Patent Publication Number: US-11649713-B2

Title: Rope tensioning system for drilling rig

Description:
TECHNICAL FIELD 
     This patent disclosure relates generally to drilling rigs for drilling a hole into the earth and, more particularly, relates to a wire rope system that can move a rotary head with respect to a mast of the drilling rig. 
     BACKGROUND 
     Drilling rigs are integrated systems used to drill holes into the ground of the earth. Drilling rigs are commonly used in the petroleum and gas industry, but may also be used for developing water wells, mineral excavation, and other uses. Drilling rigs typically include a mast that can be positioned vertically with respect to the surface of the ground to be drilled and a rotary head that can be vertically moved along the mast. The rotary head includes a driver that can rotate with respect to the rotary head body. The driver may be coupled to a drill string that is an elongated column or drill pipe of multiple string segments that are attached at the distal end to a drill bit. When the driver is rotated, it transmits torque through the drill string to the drill bit that cuts into the surface and subsurface of the earth. 
     To vertically move the rotary head with respect to the mast, the drilling rig includes a wire rope feed system formed of wire ropes that may be hydraulically actuated to pull down (move vertically downward) and hoist (move vertically upwards) the rotary head. In operation, the rotary head is pulled down over the length of the mast, decoupled from the drill string, and hoisted back up the length of the mast. Once hoisted, another string segment is coupled between the rotary head and the rest of the drill string. The rotary head is then pulled down again thereby feeding the drill string into the ground. 
     During use the wire ropes may wear and stretch. To maintain tension on the wire ropes, the drilling rig may include one or more hydraulic tensioning actuators that are coupled to the wire ropes of the wire rope feed system. The tensioning actuators reduce or eliminate slack in the wire rope feed system and facilitate operation of the drilling rig. An example of hydraulic tensioning actuators is described in U.S. Pat. No. 10,683,712 (the &#39;712 patent) in which a first tensioning device or actuator is disposed at the top or crown of the mast and a second tensioning device or actuator is secured to the base of the mast. The first and second tensioning devices are operatively coupled to the wire rope system in conjunction with a series of pulleys to maintain tension on the wire ropes. The &#39;712 patent describes a method of monitoring the elongation or stretch of the wire ropes during operation of the drilling rig. The present application is related to a system and method of compensating for elongation and stretch of the wire ropes during pulldown and/or hoist actions. 
     SUMMARY 
     The disclosure describes, in one aspect, a mobile rotary drilling rig for forming a hole in the earth. The drilling rig includes a rig frame supported on a plurality of propulsion devices for propelling the mobile rotary drilling rig over a work surface. A mast is mounted to the rig frame and can stand vertically erect over the work surface. Movably supported along the mast can be a rotary head that is coupled to and adapted to rotate a drilling string with respect to the work surface. To move the rotary head, a hydraulic feed actuator can be movably guide along the mast. A wire rope feed system connects the rotary head with the hydraulic feed actuator. The wire rope feed system includes a hoist wire rope connected at a first hoist rope end to a hoist tensioning actuator disposed on the mast and connected at a second hoist rope end to the rotary head and a pulldown wire rope connected at a first pulldown rope end to a pulldown tensioning actuator and connected at a second pulldown rope end to the rotary head. To maintain the hoist and pulldown wire ropes in tension, the wire rope feed system can be associated with a tensioning hydraulic circuit configured to direct hydraulic fluid at a tensioning pressure to the hoist tensioning actuator and to the pulldown tensioning actuator. The tensioning hydraulic circuit including a hoist hydraulic circuit operatively associated with the hoist tensioning actuator and having a pressure relief valve in fluid communication with the hoist tensioning actuator to relieve hydraulic pressure therein. 
     In another aspect, there is disclosed a method of tensioning a wire rope feed system for a drilling rig. The method involves directing hydraulic fluid at a tensioning pressure to a hoist tensioning actuator connected to a first hoist rope end of a hoist wire rope that has a second hoist rope end connected to a rotary head of the drilling system. The method further involves directing hydraulic fluid at the tensioning pressure to a pulldown tensioning actuator connected to a first pulldown rope end of a pulldown wire rope that has a second pulldown rope end connected to the rotary head of the drilling system. A pulldown operation is commenced by moving the rotary head toward a work surface with the pulldown wire rope resulting in stretching of the pulldown wire rope and slackening of the hoist wire rope. To reduce slack in the hoist wire rope, the hoist tensioning actuator connected to the first hoist rope end of the hoist wire rope is retracted. If the pulldown operation is ceased, the hydraulic pressure in the hoist tensioning actuator may exceed a relief pressure threshold. To relieve the hydraulic pressure in the hoist tensioning actuator a pressure relief valve in fluid communication with the hoist tensioning actuator may be opened directing hydraulic fluid to a hydraulic reservoir. 
     In a further aspect, the disclosure describes a rotary drilling rig including a rig frame and a mast mounted to the rig frame. A rotary head is movably supported along the mast and coupled with a rotatable drilling string. To move the rotary head vertically along the mast, a hydraulic feed actuator is coupled to the mast and a wire rope feed system connects the rotary head with the hydraulic feed actuator. The rope feed system includes a hoist wire rope connected at a first hoist rope end to a hoist tensioning actuator disposed on the mast and connected at a second hoist rope end to the rotary head. The wire rope system also includes a pulldown wire rope connected at a first pulldown rope end to a pulldown tensioning actuator and connected at a second pulldown rope end to the rotary head. To maintain tension on the hoist and pulldown wire ropes, a tensioning hydraulic circuit is configured to direct hydraulic fluid to the hoist tensioning actuator and to the pulldown tensioning actuator. The tensioning hydraulic circuit includes a hoist hydraulic circuit operatively associated with the hoist tensioning actuator and having a pressure relief feature configured to relieve hydraulic pressure in the hoist tensioning actuator in excess of a relief pressure threshold. The tensioning hydraulic circuit also includes a pulldown hydraulic circuit having a pressure isolation feature configured to isolate hydraulic pressure in the pulldown tensioning actuator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic illustration of a mobile rotary drilling rig for forming a hole by feeding a drill string into the earth. 
         FIG.  2    is a schematic illustration of the wire rope feed system that can vertically pulldown and hoist a rotary head coupled to the drill string with respect to the mast, the wire rope feed system including a tensioning hydraulic circuit to maintain tension on the hoist and/or pulldown wire rope of the wire rope feed system. 
         FIG.  3    is a schematic illustration of the tensioning hydraulic system including a hoist tensioning actuator and a pulldown tensioning actuator to maintain tension on the wire rope feed system during a pulldown operation. 
         FIG.  4    is a schematic representation of a flow diagram illustrating a possible sequence of actions that may be conducted to maintain tension on the hoist and/or pulldown wire rope of the wire rope feed system. 
     
    
    
     DETAILED DESCRIPTION 
     Now referring to the figures, wherein whenever possible like reference numbers refer to like elements, there is illustrated a mobile drilling rig  100  that can form holes in the work surface  102  and the underlying subsurface of the earth for oil and gas extraction, mineral procurement, well formation, and other uses. One particular drilling operation is blast hole drilling in which explosives are packed into the hole formed by the drilling rig  100  and are detonated with the resulting explosion fracturing the underlying rock of the subsurface of the work surface  102 . 
