Abstract:
An air compressor that can take in air at a particular pressure at the input and compress the air such that it exits an output at a much greater pressure until a desired pressure is reached in a piston assembly, at which point, the air compressor can shut off automatically by moving a switch. A tank does not need to be part of the compressor assembly, and thus, the air compressor is capable of determining the pressure and shutting off at the desired pressure regardless of the particular tank that is removeably connected to the air compressor. The switch can be moved to an off position by an arm pivotally connected to a carriage. In addition, the air compressor can utilize a piston assembly having a plurality of stationary o-rings for receiving a piston.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This patent application claims the benefit of U.S. Provisional Patent Application No. 60/441,909, filed Feb. 11, 2011, which is incorporated by reference in its entirety herein. 
     
    
     BACKGROUND 
       [0002]    Air compressors are known in the art for supplying a flow of pressurized air for a variety of applications. They often use a motor that repetitively drives a piston to compress the air. As the air is compressed, it is often provided to and stored in a tank from which it can then be dispensed. The tank is typically brought up to a particular pressure by the compressor, at which point, a pressure sensor provides a signal that shuts off the motor. When the pressure in the tank drops to a particular pressure, as sensed by the pressure switch, or the compressor is manually turned on again, the motor will turn back on to continue the flow of pressurized air to the tank. 
         [0003]    Typical consumer air compressors provide air pressures of about 200 psi or lower. Some applications, however, may require pressures greatly exceeding 200 psi. For example, paintball guns often have tanks that are filled to very high pressures such as 3000 psi-4500 psi. Similarly, scuba tanks are also filled to very high pressures. Thus, most consumer air compressors are not suitable for high pressure applications. 
         [0004]    Furthermore, piston assemblies used for common air compressors utilize an interference fit of metallic sealing ring that is attached to and moves with the piston. Due to the number of cycles that the piston is required to undergo during operation, piston failure, and thus compressor failure, is often attributed to wear experienced by the piston components. 
       BRIEF SUMMARY 
       [0005]    An air compressor is disclosed that can take in air at a particular pressure at the input and compress the air such that it exits an output at a much greater pressure until a desired pressure is reached in a piston assembly, at which point, the air compressor can shut off automatically by moving a switch. A tank does not need to be part of the compressor assembly, and thus, the air compressor is capable of determining the pressure and shutting off at the desired pressure regardless of the particular tank that is removeably connected to the air compressor. The switch can be moved to an off position by an arm pivotally connected to a carriage, and thus, an electronic pressure sensor is not required. The air compressor is relatively inexpensive to manufacture, durable, and easy to maintain. In addition, the air compressor can utilize a piston assembly having a plurality of stationary seals, such as o-rings, for receiving a piston. 
         [0006]    An air compressor is disclosed including a housing, a motor mounted to the housing, a switch for turning the motor off, a piston assembly disposed within the housing, and a linkage assembly. The switch can be disposed at least partially within the housing. The carriage can be coupled to the piston assembly and can have a pivotally mounted arm. The linkage assembly can be disposed within the housing and can be moveable by the motor. The linkage assembly can be connected to the arm such that when the motor moves the linkage assembly, the linkage assembly can pivot the arm to move the switch. 
         [0007]    In addition, an air compressor is disclosed including a housing and a piston assembly disposed within the housing. The piston assembly can include a piston housing, a first o-ring, a second o-ring, and a piston. The piston housing can have a first end and a second end, and can include an air inlet disposed between the first end and the second end. The first o-ring can be disposed within the piston housing between the first end and the air inlet. The second o-ring can be disposed within the piston housing between the second end and the air inlet. The piston can be disposed at least partially within the piston housing. The piston can be moveable with respect to the piston housing. The first o-ring and the second o-ring can be mounted stationary within the piston housing such that the piston is moveable within the first o-ring and the second o-ring. 
