Abstract:
This document discloses, among other things, an air-powered auto-injector device for subcutaneous delivery of a rescue drug. The device is configured for self-administered treatment of anaphylactic shock. Air is compressed by relative movement of a piston and a cylinder and released to subcutaneously drive an hypodermic needle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application Ser. No. 61/043,268, filed Apr. 8, 2008, which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This document pertains generally to medical devices, and more particularly, but not by way of limitation, to a pneumatic injector. 
     BACKGROUND 
     Current rescue devices are inadequate. Such devices are generally too large to carry conveniently and the widely varying storage environments negatively affect potency longevity. 
     OVERVIEW 
     An example includes an auto-injector having a housing with a pneumatic cylinder. A piston located in the cylinder is coupled to a nose piece. A passage couples the cylinder and a conduit. A needle carrier is located within a member and the member is within the conduit. An hypodermic needle is affixed to the needle carrier. A diaphragm, also coupled to a portion of the nose piece, isolates the needle carrier from pressure within the conduit. An end cap affixed to a housing includes a spike. The spike is configured to pierce the diaphragm. 
     A guide affixed to a portion of the nose piece supports an end of the hypodermic needle. The needle carrier holds a fluid reservoir for storing a medicament. 
     In one example, the conduit is located between, and in parallel alignment with, two flanking cylinders and the nose piece carries two corresponding pistons. 
     After having removed the cover, a user can self-inject by swiftly thrusting the nose piece against the injection site. Movement of the piston relative to the housing causes air to be compressed in the cylinder, the passage, and in the conduit. At a predetermined relative position of the nose piece, the spike ruptures the diaphragm. Upon rupturing of the diaphragm, the pressure developed in the conduit is released to the member and a pressure is applied to the needle carrier. The pressure causes the needle carrier, and the needle, to travel in the member. The needle passes through the guide and into the injection site. The needle carrier travel is limited by the nose piece. Upon reaching the travel limit, the compressed air collapses the fluid reservoir, thus discharging the contents through the needle. After discharge, the needle can be safeguarded by replacement of the cover on the housing. In one example, the needle is retracted back within the nose piece before installing the cover. 
     This overview is intended to provide an overview of one example of the present subject matter. It is not intended to provide an exclusive or exhaustive explanation. The detailed description is included to provide further information. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document. 
         FIG. 1  includes a perspective section view of a device. 
         FIG. 2A  includes a perspective section view of a cover of a device. 
         FIG. 2B  includes a perspective section view of a nose piece of a device. 
         FIG. 2C  includes a perspective section view of a housing of a device. 
         FIG. 2D  includes a perspective section view of an end cap of a device. 
         FIG. 3A  includes a perspective section view of a nose piece of a device. 
         FIG. 3B  includes a perspective section view of a needle of a device. 
         FIG. 3C  includes a perspective section view of a diaphragm of a device. 
         FIG. 4A  includes a perspective section view of a shuttlecock of a device. 
         FIG. 4B-1  includes a perspective section view of a guide of a device. 
         FIG. 4B-2  includes a section view of a guide of a device. 
         FIG. 4C  includes a perspective section view of a needle of a device. 
         FIG. 4D  includes a perspective section view of a block of a device. 
         FIG. 4E  includes a perspective section view of a reservoir of a device. 
         FIG. 5  includes a method of manufacturing a device. 
         FIG. 6  includes a method of using a device. 
         FIG. 7  includes a perspective view of a surface of a device. 
         FIGS. 8A-8G  include a sequence of device images. 
         FIG. 9  includes a view of a piston and cylinder according to one example. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  includes a perspective section view of device  100 . Device  100 , in the example illustrated, includes (among other things) cover  105 , nose piece  110 , housing  120 , and end cap  125 . 
     In the example shown, the overall dimensions of the device, with cover  105  in position, is approximately 2.9 inches long by 1.375 inches wide and 0.25 inches high. For comparison, a typical credit card is about 3.375 inches by 2.125 inches by 0.030 inches and a typical cigarette lighter is approximately 0.5 inches thick. It is believed that the present subject matter can be readily carried in a pants pocket. 
     Cover  105  is configured to mate with a complementary feature of housing  120 . Cover  105  is fabricated of molded plastic. Cover  105  is configured to enclose nose piece  110 . An interlocking feature of cover  105  engages with a corresponding element of housing  120 . With little force, a user can readily separate cover  105  from housing  120 , thus exposing nose piece  110 . 