     While the illustrated embodiment of the drilling rig  100  is mobile and can move with respect to the work surface  102 , the present disclosure is also applicable to fixed drilling rigs, offshore drilling rigs or platforms, and other configurations. The drilling rig  100  includes a rig frame  104  that is supported on a plurality of propulsion devices  106  that contact the work surface  102 . The propulsion devices  106  may be continuous tracks or crawler tracks that can translate with respect to the rig frame  104  thereby moving the drilling rig over the work surface  102 . In other embodiments, the propulsion devices  106  can be wheels or, as stated above, the drilling rig  100  may be fixed with respect to the work surface  102  or it may be marine based and operate offshore. To power the propulsion devices  106  and other systems of the drilling rig  100 , a motor  108  is disposed on the rig frame  104 . The motor  108  may be an internal combustion engine that combusts hydrocarbon-based fuels and converts the energy therein to a motive force. In other embodiments, the motor  108  may be operatively connected to an external source of electrical power and receive electric current to power operation of the drilling rig  100 . 
     The drilling rig  100  can include a mast  110  that is an erect structure that can be vertically positioned with respect to the work surface  102 . The mast  110  is an elongated structure that extends between a top or crown  112  that is vertically elevated above the rig frame  104  and a base  114  that is located proximate to the work surface  102 . The mast  110  can be assembled as a truss made from a plurality of metal beams and bars interconnected together to form a rigid structure capable of standing upright in the vertically elevated position. In an embodiment, the mast  110  can be pivotally coupled to the rig frame  104  so that the mast  110  can be raised and lowered between the vertical and non-vertical positions via a lift cylinder  116 . When the mast  110  is in the raised position, the drilling rig  100  is configured for a drilling operation and when the mast is lowered, the drilling rig  100  is configured for a traveling operation. Additionally, in the embodiments where the mast  110  is pivotally coupled to the rig frame  104 , the mast may be oriented at an angle with respect to the work surface  102  so that a hole can be formed angularly into the earth. 
     To accommodate one or more human operators for conducting drilling operations, an onboard operator station  118  may be accommodated on the rig frame  104 . Located within the operator station  118  can be various operator control devices  119  such as levers, pedals, wheels, displays, and the like. In the illustrated embodiment, the operator station  118  can be an enclosed space but in other embodiments, the operator station may be located exteriorly. Furthermore, in possible embodiments, the drilling rig  100  can be configured for remote operation with the operator station  118  and the operator control devices  119  located off board of and remote from the drilling rig  100 . 
     Referring to  FIG.  2   , there is illustrated the components of the drilling system  120  of the drilling rig  100 . The drilling system  120  includes a rotary head  122  that is guided by and movable along the mast  110  during pulldown and hoist actions. The rotary head  122  includes a body  124  that is operatively connected to the mast  110 , for example, by guide tracks, and a driver  126  that rotates within the body  124 . The driver  126  can be coupled to an elongated drill string  128  that is formed of a plurality of string sections  130 . The string sections  130  are straight pipe-like structures that can be coupled together to adjust the length of the drill string  128 . The string sections  130  may be solid for rigidity or may be hollow and adapted to convey drilling fluid into the hole or bore formed during the drilling operation. Attached at the distal end of the drill string  128  can be a drill bit  134  that is structurally configured to penetrate into the work surface  102  and the subsurface underneath. To rotate the drill string  128 , the rotary head  122  can include one or more hydraulic motors  136  that are operatively associated with a hydraulic system  140  of the drilling rig. The hydraulic system  140  may include a hydraulic reservoir  142  and hydraulic pump  144  as described below. The hydraulic motor  136  can receive pressurized hydraulic fluid from the hydraulic system  140  and rotate the driver  126  with respect to the body  124  of the rotary head  122 . 
     To move the rotary head  122  with respect to the mast  110 , the drilling system  120  includes a hydraulic feed actuator  150  that includes a disc-shaped feed piston  152  disposed within a tubular feed cylinder  154 . The feed piston  152  can separate the feed cylinder  154  into an upper chamber  156  and a lower chamber  158 . The hydraulic feed actuator  150  can be fluidly coupled to the hydraulic system  140  of the drilling rig  100  to receive pressurized hydraulic fluid to either the upper chamber  156  or the lower chamber  158  of the feed cylinder  154 . The feed piston  152  can be fixedly connected with the mast  110  so that when hydraulic fluid is introduced, for example, into the upper chamber  156 , the feed cylinder  154  is forcibly moved upwards with respect to the mast  110 . Similarly, when hydraulic fluid is introduced into the lower chamber  158 , the feed cylinder  154  is forcibly move downwards with respect to the mast  110 . 
     In the illustrated embodiment, to fix the feed piston  152  to the mast  110  and enable vertical motion of the feed cylinder  154 , the feed actuator  150  can include a first feed piston rod  160  joined to the feed piston  152  that extends axially upwards through the upper chamber  156  of the hollow feed cylinder  154  and can be fixedly connected proximate to the crown  112  of the mast  110 . Likewise, a second feed piston rod  162  joined to the feed piston  152  can extend axially downwards through the lower chamber  158  of the hollow feed cylinder  154  and can be fixedly connected proximate to the base  114  of the mast  110 . Accordingly, the relative vertical position of the feed piston  152  with respect to the mast  110  is rigidly fixed. The feed cylinder  154  therefore acts as a free body such that introduction of hydraulic fluid into either the upper chamber  156  or the lower chamber  158  of the hydraulic feed actuator  150  results in vertical movement of the feed cylinder  154  generally between the mast crown  112  and the mast base  114 . In another embodiment, the feed cylinder  154  may be fixed with respect to the mast  110  and the feed piston  152  and the first and second feed pistons rods  160 ,  162  may move with respect to the mast. In other possible embodiments, the feed actuator  150  can have other configurations enabling relative vertical movement with respect to the mast  110  and may utilize actuating technologies other than or in addition to hydraulics such as, for example, a mechanical ball screw, linear electrical motors, or the like. 
     To translate vertical movement of the feed actuator  150  with respect to the mast  110  to relative movement of the rotary head  122 , the drilling system  120  can include a wire rope feed system  170  including a plurality of wire ropes that can operatively connect the feed actuator  150  to the body  124  of the rotatory head  122 . The wire ropes can be formed as steel wire ropes assembled from many individual strands of thinner metal wires wound or braided together to form a flexible, elongated, and larger diameter wire rope. The flexible steel wire rope can be used as the running rigging of the wire rope feed system  170  and are adapted to bend around and extend about sheaves and pulleys. Depending on the drilling operation, the wire rope feed system  170  can be further differentiated into a hoist rope system  172  responsible for hoisting the rotary head  122  and a pulldown rope system  174  responsible for pulling down the rotary head  122  with respect to the work surface  102 . It should be appreciated however that the hoist rope system  172  and the pulldown rope system  174  operate in cooperation to perform their respective operations. 
