with the bottom of the formation or when there is a significant upward force acting upon the integrated claw bit  92 , the integrated claw bit  92  is in the dash-lined position as shown in  FIG. 1B . Conversely, when the integrated claw bit  92  is not in contact with the bottom of the formation or there is no significant upward force acting upon the integrated claw bit  92 , the integrated claw bit  92  is in the solid-lined position as shown in  FIG. 1B . 
     The piston  44  is a single-walled tube that includes a piston passage  70  extending substantially centrally therethrough. An orifice plug  74 , or choke valve, is positioned within the piston passage  70  at a top end of the piston  44 . The piston passage  70  is in fluid communication with piston base passage  72  formed within an opposing end of the piston  44 . The piston  44  also includes at least two pressurized fluid inlet ports  82  formed along a top portion of a sidewall of the piston  44  and extending into an interior of the piston  44 . The piston  44  further includes pressurized fluid conducting piston passageways  80  extending from the pressurized fluid inlet ports  82  to the opposing end of the piston  44 . Piston  44  further includes one or more exhaust passages  96  that extend from the piston base passage  72  to the annular chamber  97  formed between the piston  44  and the housing  12 . The exhaust passages  96  are offset from the pressurized fluid conducting piston passageways  80 . The piston  44  is movably positioned within the housing  12 . Once the piston  44  is properly assembled within the housing  12 , the top pressure fluid chamber  78 , the annular chamber  97 , and the bottom pressure fluid chamber  88  are formed. The top pressure fluid chamber  78  is formed between the one end of the piston  44  having the orifice plug  74  and the check valve  36 . The annular chamber  97  is formed between a portion of the perimeter of the piston  44  and the housing  12 . The bottom pressure fluid chamber  88  is formed between the opposing end of the piston  44  and the integrated claw bit  92 . 
     During operation of the conventional downhole percussion tool  10 , the tool  10  is placed in a position such that the bit  92  is urged upwardly to the position indicated by the dashed lines in  FIG. 1B  and the piston  44  will be urged to the position shown by the solid lines in  FIGS. 1A and 1B . In this position, the flow of high pressure fluid from top pressure fluid chamber  78  to annular chamber  97  is terminated since a reduced diameter portion  56  of the piston  44  is in close fitting relationship with a sleeve  62  positioned within the housing  12  and about the perimeter of a portion of the piston  44 . In this condition, pressure fluid is still communicated through pressurized fluid conducting piston passageways  80  to bottom pressure fluid chamber  88  while pressure fluid is vented from annular chamber  97  through exhaust passages  96  to the exterior of the tool  10  by way of the bit passage  118  and secondary bit passages  120 . Thus, a resultant force is exerted on the piston  44  driving it upwardly, viewing  FIGS. 1A and 1B , until the reduced diameter portion  56   a  of the piston  44  is positioned such that the communication of high pressure fluid to pressurized fluid inlet ports  82 , pressurized fluid conducting piston passageways  80 , and bottom pressure fluid chamber  88  is cut-off. A resultant pressure fluid force acting on piston  44  will continue to drive the piston  44  upwardly, viewing  FIGS. 1A and 1B , until the pressure fluid from bottom pressure fluid chamber  88  is able to vent through bit passage  118  and secondary bit passages  120 . This occurs when the bottom of the piston  44  is raised elevationally above the top of a tube  124 , which is positioned at least partially within bit passage  118  and extends outwardly from the top of the bit  92 . In this condition, a net resultant pressure fluid force acting on the top surface of the piston  44  is sufficient to drive the piston  44  downwardly to deliver an impact blow to the top surface of the bit  92  and the cycle just described will then repeat itself rapidly and in accordance with the design parameters of the tool  10 . 
     As seen in  FIGS. 1A and 1B  along with the description provided, it can be seen that the choke valve  74  is coupled to the movable piston  44  and is positioned at the top end of the piston passage  70 . Further, the check valve  36  is positioned upstream of the choke valve  74  and is coupled to at the end of the sub passage  30 . Once the tool  10  is decoupled from the drill string or other downhole tool, an operator is prevented from accessing the choke valve  74  through the sub passage  30  since the check valve blocks access to the choke valve  74 . Hence, the tool  10  must be disassembled for an operator to service the choke valve  74  and/or replace the choke valve  74 , which results in increased costs and increased time delay in drilling the hole. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and aspects of the invention will be best understood with reference to the following description of certain exemplary embodiments of the invention, when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1A  is a longitudinal cross-sectional view of a portion of a conventional downhole percussion tool in accordance with the prior art; 
         FIG. 1B  is a longitudinal cross-sectional view of a remaining portion of the conventional downhole percussion tool of  FIG. 1A  whereby  FIG. 1A  is intended to be joined to  FIG. 1B  along common line a-a in accordance with the prior art; 
         FIG. 2  is a side view of a percussion tool in accordance with an exemplary embodiment of the present invention; 
         FIG. 3  is a cross-sectional view of the percussion tool of  FIG. 2  in accordance with an exemplary embodiment of the present invention; 
         FIGS. 4A-4J-2  are cross-sectional views of the percussion tool of  FIG. 3  without the bit illustrating the operation of the percussion tool in accordance with an exemplary embodiment of the present invention; 
         FIG. 5  is a cross-sectional view of a percussion tool in accordance with another exemplary embodiment of the present invention; 
         FIG. 6  A is a perspective view of a check valve used in the percussion tool of  FIG. 5  in accordance with another exemplary embodiment of the present invention; 
         FIG. 6B  is a cross-sectional view of the check valve of  FIG. 6A  in accordance with another exemplary embodiment of the present invention; 
         FIG. 7A  is a bottom view of a check valve useable in the percussion tool of  FIG. 5  in lieu of the check valve of  FIGS. 6A and 6B , in accordance to yet another exemplary embodiment; and 
         FIG. 7B  is a cross-sectional view of the check valve of  FIG. 7A  in accordance with that exemplary embodiment of the present invention. 
     
    
    
     The drawings illustrate only exemplary embodiments of the invention and are therefore not to be considered limiting of its scope, as the invention may admit to other equally effective embodiments. 
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention relates generally to percussion tools used in downhole drilling. More particularly, this invention relates to an apparatus and method for controlling air flow within percussion tools, such as rotary bits, shear bits, and lighter hammer bits, used in downhole drilling. Although the description provided below is related to a percussion tool with a rotary bit, exemplary embodiments of the invention relate to any downhole percussion tool including, but not limited to, percussion tools having a shear bit, a lighter hammer bit, or other known bit used in percussion tools. 
       FIG. 2  is a side view of a percussion tool  200  in accordance with an exemplary embodiment of the present invention.  FIG. 3  is a cross-sectional view of the percussion tool  200  in accordance with an exemplary embodiment of the present invention. Referring to  FIGS. 2 and 3 , the percussion tool  200  includes a top sub  210 , a case  230 , a drive sub  250 , a mandrel  270 , and a bit  290 , which are viewable and accessible from exterior of the percussion tool  200 . The percussion tool  200  further includes a feed tube  320 , a feed tube mount  340 , a choke  360 , a piston  380 , one or more drive lugs  394 , an exhauster  365 , a split retaining ring  396 , and a check valve  302 , which are all positioned internally of the percussion tool  200 . Although certain components have been mentioned, greater or fewer components may be included in the percussion tool  200  without departing from the scope and spirit of the exemplary embodiment. Further, one or more components may be combined or separated from another mentioned component without departing from the scope and spirit of the exemplary embodiment. Once the percussion tool  200  is assembled, a top pressure fluid chamber  305  and a bottom pressure fluid chamber  308  are formed. 