     Nose piece  110 , in the example illustrated, includes two pistons coupled by a rigid structure. The rigid structure also is coupled to member  165  in which needle carrier  130  travels. Needle carrier  130  carries needle  140 . The rigid structure also includes a vent hole (not visible in this figure) and receiver for guide  150 . Diaphragm  160  is disposed across an end of member  165 . Nose piece  110  is fabricated of molded plastic. 
     Housing  120  includes two cylinders in which the pistons of nose piece  110  travel. The two cylinders flank a conduit for the member. The two cylinders and the conduit are in parallel alignment. The walls of the two cylinders are configured to form a passage in which compressed air in the cylinders is communicated to the member traveling in the conduit. Housing  120  is fabricated of molded plastic. 
     End cap  125  is configured to mate with housing  120 . End cap  125  includes a void that serves as an internal passage for communicating compressed air. End cap  125  includes spike  155  configured to rupture diaphragm  160  at an end of the member. End cap  125  is fabricated of molded plastic. 
       FIG. 2A  includes a perspective section view of cover  105  of device  100 . As illustrated, cover  105  includes interlocking feature  202 . An exterior surface of cover  105  includes detailing to enable a user to easily grip and remove cover  105  from engagement with housing  120 . 
     In the normal service of device  100 , needle  140  is substantially extended from nose piece  110 . Following usage of device  100 , cover  105  can be snapped into a position to enclose the end of housing  120 . Following usage and installation of cover  105 , needle  140  can remain in the extended position or needle  140  can be retracted. Needle  140  can be retracted by grasping along its length or by pushing at an end of the needle using, for example, region  206  of cover  105 . Cover  105  is configured to substantially encase nose piece  110  when fitted to housing  120 . 
       FIG. 2B  includes a perspective section view of nose piece  110  of device  100 . Nose piece  110  is configured to slidably engage with structure of housing  120 . 
     In the example illustrated, nose piece  110  is held in an extended position by engagement of catch  220  (of housing  120 ) and stop  222  (of nose piece  110 ). The engagement of catch  220  and stop  222  can be readily overcome by a slight compressive force applied to nose piece  110 . Having disengaged catch  220  and stop  222 , nose piece  110  can be fully seated, limited by the wall structure of cylinder  212 A and cylinder  212 B and the depth of the slots separating piston  210 A and piston  210 B from member  165 . As such, nose piece  110  can be viewed as having a variable location between first position (engagement of catch  220  and stop  222 ) and a second position (fully seated with housing  120 ). 
     Needle  140  is coupled to needle carrier  130 . Needle carrier  130  lies within member  165 . Needle carrier  130  can have a variable position within member  165  with a first position, as shown, wherein a tip of needle  140  lies within guide  150 , and a second position wherein needle  140  is extended from nose piece  110  and needle carrier  130  has bottomed on internal structure of member  165  adjacent to guide  150  and a different portion of needle  140  lies within guide  150 . 
     Diaphragm  160  is bonded to an end surface of member  165 . 
       FIG. 2C  includes a perspective section view of housing  120  of device  100 . Housing  120  has an external surface with details to facilitate grasping by a user. Housing  120  also includes catch  220  that can be deflected to enable engagement of housing  120  with nose piece  110 . In addition, housing  120  includes feature  204  configured to engage with retainer  202  of cover  105 . In the figure, cylinder  212 A and cylinder  212 B and conduit  214  have a similar bore profile. Cylinder  212 A, cylinder  212 B, and conduit  214  are open ended and are configured to mate with piston  210 A, piston  210 B, and member  165 , respectively. The walls of cylinder  212 A, cylinder  212 B, and conduit  214  have radiused corners to facilitate efficient sealing along the length of the walls. 
     While diaphragm  160  remains intact, member  165  operates like a piston operating in a cylinder. In this document, the cylinder is referred to as conduit  214 . Relative movement of member  165  within conduit  214  can compress the air within conduit  214 . Upon rupture of diaphragm  160  (by spike  155 ), member  165  no longer functions as a piston and the compressed air within conduit  214  is applied to the interior structure of member  165 . The interior structure of member  165  includes needle carrier  130 . While diaphragm  160  is breached, member  165  operates like a cylinder. While functioning as a cylinder, the compressed air within member  165  causes needle carrier  130  (along with needle  140 ) to travel to an extended position, thus ejecting the needle. Needle carrier  130  can be construed as a piston that carries needle  140 . Member  165  can be referred to as a channel. 