     The hoist rope system  172  can encompass the upper components of the wire rope feed system  170  and can include a cylinder hoist pulley  180  that may be exteriorly mounted, for example, to the upper end of the feed cylinder  154  such that the cylinder hoist pulley  180  can vertically move in unison with the feed cylinder  154 . The hoist rope system  172  can also include a mast hoist pulley  182  fixedly mounted to the crown  112  of the mast  110  and is thus suspended vertically high above the work surface  102 . Directed around and operatively linking the cylinder hoist pulley  180  and the mast hoist pulley  182  can be a fixed length of flexible hoist wire rope  184  as described above. The hoist wire rope  184  can extend between a first hoist rope end  186  proximately connected with the crown  112  of the mast  110  and a second hoist rope end  188  fixedly connected to the exterior upper end of the body  124  of the rotary head  122 . To enable the hoist wire rope  184  to run between and extend around the cylinder hoist pulley  180  and the mast hoist pulley  182 , those components can each include a rotating sheave supported by a pulley frame and which is formed as a grooved wheel that holds and guides the hoist wire rope. 
     The pulldown rope system  174  can encompass the lower components of the wire rope feed system  170  and can include a cylinder pulldown pulley  190  that may be exteriorly mounted, for example, to the lower end of the feed cylinder  154  such that the cylinder pulldown pulley  190  can vertically move in unison with the feed cylinder  154 . The pulldown rope system  174  can also include a mast pulldown pulley  192  fixedly mounted to the base  114  of the mast  110  and is thus generally located proximate to the work surface  102 . Directed around and operatively linking the cylinder pulldown pulley  190  and the mast pulldown pulley  192  can be a fixed length of flexible pulldown wire rope  194  as described above. The pulldown wire rope  194  can extend between a first pulldown rope end  196  proximately connected with the base  114  of the mast  110  and a second pulldown rope end  198  fixedly connected to the exterior lower end of the body  124  of the rotary head  122 . To enable the pulldown wire rope  194  to run between and extend around the cylinder pulldown pulley  190  and the mast pulldown pulley  192 , those components can each include a rotating sheave supported by a pulley frame and which is formed as a grooved wheel that holds and guides the pulldown wire rope. 
     The pulleys and wire rope of the hoist rope system  172  and the pulleys and wire rope of the pulldown rope system  174  form block and tackle systems for vertically hoisting and pulling down the rotary head  122 . For example, during a hoist operation, pressurized hydraulic fluid is directed into the lower chamber  158  of the feed actuator  150 , causing the feed cylinder  154  acting as a free body to move vertically downwards with respect to the mast  110 . The cylinder hoist pulley  180  likewise moves vertically downwards with the feed cylinder  154  and thus moves vertically apart from the mast hoist pulley  182 . To accommodate the increasing vertical distance between the cylinder hoist pulley  180  and mast hoist pulley  182 , and likewise the increasing vertical distance between the cylinder hoist pulley  180  and the crown  112  of the mast  110 , the length of the hoist wire rope  184  between those elements must be increased. Because the hoist wire rope  184  has a fixed length between the first rope end  186  connected to the mast crown  112  and the second hoist rope end  188  connected to the body  124  of the rotary head  122 , the increase in the length of the hoist wire rope  184  between the cylinder hoist pulley  180  and mast hoist pulley  182  is accompanied by a corresponding decrease in length of the hoist wire rope  184  between the mast hoist pulley  182  and the rotary head  122 . The result is that the rotary head  122  is pulled vertically upwards with respect to the mast  110  and towards the crown  112 . It will be appreciated that pulldown rope system  174  must function in an opposite manner to increase the length of the pulldown wire rope  194  extending between the mast pulldown pulley  192  and the body  124  of the rotary head  122  to allow the rotary head to vertically rise with respect to the mast  110 . 
     Correspondingly, during a pulldown operation, pressurized hydraulic fluid is directed into the upper chamber  156  of the feed actuator  150 , causing the feed cylinder  154  acting as free body to move vertically upwards with respect to the mast  110 . The cylinder pulldown pulley  190  likewise moves vertically upwards with the feed cylinder  154  and thus moves vertically apart from the mast pulldown pulley  192 . To accommodate the increasing vertical distance between the cylinder pulldown pulley  190  and mast pulldown pulley  192 , and likewise the increasing vertical distance between the cylinder pulldown pulley  190  and base  114  of the mast  110 , the length of the pulldown wire rope  194  between those elements must be increased. Because of the fixed length of the pulldown wire rope  194 , the increase in the length of the pulldown wire rope  194  between the cylinder pulldown pulley  190  and mast pulldown pulley  192  is accompanied by a corresponding decrease in length of the pulldown wire rope between the mast pulldown pulley  192  and the rotary head  122 . This results in the rotary head  122  being pulled downwards with respect to the mast  110  and towards the base  114 . Downward movement of the rotary head  122  drives the drill string  128  and drill bit  134  into the work surface  102 . It will be appreciated that the hoist rope system  172  must cooperatively function to increase the length of the hoist wire rope  184  extending between the mast hoist pulley  182  and the body  124  of the rotary head  122  to allow the rotary head to move vertically downwards. 
     The hoist wire rope  184  and the pulldown wire rope  194  are placed under significant stress and tension during the respective hoist and pulldown operations. The tension can stretch and cause elongation of the hoist ca wire rope  184  and pulldown wire rope  194  and, because of the substantial lengths of the hoist and pulldown wire ropes, elongation of the wire ropes may be approximately several millimeters or inches. Maintaining the hoist wire rope  184  and the pulldown wire rope  194  in tension may compensate for elongation of the wire rope. However, if tension on the hoist wire rope  184  or the pulldown wire rope  194  is suddenly released, for example, when switching between hoist and pulldown operations or if the drilling system  120  were to encounter a hard rock formation during a pulldown operation, the wire ropes may become slack as result of the previous stretching and elongation. Slack in the hoist wire rope  184  and the pulldown wire rope  194  may allow the wire ropes to dislodge or come off of the pulleys and the freed wire ropes may swing about and cause damage to the surrounding components of the drilling system  120 . 
     Therefore, to maintain tension on the hoist wire rope  184  and the pulldown wire rope  194 , the drilling system  120  may be associated with tensioning system  200  including a hoist tensioning actuator  202  and a pulldown tensioning actuator  204 . The hoist and pulldown tensioning actuators  202 ,  204  may be embodied as double acting cylinders or as a spring loaded single acting cylindrical responsive to the receipt and discharge of hydraulic fluid therein. The hoist and pulldown tensioning actuators  202 ,  204  each may be embodied as a single rod hydraulic cylinder including a hollow, tubular hydraulic cylinder body  210   a ,  210   b  with a hydraulic piston  212   a ,  212   b  disposed therein. The hydraulic piston  212   a ,  212   b  can separate the hydraulic cylinder body  210   a ,  212   b  into a first hydraulic chamber, referred to as the rod end chamber  214   a ,  214   b  and a second hydraulic chamber, referred to as the piston end chamber  216   a ,  214   b . To connect with the terminal end of a respective wire rope, a hydraulic piston rod  218   a ,  218   b  joined to the hydraulic piston  212   a ,  212   b  extends through the rod end chamber  214   a ,  214   b  and protrudes exteriorly of the hydraulic cylinder body  210   a ,  210 B. To receive and discharge hydraulic fluid, the hoist tensioning actuator  202  and a pulldown tensioning actuator  204  may be operatively associated with the hydraulic system  140  of the drilling rig or may be supplied by a separate source of hydraulic fluid. 