         [0008]    Further, a piston assembly is disclosed including a piston housing, a first o-ring, a second o-ring, and a piston. The piston housing can have a first end and a second end, and can include an air inlet disposed between the first end and the second end. The first o-ring can be disposed within the piston housing between the first end and the air inlet. The second o-ring can be disposed within the piston housing between the second end and the air inlet. The piston can be disposed at least partially within the piston housing. The piston can be moveable with respect to the piston housing. The first o-ring and the second o-ring can be mounted stationary within the piston housing such that the piston is moveable within the first o-ring and the second o-ring. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a perspective view of an air compressor; 
           [0010]      FIG. 2  is a perspective view of the air compressor of  FIG. 1  with the cover removed; 
           [0011]      FIG. 3  is a front view of the air compressor of  FIG. 1  with the cover removed; 
           [0012]      FIG. 4  is another front view of the air compressor of  FIG. 1  with the cover removed; 
           [0013]      FIG. 5  is a section view taken through line  5 - 5  in  FIG. 6 ; 
           [0014]      FIG. 6  is a left elevational side view of the air compressor of  FIG. 1  with the cover removed; 
           [0015]      FIG. 7  is a right elevational side view of the air compressor of  FIG. 1  with the cover removed; 
           [0016]      FIG. 8  is an exploded perspective view of a carriage and connecting arm for the air compressor of  FIG. 1 ; 
           [0017]      FIG. 9  is an enlarged fragmentary view of the carriage and switch for the air compressor of  FIG. 1 ; 
           [0018]      FIG. 10  is another enlarged fragmentary view of the carriage and switch for the air compressor of  FIG. 1   
           [0019]      FIG. 11  is a simplified fragmentary partial sectional view of two piston assemblies with the pistons retracted for the air compressor of  FIG. 1 ; and 
           [0020]      FIG. 12  is another simplified fragmentary partial sectional view of two piston assemblies with the pistons advanced for the air compressor of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    With reference to the figures, wherein like reference numbers represent like features, an air compressor is described herein. Referring to  FIG. 1 , the air compressor  100  can include a housing  102 , a cover  104 , and a motor  106 . The housing  102  can provide a portion of the external structure of the air compressor  100  for protecting the interior components. The housing  102  can also provide a support structure for mounting internal components of the air compressor  100 . The housing  102  can include one or more apertures  109  providing access to interior components of the compressor and/or permitting one or more components to extend from the interior to the exterior of the air compressor  100 . For example, an air input fitting  108  may extend from the housing  102  and provide a structure for attaching an air hose. The air input fitting  108  may be fixed to the air compressor  100  or can be removeable such that alternative fittings of different shapes and/or sizes could be used. The air input fitting  108  provides access to the compressor air input, which is described further below. It will be appreciated that the housing  102  can include any suitable number of apertures for any suitable number of purposes. 
         [0022]    Referring to  FIG. 2 , the housing  100  can include an opening  110  for providing access to the interior of the housing  102 . Turning back to  FIG. 1 , the cover  104  can be disposed over the opening  110  in the housing  102  and can be removeable from the housing  102  in order to provide access to interior components of the air compressor  100 . The cover  104  also protects the interior components of the housing  102  when the cover  104  is disposed over the opening  110  in the housing  102 . The cover  104  can provide one or more apertures permitting access to interior components of the air compressor  100  and/or permitting one or more components to extend from the interior to the exterior of the air compressor  100 . For example, the cover  104  can include an aperture  112  for a switch, which is described further below. As another example, the cover  104  can include an aperture  114  for a vent knob and/or an air compressor output, which are described further below. It will be appreciated that the cover  104  can include any suitable number of apertures for any suitable number of purposes. The motor  106  can be mounted to the housing, such as the rear of the housing, and may be removeable for servicing, replacement, and the like. As shown, the motor  106  can be an electric motor, and accordingly, can include a power cord  116 . It will be appreciated, however, that any suitable motor could be used, such as a hydraulic or combustion motor. 