     A portion of housing  120  is configured to mate with end cap  125 . 
       FIG. 2D  includes a perspective section view of end cap  125  of device  100 . End cap  125  includes spike  155  and passage  218 . Spike  155  has a sharp end configured to pierce diaphragm  160 . Passage  218  provides an airway through which compressed air in cylinder  212 A and in cylinder  212 B is communicated to conduit  214 , and thus to member  165 . End cap  125  is fabricated of molded plastic and is fixedly mounted on an end of housing  120 . In one example, end cap  125  is adhesively bonded to housing  120  at region  216 . 
       FIG. 3A  includes a perspective section view of nose piece  110  of device  100 . In the figure, vent  112  is shown in a location near an end of member  165 . Vent  112  equalizes the internal pressure on the needle-side of needle carrier  130  to atmospheric pressure. As needle carrier  130  travels to extend needle  140 , the air within member  165  flows outward through vent  112 . 
     Piston  210 A and piston  210 B are configured to form a seal with the interior surfaces of the walls of the respective cylinders. In addition, piston  210 A and piston  210 B are free to slide along the length of the respective cylinders. 
     An end of member  165  includes surface  162 . In one example, diaphragm  160  is affixed to surface  162  with an adhesive bond. In one example, surface  162  is flat and lies in a plane oriented substantially perpendicular to the direction of travel of needle carrier  130 . 
       FIG. 3B  includes a perspective section view of needle  140  of device  100 . In the figure, a tip of needle  140  is coupled to guide  150  and an end of needle  140  is coupled to needle carrier  130 . Needle carrier  130 , shown with assembled components, includes block  310 , shuttlecock  315 , and reservoir  325 . Shuttlecock  315  includes skirt  320  which is configured to slidably seal with the interior walls of member  165 . 
       FIG. 3C  includes a perspective section view of diaphragm  160  of device  100 . Diaphragm  160  is fabricated of a thin section of material that can sustain a differential air pressure and that readily fails when pierced. In one example, diaphragm  160  is fabricated of a membrane of cellophane or other plastic material. 
       FIG. 4A  includes a perspective section view of shuttlecock  315  of device  100 . Shuttlecock  315  is fabricated of a molded plastic. In one example, shuttlecock  315  is fabricated of a flexible material, such as nylon, and is crimped or wedge-locked in position over block  310  and reservoir  325 . 
     Shuttlecock  315  includes lip  317  and skirt  320 . Shuttlecock  315  is configured to slidably engage block  310  and retain reservoir  325  in a fixed position. A wall section of shuttlecock  315  includes an interference detail that allows shuttlecock  315  to snap into a fixed position over the underlying structure. Lip  317  captivates shuttlecock  315  on block  310 . In one example, a wall thickness of skirt  320  is configured to expand and form an air seal against the interior walls of member  165  when a pressure is applied. As such, skirt  320  is sufficiently flexible to assure positive movement of the needle carrier when subjected to a differential pressure. 
       FIG. 4B-1  includes a perspective section view of guide  150  of device  100  and  FIG. 4B-2  includes a section view of guide  150 . Guide  150  is fabricated of an elastomeric material and, in the example illustrated, in the form of a cylinder having parallel bases. One base includes chamfer  154  and the other base includes aperture  156 . Void  158  is spherical and substantially centered within the body dimensions of guide  150 . The wall thickness at aperture  156  and the wall thickness at the chamfered base are configured to allow needle  140  to pass with low frictional resistance. Aperture  156  is configured to provide a fluid seal on the shaft of needle  140  and void  158  is configured to retain any fluid that may drip from the end of needle  140 . 
       FIG. 4C  includes a perspective section view of needle  140  of device  100 . Needle  140  includes a sharp tip  142 , end  144 , and an internal bore or lumen. Tip  142  is configured to pierce the chamfered base of guide  150  as well as the tissue at the injection site. End  144  is configured normal to an axis of needle  140 . In one example, needle  140  is fabricated of a surgically sterile metal such as stainless steel. 
       FIG. 4D  includes a perspective section view of block  310  of device  100 . Block  310  is fabricated of molded plastic and includes orifice  312 . Orifice  312  is bonded to needle  140  at end  144 . In the example illustrated, block  310  is configured as a rounded rectangular shaped solid. In one example, block  310  is insert-molded onto needle  140 . 