     In an embodiment, the hoist tensioning actuator  202  can be fixedly disposed within the crown  112  of the mast and can be arranged so that the hydraulic piston rod  218   a  extends vertically downwards and can be connected with the first hoist rope end  186  of the hoist wire rope  184 . Likewise, in an embodiment, the pulldown tensioning actuator  204  can be fixedly disposed within the base  114  of the mast  110  and can be arranged so that the hydraulic piston rod  218   b  extends vertically upwards and connects with the first pulldown rope end  196  of the pulldown wire rope  194 . Directing pressurized hydraulic fluid to the rod end chamber  214   a ,  214   b  linearly moves the hydraulic piston  212   a ,  212   b  to retract the hydraulic piston rod  218   a ,  218   b  into the hydraulic cylinder body  210   a ,  210   b . Retraction of the hydraulic piston rod  218   a ,  218   b  maintains the respective hoist wire rope  184  or the pulldown wire rope  194  in tension, reducing wire rope slack and preventing the wire ropes from dislodging from the pulleys. Because the hydraulic piston  212   a ,  212   b  can move linearly in either axial direction in the hydraulic cylinder body  210   a ,  210   b , the hoist and pulldown tensioning actuators  202 ,  204  can accommodate temporary variations of the stresses applied to the hoist wire rope  184  and the pulldown wire rope  194 . 
     In other embodiments, the hoist and pulldown tensioning actuators  202 ,  204  may be positioned at other locations and in other orientations suitable for maintaining appropriate tension on the hoist and pulldown wire ropes  184 ,  194 . For example, the hoist and pulldown tensioning actuators  202 ,  204  may be located on and fixed to the feed cylinder  144  of the hydraulic feed actuator  140  and can be operatively connected to the cylinder hoist pulley  180  and cylinder pulldown pulley  190 , respectively, to interact with the hoist wire rope  184  and the pulldown wire rope  194  passing there around. For example, the first rope ends  186 ,  196  of the hoist and pulldown wire ropes  184 ,  194  may be fixed to the crown  112  and base  114  of the mast  110  while the length of the hoist and pulldown wire ropes passes around the respective cylinder hoist pulley  180  and cylinder pulldown pulley  190 . Extension and retraction of the hydraulic piston rod  218   a ,  218   b , which may be connected to the cylinder hoist pulley  180  and/or cylinder pulldown pulley  190 , thereby enables the hoist and pulldown tension actuators  202 ,  204  to displace the hoist and pulldown wire ropes  184 ,  194  and thereby vertically move the rotary head  122  attached to the second hoist rope end  188  and/or second pulldown rope end  198 . 
     In an embodiment, to determine the depth of the hole being formed by the drilling system  120 , a rotary sensor  230  such as a rotary encoder can be operatively associated with the wire rope feed system  170 . For example, the rotary sensor  230  can be disposed proximate to the crown  112  of the mast  110  and configured to measure the rotations made by the mast hoist pulley  182 . By counting the number of rotations made by the sheave of the mast hoist pulley  182 , and if its diameter is known, the cumulative run or payout of the hoist wire rope  184  between the mast host pulley  128  and the rotary head  122  over the course of the pulldown operation can be calculated. That calculation also determines how far the drill string  128  has penetrated into the work surface  102  and thus the depth of the hole or bore being formed. A related advantage of the hoist tensioning actuator  202  in reducing slack in the hoist wire rope  184  is that it prevents slipping of the hoist wire rope with respect to the mast host pulley  182  and improves accuracy in estimating the cumulative length of rope paid out during a pulldown operation and thus the depth of the hole. 
     In the embodiment where a hoist tensioning actuator  202  and the pulldown tensioning actuator  204  receive hydraulic fluid of the same hydraulic pressure in equal quantities from the same drill system hydraulic circuit  140 , the hoist and pulldown tensioning actuators can maintain the same tension on the respective hoist and pulldown wire ropes  184 ,  194 . This may be referred to as nominal tension. However, maintaining the hoist and pulldown wire ropes  184 ,  194  under consistent nominal tension at all times may be disadvantageous. For example, maintaining the pulldown wire rope  194  under nominal tension regardless of the actual hoist forces being applied to the wire ropes may result in excessive nominal tension once the hoisting force subsides, which may negatively impact the wire rope life. Further, the hoist and pulldown forces applied to the hoist wire rope  184  may not be the same as applied to the pulldown wire rope  194  for example, once the drilling system  120  penetrates the work surface  102  and counter forces are directed through the drill string  128 . 
     Accordingly, to accommodate changes to operation of the drilling system  120 , a tensioning hydraulic circuit  240  can be operatively associated with the tensioning system  200 . Further, to enable the hoist tensioning system and the pulldown tensioning system to independently respond to changes in the drilling operation, the tensioning hydraulic circuit  240  can be operatively separated into a hoist hydraulic circuit  242  and a pulldown hydraulic circuit  244 . Referring to  FIG.  2   , there is illustrated an embodiment of a possible arrangement for the tensioning hydraulic circuit  240  including the hoist hydraulic circuit  242  and a pulldown hydraulic circuit  244 . The tensioning hydraulic circuit  240 , hoist hydraulic circuit  242 , and a pulldown hydraulic circuit  244  are generally indicated by dashed lines. 
     To supply the hydraulic fluid that actuates the hoist and pulldown tensioning actuators  202 ,  204 , the tensioning hydraulic circuit  240  can be operatively associated with the hydraulic circuit  140  and in fluid communication with the hydraulic reservoir  142  and hydraulic pump  144 . The hydraulic reservoir  142  contains a volume of relatively low pressure hydraulic fluid and may be vented to the atmosphere or may be enclosed so that the hydraulic fluid is maintained in a slightly pressurized state. The hydraulic fluid can be any suitable type of incompressible fluid such as lubrication oil or the like and may have a sufficient viscosity to enable the fluid to readily flow in the hydraulic system. In an embodiment, the hydraulic reservoir  142  may function as a sump to which the tensioning hydraulic circuit  240  returns and hydraulic fluid can collect. 
     To pressurize and direct hydraulic fluid from the hydraulic reservoir  142  to the tensioning hydraulic circuit  240 , a hydraulic pump  144  can be included and in fluid communication with hydraulic reservoir  142 . The tensioning hydraulic circuit  240  thus receives hydraulic fluid at the hydraulic pressure established by the hydraulic motor  144 . 