         [0023]    Turning to  FIGS. 2 ,  3 , and  5 - 7 , wherein the cover  104  has been removed for illustration, the interior components of the air compressor  100  are shown. The motor  106  can have a motor body  118  and a motor shaft  120  extending from the motor body  118 . The motor shaft  120  can have a drive gear  122  fixed to the motor shaft  120 . As shown in  FIGS. 2 ,  3 , and  5 , the drive gear  122  can be connected via a motor chain  124  to a first transition gear  126 . The first transition gear  126  may be fixed to a second transition gear  128  via a jackshaft  130 . The second transition gear  128  can be connected by a jackshaft chain  132  to a linkage gear  134 . As the motor  106  rotates, the drive gear  122  can turn the motor chain  124  to rotate the jackshaft  130  via the first transition gear  126 . The rotation of the jackshaft  130  can also rotate second transition gear  128 , which in turn rotates the linkage gear  134 . It will be appreciated that the motor  106  may drive components of the air compressor  100  via any suitable number, types, and sizes of gears, shafts, and linkages. 
         [0024]    Referring to  FIGS. 2 ,  3 ,  5 , and  6 , the linkage gear  134  may be connected to a linkage shaft  136  to rotate a linkage assembly  138 . As shown in  FIGS. 2 and 3 , the linkage assembly  138  can include a crank arm  140  and a connecting arm  142 . The crank arm  140  may be mounted to the linkage shaft  136  near an end such that the crank arm  140  can be rotated by the linkage shaft  136 . The connecting arm  142  can be pivotally attached to the crank arm  140  near another end of the crank arm  140 . The other end of the connecting arm  142  can be pivotally attached to a carriage  144 . 
         [0025]    As shown in  FIGS. 2 ,  3 , and  8 , the carriage  144  can include a shaft block  146 , a release arm  148 , and a guide pin  150 . The carriage  144  can be linearly moveable as it is pulled and pushed by the connecting arm  142 . The guide pin  150  can extend from the shaft block  146  such that it can ride within a guide bracket  152  as it moves. The guide bracket  152  can be mounted to the housing  102  and can include first and second parallel sidewalls  154 ,  156  that permit the guide pin  150  to travel therebetween. The guide pin  150  and guide bracket  152  can restrict movement of the carriage  144  in a direction perpendicular to the first and second sidewalls  154 ,  156 , which alleviates stresses on the linkage assembly  138  when in motion. 
         [0026]    Referring to  FIGS. 8 and 9 , the release arm  148  may be pivotally attached to the shaft block  146  using a bolt  158  or other suitable structure and one or more roller bearings  160  that can fit at least partially within the shaft block  146 . The release arm  148  can include an oversized aperture  162  that receives a projection  164  such as a bolt or other suitable structure extending from the shaft block  146 . The oversized aperture  162  restricts the freedom of pivotal movement of the release arm  148  with respect to the shaft block  146 . In addition, the release arm  148  can include a spring aperture  166  for receiving a tension spring  168 . The connecting arm  142  can be pivotally attached to the release arm  148  with a bearing  172  and bolt  170  or other suitable structure. The guide pin  150  can extend from the shaft block  146 , and can include a bearing  151 . 
         [0027]    Referring to  FIGS. 2 ,  3 ,  6 , and  11 , the air compressor  100  can have one or more piston assemblies. For example, the air compressor  100  can include a first piston assembly  174  and a second piston assembly  176 . The first piston assembly  174  can include a cylindrical housing  178 , a piston  180 , a back check valve  182 , an air inlet  184 , suitable sealing structures such as o-rings  186 ,  188  on each side of the air inlet  184 , one or more spacers  187 ,  189 , and an exit air line  190 . The piston  180  can include a collar  192  for attaching the tension spring  168  to the piston  180 . The piston  180  can be attached to and pass through the shaft block  146 . The piston  180  can also pass through and be moveably coupled to a support bracket  193  that can be mounted to the housing  102 . The piston  180  can be moveable within a bearing  195  mounted to the support bracket  193 . The support bracket  193  can help to maintain the linear movement of the carriage  144  by resisting movement of the piston  180  and carriage  144  in a direction perpendicular to the longitudinal axis of the piston  180 , which alleviates stresses on the linkage assembly  138  when in motion. In addition, the support bracket  193  can permit the tension spring  168  to pass therethrough. 
         [0028]    The cylindrical housing  178  can include a chamber  179  for receiving a portion of the piston  180  at an end  183  and permitting movement of the piston  180  within the cylindrical housing  178 . The air inlet  184  can be disposed on the sidewall of the cylindrical housing  178 . When the first piston assembly  174  is assembled to the air compressor  100 , the air inlet  184  can be disposed within an air block  194 . The air block  194  can provide an internal pathway for air from the air input  196  to reach the air inlet  184  of the first piston assembly  174 . Seals  198 ,  200  can be disposed on the outside of the cylindrical housing  178  on each side of the air inlet  184  for contacting the interior of the air block  194 . 
         [0029]    Likewise, the sealing structures, shown as two o-rings  186 ,  188 , can be disposed on each side of the air inlet  184  within the chamber  179  and can be mounted such that they are stationary within the chamber  179 . The o-rings  186 ,  188  can be sized to receive the piston  180 . The o-rings  186 ,  188  can be mounted in a stationary position such that they do not move as the piston  180  moves through them. The o-rings  186 ,  188  can be maintained in a stationary position using one or more spacers  187 ,  189 , which can be tubular or any other suitable shape. For example, spacer  187  can be disposed within the chamber  179  between the o-rings  186 ,  188  to maintain a desired spacing between the o-rings  186 ,  188  and to help hold the o-rings  186 ,  188  in a stationary position. As shown, spacer  187  can hold o-ring  186  against a ledge in the chamber  179  formed by a change in diameter of the chamber  179 . The spacer  187  can have one or more apertures  197  for allowing air into the interior of the spacer  187 . Another spacer  189  can also be provided near the end  183  to help hold the o-rings  186 ,  188  in a stationary position. As shown, o-ring  188  can be held in position between the spacers  187 ,  189 . The piston  180  can be disposed within the spacers  187 ,  189 . A threaded nut  185  can be provided at the end  183 , which can be tightened to further secure and retain the o-rings  186 ,  188  and spacers  187 ,  189  in position. The threaded nut  185  can also be removed to provide access to the chamber  179  for repair or replacement of parts. It will be appreciated that the sealing structures, such as o-rings  186 ,  188 , can be mounted in a stationary position in any suitable manner. In addition, the sealing structures, such as o-rings  186 ,  188 , can have any suitable shape and can be made of any suitable material. 
         [0030]    The back check valve  182  can include a spring  202 , a plug  204 , and a seal  206  to restrict the flow of air to a single direction toward the exit air line  190 . The seal  206  can be an o-ring, which can be mounted to the plug  204  within the cylindrical housing  178 . When the valve  182  is closed, the seal  206  can abut a ledge formed by a change in diameter of the chamber  179 . The spring  202  can bias the plug  204  and seal  206  against the ledge. The valve  182  can open by moving away from the ledge when a particular pressure is reached in the chamber  179 . When this occurs, air is permitted to flow through a space between the plug  204  and the chamber  179  and then into the exit air line  190 . The exit air line  190  is attached to an end  181  of the piston housing  178  and feeds to an inlet for the second piston assembly  176 . As shown in  FIG. 6 , the exit air line  190  can feed into the air block  194 , which can provide an internal conduit to an air inlet  214  for the second piston assembly  176 . 
         [0031]    Referring again to  FIGS. 2 ,  3 ,  6 , and  11 , the air compressor can include a second piston assembly  176  that can be similar to the first piston assembly  174 . The second piston assembly  176  can include a cylindrical housing  208 , a piston  210 , a back check valve  212 , an air inlet  214 , suitable sealing structures such as o-rings  216 ,  218  on each side of the air inlet  214 , and an exit air line  220 . The piston  210  can be attached to the shaft block  146 . The cylindrical housing  208  can include a chamber  209  for receiving a portion of the piston  210  at an end  213  and permitting movement of the piston  210  within the cylindrical housing  208 . The air inlet  214  can be disposed on the sidewall of the cylindrical housing  208 . When the second piston assembly  176  is assembled to the air compressor  100 , the air inlet  214  can be disposed within the air block  194 . The air block  194  can provide an internal pathway for air from the exit air line  190  of the first piston assembly  174  to reach the air inlet  214  of the second piston assembly  176 . Seals  222 ,  224  can be disposed on the outside of the cylindrical housing  208  on each side of the air inlet  214  for contacting the interior of the air block  194 . 
         [0032]    Likewise, the sealing structures, shown as two o-rings  216 ,  218 , can be disposed on each side of the air inlet  214  within the chamber  209  and can be mounted such that they are stationary within the chamber  179 . The o-rings  216 ,  218  can be sized to receive the piston  210 . The o-rings  216 ,  218  can be mounted in a stationary position such that they do not move as the piston  210  moves through them. The o-rings  216 ,  218  can be maintained in a stationary position using one or more spacers  217 ,  219 , which can be tubular or any other suitable shape. For example, spacer  217  can be disposed within the chamber  209  between the o-rings  216 ,  218  to maintain a desired spacing between the o-rings  216 ,  218  and to help hold the o-rings  216 ,  218  in a stationary position. As shown, spacer  217  can hold o-ring  216  against a ledge in the chamber  209  formed by a change in diameter of the chamber  209 . The spacer  217  can have one or more apertures  227  for allowing air into the interior of the spacer  217 . Another spacer  219  can also be provided near the end  213  to help hold the o-rings  216 ,  218  in a stationary position. As shown, o-ring  218  can be held in position between the spacers  217 ,  219 . The piston  210  can be disposed within the spacers  217 ,  219 . A threaded nut  215  can be provided at the end  213 , which can be tightened to further secure and retain the o-rings  216 ,  218  and spacers  217 ,  219  in position. The threaded nut  215  can also be removed to provide access to the chamber  209  for repair or replacement of parts. It will be appreciated that the sealing structures, such as o-rings  216 ,  218 , can be mounted in a stationary position in any suitable manner. In addition, the sealing structures, such as o-rings  216 ,  218 , can have any suitable shape and can be made of any suitable material. 
         [0033]    The back check valve  212  can include a spring  230 , a plug  232 , and a seal  234  to restrict the flow of air to a single direction toward the exit air line  220 . The seal  234  can be an o-ring, which can be mounted to the plug  232  within the cylindrical housing  208 . When the valve  212  is closed, the seal  234  can abut a ledge formed by a change in diameter of the chamber  209 . The spring  230  can bias the plug  232  and seal  234  against the ledge. The valve  212  can open by moving away from the ledge when a particular pressure is reached in the chamber  209 . When this occurs, air is permitted to flow through a space between the plug  232  and the chamber  209  and then into the exit air line  220 . As shown in  FIG. 6 , the exit air line  220  can be attached to an end  211  of the piston housing  208  and can feed into the air block  194 , which can provide an internal conduit to an air output  236  of the air compressor  100  extending from the air block  194 . The air output  236  can be accessed through an aperture  114  in the cover  104  shown in  FIG. 1 , and an output fitting  238  can be attached to the air output  236  as shown in  FIG. 2 . 
         [0034]    It will be appreciated that the second piston chamber  209  can be of a different size than the first piston chamber  179 . As shown in  FIG. 11 , the second piston chamber  209  can have a smaller diameter than the first piston chamber  179  in order to expel the air provided into the second piston chamber  209  at a higher pressure than the air expelled from the first piston chamber  179 . 
         [0035]    Referring to  FIGS. 1 and 2 , the air block  194  can include a vent knob  240  that can be rotated to a position that allows air in the compressor  100  to be vented. The vent knob  240  can extend out through an aperture  114  in the cover  104  such that a user can access the vent knob  240  when the cover  104  is mounted to the housing  102 . In addition, the air compressor  100  can include a switch  242  for turning the air compressor  100  on and off. The switch  242  can be electrically connected to the motor  106  to turn the motor  106  on and off. The switch  242  can extend out through an aperture  112  in the cover  104  such that a user can access the switch  242  when the cover  104  is mounted to the housing  102 . 
         [0036]    During operation, as described further below, the switch  242  can be moved from the on position to the off position by the release arm  148 . The switch  242  can include a sleeve in the form of a spring that slides over and extends from the switch  242 . The central axis of the spring can align with the central axis of the switch  242 . The sleeve can be longer than the switch  242  and can operate as an extension to the length of the switch  242 . The sleeve can extend through the aperture  112  for gripping the switch  242  from the exterior of the air compressor  100 . 
         [0037]    For example purposes only, the operation of an embodiment of the air compressor  100  will be described herein. Referring again to  FIG. 1 , a user may provide a supply of air via a hose connected to the air input fitting  108 . The input air supply may be at a relatively low pressure, such as may be provided by a common shop compressor. In one embodiment, the input air may be provided at approximately 85 psi. It will be appreciated, however, that the input air supply may be at any suitable pressure. A hose may also be used to connect the air output  236  to a tank or other storage vessel being filled. The motor may then be activated by moving the switch to the on position. 
         [0038]    Turning to  FIGS. 2 ,  3 , and  5 , once activated, the motor  106  can rotate the motor shaft  120  and the drive gear  122 , which can turn the first transition gear  126  and the jackshaft  130  via the motor chain  124 . The second transition gear  128  can rotate with the jackshaft  130  to rotate the linkage gear  134  and linkage shaft  136  via the jackshaft chain  132 . The rotation of the linkage shaft  136  can rotate the crank arm  140  360° about the linkage shaft  136 . As the crank arm  140  rotates, it can pull and push the carriage  144  via the connecting arm  142 . For example, when the crank arm  140  has been rotated from the position shown in  FIG. 3  to the position shown in  FIG. 4 , the connecting arm  142  can be approximately horizontal and the carriage  144  can be pulled to approximately its closest position to the switch  242 . As the crank arm  140  continues to rotate from the position shown in  FIG. 4 , it can push the carriage  144  away from the switch  242  via the connecting arm  142 . 
         [0039]    Referring to  FIGS. 2-4 , as the carriage  144  moves toward and away from the switch  242 , its movement can be maintained in a generally linear direction by the guide pin  150  riding between the sidewalls  154 ,  156  of the guide bracket  152  and/or the piston  180  extending through the support bracket  193 . As the carriage  144  moves, it moves the first and second pistons  180 ,  210  both away from the back check valves  182 ,  212 , as shown in  FIG. 11 , and toward the back check valves  182 ,  212  as shown in  FIG. 12 . As the first and second pistons  180 ,  210  move, the o-rings  186 ,  188 ,  216 ,  218  on each side of the air inlets  184 ,  214  remain stationary. As shown in  FIG. 11 , when the pistons  180 ,  210  are pulled to the furthest extent away from the back check valves  182 ,  212 , the ends  191 ,  221  of the pistons  180 ,  210  can be between the respective two o-rings  186 ,  188 ,  216 ,  218  in each chamber  179 ,  209 . This permits the air from the respective air inlets  184 ,  214  to enter into the chambers  179 ,  209 . The carriage  144  can then begin to push the pistons  180 ,  210  toward the back check valves  182 ,  212 , as shown in  FIG. 12 , such that the pistons  180 ,  210  pass through the o-rings  186 ,  216  positioned closer to the back check valves  182 ,  212 . When this occurs, the respective inlets  184 ,  214  are cut off from portions of the chambers  179 ,  209  by the seal formed between the o-rings  186 ,  216  and the pistons  180 ,  210 . As the pistons  180 ,  210  continue to move toward the back check valves  182 ,  212 , they compress the air in the chambers  179 ,  209  and send the compressed air past the respective back check valves  182 ,  212 . 
         [0040]    Referring again to  FIGS. 11 and 12 , as the pistons  180 ,  210  move away from the back check valves  182 ,  212  with the next stroke, the o-rings  186 ,  216  closer to the back check valves  182 ,  212  do not permit air to flow past the o-rings  186 ,  216  when the pistons  180 ,  210  are still encircled by the o-rings  186 ,  216 , which forms a vacuum within the chambers  179 ,  209  when the pistons  180 ,  210  are retracted. The vacuum creates a vacuum force against the o-rings  186 ,  216  that helps to counter-balance the friction force asserted against the o-rings  186 ,  216  by the moving pistons  180 ,  210 . The counteracting vacuum and friction forces can help reduce the amount of wear experienced by the o-rings  186 ,  216 . 
         [0041]    The motor  106  can continue to drive the pistons  180 ,  210  until the switch  242  is turned off. The air compressor  100  can be equipped with an automatic shut-off mechanism to turn off the air compressor  100  when a desired pressure has been reached in a piston assembly. The automatic shut-off mechanism can be a mechanical structure incorporated into the carriage  144 . Referring to  FIG. 9 , prior to the desired pressure being reached in the piston assemblies  174 ,  176 , the carriage  144  can move back and forth within the housing  102  such that the carriage  144  will not contact the switch  242  with sufficient force to turn it off, even when the carriage  144  is in its closest position to the switch  242 . As mentioned, the release arm  148  may be pivotally mounted to the shaft block  146 . As shown in  FIG. 9 , the pivot connection at  170  of the connecting arm  142  with the release arm  148  can be offset with respect to the pivot connection at  158  of the release arm  148  with the shaft block  146 . Thus, as the connecting arm  142  pulls the carriage  144 , a pivot force is created about the pivot connection at  158  of the release arm  148  and the shaft block  146 . Before an approximate desired pressure in the piston assemblies  174 ,  176  reaches a certain threshold, the spring force exerted by the spring  168  attached to the release arm  148  and piston collar  192  counterbalances the pivot force created by the connecting arm  142 . 
         [0042]    The amount of pivot force is related to the amount of pressure in the piston assemblies  174 ,  176 . When the connecting arm  142  is pulling the carriage  144  and second piston  210  toward the back check valve  212 , the pressure in the piston assemblies  174 ,  176  exerts a force against the piston  210  and carriage  144 . The connecting arm  142  works against this force in order to pull the carriage  144  toward the switch  242 , but the pivot force about the pivot connection at  158  between the release arm  148  and shaft block  146  increases with the increase in pressure in the piston assemblies  174 ,  176 . Thus, when a certain piston assembly pressure threshold is reached, the pivot force will be great enough to overcome the spring force of the spring, which permits the release arm  148  to rotate with respect to the shaft block  146  as shown in  FIG. 10 . The distance that the release arm  148  can pivot is limited by the size of the oversized aperture  162  in the release arm  148  and the projection  164  within the aperture  162 , which can act as a pivot stop in both pivoting directions. When the spring force has been overcome a sufficient amount to pivot the release arm  148  far enough to move the switch  242 , the switch  242  will be forced to the off position. 
         [0043]    It will be appreciated that the shut-off pressure can be adjusted by using a spring  168  capable of asserting a different spring force, and/or by altering various connection positions on the release arm  148 . For example, the shut-off pressure can be affected by modifying the chosen positions of the connecting arm/release arm pivot connection at  170 , the release arm/drive block pivot connection at  158 , and/or the position of the spring aperture  160 . It will be appreciated that the automatic shut-off mechanism can include any suitable structure to shut off the air compressor  100  at any desired pressure. 
         [0044]    Thus, the air compressor  100  can operate as a two-stage compressor that takes in air at particular pressure, compresses that air to a higher pressure in the first piston assembly  174 , and then further compresses the air to an even higher pressure with the second piston assembly  176 . The pressure of the compressed air at each stage can be any suitable amount. By way of example and not limitation, in certain embodiments, the air compressor can take in air at approximately 85 psi and further compress the air to approximately 800 psi with the first piston assembly  174 . This higher pressure air can then be fed into the second piston assembly  176  for further compression to approximately 4500 psi. In addition, once a certain pressure in a piston assembly has been reached, the air compressor  100  can include a mechanical structure for shutting off the air compressor  100 . The particular piston assemblies utilized can help determine the amount of compression through the air compressor  100 . 
         [0045]    The air compressor is capable of providing compressed air at a high pressure suitable for filling paintball gun tanks, scuba tanks, and any other suitable applications. 
         [0046]    All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
         [0047]    The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
         [0048]    Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.