       FIG. 4E  includes a perspective section view of reservoir  325  of device  100 . Reservoir  325  is fabricated of an elastomeric material, such as a sterile, epinephrine-compatible polymer balloon, and includes mouth  330 . When assembled, mouth  330  is stretched over block  310  and shuttlecock  315  is snapped in position to retain reservoir  325  and resist separation. Reservoir  325  carries the fluid to be injected and is configured for a particular dosage. Reservoir  325  is sufficiently flexible that an air pressure will discharge the contents of reservoir  325  into the bore of needle  140 . In one example, reservoir  325  is configured to hold a medicament and configured to collapse and discharge any contents under application of a compressive pressure. Reservoir  325  can be viewed as a collapsible chamber. 
       FIG. 5  includes method  500  for manufacturing device  100 . At  510 , method  500  includes bonding needle  140  and block  310 . In various examples, this includes forming an adhesive bond or molding block  310  directly on needle  140 . 
     At  515 , reservoir  325  is installed on block  310 . This can include stretching reservoir  325  over block  310  in a manner similar to installing a balloon on a filling nozzle. The elasticity of the reservoir establishes a fluid tight seal on the external surfaces of block  310 . 
     At  520 , shuttlecock  315  is installed. Skirt  320  of shuttlecock  315  is passed over block  315  and snapped into position by a detail formed on an interior surface of shuttlecock  315 . In one example, shuttlecock  315  is retained in position without need of an adhesive. 
     At  525 , reservoir  325  is filled. Filling can include manual or automated manipulation of reservoir  325  at a time when tip  142  of needle  140  is immersed in fluid. For example, tip  142  can be injected in a septum of an inverted vial and by repeatedly squeezing reservoir  325  and releasing reservoir  325 , air is exhausted and the contents of the vial are drawn into reservoir  325 . 
     At  530 , guide  150  is positioned on tip  142  of needle  140 . This can include piercing a wall of guide  150  or insertion of tip  142  in a hole formed in a wall of guide  150 . 
     At  535 , needle carrier  130  and nose piece  110  are assembled. This can include placing guide  150  in guide receiver  152  formed in nose piece  110 , as shown in the various figures. In addition, this can include positioning needle carrier  130  within member  165 . 
     At  540 , diaphragm  160  is bonded to surface  162  of nose piece  110 . The adhesive used for bonding diaphragm  160  can include a cyanoacrylate adhesive or other type of adhesive. 
     At  545 , a first pressure test is conducted to establish that diaphragm  160  is properly bonded to member  165 . A pressure test can, for example, detect a leak in the joint between diaphragm  160  and member  165 . Pressure testing can entail applying a predetermined air pressure and monitoring for evidence of leakage. 
     At  550 , nose piece  110 , housing  120 , and end cap  125  are assembled. This can include engaging cylinder  212 A with piston  210 A, engaging cylinder  212 B with piston  210 B, and engaging member  165  with conduit  214  in the manner illustrated. In the example illustrated, nose piece  110  and housing  120  are assembled together without an adhesive. In the example illustrated, end cap  125  is assembled to housing  120  with an adhesive bond. 
     At  555 , a second pressure test is conducted to establish that the assembled structure is properly configured. Pressure testing can entail applying a predetermined air pressure and checking for evidence of leakage as well as proper movement of the various components. 
     At  560 , cover  105  is installed over nose piece  110  and onto housing  120 . Cover  105  is assembled without adhesive and using a friction fit. 
       FIG. 6  includes method  600  for using device  100 . At  610 , method  600  includes removing cover  105  from device  100 . The user can remove this by overcoming the friction fit. A textured or detailed exterior surface of cover  105  and exterior surface of housing  120  facilitates the user&#39;s grip and, in one example, a color difference serves to readily identify the parting line for separating these components. Having removed cover  105  from an unused device, needle  140  will remain retracted within the structure of nose piece  110  and the tip will be positioned within guide  150 . 
     At  615 , the user grasps housing  120 , along with end cap  125 , and positions the device near the target injection site. 
     At  620 , the user strikes the injection site with the exposed portion of nose piece  110  using a sharp blow. With such a force, nose piece  110  will break free of the position captivated by catch  220  and stop  222  and recede into the structure of housing  120 . 
     At  625 , the relative movement of the cylinder  212 A with piston  210 A, cylinder  212 B with piston  210 B, and member  165  with conduit  214 , will cause compression of the air within cylinder  212 A, cylinder  212 B, and conduit  214 . 