     To change the tensioning hydraulic circuit  240  between an active state and an inactive state, a control valve  250  can be disposed downstream of and in fluid communication with the hydraulic pump  144 . The control valve  250  can be a two positioned one-way directional control valve including an opened position  252  in which hydraulic fluid is readily directed to the tensioning hydraulic circuit  240  and a closed position  254  which prevents hydraulic fluid from flowing to the tensioning hydraulic circuit  240 , however, in other embodiments the control valve  250  may have other configurations. In addition, the control valve  250  may be actuated electrically, hydraulically, or mechanically. When the control valve  250  is in the opened position  252 , the tensioning hydraulic circuit  240  is in the active state and the hoisting tensioning actuator  202  and the pulldown tensioning actuator  204  are able to receive pressurized hydraulic fluid. When the control valve  250  is in the closed position  254 , the tensioning hydraulic circuit  240  is in the inactive state and no hydraulic fluid can no longer flow to the tensioning hydraulic circuit  240 . 
     In an embodiment, to control or reduce the hydraulic pressure of the inflowing hydraulic fluid, the tensioning hydraulic circuit  240  can include a pressure reducing valve  260 . The pressure reducing valve  260  can be a spring biased valve that is normally opened but that can throttle or reduce the flow there through to lower the pressure of the hydraulic fluid from system pressure to a hydraulic pressure suitable for regulating operation of the tensioning system  200 . In various embodiments, the pressure reducing valve  260  may be actuated electrically, hydraulically, or mechanically. The hydraulic pressure of the hydraulic fluid established by the pressure reducing valve  260  may be referred to as the tensioning pressure of the tensioning hydraulic system  240 . In other embodiments, the tensioning pressure may be established by other pressure control devices such as variable control pumps, restrictors, and the like. 
     The pressure reducing valve  260  can be in fluid communication with and deliver pressurized hydraulic fluid to both the hoist hydraulic circuit  242  and the pulldown hydraulic circuit  244 . To direct hydraulic fluid to the rod end chamber  214   a  of the hoist tensioning actuator  202 , the hoist hydraulic circuit  242  can include a hoist actuator supply conduit  262  downstream of and in fluid communication with the pressure reducing valve  260 . Similarly, to supply hydraulic fluid at the tensioning pressure to the rod end chamber  214   b  of the pulldown tensioning actuator  204 , the pulldown hydraulic circuit  244  can include a pull actuator supply conduit  264  downstream of and in fluid communication with the pressure reducing valve  260 . As stated above, the hoist actuator supply conduit  262  and the pulldown actuator supply conduit  264  can have any suitable construction for channeling fluid such as flexible hoses, tubing, pipes and the like. 
     Because the hoist actuator supply conduit  262  establishes fluid communication between the pressure reducing valve  260  and the rod end chamber  214   a  of the hoist tensioning actuator  202 , the rod end chamber  214   a  is maintained at the tensioning pressure established by the pressure reducing valve  260  that attempts to linearly retract the hydraulic piston rod  218   a  into the hydraulic cylinder body  210   a . More specifically, the tensioning pressure attempts to displace the hydraulic piston  212   a  toward the piston end chamber  216   a  and increase the volume of the rod end chamber  214   a . Thus, the tension pressure in the rod end chamber  214   a  that retracts the hydraulic piston rod  218   a  into the hoist tensioning actuator  202  maintains the hoist wire rope  184  under tension in accordance with the tensioning pressure and reduces any slack therein. To maintain the piston end chamber  216   a  of the hoist tensioning actuator  202  at a relatively reduced pressure, and thus facilitate retraction of the hydraulic piston rod  218   a  into the hydraulic cylinder body  210   a , a hoist actuator return conduit  268  can establish fluid communication between the piston end chamber  216   a  and the hydraulic reservoir  142 . In other embodiments, the hoist tensioning actuator  202  may be a spring loaded, single acting cylinder with a spring biasing the hydraulic piston  212   a  and hydraulic piston rod  218   a  toward the rod end chamber  214   a  and the hoist actuator return conduit  268  can be omitted. 
     To maintain or limit the hydraulic pressure in the rod end chamber  214   a  of the hoist tensioning actuator  202  at a predetermined threshold pressure, which may be referred to as the relief pressure threshold, the hoist hydraulic circuit  242  can include a pressure limiting feature that is configured to relief hydraulic pressure in the hoist tensioning actuator  202 . The pressure limiting feature can be configured to direct a portion of the inflowing hydraulic fluid away from the hoist actuator supply conduit  262  and thus away from the hoist tensioning actuator  202 . In an embodiment, the pressure limiting feature may be a pressure relief valve  270 . A valve inlet  272  of pressure relief valve  270  can be in fluid communication with the hoist actuator supply conduit  262  and a valve outlet  274  of the pressure relief valve  270  can be in fluid communication with the hoist actuator return conduit  268  and thus the hydraulic reservoir  142 . The pressure relief valve  270  may be located in a bypass conduit  275  associated with the hoist hydraulic circuit  242  that is fluidly connected between the hoist actuator supply conduit  262  and the hoist actuator return conduit  268 . The pressure relief valve  270  can be in a normally closed state so that the rod end chamber  214   a  of the hoist tensioning actuator  202  only receives inflowing hydraulic fluid at the tensioning pressure established by the pressure reducing valve  260 . 
     In the event the hydraulic pressure in the rod end chamber  214  exceeds a predetermined relief pressure threshold, the pressure relief valve  270  partially opens to divert or direct a portion of the hydraulic fluid to the hoist actuator return conduit  268  and thus the hydraulic reservoir  142 . The pressure relief valve  270  allows a portion of the hydraulic fluid to bypass or the flow from the hoist tensioning actuator  202  and be directly returned to the hydraulic reservoir  142 . The rod end chamber  214   a  of the hoist tensioning actuator  202  is thus maintained at or limited to the relief pressure threshold and the hoist wire rope  184  is maintained in tension in accordance with the relief pressure threshold. 
     The relief pressure threshold can be set to any suitable pressure for maintaining the hoist wire rope  184  under tension by action of the hoist tensioning actuator. In an embodiment, the relief pressure threshold may be set at the tensioning pressure established by the pressure reducing valve  260 . In another embodiment, the relief pressure threshold may be set above the tensioning pressure and may for example be a multiple of the tension pressure. In an embodiment, the relief pressure threshold may fall within a range of one to six times the tension pressure set by the pressure reducing valve  260 . For example, if the tensioning pressure established by the pressure reducing valve  260  is 10 bars, the relief pressure threshold may fall within a range of 10 to 60 bars. Accordingly, the hydraulic pressure in the hoist tensioning actuator  202  may rise above the tensioning pressure before the pressure relief valve  270  opens. 
     In an embodiment, the pressure relief valve  270  can be a spring loaded or solenoid controlled valve and can be actuated mechanically, electrically, or electromechanically. The pressure relief valve  270  may be linearly functioning so that the quantity of inflowing hydraulic fluid diverted to the hoist actuator return line  268  is proportional to the degree by which hydraulic pressure in the rod end chamber  214   a  of the hoist tensioning actuator  202  exceeds the pressure relief threshold. The pressure relief valve  270  can thus quickly react to pressure spikes in the hoist tensioning actuator  202  arising from sudden changes or disruptions in the pulldown or hoisting operations. 