     The top sub  210  includes a top end  311 , a bottom end  313 , a sub passage  312  extending longitudinally therein from the top end  311  towards the bottom end  313 , and a secondary sub passage  314  extending from the end of the sub passage  312  to the bottom end  313 . The top end  311  is threaded and is coupleable to a drill string (not shown) or some other down hole tool according to certain exemplary embodiments. Similarly, the bottom end  313  also is threaded and is coupled to the case  230  according to certain exemplary embodiments. The secondary sub passage  314  is in fluid communication with the sub passage  312 . The secondary sub passage  314  is larger in diameter than the sub passage  312  according to some exemplary embodiments. The secondary sub passage  314  houses a portion of the feed tube  320 , at least a portion of the feed tube mount  340 , and the choke  360  depending upon the length and positioning of the feed tube  320  according to certain exemplary embodiments. In certain other exemplary embodiments, the choke  360  is housed within the sub passage  312  or a combination of the sub passage  312  and the secondary sub passage  314  according to certain exemplary embodiments. Although not illustrated in this exemplary embodiment, the check valve  302  is optionally coupled to the top sub  210  either within the sub passage  312  or within the secondary sub passage  314  above the choke  360  and prevents the upward flow of pressurized fluid, such as air, from the top pressure fluid chamber  305  and/or the feed tube  320  to the drill string or other down hole tool positioned above the top sub  210 . This optional exemplary embodiment is illustrated and described with respect to  FIGS. 5-7B  below. Hence, in this optional exemplary embodiment, the check valve  302  allows for pressurized fluid to flow in the direction from the sub passage  312  to the case  230 ; however, the check valve  302  prevents pressurized fluid from flowing in the opposite direction. In these exemplary embodiments, the check valve  302  is removable without disassembly of the percussion tool  200  or is able to be locked open, thereby providing access to the choke  360  for replacement or service. In the current exemplary embodiment illustrated in  FIG. 3 , however, this check valve  230  is positioned within the bit  290 , which is described in further detail below. Thus, since the check valve  302  has been repositioned from the positioning in the prior art, access to the choke  360  is available without disassembly of the percussion tool  200 . 
     The case  230  is tubularly shaped and includes a top end  331 , a bottom end  333 , and a case passageway  332  extending from the top end  331  to the bottom end  333 . The case passageway  332  has a variable internal diameter along its length according to certain exemplary embodiments, however, this internal diameter is not variable in other exemplary embodiments. The top end  331  is threaded and is coupled to the bottom end  313  of the top sub  210 . Similarly, the bottom end  333  also is threaded and is coupled to the drive sub  250  according to certain exemplary embodiments. The case  230  houses at least a portion of the top sub  210 , the feed tube mount  340 , the feed tube  320 , the piston  380 , one or more drive lugs  394 , the exhauster  365 , the split retaining ring  396 , a portion of the drive sub  250 , and a portion of the mandrel  270 . Once the components of the percussion tool  200  are assembled, the top pressure fluid chamber  305  and the bottom pressure fluid chamber  308  are formed within the case  230 . 
     The drive sub  250  is tubularly shaped and includes a first portion  352  and a second portion  354 . The first portion  352  has an outer diameter equal to the outer diameter of the case  230 . The second portion  354  extends substantially orthogonally away from the first portion  352  and has an outer diameter less than the outer diameter of the first portion  352  and an inner diameter greater than the inner diameter of the first portion  352 . According to certain exemplary embodiments, the second portion  354  is threaded and coupled to the bottom end  333  of the case  230 . Once the drive sub  250  is assembled to the case  230 , the outer surfaces of both the first portion  352  of the drive sub  250  and the case  230  are substantially aligned. The drive sub  250  houses the one or more drive lugs  394  and a portion of the mandrel  270  and the feed tube  320  according to certain exemplary embodiments. 
     The mandrel  270  is a substantially solid component having a mandrel passageway  372  extending axially therethrough. The mandrel passageway  372  houses a portion of the feed tube  320  and is in fluid communication with the sub passage  312  via the feed tube  320 , which is described in greater detail below, in accordance with certain exemplary embodiments. The mandrel  270  further includes a top portion  374 , a bottom portion  378 , and a middle portion  376  extending from the top portion  374  to the bottom portion  378 . The middle portion  376  has an outer diameter less than the outer diameters of both the top portion  374  and the bottom portion  378 . The bottom portion  378  has an outer diameter equal to the outer diameter of the first portion  352  of the drive sub  250 . Further, the top portion  374  has an outer diameter less than the outer diameter of the bottom portion  378  and greater than the outer diameter of the middle portion  376 . The mandrel  270  houses a portion of the feed tube  320  and at least a portion of the exhauster  365 . Once the mandrel  270  is assembled to form the percussion tool  200 , the mandrel  270  is axially moveable with respect to both the case  230  and the drive sub  250  and a portion of the mandrel  270  is inserted and housed within the case  230 . The bottom portion  378  of the mandrel  270  is positioned adjacent to the first portion  352  of the drive sub  250  when the bit  290  is placed within the formation in contact with the bottom of the hole and with a downward force applied onto the bottom of the hole. However, the bottom portion  378  of the mandrel  270  is not positioned adjacent to the first portion  352  of the drive sub  250  when the bit  290  is placed within the formation and is not in contact with the bottom of the hole. The mandrel passageway  372  has a larger diameter at the bottom portion  378  of the mandrel  270  and is configured to receive a portion of the bit  290  therein according to certain exemplary embodiments. In certain of these exemplary embodiments, the lower portion of the mandrel passageway  372  is threaded and engages with a portion of the bit  290 . However, in alternative exemplary embodiments, the bit  290  and the mandrel  270  are formed as an integral component, such as when the percussion tool includes a hammer bit. 
     Bit  290  is a roller cone bit that is coupled to the mandrel  270  within the lower portion of the mandrel passageway  372  according to certain exemplary embodiments. The bit  290  is threadedly engaged to the mandrel  270  according to some exemplary embodiments. Although the bit  290  is illustrated as a roller cone bit in certain exemplary embodiments, the bit  290  is a different type of bit, such as a polycrystalline diamond cutter (PDC) bit, or other type of drag bit or fixed cutter bit. Alternatively, in other exemplary embodiments, the bit  290  is integrally formed with the mandrel  270 , such as a hammer bit, as a single component. Bit  290  includes a bit passageway  392  extending therein and in fluid communication with the mandrel passageway  372 . The bit passageway  392  communicates pressurized fluid, such as air, from the mandrel passageway  372  to an environment external of the bit  290 . Further, according to certain exemplary embodiments, the check valve  302  is coupled within the bit passageway  392  of the bit  290 . The check valve  302  is designed to allow flow from the mandrel passageway  372  to the environment external to the bit  290 ; however, the check valve  302  prevents flow in the reverse direction. As previously mentioned, according to some alternative exemplary embodiments as illustrated and described with respect to  FIGS. 5-7B , this check valve  302  is positioned upstream, or vertically above, the choke  360  when the check valve  302  is replaceable or is capable of being locked open. 
     As previously mentioned, the percussion tool  200  further includes the feed tube  320 , the feed tube mount  340 , the choke  360 , the piston  380 , one or more drive lugs  394 , the exhauster  365 , and the split retaining ring  396 . According to certain exemplary embodiments, the feed tube  320  is a double-wall feed tube and is tubular in shape. The feed tube  320  includes a top end  321 , a bottom end  322 , an upper portion  323 , and a lower portion  324 . The feed tube  320  also includes an inner wall  398  and an outer wall  399 . The upper portion  323  extends from the top end  321  towards the bottom end  322  and the lower portion  324  extends from the upper portion  323  to the bottom end  322 . According to certain exemplary embodiments, the upper portion  323  has a greater outer diameter than the lower portion  324 . The feed tube  320  includes a central feed tube channel  325  extending from the top end  321  to the bottom end  322  and is defined by the inner wall  398 . The central feed tube channel  325  communicates pressurized fluid from the sub passage  312  to the mandrel passageway  372 . The feed tube  320  also includes an outer feed tube channel  326 , which extends from the top end  321  towards the lower portion  324 , but remains within the upper portion  323  according to certain exemplary embodiments. The outer feed tube channel  326  is defined by the outer wall  399  and the inner wall  398  and is positioned therebetween. However, in other exemplary embodiments, the outer feed tube channel  326  extends into the lower portion  324  but not through the feed tube  320 . The outer feed tube channel  326  circumferentially surrounds a portion of the length of the central feed tube channel  325 ; however, in other exemplary embodiments, the outer feed tube channel  326  does not circumferentially surround a portion of the central feed tube channel  325 . For example, the outer feed tube channel  326  may be a single channel extending from the top end  321  or may be several discrete channels extending from the top end  321 . Additionally, the feed tube  320  includes one or more first openings  327  and one or more second openings  328  positioned about the perimeter of the upper portion  323  through the outer wall  399 . However, in other exemplary embodiments, some or all of these openings  327 ,  328  are positioned about the perimeter of the lower portion  324  when the outer feed tube channel  326  extends into the lower portion  324 . The first openings  327  communicate pressurized fluid from within the outer feed tube channel  326  to the bottom pressure fluid chamber  308  through an interior of the piston  380 , while the second openings  328  communicate pressurized fluid from within the outer feed tube channel  326  to the top pressure fluid chamber  305  via the interior of the piston  380 . According to some exemplary embodiments, the first openings  327  are radially aligned with one another at substantially the same elevation; however, in other exemplary embodiments, one or more first openings  327  are not radially aligned with one another at the same elevation. Similarly, according to some exemplary embodiments, the second openings  328  are radially aligned with one another at substantially the same elevation; however, in other exemplary embodiments, one or more second openings  328  are not radially aligned with one another at the same elevation. Yet, in other exemplary alternative exemplary embodiments, there are only one or more first openings  327  and no second openings  328  as the first openings are configured to convey pressurized fluid either to the bottom pressure fluid chamber  308  or to the top pressure fluid chamber  305  depending upon the elevational positioning of the piston  380 . In other exemplary embodiments, the first openings  327  communicate pressurized fluid from within the outer feed tube channel  326  to the top pressure fluid chamber  305  through an interior of the piston  380 , while the second openings  328  communicate pressurized fluid from within the outer feed tube channel  326  to the bottom pressure fluid chamber  308  via the interior of the piston  380 . 
     The feed tube  320  extends from within a portion of the top sub  210  to within a portion of the mandrel  270  and facilitates the communication of pressurized fluid from the sub passage  312  of the top sub  210  to the mandrel passageway  372  of the mandrel  270  and also facilitates the communication of pressurized fluid from the sub passage  312  of the top sub  210  to either to the bottom pressure fluid chamber  308  or to the top pressure fluid chamber  305  depending upon the elevational positioning of the piston  380 . According to some exemplary embodiments, the top end  321  of the feed tube  320  extends into the sub passage  312 . According to some exemplary embodiments, the outer diameters of the top end  321  of the feed tube  320  and the sub passage  312  are substantially the same such that the top end  321  frictionally fits within the sub passage  312 . The feed tube  320  is surrounded by a portion of the top sub  210 , the casing  230 , a portion of the drive sub  250 , a portion of the mandrel  270 , the feed tube mount  340 , the piston  380 , the one or more drive lugs  394 , the exhauster  365 , and the split retaining ring  396 . According to certain exemplary embodiments, the feed tube  320  is fixedly coupled within the interior of the percussion tool  200  using at least one of the feed tube mount  340  and/or the exhauster  365 . For example, in one or more exemplary embodiments, the feed tube  320  frictionally fits within the feed tube mount  340  and/or the exhauster  365 . 
     The feed tube mount  340  is annularly shaped with a feed tube mount passageway  342  extending longitudinally therethrough according to certain exemplary embodiments. The feed tube mount  340  is positioned within the secondary sub passage  314  according to some exemplary embodiments, but can be positioned elsewhere, such as within the top pressure fluid chamber  305  in other exemplary embodiments. The feed tube mount passageway  342  receives at least a portion of the feed tube  320  and may assist in mounting the feed tube  320  within the percussion tool  200 . According to certain exemplary embodiments, the feed tube  320  extends entirely through the feed tube mount  340 . However, according to some exemplary embodiments, the feed tube  320  is a single-walled feed tube or is omitted as the function of the feed tube is carried out as described in the prior art. 
     The choke  360  also is annularly shaped and forms a plug that fits into the central feed tube channel  325  at the top end  321  of the feed tube  320 . The choke  360  includes a choke passageway  362  formed longitudinally therethrough. The dimension, or diameter, of this choke passageway  362  limits the amount of pressurized fluid flowing into the central feed tube channel  325  from the sub passage  312 . The pressurized fluid generally flows from the sub passage  312  into the outer feed tube channel  326  and then into either the bottom pressure fluid chamber  308  or to the top pressure fluid chamber  305  depending upon the elevational positioning of the piston  380 . However, the excess pressurized fluid flows into the central feed tube channel  325  through the choke  360 . The choke  360  is replaceable depending upon the desired restriction, which determines the amount of pressurized fluid that flows into the central feed tube channel  325  through the choke  360 . For example, less pressurized fluid flows into the central feed tube channel  325  through the choke  360  when the dimension, or diameter, of the choke passageway  362  is small when compared to when the dimension, or diameter, of the choke passageway  362  is larger. The replacement of the choke  360  is fairly simple and does not require several components of the percussion tool  200  to be dismantled considering that the check valve  302  has been relocated to downstream of the choke  360  according to some of the exemplary embodiments. The top sub  210 , along with the remaining components of the percussion tool  200  positioned below the top sub  210 , is threadedly removed, or disengaged, from the drill string, or other down hole tool, that it is coupled to. Once the top sub  210  is disengaged, an operator is able to remove the choke  360  by accessing it through the sub passage  312  from the top end  311 . Once the operator removes the choke  360 , the operator is able to install a different choke of a different size, or the same size if choke  360  has been damaged, depending upon the operating requirements through the same sub passage  312  from the top end  311 . Once the choke  360  has been replaced, the top sub  210 , along with the remaining attached components, are threadedly coupled, or re-engaged, to the drill string, or other down hole tool, that it is to be coupled to. Alternatively, if the check valve  302  remained in the position as shown in the prior art, i.e. upstream of the choke, the check valve  302  would need to be locked open or removable without dismantling of the percussion tool  200 , thereby allowing repair or replacement of the choke also without dismantling of the percussion tool  200 . This is illustrated and described with respect to  FIGS. 5-7B  below. 
     Piston  380  is annularly shaped and includes a top end  381 , a bottom end  382 , an exterior surface  383 , and an interior surface  384  that defines a piston passageway  385  extending longitudinally through the piston  380 . The piston  380  further includes at least one first pressurized fluid conduit  386  that extends from the interior surface  384  to the top end  381  and at least one second pressurized fluid conduit  387  that extends from the interior surface  384  to the bottom end  382 . Further, the piston  380  includes at least one top exhaust conduit  430  ( FIG. 4B-2 ) that extends from the top end  381  to a lower portion of the interior surface  384  such that the top exhaust conduit  430  ( FIG. 4B-2 ) can communicate pressurized fluid from the top pressure fluid chamber  305  to the exhauster  365  when the at least one second pressurized fluid conduit  387  communicates pressurized fluid to the bottom pressure fluid chamber  308 . The piston  380  is positioned within the case passageway  332  such that the interior surface  384  is positioned slidably and in contact with the feed tube  320  and the exterior surface  383  is positioned slidably and in contact with the casing  230 . Once the piston  380  is slidably positioned within the case passageway  332 , the top pressure fluid chamber  305  is formed within the case passageway  332  adjacently above the top end  381  and the bottom pressure fluid chamber  308  is formed within the case passageway  332  adjacently below the bottom end  382 . As the piston slidably moves upward towards the top sub  210 , the volume of the top pressure fluid chamber  305  decreases while the volume of the bottom pressure fluid chamber  308  increases. Conversely, as the piston  380  slidably moves downward towards the mandrel  270 , the volume of the top pressure fluid chamber  305  increases while the volume of the bottom pressure fluid chamber  308  decreases. The piston  380  is used to deliver a downward force onto the mandrel  270  when the bottom end  382  makes downward contact with the mandrel  270 . The piston  380  is forced back up and then cycles down again to make contact with the mandrel  270 . This cycling of the piston  380  continues until the flow of pressurized fluid through the outer feed tube channel  326  is stopped. The details of this piston  380  operation is provided below in conjunction with  FIGS. 4A-J  in accordance with one or more exemplary embodiments. 
     One or more drive lugs  394  are annularly shaped, stacked on top of one another, and positioned between and in contact with the second portion  354  of the drive sub  250  and the middle portion  376  of the mandrel  270 . Each drive lug  394  includes a drive lug passageway  395  that extends longitudinally therethrough and receives a portion of the mandrel  270  therein. Specifically, once the drive lugs  394  and the mandrel  270  are properly installed, the middle portion  376  of the mandrel  270  slidably engages with the one or more drive lugs  394  through the drive lug passageway  395 . When an upward force is placed onto the bottom of the bit  290 , the mandrel  270  slidably moves toward the top sub  210  such that the bottom portion  378  of the mandrel  270  and the drive sub  250  are adjacent and/or in contact with one another. Conversely, when an upward force is not placed onto the bottom of the bit  290 , the mandrel  270  slidably moves away the top sub  210  such that the bottom portion  378  of the mandrel  270  and the drive sub  250  are not adjacent and/or not in contact with one another. According to the exemplary embodiment, three drive lugs  394  are shown; however, greater or fewer drive lugs  394  are used in other exemplary embodiments. 
     The split retaining ring  396  also is annularly shaped, stacked on top of one of the drive lugs  394  and the second portion  354  of the drive sub  250 , and positioned between and in contact with the lower portion of the case  230  and the middle portion  376  of the mandrel  270 . The split retaining ring  396  includes a split retaining ring passageway  397  that extends longitudinally therethrough and receives a portion of the mandrel  270  therein. Specifically, once the split retaining ring  396  and the mandrel  270  are properly installed, the middle portion  376  of the mandrel  270  slidably engages with the split retaining ring  396  through the split retaining ring passageway  397 . When an upward force is placed onto the bottom of the bit  290 , the mandrel  270  slidably moves toward the top sub  210  such that the top portion  374  of the mandrel  270  and the split retaining ring  396  are not adjacent and/or in contact with one another. Conversely, when an upward force is not placed onto the bottom of the bit  290 , the mandrel  270  slidably moves away the top sub  210  such that the top portion  374  of the mandrel  270  and the split retaining ring  396  are adjacent and/or in contact with one another. The split retaining ring  396  prevents the mandrel  270  and the bit  290  from disengaging from the remaining components of the percussion tool  200 , such as the casing  230 . According to the exemplary embodiment, a single split retaining ring  396  is shown; however, greater number of split retaining rings  396  are used in other exemplary embodiments. 
     The exhauster  365  also is annularly shaped and is doubled-walled in accordance with some exemplary embodiments. The exhauster  365  includes an inner wall  366  and an outer wall  367 . The inner wall  366  is tubularly shaped and defines an exhauster inner passageway  368  that extends longitudinally therethrough. The exhauster inner passageway  368  receives a portion of the lower portion  324  of the feed tube  320 , which extends through the entire exhauster inner passageway  368 . According to certain exemplary embodiments, the inner wall  366  provide some support to the feed tube  320 . The outer wall  367  also is tubularly shaped and surrounds the inner wall  366 . The outer wall  367  and the inner wall  366  collectively define an exhauster outer passageway  369  that extends longitudinally through the exhauster  365 . The exhauster outer passageway  369  provides a pathway to exhaust pressurized fluid from the top fluid pressure chamber  305 , through the piston  380 , and into mandrel passageway  372  so that the pressurized fluid may exit to the external environment as the piston  380  moves upwardly towards the top sub  210 . The exhauster  365  is positioned around a portion of the feed tube  320  and located between the feed tube  320  and a portion of the mandrel  270  and a portion of the piston  380  when the piston  380  is at its lower position. When the piston moves to its lower position, i.e. towards the mandrel  270 , a portion of the exhauster  365  slides into the piston passageway  385 , thereby preventing the exhaust of pressurized fluid from the bottom fluid pressure chamber  308 . 
       FIGS. 4A-4J-2  are cross-sectional views of the percussion tool  200  without the bit  290  ( FIG. 2 ) illustrating the operation of the percussion tool  200  in accordance with an exemplary embodiment of the present invention. Specifically,  FIG. 4A  is a cross-sectional view of the percussion tool  200  when no upward force is exerted on the mandrel  270  in accordance with an exemplary embodiment of the present invention. Referring to  FIG. 4A  and as previously mentioned, the bottom portion  378  of the mandrel  270  is not positioned adjacent to the first portion  352  of the drive sub  250  when the bit  290  ( FIG. 2 ) is placed within the formation and is not in contact with the bottom of the hole, for example, when an upward force is not exerted on the mandrel  270 . Further, the top portion  374  of the mandrel  270  is in contact with the split retaining ring  396  and is prevented from being disengaged from the remaining components of the percussion tool  200 . Hence, the mandrel  270  remains housed within at least a portion of the casing  230 . Additionally, the piston  380  is positioned adjacently and in contact with the top portion  374  of the mandrel  270 . However, once an upward force is exerted on the bottom of the mandrel  270 , such as when the bit  290  ( FIG. 2 ) is in contact with the bottom of the hole during drilling and as shown in each of  FIGS. 4B-1-4J-2 , the bottom portion  378  of the mandrel  270  is positioned adjacently and in contact with the first portion  352  of the drive sub  250 . 
     For convenience purposes, it is assumed that an upward force is exerted on the bottom of the mandrel  270  in each of  FIGS. 4B-1-4J-2  and therefore is not reiterated in the descriptions for each of those figures. Further, the non-illustration of the bit  290  ( FIG. 2 ) in each of  FIGS. 4B-1-4J-2  is not reiterated in the description for each of those figures. Either a bit, such as bit  290  ( FIG. 2 ) is coupled to the mandrel  270  or an integrated bit, such as a hammer, is formed with the mandrel  270 . 
       FIG. 4B-1  is a cross-sectional view of the percussion tool  200  with the piston  380  in the down position  410  and showing the positioning of the at least one first pressurized fluid conduit  386  and the at least one second pressurized fluid conduit  387  in accordance with an exemplary embodiment of the present invention.  FIG. 4B-2  is a cross-sectional view of the percussion tool  200  with the piston  380  in the down position  410  and showing the positioning of the at least one top exhaust conduit  430  in accordance with an exemplary embodiment of the present invention. Referring to  FIGS. 4B-1 and 4B-2 , the piston  380  is positioned in the down position  410  and facilitates forming the top pressure fluid chamber  305  above it and the bottom pressure fluid chamber  308  below it, where the bottom pressure fluid chamber  308  is smaller in volume than the top pressure fluid chamber  305 . At this down position  410 , the second pressurized fluid conduits  387  within the piston  380  are in fluid communication with at least one respective first opening  327  of the feed tube  320  and hence is able to communicate pressurize fluid from the outer feed tube channel  326  to the bottom pressure fluid chamber  308 . However, at this down position  410 , the first pressurized fluid conduits  386  within the piston  380  are not in fluid communication with any of the second openings  328  of the feed tube  320  and hence is not able to communicate pressurize fluid from the outer feed tube channel  326  to the top pressure fluid chamber  305 . Thus, only the bottom pressure fluid chamber  308  is filled with pressurized fluid while the top pressure fluid chamber  305  is not, when the piston  380  is at this down position  410 . As the bottom pressure fluid chamber  308  is filled and the pressure therein increases, the piston  380  commences rising, thereby decreasing the volume of the top pressure fluid chamber  305  and increasing the volume of the bottom pressure fluid chamber  308 . The pressurized fluid within the bottom pressure fluid chamber  308  does not exhaust through the exhauster  365  when the piston  380  is at this down position  410 . As the volume on the top pressure fluid chamber  305  decreases, the fluid therein is exhausted to the outside environment through the at least one top exhaust conduit  430 . This fluid proceeds from the top pressure fluid chamber  305 , into the at least one top exhaust conduit  430 , through the exhauster  365 , through the mandrel passageway  372 , and out the bit  290  ( FIG. 2 ) through the check valve  302  ( FIG. 3 ), if positioned within the bit  290  ( FIG. 2 ), and the bit passageway  392  ( FIG. 3 ). The excess pressurized fluid flowing from the sub passage  312 , which is not used for filling the bottom pressure fluid chamber  308 , flows into the central feed tube channel  325  of the feed tube  320  via the choke  360 , then through the exhauster  365  into the mandrel passageway  372 , and out the bit  290  ( FIG. 2 ) through the check valve  302  ( FIG. 3 ), if positioned within the bit  290  ( FIG. 2 ), and the bit passageway  392  ( FIG. 3 ). As seen, the pressurized fluid enters only the bottom pressure fluid chamber  308  and therefore is not used to counteract, or work against, itself when being used to move the piston  380 . 
       FIG. 4C-1  is a cross-sectional view of the percussion tool  200  with the piston  380  in a first intermediate upward moving position  411  and showing the positioning of the at least one first pressurized fluid conduit  386  and the at least one second pressurized fluid conduit  387  in accordance with an exemplary embodiment of the present invention.  FIG. 4C-2  is a cross-sectional view of the percussion tool  200  with the piston  380  in the first intermediate upward moving position  411  and showing the positioning of the at least one top exhaust conduit  430  in accordance with an exemplary embodiment of the present invention. Referring to  FIGS. 4C-1 and 4C-2 , the piston  380  is positioned in the first intermediate upward moving position  411  and facilitates forming the top pressure fluid chamber  305  above it and the bottom pressure fluid chamber  308  below it. The bottom pressure fluid chamber  308  has increased in volume and the top pressure fluid chamber  305  has decreased in volume when compared to when the piston  380  was in the down position  410  ( FIG. 4B-1 ). At this first intermediate upward moving position  411 , the second pressurized fluid conduits  387  within the piston  380  are still in fluid communication with at least one respective first opening  327  of the feed tube  320  and hence still communicates pressurize fluid from the outer feed tube channel  326  to the bottom pressure fluid chamber  308 . However, at this first intermediate upward moving position  411 , the first pressurized fluid conduits  386  within the piston  380  are not in fluid communication with any of the second openings  328  of the feed tube  320  and hence is not able to communicate pressurize fluid from the outer feed tube channel  326  to the top pressure fluid chamber  305 . Thus, only the bottom pressure fluid chamber  308  is filled with pressurized fluid while the top pressure fluid chamber  305  is not, when the piston  380  is at this first intermediate upward moving position  411 . As the bottom pressure fluid chamber  308  continues to be filled and the pressure therein increases, the piston  380  continues rising, thereby further decreasing the volume of the top pressure fluid chamber  305  and further increasing the volume of the bottom pressure fluid chamber  308 . The pressurized fluid within the bottom pressure fluid chamber  308  still does not exhaust through the exhauster  365  when the piston  380  is at this first intermediate upward moving position  411 . As the volume on the top pressure fluid chamber  305  continues to decrease, the fluid therein continues to be exhausted to the outside environment through the at least one top exhaust conduit  430 . This fluid proceeds from the top pressure fluid chamber  305 , into the at least one top exhaust conduit  430 , through the exhauster  365 , through the mandrel passageway  372 , and out the bit  290  ( FIG. 2 ) through the check valve  302  ( FIG. 3 ), if positioned within the bit  290  ( FIG. 2 ), and the bit passageway  392  ( FIG. 3 ). The excess pressurized fluid flowing from the sub passage  312 , which is not used for filling the bottom pressure fluid chamber  308 , flows into the central feed tube channel  325  of the feed tube  320  via the choke  360 , then through the exhauster  365  into the mandrel passageway  372 , and out the bit  290  ( FIG. 2 ) through the check valve  302  ( FIG. 3 ), if positioned within the bit  290  ( FIG. 2 ), and the bit passageway  392  ( FIG. 3 ). As seen, the pressurized fluid still enters only the bottom pressure fluid chamber  308  and therefore is not used to counteract, or work against, itself when being used to move the piston  380 . 
       FIG. 4D-1  is a cross-sectional view of the percussion tool  200  with the piston  380  in a second intermediate upward moving position  412  and showing the positioning of the at least one first pressurized fluid conduit  386  and the at least one second pressurized fluid conduit  387  in accordance with an exemplary embodiment of the present invention.  FIG. 4D-2  is a cross-sectional view of the percussion tool  200  with the piston  380  in the second intermediate upward moving position  412  and showing the positioning of the at least one top exhaust conduit  430  in accordance with an exemplary embodiment of the present invention. Referring to  FIGS. 4D-1 and 4D-2 , the piston  380  is positioned in the second intermediate upward moving position  412  and facilitates forming the top pressure fluid chamber  305  above it and the bottom pressure fluid chamber  308  below it. The bottom pressure fluid chamber  308  has further increased in volume and the top pressure fluid chamber  305  has further decreased in volume when compared to when the piston  380  was in the first intermediate upward moving position  411  ( FIG. 4C-1 ). At this second intermediate upward moving position  412 , the second pressurized fluid conduits  387  within the piston  380  are no longer in fluid communication with the first openings  327  of the feed tube  320  and hence do not communicate pressurized fluid from the outer feed tube channel  326  to the bottom pressure fluid chamber  308 . Similarly, at this second intermediate upward moving position  412 , the first pressurized fluid conduits  386  within the piston  380  also are not in fluid communication with any of the second openings  328  of the feed tube  320  and hence are not able to communicate pressurized fluid from the outer feed tube channel  326  to the top pressure fluid chamber  305 . Thus, neither the bottom pressure fluid chamber  308  nor the top pressure fluid chamber  305  is filled with pressurized fluid, when the piston  380  is at this second intermediate upward moving position  412 . However, the piston  380  continues moving in an upward direction from the forces previously applied to the bottom of the piston. Hence, as the piston  380  continues rising, the volume of the top pressure fluid chamber  305  continues to further decrease, while the volume of the bottom pressure fluid chamber  308  continues to further increase. The pressurized fluid within the bottom pressure fluid chamber  308  still does not exhaust through the exhauster  365  when the piston  380  is at this second intermediate upward moving position  412 . Similarly, the fluid within the top pressure fluid chamber  305  no longer continues to exhaust through the exhauster  365  since the top exhaust conduits  430  are not in fluid communication with the exhauster  365 . The excess pressurized fluid flowing from the sub passage  312 , which is substantially all the pressurized fluid therein, flows into the central feed tube channel  325  of the feed tube  320  via the choke  360 , then through the exhauster  365  into the mandrel passageway  372 , and out the bit  290  ( FIG. 2 ) through the check valve  302  ( FIG. 3 ), if positioned within the bit  290  ( FIG. 2 ), and the bit passageway  392  ( FIG. 3 ). As seen, the pressurized fluid does not enter any of the bottom pressure fluid chamber  308  or the top pressure fluid chamber  305 , and therefore is not used to counteract, or work against, itself when being used to move the piston  380 . 
       FIG. 4E-1  is a cross-sectional view of the percussion tool  200  with the piston  380  in a third intermediate upward moving position  413  and showing the positioning of the at least one first pressurized fluid conduit  386  and the at least one second pressurized fluid conduit  387  in accordance with an exemplary embodiment of the present invention.  FIG. 4E-2  is a cross-sectional view of the percussion tool  200  with the piston  380  in the third intermediate upward moving position  413  and showing the positioning of the at least one top exhaust conduit  430  in accordance with an exemplary embodiment of the present invention. Referring to  FIGS. 4E-1 and 4E-2 , the piston  380  is positioned in the third intermediate upward moving position  413  and facilitates forming the top pressure fluid chamber  305  above it and the bottom pressure fluid chamber  308  below it. The bottom pressure fluid chamber  308  has increased in volume and the top pressure fluid chamber  305  has decreased in volume when compared to when the piston  380  was in the second intermediate upward moving position  412  ( FIG. 4D-1 ). At this third intermediate upward moving position  413 , the first pressurized fluid conduits  386  within the piston  380  are now in fluid communication with at least one respective second opening  328  of the feed tube  320  and hence communicates pressurized fluid from the outer feed tube channel  326  to the top pressure fluid chamber  305 . However, at this third intermediate upward moving position  413 , the second pressurized fluid conduits  387  within the piston  380  are not in fluid communication with any of the first openings  327  of the feed tube  320  and hence are not able to communicate pressurized fluid from the outer feed tube channel  326  to the bottom pressure fluid chamber  308 . Thus, now only the top pressure fluid chamber  305  is filled with pressurized fluid while the bottom pressure fluid chamber  308  is not, when the piston  380  is at this third intermediate upward moving position  413 . As the top pressure fluid chamber  305  is now filled with pressurized fluid and the pressure therein increases, the piston  380  continues rising but starts slowing down, thereby further decreasing the volume of the top pressure fluid chamber  305  and further increasing the volume of the bottom pressure fluid chamber  308 . The pressurized fluid within the bottom pressure fluid chamber  308  now exhausts through the exhauster  365  when the piston  380  is at this third intermediate upward moving position  413 . This fluid proceeds from the bottom pressure fluid chamber  308 , through the exhauster  365 , through the mandrel passageway  372 , and out the bit  290  ( FIG. 2 ) through the check valve  302  ( FIG. 3 ), if positioned within the bit  290  ( FIG. 2 ), and the bit passageway  392  ( FIG. 3 ). As the volume in the top pressure fluid chamber  305  continues to decrease, the fluid therein is pressurized more since the fluid therein is not exhausted through the exhauster  365 . The at least one top exhaust conduit  430  is no longer fluidly communicable with the exhauster  365 . This pressurized fluid within the top pressure fluid chamber  305  causes the piston  380  to slow down in its upward movement. The excess pressurized fluid flowing from the sub passage  312 , which is not used for filling the top pressure fluid chamber  305 , flows into the central feed tube channel  325  of the feed tube  320  via the choke  360 , then through the exhauster  365  into the mandrel passageway  372 , and out the bit  290  ( FIG. 2 ) through the check valve  302  ( FIG. 3 ), if positioned within the bit  290  ( FIG. 2 ), and the bit passageway  392  ( FIG. 3 ). As seen, the pressurized fluid now enters only the top pressure fluid chamber  305  and therefore is not used to counteract, or work against, itself when being used to slow the movement of the piston  380 . 
       FIG. 4F-1  is a cross-sectional view of the percussion tool  200  with the piston  380  in an up position  414  and showing the positioning of the at least one first pressurized fluid conduit  386  and the at least one second pressurized fluid conduit  387  in accordance with an exemplary embodiment of the present invention.  FIG. 4F-2  is a cross-sectional view of the percussion tool  200  with the piston  380  in the up position  414  and showing the positioning of the at least one top exhaust conduit  430  in accordance with an exemplary embodiment of the present invention. Referring to  FIGS. 4F-1 and 4F-2 , the piston  380  is positioned in the up position  414  and facilitates forming the top pressure fluid chamber  305  above it and the bottom pressure fluid chamber  308  below it. The bottom pressure fluid chamber  308  has increased in volume and the top pressure fluid chamber  305  has decreased in volume when compared to when the piston  380  was in the third intermediate upward moving position  413  ( FIG. 4E-1 ). At this up position  414 , the first pressurized fluid conduits  386  within the piston  380  are still in fluid communication with at least one respective second opening  328  of the feed tube  320  and hence communicates pressurized fluid from the outer feed tube channel  326  to the top pressure fluid chamber  305 . However, at this up position  414 , the second pressurized fluid conduits  387  within the piston  380  are not in fluid communication with any of the first openings  327  of the feed tube  320  and hence are not able to communicate pressurized fluid from the outer feed tube channel  326  to the bottom pressure fluid chamber  308 . Thus, now only the top pressure fluid chamber  305  is filled with pressurized fluid while the bottom pressure fluid chamber  308  is not, when the piston  380  is at this up position  414 . At this up position  414 , the piston  380  is at its highest elevational position and the top pressure fluid chamber  305  is at its smallest volume. As the top pressure fluid chamber  305  continues to be filled with pressurized fluid and the pressure therein increases, the piston  380  will start falling, thereby eventually increasing the volume of the top pressure fluid chamber  305  and decreasing the volume of the bottom pressure fluid chamber  308 . The pressurized fluid within the bottom pressure fluid chamber  308  continues to be exhausted through the exhauster  365  when the piston  380  is at this up position  414 . This fluid proceeds from the bottom pressure fluid chamber  308 , through the exhauster  365 , through the mandrel passageway  372 , and out the bit  290  ( FIG. 2 ) through the check valve  302  ( FIG. 3 ), if positioned within the bit  290  ( FIG. 2 ), and the bit passageway  392  ( FIG. 3 ). As the volume in the top pressure fluid chamber  305  is relatively constant, the fluid therein is pressurized more as more pressurized fluid enters the top pressure fluid chamber  305  and since the fluid therein is not exhausted through the exhauster  365 . The at least one top exhaust conduit  430  is still not fluidly communicable with the exhauster  365 . This pressurized fluid within the top pressure fluid chamber  305  causes the piston  380  to stop its upward movement. The excess pressurized fluid flowing from the sub passage  312 , which is not used for filling the top pressure fluid chamber  305 , flows into the central feed tube channel  325  of the feed tube  320  via the choke  360 , then through the exhauster  365  into the mandrel passageway  372 , and out the bit  290  ( FIG. 2 ) through the check valve  302  ( FIG. 3 ), if positioned within the bit  290  ( FIG. 2 ), and the bit passageway  392  ( FIG. 3 ). As seen, the pressurized fluid now enters only the top pressure fluid chamber  305  and therefore is not used to counteract, or work against, itself when being used to stop the movement of the piston  380 . 
       FIG. 4G-1  is a cross-sectional view of the percussion tool  200  with the piston  380  in a first intermediate downward moving position  415  and showing the positioning of the at least one first pressurized fluid conduit  386  and the at least one second pressurized fluid conduit  387  in accordance with an exemplary embodiment of the present invention.  FIG. 4G-2  is a cross-sectional view of the percussion tool  200  with the piston  380  in the first intermediate downward moving position  415  and showing the positioning of the at least one top exhaust conduit  430  in accordance with an exemplary embodiment of the present invention. Referring to  FIGS. 4G-1 and 4G-2 , the piston  380  is positioned in the first intermediate downward moving position  415  and facilitates forming the top pressure fluid chamber  305  above it and the bottom pressure fluid chamber  308  below it. The bottom pressure fluid chamber  308  has decreased in volume and the top pressure fluid chamber  305  has increased in volume when compared to when the piston  380  was in the up position  414  ( FIG. 4F-1 ). At this first intermediate downward moving position  415 , the first pressurized fluid conduits  386  within the piston  380  are still in fluid communication with at least one respective second opening  328  of the feed tube  320  and hence continue to communicate pressurized fluid from the outer feed tube channel  326  to the top pressure fluid chamber  305 . However, at this first intermediate downward moving position  415 , the second pressurized fluid conduits  387  within the piston  380  are still not in fluid communication with any of the first openings  327  of the feed tube  320  and hence still does not communicate pressurized fluid from the outer feed tube channel  326  to the bottom pressure fluid chamber  308 . Thus, only the top pressure fluid chamber  305  is filled with pressurized fluid while the bottom pressure fluid chamber  308  is not, when the piston  380  is at this first intermediate downward moving position  415 . As the top pressure fluid chamber  305  continues to be filled and the pressure therein increases, the piston  380  continues falling, thereby further decreasing the volume of the bottom pressure fluid chamber  308  and further increasing the volume of the top pressure fluid chamber  305 . The pressurized fluid within the top pressure fluid chamber  305  still does not exhaust through the exhauster  365  when the piston  380  is at this first intermediate downward moving position  415 . As the volume in the bottom pressure fluid chamber  308  continues to decrease, the fluid therein continues to be exhausted to the outside environment through the exhauster  365  when the piston  380  is at this first intermediate downward moving position  415 . This fluid proceeds from the bottom pressure fluid chamber  308 , through the exhauster  365 , through the mandrel passageway  372 , and out the bit  290  ( FIG. 2 ) through the check valve  302  ( FIG. 3 ), if positioned within the bit  290  ( FIG. 2 ), and the bit passageway  392  ( FIG. 3 ). As the pressurized fluid enters the top pressure fluid chamber  305  and the pressurized fluid within the top pressure fluid chamber  305  is not exhausted, the fluid therein forces the piston  380  to move further downward. The at least one top exhaust conduit  430  is still not fluidly communicable with the exhauster  365 . The excess pressurized fluid flowing from the sub passage  312 , which is not used for filling the top pressure fluid chamber  305 , flows into the central feed tube channel  325  of the feed tube  320  via the choke  360 , then through the exhauster  365  into the mandrel passageway  372 , and out the bit  290  ( FIG. 2 ) through the check valve  302  ( FIG. 3 ), if positioned within the bit  290  ( FIG. 2 ), and the bit passageway  392  ( FIG. 3 ). As seen, the pressurized fluid still enters only the top pressure fluid chamber  305  and therefore is not used to counteract, or work against, itself when being used to move the piston  380 . 
       FIG. 4H-1  is a cross-sectional view of the percussion tool  200  with the piston  380  in a second intermediate downward moving position  416  and showing the positioning of the at least one first pressurized fluid conduit  386  and the at least one second pressurized fluid conduit  387  in accordance with an exemplary embodiment of the present invention.  FIG. 4H-2  is a cross-sectional view of the percussion tool  200  with the piston  380  in the second intermediate downward moving position  416  and showing the positioning of the at least one top exhaust conduit  430  in accordance with an exemplary embodiment of the present invention. Referring to  FIGS. 4H-1 and 4H-2 , the piston  380  is positioned in the second intermediate downward moving position  416  and facilitates forming the top pressure fluid chamber  305  above it and the bottom pressure fluid chamber  308  below it. The top pressure fluid chamber  305  has further increased in volume and the bottom pressure fluid chamber  308  has further decreased in volume when compared to when the piston  380  was in the first intermediate downward moving position  415  ( FIG. 4G-1 ). At this second intermediate downward moving position  416 , the first pressurized fluid conduits  386  within the piston  380  are no longer in fluid communication with the second openings  328  of the feed tube  320  and hence do not communicate pressurized fluid from the outer feed tube channel  326  to the top pressure fluid chamber  305 . Similarly, at this second intermediate downward moving position  416 , the second pressurized fluid conduits  387  within the piston  380  also are not in fluid communication with any of the first openings  327  of the feed tube  320  and hence are not able to communicate pressurized fluid from the outer feed tube channel  326  to the bottom pressure fluid chamber  308 . Thus, neither the top pressure fluid chamber  305  nor the bottom pressure fluid chamber  308  is filled with pressurized fluid, when the piston  380  is at this second intermediate downward moving position  416 . However, the piston  380  continues moving in a downward direction from the forces previously applied to the top of the piston  380 . Hence, as the piston  380  continues falling, the volume of the bottom pressure fluid chamber  308  continues to further decrease, while the volume of the top pressure fluid chamber  305  continues to further increase. The pressurized fluid within the top pressure fluid chamber  305  still does not exhaust through the exhauster  365  when the piston  380  is at this second intermediate downward moving position  416  since the top exhaust conduits  430  are not in fluid communication with the exhauster  365 . Similarly, the fluid within the bottom pressure fluid chamber  308  no longer continues to exhaust through the exhauster  365  since the bottom pressure fluid chamber  308  is not in fluid communication with the exhauster  365 . The excess pressurized fluid flowing from the sub passage  312 , which is substantially all the pressurized fluid therein, flows into the central feed tube channel  325  of the feed tube  320  via the choke  360 , then through the exhauster  365  into the mandrel passageway  372 , and out the bit  290  ( FIG. 2 ) through the check valve  302  ( FIG. 3 ), if positioned within the bit  290  ( FIG. 2 ), and the bit passageway  392  ( FIG. 3 ). As seen, the pressurized fluid does not enter any of the top pressure fluid chamber  305  or the bottom pressure fluid chamber  308 , and therefore is not used to counteract, or work against, itself when being used to move the piston  380 . 
       FIG. 4I-1  is a cross-sectional view of the percussion tool  200  with the piston  380  in a third intermediate downward moving position  417  and showing the positioning of the at least one first pressurized fluid conduit  386  and the at least one second pressurized fluid conduit  387  in accordance with an exemplary embodiment of the present invention.  FIG. 4I-2  is a cross-sectional view of the percussion tool  200  with the piston  380  in the third intermediate downward moving position  417  and showing the positioning of the at least one top exhaust conduit  430  in accordance with an exemplary embodiment of the present invention. Referring to  FIGS. 4I-1 and 4I-2 , the piston  380  is positioned in the third intermediate downward moving position  417  and facilitates forming the top pressure fluid chamber  305  above it and the bottom pressure fluid chamber  308  below it. The top pressure fluid chamber  305  has increased in volume and the bottom pressure fluid chamber  308  has decreased in volume when compared to when the piston  380  was in the second intermediate downward moving position  416  ( FIG. 4H-1 ). At this third intermediate downward moving position  417 , the second pressurized fluid conduits  387  within the piston  380  are now in fluid communication with at least one respective first opening  327  of the feed tube  320  and hence communicates pressurized fluid from the outer feed tube channel  326  to the bottom pressure fluid chamber  308 . However, at this third intermediate downward moving position  417 , the first pressurized fluid conduits  386  within the piston  380  are not in fluid communication with any of the second openings  328  of the feed tube  320  and hence are not able to communicate pressurized fluid from the outer feed tube channel  326  to the top pressure fluid chamber  305 . Thus, now only the bottom pressure fluid chamber  308  is filled with pressurized fluid while the top pressure fluid chamber  305  is not, when the piston  380  is at this third intermediate downward moving position  417 . As the bottom pressure fluid chamber  308  is now filled with pressurized fluid and the pressure therein increases, the piston  380  continues falling but starts slowing down, thereby further decreasing the volume of the bottom pressure fluid chamber  308  and further increasing the volume of the top pressure fluid chamber  305 . The pressurized fluid within the top pressure fluid chamber  305  now exhausts through the exhauster  365  when the piston  380  is at this third intermediate downward moving position  417 . This fluid proceeds from the top pressure fluid chamber  305 , through the at least one top exhaust conduit  430 , through the exhauster  365 , through the mandrel passageway  372 , and out the bit  290  ( FIG. 2 ) through the check valve  302  ( FIG. 3 ), if positioned within the bit  290  ( FIG. 2 ), and the bit passageway  392  ( FIG. 3 ). As the volume in the bottom pressure fluid chamber  308  continues to decrease, the fluid therein is pressurized more since the fluid therein is not exhausted through the exhauster  365 . The bottom pressure fluid chamber  308  is no longer fluidly communicable with the exhauster  365 . This pressurized fluid within the bottom pressure fluid chamber  308  causes the piston  380  to slow down in its downward movement. The excess pressurized fluid flowing from the sub passage  312 , which is not used for filling the bottom pressure fluid chamber  308 , flows into the central feed tube channel  325  of the feed tube  320  via the choke  360 , then through the exhauster  365  into the mandrel passageway  372 , and out the bit  290  ( FIG. 2 ) through the check valve  302  ( FIG. 3 ), if positioned within the bit  290  ( FIG. 2 ), and the bit passageway  392  ( FIG. 3 ). As seen, the pressurized fluid now enters only the bottom pressure fluid chamber  308  and therefore is not used to counteract, or work against, itself when being used to slow the movement of the piston  380 . 
       FIG. 4J-1  is a cross-sectional view of the percussion tool  200  with the piston  380  in the down position  410  and showing the positioning of the at least one first pressurized fluid conduit  386  and the at least one second pressurized fluid conduit  387  in accordance with an exemplary embodiment of the present invention.  FIG. 4J-2  is a cross-sectional view of the percussion tool  200  with the piston  380  in the down position  410  and showing the positioning of the at least one top exhaust conduit  430  in accordance with an exemplary embodiment of the present invention.  FIGS. 4J-1 and 4J-2  illustrate the piston  380  in the same position as illustrated in  FIGS. 4B-1 and 4B-2  since the piston  380  has completed one movement cycle. Since  FIGS. 4J-1 and 4J-2  illustrate the piston  380  in the same position as illustrated in  FIGS. 4B-1 and 4B-2 , the description previously provided with respect to  FIGS. 4B-1 and 4B-2  also applies to the description of  FIGS. 4J-1 and 4J-2 ; and therefore is not repeated again herein for the sake of brevity. 
     Although a few exemplary embodiments have been described and/or illustrated with respect to the components used in fabricating the percussion tool  200  and with respect to the operation of the percussion tool  200 , modifications made with respect to these components and/or how the percussion tool  200  operates are envisioned to be included within the exemplary embodiments of this invention. For example, as previously mentioned, the check valve  302  may be placed upstream of the choke  360  or downstream of the choke  360 , such as within the bit  290 . Other types of modifications may be made such as reducing the number of components or increasing the number of components. Further, the connection type between the components may be altered without departing from the scope and spirit of the exemplary embodiments. Further, although the exemplary embodiments has been illustrated using a roller cone bit being coupled to the mandrel  270 , other types of bits may be coupled to the mandrel  270 , such as fixed cutter bits and hammers. Alternatively, these bits may be integrally formed with the mandrel  270  without departing from the scope and spirit of the exemplary embodiments. 
       FIG. 5  is a cross-sectional view of a percussion tool  500  in accordance with another exemplary embodiment of the present invention. Referring to  FIG. 5 , the percussion tool  500  includes a top sub  510 , a case  230 , a drive sub  250 , a mandrel  270 , and a bit  290 , which are viewable and accessible from exterior of the percussion tool  500 . The percussion tool  500  further includes a feed tube  320 , a feed tube mount  340 , a choke  360 , a piston  380 , one or more drive lugs  394 , an exhauster  365 , a split retaining ring  396 , a check valve  580 , and a retaining ring  590 , which are all positioned internally of the percussion tool  500 . Although certain components have been mentioned, greater or fewer components may be included in the percussion tool  500  without departing from the scope and spirit of the exemplary embodiment. Further, one or more components may be combined or separated from another mentioned component without departing from the scope and spirit of the exemplary embodiment. Once the percussion tool  500  is assembled, a top pressure fluid chamber  305  and a bottom pressure fluid chamber  308  are formed. 
     Each of the case  230 , the drive sub  250 , the mandrel  270 , the bit  290 , the feed tube  320 , the feed tube mount  340 , the choke  360 , the piston  380 , the one or more drive lugs  394 , the exhauster  365 , the split retaining ring  396 , the top pressure fluid chamber  305 , and the bottom pressure fluid chamber  308  have been previously described. For the sake of brevity, these components are not described again herein. 
     Top sub  510  is similar to top sub  210  ( FIG. 3 ) except that top sub  510  forms a first sub passage  508 , a second sub passage  512 , and a third sub passage  514  collectively extending therethrough. The first sub passage  508  is formed at a top end  511  of the top sub  510  and extends downwardly to the second sub passage  512 . The first sub passage  508  is fluidly communicable with the second sub passage  512 . The first sub passage  508  is larger in diameter than the second sub passage  512 . The first sub passage  508  houses the check valve  580  and the retaining ring  590  therein according to certain exemplary embodiments. The first sub passage  508  is dimensioned to receive the check valve  580  and the retaining ring  590  in a secure manner. The second sub passage  512  is similar to sub passage  312  ( FIG. 3 ) except that the second sub passage  512  extends from an end of the first sub passage  508  instead of from the top end  511  of the top sub  510 , which is similar to the top end  312  ( FIG. 3 ). Since the second sub passage  512  is similar to the sub passage  312  ( FIG. 3 ), the details are not repeated herein for the sake of brevity. Further, the third sub passage  314  is fluidly communicable with the second sub passage  512 . Since, the third sub passage  314  is similar to the secondary sub passage  314  ( FIG. 3 ), it is therefore not described again in detail for the sake of brevity. 
       FIG. 6  A is a perspective view of the check valve  580  used in the percussion tool  500  in accordance with another exemplary embodiment of the present invention.  FIG. 6B  is a cross-sectional view of the check valve  580  in accordance with that exemplary embodiment of the present invention. Referring to  FIGS. 5-6B , the check valve  580  is a butterfly valve that includes a housing  610 , a spring clip  620 , a first flap  630 , and a second flap  640 . The housing  610  is annularly shaped and forms a valve passageway  612  extending therethrough. The valve passageway  612  has a circular cross-section according to some exemplary embodiments. However, in other exemplary embodiments, the housing  610  and/or the valve passageway  612  have a different shape without departing from the scope and spirit of the exemplary embodiment. The outer surface  611  of the housing  610  is slightly smaller than the dimension of the first sub passage  508  such that the housing  610  is positioned securely within the first sub passage  508 . According to some exemplary embodiments, the housing  610  is in contact with a platform  513  formed where the first sub passage  508  transitions into the second sub passage  512 . 
     The spring clip  620  extends latitudinally across the diameter of the valve passageway  612 . The first flap  630  extends outwardly from the spring clip  620  within the valve passageway  612  such that the first flap  630  occupies about half the cross-sectional area defined by the valve passageway when in a closed position  650 , or biased position. Similarly, the second flap  640  extends outwardly from the spring clip  620  within the valve passageway  612  in an opposite direction than the first flap  630  when in a closed position  650 , or biased position. The second flap  640  occupies about the remaining half of the cross-sectional area defined by the valve passageway  612 . Hence, the spring clip  620 , the first flap  630 , and the second flap  640  collectively occupy substantially the cross-sectional area defined by the valve passageway  612 , when the first flap  630  and the second flap  640  are in a closed position  650 , or biased position. The first flap  630  and the second flap  640  are moveable from the closed position  650  to an open position  655  when air, or some other fluid, flows from a top end  615  of the housing  610  towards a bottom end  617  of the housing  610 . The open position  655  is illustrated in  FIG. 6B  when the first flap  630  and the second flap  640  are in the dashed orientation. The spring clip  620  facilitates biasing the first flap  630  and the second flap  640  into the closed position  650  and allows for these flaps  630 ,  640  to open when air, or some other fluid flows from the top end  615  to the bottom end  617 . According to some exemplary embodiments, the check valve  580  is placed into proper position, however, according to other exemplary embodiments, the check valve  580  may be threadedly coupled to the interior of the first sub passage  508  near the top end  511  of the top sub  510  or coupled according to any other method known to people having ordinary skill in the art. 
     The retaining ring  590  is a snap ring according to some exemplary embodiments and is configured to be positioned immediately adjacent the top end  615  of the housing  610 . The retaining ring  590  is positioned at the top end  511  of the top sub  510  and prevents the check valve  580  from moving about unintentionally. According to some exemplary embodiments, the retaining ring  590  snaps into position, however, according to other exemplary embodiments, the retaining ring  590  may be threadedly couple to the interior of the first sub passage  508  at the top end  511  of the top sub  510  or coupled according to any other method known to people having ordinary skill in the art. 
     When the check valve  580  is positioned upstream of the choke  360 , as illustrated in  FIG. 5 , the check valve  580  is easily removable such that maintenance or replacement of the choke  360  is able to be performed without dismantling, or disassembling, the percussion tool  500 . For example, the retaining ring  590  is removed from the top end  511  of the top sub  510  via unthreading or unsnapping the retaining ring  590 . The check valve  580  is then removed via removing or unthreading the check valve  580 . Access to the choke  360  is now possible using a tool (not shown), such a rod with one or more features at its end. The tool is used to provide maintenance to the choke  360 . In other exemplary embodiments, the tool is used to threadedly remove the choke  360  and replace the choke  360  with a different choke  360 , of the same type or of a different type, such as a choke with a different diameter opening. 
       FIG. 7A  is a bottom view of a check valve  700  useable in the percussion tool  500  ( FIG. 5 ) in lieu of the check valve  580  ( FIGS. 5-6B ) in accordance to yet another exemplary embodiment.  FIG. 7B  is a cross-sectional view of the check valve  700  in accordance with that exemplary embodiment of the present invention. The check valve  700  is similar to check valve  580  ( FIGS. 5-6B ), except that check valve  700  includes a spring clip  720  and a single flap  730 . The spring clip  720  is similar to spring clip  620  ( FIGS. 6A and 6B ), except that the spring clip  720  is positioned near a perimeter of a valve passageway  712 , which is similar to the valve passageway  612  ( FIGS. 6A and 6B ). The spring clip  720  is configured to bias the single flap  730  in a closed position  750 . The single flap  730  is moveable from a closed position  750  to an open position  755  and back again in a similar manner that that the first flap  630  ( FIGS. 6A and 6B ) and the second flap  640  ( FIGS. 6A and 6B ) are moved. The single flap  730  is moveable into an even more open position  755  than illustrated in  FIG. 7B . Hence, the check valve  580 ,  700  can have one or more flaps, including more than two flaps, if desired. Further, the check valve  700  operates in a similar manner as check valve  580  ( FIGS. 5-6B ) and is removable in a similar manner as check valve  580  ( FIGS. 5-6B ) such that maintenance or replacement of the choke  360  is able to be performed without dismantling, or disassembling, the percussion tool  500 . 
     Although the invention has been described with reference to specific embodiments, these descriptions are not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention will become apparent to persons skilled in the art upon reference to the description of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. It is therefore, contemplated that the claims will cover any such modifications or embodiments that fall within the scope of the invention.