     At  630 , continued travel of nose piece  110  relative to housing  120  will cause a valve to be opened. In the example illustrated, the valve is formed by diaphragm  160  and spike  155 . Spike  155  will breach diaphragm  160  and allow the pressurized air in conduit  214  to flow into member  165 . 
     At  635 , needle  140  is driven to an extended position by the difference in air pressure present within member  165  and in the surrounding atmosphere. The surrounding atmosphere is present on the needle side of needle carrier  130  by virtue of vent  112 . The differential air pressure is sufficient to drive needle  140  through guide  150  as well as into the tissue at the injection site. 
     At  640 , the fluid in reservoir  325  is delivered through needle  140 . The fluid in reservoir  325  is expelled by the compressed air remaining in member  165  after needle carrier  130  has moved to the extended position. 
       FIG. 7  includes a perspective section view of a surface of device  100 . In contrast to  FIG. 1 ,  FIG. 2 ,  FIG. 3 , and  FIG. 4  (each of which illustrate selected internal elements in a section view),  FIG. 7  illustrates an external view including cover  105  and housing  120 . The section views of this document depict the various components with a cutting plane that corresponds to approximately a mid-line.  FIG. 7  illustrates the molded details appearing on an outer edge. The molded details are configured to facilitate grasping of device  100 . 
       FIG. 8  includes a sequence of images corresponding to a method of using device  100 . The various figures identify selected elements including cover  105 , nose piece  110 , housing  120 , needle  140 , and diaphragm  160 . In  FIG. 8A , cover  105  has been removed in preparation for injecting a drug using device  100 . Nose piece  110  remains in an extended position, needle  140  remains in a retracted position, and diaphragm  160  is intact. 
     In  FIG. 8B , nose piece  110  is shown partially retracted into housing  120 . Air pressure inside the chambers of housing  120  is elevated above ambient pressure. 
     In  FIG. 8C , nose piece  110  is shown nearly fully retracted and diaphragm  160  is beginning to rupture. At this point, air pressure within device  100  is at a maximum value. 
     In  FIG. 8D , nose piece  110  is shown fully retracted and diaphragm  160  has ruptured. Air pressure within device  100  is beginning to drop since needle  140  has started to move to an extended position. In the configuration shown, nose piece  110  would typically be in contact with an injection site and needle  140  would be partially inserted. 
     In  FIG. 8E , nose piece  110  remains fully retracted and needle  140  is fully extended, having reached the end of its travel. Air pressure within device  100  remains elevated relative to ambient pressure. 
     In  FIG. 8F , the remaining air pressure within device  100  operates to collapse the reservoir and eject the contents via needle  140 , thus injecting the site with the fluid. 
     In  FIG. 8G , the needle is manually withdrawn from the injection site and cover  105  is installed on housing  120 . In this example, needle  140  remains in an extended position within the confines of cover  105 . Nose piece  105  remains in the fully retracted position. 
     Additional Notes 
     In one example, after having filled reservoir  325  with the fluid, guide  150  is placed over tip  142 . Guide  150  prevents contamination of tip  142 , precludes evaporation, and retains fluid leakage from needle  140 . When needle  140  is passing through guide  150 , the walls of guide  150  collapse in a direction away from the needle. This reduces the drag force acting on the needle while the needle is advancing. Low drag force reduces the burden of injecting the needle. 
     In one example, skirt  320  of shuttlecock  315  is the only portion of needle carrier  130  in physical contact with member  165 . This reduces the frictional drag of the needle travel and also enables a user to readily retract needle  140  after usage. The user can exert a force using cover  105  to drive needle  140  back into nose piece  110 . 
     Cover  105  is configured to prevent accidental discharge. Cover  105  precludes relative movement of nose piece  110  and housing  120  and, in the absence of relative movement, a differential air pressure cannot be developed. In the absence of a differential air pressure, needle  140  will remain stationary. 
     The length of spike  155  and position of diaphragm  160  determine the point in the movement of nose piece  110  at which needle  140  travel commences. The needle delivery force increases linearly until diaphragm  160  is burst. When diaphragm  160  bursts, the internal pressure is applied to needle carrier  130  which drives needle  140  into, for example, the patient&#39;s leg, while the user completes the operating stroke. By bursting diaphragm  160  before the end of the stroke, the peak force required of the user is reduced. This also reduces the force that the user feels against their leg from the device. After nose piece  110  has reached the end of travel, the epinephrine is injected. The user then withdraws the device and installs cover  105  so that it can be safely discarded and avoid needle sticks. Thus, the length of spike  155  also affects the peak forces developed within the device. 
     In one example, needle carrier  130  is retained in a fixed position relative to member  165 . For example, corresponding features of carrier  130  and member  165  can retain relative position until the motive pressure exceeds a predetermined value and carrier  130  commences travel down the length of member  165 . A complementary feature can include a friction fit or a catch and stop assembly configured to stabilize carrier  130  and reduce movement until deliberately called for by action of a user. 
     In one example, spike  155  is configured to dislodge needle carrier  130  from a fixed position within member  165 . For example, an extended portion of spike  155  can be configured to contact carrier  130  and overcome a retention feature or mechanism, thereby enabling carrier  130  to travel within the length of member  165 . 
     In one example, different dosages are provided. The dosages can be determined, for example, by selecting a suitable size reservoir. In one example, the dosages are 0.1 ml, 0.2 ml, and 0.3 ml. In one example, different fill levels are used with a particular reservoir. The needle and needle carrier can include a color code or label to denote contents and dosages. 
     Additional methods can include testing for seal integrity. For example, the various sealed assemblies can be tested at different stages of fabrication. 
     The present subject matter can be configured for carrying in a pocket or in a convenient manner that may provide a more stable storage environment. For example, some drugs deteriorate rapidly with exposure to temperature extremes. By configuring the present subject matter for carrying in a pocket, the useful life of the product can be improved. 
     In one example, end cap  125  and housing  120  are formed as a single component and include through holes to communicate compressed air from cylinders to the conduit. 
     In one example, a feature within member  165  limits the travel of needle carrier  130 . The feature, such as a stop, can limit forward or rearward travel of needle carrier  130 . 
     In one example, guide  150  provides a fluid-tight seal closing on needle  140 . The seal can include a self-sealing septum, and fabricated of various materials including polytetrafluorethylene (PTFE), rubber or silicone. 
     Various elements shown in the figures and described herein can have different shapes and arrangements. For example, needle carrier  130  can have a circular, oval, or rounded rectangular cross section. In particular, needle carrier  130  and the interior bore of member  165  can be circular. In a similar manner, the exterior profile of member  165  as well as the interior bore of conduit  214  can be circular. Furthermore, piston  210 A, piston  210 B, cylinder  212 A, and cylinder  212 B can have a circular cross-section. 
       FIG. 9  illustrates a partial sectional view of an example of a complex piston arrangement. In the figure, cylinder  213 C and piston  210 C compares with cylinders  213 A and  213 B and pistons  210 A and  210 B of earlier figures, such as shown in  FIGS. 2B and 2C . Cylinder  212 C includes shoulder  211  and piston  210 C includes shoulder  217 . An aperture of sleeve  213  is fitted to a small diameter portion of piston  210 C and the outer diameter of sleeve  213  is fitted within the large diameter of cylinder  212 C. Shoulder  211  and shoulder  217  limit the travel of sleeve  213  relative to the cylinder  212 C and piston  210 C, respectively. 
     In one example, the upper portion of the figure corresponds to housing  120  and the lower portion of the figure corresponds to cover  105 . In operation, user-action drives piston  210 C in a direction toward the upper portion of the figure. The internal pressure increases linearly with the movement of piston  210 C and is proportional to the area at the end of the piston. When shoulder  217  engages the lower surface of sleeve  213 , the effective piston area is increased and internal pressure rises more rapidly. This arrangement of shoulders and the sleeve allows for increasing the internal pressure during selected portions of the device operation that may be more suitable for some applications. 
     The cylinders of the present subject matter can be air-filled (in which case, the device operates using pneumatic pressure), or fluid-filled (in which case, the device operates using a fluid pressure). The fluid can be a liquid such as water or other such fluid. 
     Additional Notes 
     The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the present subject matter can be practiced. These embodiments are also referred to herein as “examples.” Such examples can include elements in addition to those shown and described. However, the present inventors also contemplate examples in which only those elements shown and described are provided. 
     All publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference(s) should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls. 
     In this document, the terms “a” or “an” are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of “at least one” or “one or more.” In this document, the term “or” is used to refer to a nonexclusive or, such that “A or B” includes “A but not B,” “B but not A,” and “A and B,” unless otherwise indicated. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Also, in the following claims, the terms “including” and “comprising” are open-ended, that is, a system, device, article, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. 
     The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to comply with 37 C.F.R. §1.72(b), to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.