     In an embodiment, the hoist hydraulic circuit  242  can include a hoist circuit check valve  276  that is disposed in the hoist circuit supply conduit  262  upstream of the pressure relief valve  270  and the bypass conduit  275 . The hoist circuit check valve  276  is configured as a one-way flow control valve that allows inflowing hydraulic fluid to flow into the hoist tensioning actuator  202  but prevents hydraulic fluid from flowing back upstream towards the pressure reducing valve  260 . The hoist circuit check valve  276  maintains hydraulic pressure downstream in the hoist circuit supply conduit  262  and in the hoist tensioning actuator  202 . If the hydraulic pressure in the hoist tensioning actuator  202  exceeds the inflowing pressure, for example, the tensioning pressure established by the pressure reducing valve  260 , a portion of the hydraulic fluid in the hoist hydraulic circuit  242  is directed to the pressure relief valve  270  and cannot flow back to the pressure reducing valve  260  or the pulldown actuator supply conduit  264  communicating with the pulldown tensioning actuator  204  due to the hoist circuit check valve  276 . The hoist circuit check valve  276  ensures that, in the event hydraulic pressure exceeds the relief pressure threshold, excess hydraulic fluid from the hoist tensioning actuator  202  is directed through the pressure relief valve  270  and cannot flow back upstream in the hoist hydraulic circuit  242 . The pressure setting at which the pressure relief valve  270  opens, for example, the relief pressure threshold, is therefore the pressure limit of the hoist hydraulic circuit  202 . 
     The pulldown actuator supply conduit  264  is fluidly connected to the hoist actuator supply conduit  262  between the pressure reducing valve  260  and the hoist circuit check valve  276  to receive inflowing hydraulic fluid at the predetermined hydraulic pressure, for example, the tensioning pressure established by the pressure reducing valve  260 . The pulldown actuator supply conduit  264  directs inflowing hydraulic fluid to the rod end chamber  214   b  of the pulldown tensioning actuator  204  so that the rod end chamber is maintained at the tensioning pressure. The tensioning pressure in the rod end chamber  214   b  displaces the hydraulic piston  212   b  towards the piston end chamber  216   b  and retracts the hydraulic piston rod  218   b  into the hydraulic cylinder body  210   b  of the pulldown tensioning actuator  204 . Retraction of the hydraulic piston rod  218   b  places the pulldown wire rope  194  to which it is connected under tension in accordance with the tensioning pressure and reduces any slack therein. To maintain the piston end chamber  216   b  of the pulldown tensioning actuator  204  at a relative reduced pressure, and thus facilitate retraction of the hydraulic piston rod  218  into the hydraulic cylinder body  210 , a pulldown actuator return conduit  278  can establish fluid communication between the piston end chamber  216   b  and the hydraulic reservoir  142 . In other embodiments, the pulldown tensioning actuator  204  may be a spring-loaded, single acting cylinder with a spring biasing the hydraulic piston  212   b  and hydraulic piston rod  218   b  toward the rod end chamber  214   b  and the pulldown actuator return conduit  278  can be omitted. 
     In an embodiment, the pulldown hydraulic circuit  244  can include a pressure isolation feature that is configured to isolate the hydraulic pressure established in the pulldown tensioning actuator  204 . More specifically, the pressure isolation feature may function to isolate or trap hydraulic fluid in the rod end chamber  214   b  of the pulldown tensioning actuator  204  and thus maintains the hydraulic pressure established therein, even if above the tensioning pressure established by the pressure reducing valve  260 . In an embodiment, the pressure isolation feature may be a pulldown circuit check valve  280  disposed in the pulldown actuator supply line  264  and located between the fluid connection to the hoist actuator supply conduit  262  and the pulldown tensioning actuator  204 . The pulldown circuit check valve  280  is a one-way flow valve that allows inflowing hydraulic fluid to flow into the pulldown tensioning actuator  204  but prevents hydraulic fluid from flowing back upstream toward the pressure reducing valve  260 . 
     The pulldown circuit check valve  280  ensures the pulldown tensioning actuator  204  is maintained at least at the predetermine pressure set by the pressure reducing valve  260 , for example, the tensioning pressure. For example, if the rod end chamber  214   b  of the pulldown tensioning actuator  204  were to fall below the tensioning pressure, the pulldown circuit check valve  280  would open to direct inflowing hydraulic fluid to the rod end chamber  214   b  and return the hydraulic pressure therein to the tensioning pressure. If the hydraulic pressure in the rod end chamber  214   b  were to exceed the tensioning pressure established by the inflowing hydraulic fluid, the pulldown circuit check valve  280  would prevent hydraulic fluid flowing back upstream towards the hoist actuator supply circuit  262  and pressure reducing valve  260  and maintain the rod end chamber  214   b  of the pulldown tensioning actuator  204  at the elevated hydraulic pressure. 
     INDUSTRIAL APPLICABILITY 
     Referring to  FIGS.  3  and  4   , there is illustrated the actions and effects of the tensioning system  200  in cooperation with the tensioning hydraulic circuit  240  during a pulldown operation conducted by the drilling system  120 . Hydraulic fluid from the hydraulic reservoir  142  is pressurized by the hydraulic pump  144  and delivered to the tensioning hydraulic circuit  240 . The pressure reducing valve  260  can reduce the hydraulic pressure of the inflowing hydraulic fluid to a tensioning pressure that the hoist tensioning actuator  202  and the pulldown tensioning actuator  204  of the tensioning system  200  can utilize. Downstream of the pressure reducing valve  260 , the inflowing hydraulic fluid at the tensioning pressure is directed to the rod end chambers  214   a ,  214   b  of the hoist tensioning actuator  202  and of the pulldown tensioning actuator  204  by the hoist actuator supply conduit  262  and the pulldown actuator supply conduit  264  respectively. In the flow diagram of  FIG.  4   , this is represented in supplying step  302  in which hydraulic fluid at tensioning pressure is supplied to the hoist and pulldown tensioning actuators  202 ,  204 . 
     When the rod end chambers  214   a ,  214   b  of the hoist and pulldown tensioning actuators  202 ,  204  both receive inflowing hydraulic fluid at the tensioning pressure, the tensioning pressure will tend to displace the hydraulic piston  212   a , 212   b  toward the piston end chamber  216   a ,  216   b  and retract the hydraulic piston rod  218   a ,  218   b  into the hydraulic cylinder body  210   a ,  210   b . Retraction of the hydraulic piston rod  218   a ,  218   b  into the respective hoist and pulldown tensioning actuators  202 ,  204  places the hoist wire rope  184  and pulldown wire rope  194  in tension, which may be referred to as hoist rope tension  290  and pulldown rope tension  292  respectively. The hoist rope tension  290  and pulldown rope tension  292  are represented by arrows in  FIG.  3   . Prior to contact between the drill string  128  and the work surface  102 , the hydraulic pressure in the rod end chambers  214   a ,  214   b  of the hoist and pulldown actuators  202 ,  204  and thus the hoist rope tension  290  and pulldown rope tension  292  are generally equal. 
     The pulldown operation commences, as indicated in commence pulldown step  304 , by introducing pressurized hydraulic fluid to the hydraulic feed actuator  150  to move the feed cylinder  154  vertically upwards with respect to the mast  110 . Correspondingly, the block and tackle configuration provided by the pulldown cylinder pulley  190 , mast pulldown pulley  192 , and pulldown wire rope  194  moves the rotary head  122  vertically downwards toward the work surface  102 . When the drill bit  134  coupled to the rotary head  122  contacts the work surface  102 , the counterforce transmitted through the drill string  128  to the rotary head  122  adds to the pulldown rope tension  292  on the pulldown wire rope  194 . The hydraulic pressure in the pulldown tensioning actuator  204  rises above the tensioning pressure because hydraulic fluid is trapped in the rod end chamber  214   b  by the pulldown circuit check valve  280  in the pulldown hydraulic circuit  244 . Further vertically downward movement of the rotary head  122  will increase the pulldown rope tension  292  and consequentially the pulldown wire rope  194  will stretch because the hydraulic piston rod  218   b  of the pulldown tensioning actuator  204  cannot extend further. This is represented by the pulldown rope stretch step  306  of  FIG.  4   . 
     The hoist rope tension  290  of the hoist wire rope  184 , in contrast, may decrease because the vertically upward movement of the cylinder hoist pulley  180  in unison with the feed cylinder  154  allows the hoist wire rope  184  to be pulled downward with the rotary head  122 . The reduction in hoist rope tension  290  causes the hoist wire rope  184  to slacken. To prevent the slackening hoist wire rope  184  from dislodging from the cylinder hoist pulley  180  and the mast hoist pulley  182 , the tensioning pressure exerted by the hydraulic fluid in rod end chamber  214  of the hoist tensioning actuator  202  displaces the hydraulic piston  212   a  toward the piston end chamber  216   a  and causes the hydraulic piston rod  218   a  to retract into the hydraulic cylinder body  210   a . Formation of slack in the hoist wire rope  184  is therefore prevented. Further, the hydraulic pressure in the rod end chamber  214   a  of the hoist tensioning actuator  202  remains at the tensioning pressure as set by the pressure reducing valve  260  upstream of the hoist actuator supply conduit  262 . This is represented by the hoist rope slack reduction step  308  of the  FIG.  6   . 
     As represented by comparison block  310 , in this situation, the hydraulic pressure in the pulldown tensioning actuator  204  and the pulldown rope tension  292  may be equal to or greater than the hydraulic pressure in the hoist tensioning actuator  202 , which may be the tensioning pressure set by the pressure reducing valve  260 , and the hoist rope tension  290 . 
     In a cease pulldown operation step  312 , the pulldown operation of the drilling system  120  is halted, for example, as may occur prior to initiating a hoist operation. Hydraulic fluid is no longer directed to the hydraulic feed actuator  150  and the rotary head  122  consequentially no longer moves vertically downward into the work surface  102 . When the pulldown operation stops, the tensioning stresses imparted to the tensioning system  200  substantially change. 
     For example, because the feed cylinder  154  of the hydraulic feed actuator  150  no longer moves vertically upward with respect to the mast  110 , the hoist wire rope  184  connected at the second hoist rope end  188  to the rotary head  122  may no longer freely follow the movement of the rotary head. The hoist wire rope  184  may, as a result, become taut and the hoist rope tension  290  may increase. The increase in hoist rope tension  290  may cause the hoist wire rope  184  to pull the hydraulic piston rod  218  in the hydraulic cylinder body  210   a  toward the rod end chamber  214   a . The hydraulic piston  212   a  likewise moves toward the rod end chamber  216   a  compressing the hydraulic fluid therein and thereby increases the hydraulic pressure in the hoist tensioning actuator  202 . In this situation, as indicated by comparison block  314 , the hydraulic pressure in the hoist tensioning actuator  202  and the hoist rope tension  290  may approach or be approximately equal to the hydraulic pressure in the pulldown tensioning actuator  204  and the pulldown rope tension  292 , respectively. Moreover, the hydraulic pressure in the hoist and pulldown tensioning actuators  202 ,  204  may be equal to or greater than the tensioning pressure set by the pressure reducing valve  260  of the tensioning hydraulic circuit  240 . 
     To reduce the hoist rope tension  290 , the pressure relief valve  270  of the hoist hydraulic circuit  262  may open to discharge or divert inflowing hydraulic fluid in the hoist actuator supply conduit  264  from the hoist tensioning actuator  202 . For example, if the predetermined threshold pressure of the pressure relief valve  270  is set for the relief pressure threshold, the rise in the hydraulic pressure of the hoist tensioning cylinder  202  above the relief pressure threshold will cause the pressure relief valve  270  to open. A part of the hydraulic fluid in the hoist hydraulic circuit  242  at the tensioning pressure set by the pressure reducing valve  260  is diverted by the pressure relief valve  270  to the hydraulic reservoir  142 . Moreover, the hydraulic pressure in the rod end chamber  214   a  of the hoist tensioning actuator  202 , which is fluidly connected to the pressure relief valve  270  by the hoist actuator supply conduit  262 , is reduced and may establish equilibrium with the tensioning pressure. Consequentially, the hydraulic piston  212   a  can displace into the rod end chamber  214   a  and the hydraulic piston rod  218   a  can extend from the hoist tensioning actuator  202  to reduce the hoist rope tension  290  until the hydraulic piston  212   a  abuts the hydraulic cylinder  210   a  and the hydraulic piston rod  218   a  is fully extended. This is represented by the pressure relief step  316  in  FIG.  4   . 
     Accordingly, the disclosure provides a tensioning hydraulic circuit  240  that operates in cooperation with a tensioning system  200  operatively associated with wire rope feed system  170  of the drilling system  120 . The tensioning hydraulic circuit  240  is operatively separated into a hoist hydraulic circuit  242  operatively associated with a hoist tensioning actuator  202  and a pulldown hydraulic circuit  244  operatively associated with the pulldown tensioning actuator  204 . The hoist hydraulic circuit  242  includes a pressure limiting feature in the form of a pressure relief valve  270  in fluid communication with a hoist actuator supply conduit  262  to the hoist tensioning actuator  202  and with a hoist actuator return conduit  268  in fluid communication with the hydraulic reservoir  142 . The pulldown hydraulic circuit  244  includes a pressure isolation feature in the form of a pulldown circuit check valve  280  disposed in the pulldown actuator supply conduit  264  that allows hydraulic fluid to flow to the pulldown tensioning actuator  204  and prevents hydraulic flow back upstream from the pulldown tensioning actuator  204 . 
     In a pulldown operation, the pulldown rope tension  292  may rise as the drilling system  120  penetrates the work surface  102 . Consequentially, the hydraulic piston rod  218   b  extends from the pulldown tensioning actuator  204  and the hydraulic pressure therein rises above the tensioning pressure established by the pressure reducing valve  260  and is maintained at the heightened pressure by the pulldown circuit check valve  280 . During a pulldown operation, the increased pulldown rope tension  292  may assist the drill string  128  of the drilling system  120  in penetrating the work surface  102 , but may also result in stretching of the pulldown wire rope  194 . 
     When the pulldown wire rope  194  stretches, the hoist rope tension  290  may be reduced and the hoist wire rope  184  may go slack. To reduce the slack in the hoist wire rope  184 , the hydraulic piston rod  218   a  of the hoist tensioning actuator  202  may be retracted due to the hydraulic fluid therein that maintains the hoist tensioning actuator  202  at the tensioning pressure. If the pulldown operation ceases, for example, prior to initiating a hoist operation or the drilling system encounters a hard rock formation, the hoist rope tension  290  may rise as the hoist rope tension  290  and the pulldown rope tension  290  equalize and the hydraulic pressure in the hoist tensioning actuator  202  may consequentially increase. The pressure relief valve  270  may open draining the hydraulic fluid in the hoist actuator supply conduit  262  to the hydraulic reservoir  142  bypasses the hoist tensioning actuator  202  and thereby lowers the hydraulic pressure in the hoist tensioning actuator  202 . 
     In an embodiment, to ensure the hoist tensioning actuator  202  quickly and dynamically responds to any changes in hydraulic pressure therein, the hoist actuator supply conduit  262  and the hoist actuator return conduit  268  may be larger than the pulldown actuator supply conduit  264  and pulldown actuator return conduit  278 . Accordingly hydraulic fluid at tensioning pressure can be quickly directed to the hoist tensioning actuator  202  to remove slack developing in the hoist wire rope  184 . Likewise, hydraulic fluid can be quickly directed from the hoist tensioning actuator  202  to reduce a spike in hydraulic pressure therein. The hoist tensioning actuator  202  therefore can therefore compensate for temporary stretching and elastic elongation that may to the hoist and pulldown wire ropes  184 ,  194  as the drilling system  120  alternates between pulldown operation and hoist operations. 
     The pulldown tensioning actuator  204  and pulldown hydraulic circuit  242 , in contrast, may respond more gradually to changes in the operation of the drilling system  120 . For example, the pulldown tensioning actuator  204  can be arranged to compensate for permanent stretching and elongation of the hoist and pulldown wire ropes  184 ,  194  that may occur over time and from which the wire ropes may not recover. 
     In an embodiment, the drilling system  120  can commence a hoist operation in which the tensioning stresses applied to the wire rope feed system  170  are substantially converse to the pulldown operation. For example, during the hoist operation, the hoist rope tension  290  is increased as the feed cylinder  154  of the hydraulic feed actuator  150  moves vertically downward, for example, by directing hydraulic fluid to the lower chamber  158 . The corresponding downward movement of the cylinder hoist pulley  180  attached to the feed cylinder causes the hoist wire rope  184  to move the rotary head  122  vertically upwards with respect to the work surface  102 . The increase in the hoist rope tension  290  causes the hydraulic pressure in the hoist tensioning actuator  202  to increase as the hydraulic piston  212   a  is displaced into the rod end chamber  214   a  and the hydraulic piston rod  218   a  extends from the hoist tensioning actuator  202 . The hydraulic piston  212   a  may abut the hydraulic cylinder body  210   a  so the hydraulic piston rod  218   a  is fully extended. Further increase in the hoist rope tension  290  may result in stretching of the hoist wire rope  184 . 
     Conversely, the pulldown rope tension  292  may be reduced because the pulldown wire rope  194  readily moves upwards with the rotary head  122  to which it is attached. The reduction in the pulldown rope tension  292  may result in the pulldown wire rope  194  slackening and may simultaneously reduce the hydraulic pressure in the pulldown tensioning actuator  204 . However, the rod end chamber  214   a  of the pulldown tensioning actuator  204  remains in fluid communication with the pressure reducing valve  260  via the pulldown actuator supply conduit  264  and the pulldown circuit check valve  280  and can continue to receive hydraulic fluid at the tensioning pressure. The hydraulic fluid at tensioning pressure in the rod end chamber  214   a  of the pulldown tensioning actuator  204  displaces the hydraulic piston  212   a  toward the piston end chamber  216   a  and retracts the hydraulic piston rod  218   a  into the hydraulic cylinder body  210   a , thereby applying at least the tensioning pressure to the pulldown wire rope  194  and reducing or eliminating slack therein. 
     In an embodiment, when the hoist operation is generating substantial tension in the hoist wire rope  184  as a result of the substantially high hydraulic pressure in the lower chamber  148  of the hydraulic feed actuator  150 , the tensioning hydraulic circuit  220  can act to limit hydraulic pressure in the pulldown tensioning actuator  204  and limit the tensioning force applied to the pulldown wire rope  194 . For example, because hydraulic fluid in the rod end chamber  214   b  of the pulldown tensioning actuator  204  is isolated or trapped by the pulldown circuit check valve  280 , the hydraulic pressure therein may exceed the tensioning pressure established by the pressure reducing valve  260 . As the hydraulic pressure in the hydraulic feed actuator  150  continues to rise and the slack in the pulldown wire rope  194  correspondingly increases, the tensioning hydraulic circuit  220  will direct additional hydraulic fluid to the pulldown tensioning actuator  204  to compensate for the slack. Accordingly, there may be an excessive quantity of hydraulic fluid in the pulldown tensioning actuator  204  resulting in excessive hydraulic pressure therein when the hoist operation ceases. The control valve  250  can be configured in the closed position  254  preventing hydraulic fluid from flowing to the tensioning hydraulic circuit  220  and thus onto the pulldown tensioning actuator  204  thereby limiting the hydraulic pressure present and isolated in the pulldown tensioning actuator. For example, the control valve  250  may configure itself in the closed position  254  if the hydraulic pressure in the hydraulic feed actuator  150  exceeds a predetermined hoisting pressure limit. The hoisting pressure limit associated with the hydraulic feed actuator  150  may be set to prevent the flow of hydraulic fluid to the pulldown tensioning actuator  204  based on the hydraulic pressure in the hydraulic feed actuator during hoisting operations. Because the hydraulic pressure in the pulldown tensioning actuator  204  is limited under these circumstances, the pulldown tensioning actuator will not apply or result in an excessive pulldown rope tension  292  when the hoist operation ceases. Instead, the hoist rope tension  290  in the hoist wire rope  184  and the pulldown rope tension  292  in the pulldown wire rope  194  can redistribute and may equalize, thereby avoiding excessive tension or stress on the hoist and pulldown wire ropes. 
     An advantage of the foregoing is that disclosed tensioning hydraulic circuit  240  can reduce or eliminate the slackening of the hoist and/or pulldown wire ropes wire rope feed system by utilizing and manipulating the hydraulic pressure in the hoist and pulldown tensioning actuators to reduce the tension applied, or avoid prolonged application of tension, to the hoist and pulldown wire ropes. Operating the hoist and pulldown wire ropes at lower tension prolongs the operational life of the wire rope feed system and reduces operating cost of the drilling rig. These and other advantages and features of the disclosure should be apparent from the foregoing description and accompanying drawings. 
     It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure and the protection to which applicant is entitled more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated.