Apparatus for storing and discharging gas

Information

  • Patent Grant
  • 6701908
  • Patent Number
    6,701,908
  • Date Filed
    Wednesday, April 30, 2003
    21 years ago
  • Date Issued
    Tuesday, March 9, 2004
    20 years ago
Abstract
Apparatus for storing and discharging gas includes a housing having an inlet and an outlet. A floating differential piston is mounted to reciprocate in the housing and divide the housing into a storage chamber adjacent the housing inlet and a discharge chamber adjacent the housing outlet. A check valve in the housing inlet admits gas to the storage chamber. A conduit extends through the piston from the storage chamber to the discharge chamber. A pressure relief valve in the conduit is set to maintain a higher pressure in the storage chamber than in the discharge chamber. A first sliding seal is disposed between the housing and an end of the piston adjacent the housing inlet. A second sliding seal is disposed between the housing and an end of the piston adjacent the housing outlet. The cross-sectional area of the housing seal by the second seal is larger than that seal by the first seal so that when gas pressure in the storage chamber exceeds the differential pressure set by the pressure relief valve, gas flows through the conduit from the storage chamber and into the discharge chamber and forces the piston to move toward the inlet end of the housing to reduce the volume of gas in the storage chamber and increase the volume of gas stored in the discharge chamber. A discharge valve in the housing outlet permits gas to be discharged from the apparatus.
Description




BACKGROUND OF THE INVENTION




This invention relates to guns which use a charge of compressed air to fire a pellet.




Air guns have a wide following because laws limiting their use are not as restrictive as for powder guns, and air guns are relatively inexpensive to shoot. Air gun shooting is an Olympic sport, and hunting with an air gun removes much of the danger inherent with powder guns while retaining and enhancing the challenge.




Air guns fall into three major groups:




1. Pump guns: These guns use one or more strokes from a pumping device to store a charge of compressed air in a firing chamber. The required effort to charge the gun increases with each pump as the stored pressure builds. The power of the gun depends on the strength of the shooter because the relatively low mechanical advantage of the pumping mechanism. Most of these guns completely expel the air charge when fired. On firing, the pellet is initially exposed to the full pressure of the compressed air, but the available pressure falls rapidly as the pellet accelerates down the gun barrel. These guns usually have moderate power, driving a pellet at about 500 feet per second. U.S. Pat. No. 4,572,152 to Olofsson, et al., discloses an air gun which uses a floating piston to store compressed air in an auxiliary chamber. The purpose of the floating piston is to augment firing pressure by moving to displace air in the firing chamber when the gun is fired. However, with the gun disclosed in the Olofsson, et al. patent, the compressed air stored in the auxiliary chamber is limited to that provided by one stroke of the pump, and the pressure in the auxiliary chamber can never be greater than the pressure in the firing chamber.




2. Spring guns: These guns use a single stroke of a lever to compress a steel spring. On firing, the spring drives a relatively heavy piston that causes a rapid increase in air pressure within a firing chamber. The firing chamber is directly connected to the gun barrel. The pellet is held in the gun barrel by a seal until the air pressure in the chamber reaches an optimum point. When this happens, the air pressure overcomes the holding ability of the seal and drives the pellet down the barrel. The piston also continues to displace air in the firing chamber, thereby helping to maintain pressure on the pellet. This method has replaced multi-stroke pumping as the most common air gun mechanism. Only one stroke of the lever accomplishes the entire cocking procedure. Thus, a spring gun usually takes less time to place into action than a multi-stroke gun. By maintaining a more constant force on the pellet as it travels down the barrel, the imparted energy may be twice that available with a conventional pneumatic multi-pump gun. However, the drawback of a spring gun is that only one stroke of the lever is available to compress the spring. The most powerful spring guns require strength beyond the limit of many people. Moreover, the spring imposes a practical limit on the amount of energy that can be stored. At least one model has replaced the steel spring with a compressed air “spring.” The compressed air in the “spring” is not expended but is re-compressed with the gun's lever. The air spring can store more energy in a smaller space, but considerable work must be expended by the shooter.




3. Pre-charged guns: These guns use a gas charge that is pre-packaged and inserted into the gun with little expenditure of energy by the user. The most common guns of this type use a small container of liquid carbon dioxide to power the gun. Each firing of the gun uses a portion of the stored liquid, which rapidly vaporizes on firing. A method gaining popularity transfers compressed air from a storage bottle into a relatively large storage vessel attached to the gun. For example, air from a diver's scuba tank or similar storage vessel is transferred into the storage vessel on the gun through a high-pressure hose and clamp assembly. The gun gets multiple shots from charges provided by the air in the storage vessel, but the accuracy of the gun diminishes with the loss of available pressure until the storage vessel is refilled. Some carbon dioxide (CO


2


) guns use small canisters available at hardware stores. These guns are moderately powerful, but also suffer from accuracy problems with the loss of pressure in the canister. Guns which use compressed air from large detached tanks can store more energy and suffer less in accuracy lost between shots. However, the detached tank (such as a scuba tank) is heavy and cumbersome.




In summary, multiple-pump air guns are limited by the strength of the user, and the initial strokes are time consuming for the amount of useful energy transferred to the storage chamber. Spring guns use one quick pull of a lever and achieve efficiency with the available energy, but are limited by the strength of the individual loading the gun. Guns which use a pre-charged vessel of compressed gas must have the vessel in close proximity to the gun, and cannot rely on precision repeat performance with each shot.




Maximum muzzle energy for the three types of guns is about 11.5 foot-pounds for the best multi-pump guns, about 25 foot-pounds for the best spring guns, and about 30 foot-pounds for the best pre-charged gun using air from a scuba tank.




Convenient power is the goal of air guns. With more power the pellet trajectory is flatter, accuracy is enhanced, and more energy is delivered at the point of impact.




SUMMARY OF THE INVENTION




This invention provides an air gun which stores and imparts increased shooting power without requiring the shooter to be of more than average strength. The gun uses a unique pumping action with a large mechanical advantage to store energy and efficiently transfer stored energy to the pellet to achieve muzzle energy in excess of 40 foot-pounds.




The air gun of this invention uses an improved air pump which includes a pump cylinder and a pump piston mounted to reciprocate within the cylinder. The pump cylinder and a piston rod connected to the piston are each connected to the barrel of the gun to pivot about separate respective longitudinally spaced axes, which are transverse to the longitudinal axis of the barrel. As the pump cylinder and piston rod are moved back and forth around their respective the pivot points, the cylinder and piston reciprocate relative to each other to pump air into an inlet of a high pressure housing carried by the pump cylinder. A firing conduit connected to the high pressure housing releasably connects an outlet of the high pressure housing to the breech end of a gun barrel when the pump cylinder is moved to be parallel with the barrel. A trigger-responsive firing valve in the firing conduit releases air from the high pressure housing into the breech end of the barrel to fire a pellet from the gun.




In a preferred embodiment, the piston rod is secured at one end to the piston, and at the other end to a first pivot point on the gun barrel. An elongated drive link is secured at one end to a pivot point on the cylinder, and at the other end to a second pivot point on the gun barrel, so that as the cylinder and piston are moved back and forth about the first and second pivot points, the piston reciprocates in the cylinder to force air through a check valve and into the high pressure housing. The length of the drive link and the longitudinal spacing between the first and second pivot points are set so when the pump cylinder is moved to be substantially parallel to the barrel, the piston contacts the check valve which admits air into the high pressure housing so a maximum amount of compressed air is transferred to the high pressure housing with each compression stroke of the pump. The first pivot point is located to the rear of the second pivot point and is spaced slightly farther from the longitudinal axis of the gun barrel so when the pump cylinder is moved toward the gun barrel to a “dead center” position, which places the longitudinal axis of the piston rod and piston substantially in alignment with the first and second pivot points, the piston contacts the check valve with maximum force. At this point, the pump cylinder extends rearwardly and away from the gun barrel to leave ample space for gripping the rear end of the cylinder to actuate the pump. Further movement of the pump cylinder toward the gun barrel carries the piston rod and piston slightly past the “dead center” position. The elasticity inherent in the gun and pump components accommodates movement of the pump cylinder back and forth through the “dead center” position, which acts as a moderate detent to hold the pump cylinder snugly against the barrel when the gun is to be prepared for firing.




In a further preferred embodiment of the invention, a floating differential piston is disposed to move longitudinally within the high pressure housing and divide the housing into a storage chamber adjacent the housing inlet and a firing or discharge chamber adjacent the housing outlet. A pressure relief valve in a pressure relief conduit extending through the floating differential piston from the storage chamber to the firing chamber maintains a higher pressure in the storage chamber than in the firing chamber. Preferably, the pressure relief valve is adjustable. The diameter of the end of the floating differential piston adjacent the storage chamber is smaller than the diameter of the end of the piston adjacent the firing chamber. A first sliding seal is provided between the interior of the high pressure housing and the smaller end of the piston. A second sliding seal between the housing interior and the larger end of the piston seals a larger cross-sectional area of the housing than the first seal. When air pressure in the storage chamber exceeds the differential pressure set by the pressure relief valve in the pressure relief conduit, air flows through the conduit from the storage chamber and into the firing chamber until the pressure in the firing chamber reaches a value which permits the pressure relief valve to close. As the pressure in the two chambers increases, the larger cross-sectional area of the firing chamber sealed by the larger end of the floating differential piston causes the piston to move toward the inlet end of the housing, thereby reducing the volume of air in the storage chamber and increasing the volume of air stored in the firing chamber until the forces acting on each end of the piston are balanced. Additional pumping stores more compressed air in the storage and firing chambers until the desired firing pressure is reached. When the firing valve in the housing outlet releases compressed air from the firing chamber in response to pulling the trigger on the gun, compressed air in the storage chamber expands and drives the floating differential piston toward the housing outlet as compressed air in the firing chamber enters the barrel breech to drive a pellet out the barrel. Thus the compressed air in the storage chamber expands and drives the floating differential piston toward the outlet of the firing chamber to maintain a more uniform pressure on the pellet as it is fired. The pressure relief valve in the floating piston tends to open momentarily when the firing of the gun suddenly drops the pressure in the firing chamber. However, loss of compressed air from the storage chamber is minimized because the flow path for air from the storage chamber to the firing chamber is so restricted, that only a small amount of air is lost from the storage chamber before the pressure relief valve closes. The lost air is quickly replaced when the pump is operated for the next shot. Preferably, the mass of the floating differential piston is as low as practical, and a mechanical compression spring also urges the floating piston toward the firing valve to further minimize loss of air from the storage chamber when the gun is fired.




The gun of this invention supplies such a large mass of high-velocity compressed air behind the pellet as the pellet leaves the barrel, there is a tendency for the air to overrun the pellet and cause it to precess or tumble, which would destroy accuracy. To avoid this problem, the muzzle end of the rifle barrel includes at least one lateral opening through the barrel to vent some air under pressure before the pellet leaves the barrel.











BRIEF DESCRIPTION OF THE DRAWINGS




The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:





FIG. 1

is a longitudinal section of the gun in firing position;





FIG. 2

is a longitudinal section of the gun in loading position, and with the pump cylinder pulled away from the barrel to actuate the pump;





FIG. 3

is a fragmentary view taken on line


3





3


of

FIG. 1

showing the linkage for activating the pump;





FIG. 4

is an enlarged fragmentary view of the pump and high pressure housing taken in the area of


4





4


of

FIG. 2

;





FIG. 4A

is an exploded elevation, partly in section, of the pump piston and rod used in the pump;





FIG. 4B

is a view taken on line


4


B—


4


B of

FIG. 4A

showing the pumping piston secured to the piston rod;





FIG. 4C

is a longitudinal section of the pumping cylinder partially assembled;





FIG. 4D

is a view taken on line


4


D—


4


D of

FIG. 4C

;





FIG. 4E

is a view taken on line


4


E—


4


E of

FIG. 4

;





FIG. 4F

is a fragmentary view taken on line


4


F—


4


F of

FIG. 4

;





FIG. 4G

is an exploded view of some elements which fit in the forward end of the pump shown in

FIG. 4

;





FIG. 5

is an enlarged fragmentary sectional view of the floating differential piston;





FIG. 5A

is a fragmentary view similar to that of

FIG. 5

showing an alternate embodiment of the floating differential piston;





FIG. 6

is an enlarged longitudinal section of the breech end of the gun taken in the area of line


6





6


of

FIG. 1

;





FIG. 6A

is a fragmentary view similar to

FIG. 6

showing an alternate embodiment for mounting the breech end of the barrel in the gun;





FIG. 7

is a fragmentary elevation of the left (as when sighting down the barrel of the gun) side of the breech end of the gun;





FIG. 8

is a view taken on line


8





8


of

FIG. 7

;





FIG. 9

is a view taken on line


9





9


of

FIG. 7

;





FIG. 10

is a view taken on line


10





10


of

FIG. 2

;





FIG. 11

is a fragmentary view, partly broken away, taken on line


11





11


of

FIG. 2

;





FIG. 12

is an exploded view, in longitudinal section, of the elements shown in

FIG. 11

;





FIG. 13

is a view taken on line


13





13


of

FIG. 12

; and





FIG. 14

is a view taken on line


14





14


of FIG.


12


.











DESCRIPTION OF SPECIFIC EMBODIMENT




Referring to

FIGS. 1 and 2

, an air gun


20


includes an elongated barrel


22


having a breech end


24


, and a muzzle end


26


. A pump


30


includes an elongated pump cylinder


32


adjacent and parallel to the underside of the gun barrel when the gun is in the firing position shown in FIG.


1


. An externally threaded plug


34


threaded into the forward end of the pump cylinder includes a forwardly extending ear


36


(FIG.


4


D). A plug pivot pin


38


extends through a transverse bore


40


(

FIG. 4C

) offset from the longitudinal center line of the plug to secure the plug and forward end of the cylinder between the rear ends of a pair of identical elongated and laterally spaced longitudinally extending drive links


42


(

FIG. 3

) secured at their forward ends by a transverse pivot pin


44


to the forward end of an elongated and longitudinally extending barrel-stiffening web


46


welded at its upper edge to the underside of the forward end of the gun barrel. A downwardly opening notch


48


(

FIG. 2

) in the lower edge of the forward portion of the web receives a transverse reinforcing plate


50


welded across the bottom edges of the forward portions of the links


42


when the pumping cylinder is moved to the firing position shown in

FIG. 1. A

pair of longitudinally spaced and upwardly opening notches


52


in the upper edge of the web


46


reduce the weight carried by the gun.




The forward end of a piston rod


60


is forked (

FIG. 4A

) to fit on opposite sides of the rear end of the web, and is secured to the rear end of the web by a transverse pivot pin


62


extending through collinear bores


63


in the forked end of the piston rod and a collinear bore


64


(

FIG. 3

) of the web. Pivot pin


62


is slightly farther from the longitudinal axis of the gun than is pivot pin


44


for the forward end of the drive links


42


so that when the longitudinal axis of the piston rod is collinear with the pivot pins


44


and


62


, the pump cylinder extends rearwardly and away from the gun barrel at an angle of about 3°. This facilitates gripping the cylinder to actuate the pump through a full pumping cycle, as described below.




The piston rod makes a close sliding fit through a bronze sleeve


66


which makes a snug fit in a central longitudinal bore


67


(

FIG. 4G

) extending through the plug


36


at the forward end of the pump cylinder. The sleeve is locked in place by plug pivot pin


38


, the inner surface of which fits in a matching outwardly opening transverse semi-cylindrical recess


68


in the forward end of the sleeve (FIGS.


4


C and


4


G). A fiber washer


69


makes a sliding seal around the piston rod at the forward end of the bearing sleeve


66


, which holds the washer against the inner surface of an inwardly extending annular shoulder


70


at the forward end of the plug


34


. An outwardly extending annular flange


71


on the inner end of the sleeve makes a snug fit against a rearwardly facing annular shoulder


71




a


at the rear end of the plug


34


to insure proper longitudinal alignment of the sleeve recess


68


with transverse bore


40


before plug pivot pin


38


is driven into place, and to insure proper compression of fiber washer


69


.




The rear end of the piston rod is threaded into the forward face of a pump piston


72


. A lock nut


74


threaded around the rear end of the piston rod bears against the forward face of the pump piston, and locks the piston in a fixed position on the rod. A pair of longitudinally spaced U-cup seals


76


are each disposed in a respective outwardly opening annular groove


77


around the pumping piston to make a sliding seal against the interior of pump cylinder


32


. The seals


76


are set to let air flow rearwardly past the piston, and prevent flow in the opposite direction.




When the pump cylinder and piston rod are pivoted clockwise (as viewed in

FIG. 1

) about pivot pin


62


from the firing position shown in FIG.


1


through an angle of about 100°, the drive links


42


pivot about pin


44


, and force the cylinder to slide on the rod and piston away from the gun until the rear face of plug


34


contacts the forward face of the piston. The rear face of the piston is then forward of an air inlet hole


78


(

FIG. 2

) extending through the wall of the pump cylinder at the forward end of the pump. When the pump cylinder is moved back toward the firing position shown in

FIG. 1

, the pump piston moves rearwardly with respect to the pump cylinder until the rear face of the pump piston contacts the forward face of a check valve


80


(

FIG. 6

) at the forward end of a cylindrical high pressure housing


82


, which is threaded into the rear end of a cylindrical sleeve


84


, the forward end of which makes a snug fit in and is welded to the rear end of the pumping cylinder


32


(FIG.


4


).




With the piston in contact with the check valve


80


, a maximum amount of compressed air is forced through the check valve and into the high pressure housing. The pump is approximately at a “dead center”, i.e., with the longitudinal axis of the piston rod substantially collinear with the pivot pins


44


and


62


secured to the web on the muzzle end of the gun barrel. At this point in the pumping cycle, the cylinder extends rearwardly away from the barrel at an angle of about 3°, leaving adequate clearance around the rear end of the cylinder to grip it with one hand and actuate the pump. Once the high pressure housing is sufficiently charged with compressed air, the cylinder is forced past the “dead center” position to be parallel with the barrel as shown in FIG.


1


. The force required to move the cylinder past dead center is accommodated by the inherent elasticity in the assembled gun, and is sufficient to exert moderate detent action, which holds the pump cylinder against the barrel without any other support.




The forward end of the sleeve


84


includes an inwardly extending annular shoulder


86


disposed around a central bore


88


, which receives a forwardly extending cylindrical boss


90


on the forward end of an inlet check valve housing


92


for the inlet end of the high pressure housing. An O-ring


94


seals the exterior of the boss


90


to the interior surface of bore


88


. An O-ring


96


seals the main body of the check valve housing to the interior of the forward end of the high pressure housing. A check valve piston


98


with an O-ring


99


makes a sliding seal in a longitudinally extending central bore


100


in the check valve housing. Central bore


100


extends from the rear end of the check valve housing to a forwardly and inwardly tapering section


101


of the central bore, and continues as a small orifice


102


opening out the forward end of the check valve housing. A lateral bore


104


located to the rear of the check valve piston


98


extends through the check valve housing to connect the central bore


100


to a longitudinal slot


106


formed in the exterior of the check valve housing to provide communication through the check valve to the interior of the high pressure housing.




The forward end of a strong compression spring


108


bears against the rear face of a circular retaining cap


110


disposed over the rear end of central bore


100


of the check valve housing


92


. A forwardly extending central boss


112


on the forward face of the retaining cap urges a small compression spring


114


against the rear face of the check valve piston to hold the check valve in the closed position shown in

FIGS. 4 and 6

.




The rear end of the large compression spring


108


bears against the forward end of a floating differential piston


116


disposed within the high pressure housing to define a high pressure storage chamber


117


between the floating piston and the check valve housing


92


. A firing or discharge chamber


118


is formed in the high pressure housing between the rear end of the floating differential piston and the forward end of a cylindrical firing valve


119


housing sealed by an O-ring


120


in the rear end of the high pressure housing.




As shown best in

FIGS. 4

,


5


and


6


, the forward end of the floating differential piston includes an integral annular portion


121


which has an outer diameter slightly larger than that of an intermediate portion


122


of the floating piston, and makes a close sliding fit against the adjacent wall of the high pressure housing. A pair of longitudinally spaced U-cup piston seals


123


are each disposed in a separate respective outwardly opening annular groove


124


in the forward end


121


of the floating differential piston to make a sliding seal against the interior adjacent section


125


of the high pressure housing. The seals


123


are set to prevent air flow rearwardly past the floating differential piston.




The rear end


126


of the floating differential piston is of larger diameter than the forward end


121


of the piston, and makes a close sliding fit against the adjacent section


127


of the high pressure housing, which has a stepped bore


128


with an inwardly extending and rearwardly facing annular shoulder


129


to accommodate the different outer diameters of the ends of the floating piston. An annular U-cup piston seal


130


in an outwardly opening annular groove


131


around the rear end of the floating piston makes a sliding seal against the larger diameter interior section


127


of the high pressure housing. Thus, the cross-sectional area of the firing chamber sealed by the rear end of the floating differential piston is substantially greater than the cross-sectional area of the storage chamber sealed by the forward end of the piston, which provides a unique system for storing and discharging energy, as described below.




An annular space


132


between the intermediate portion


122


of the floating piston and the adjacent interior wall of the high pressure housing preferably is partially filled with a suitable lubricant, such as a light oil.




As shown best in

FIG. 5

, an adjustable pressure relief valve


133


is disposed in a stepped bore


134


extending longitudinally through the center of the floating differential piston. Starting at the rear end of the piston, the stepped bore


134


includes a first large section


135


, which tapers inwardly and forwardly down to a second section


136


, which steps down to a third section


137


, which tapers outwardly and forwardly to a fourth section


138


, which opens out of the front end of the floating piston.




An internally threaded valve cap


139


opens in a forward direction and receives the rear end of an adjustable externally threaded set screw


140


having a head


142


projecting forward of the floating differential piston and disposed within the rear end of the strong compression spring


108


. A pressure relief compression spring


144


disposed around the shank of the set screw


140


bears at its forward end against the rear face of the set screw head


142


, and at its rear end against the forward end of a cylindrical sleeve


146


, which makes a loose fit around the set screw shank. Spring


144


urges sleeve


146


rearwardly so the rear end of the sleeve bears against an O-ring


147


in a forwardly and outwardly extending tapered section


148


between the third and fourth sections


137


and


138


, respectively, of the stepped bore


134


. The O-ring seals against the adjacent interior surface bore


134


and the forward end of the internally threaded valve cap


139


on the set screw. The setting of the set screw


140


within the valve cap


139


establishes the force the pressure relief spring


144


causes the forward end of the valve cap to exert against the O-ring


147


. When the air pressure in the storage chamber at the front of the floating differential piston exceeds the air pressure in the firing chamber at the rear of the piston by an amount greater than the force set by the pressure relief valve spring


144


, valve cap


139


is forced rearwardly so that it no longer seals against O-ring


147


. This permits air to flow from the storage chamber into the firing chamber until the differential pressure between the two chambers equals the value set by the pressure relief spring


144


. Ordinarily, the spring is set so that the pressure difference is several hundred pounds per square inch, say about 600 psi.




When the gun is first used, that is, before any pumping action, the strong spring


108


in the high pressure storage chamber urges the floating differential piston rearwardly until the piston engages the forward face of a cylindrical poppet


147




a


in the firing valve


119


. A compression closure spring


148




a


(FIGS.


4


,


5


and


6


) around a rearwardly extending boss


149


on the rear face of the valve cap


139


urges the poppet in the firing valve into the closed position as described below. Preferably, the strong spring


108


is pre-loaded, say with a force of about 30 pounds, when the gun is assembled. For example, referring to

FIG. 4

, when the forward end of high pressure housing


82


is threaded into the rear end of sleeve


84


, the rear face of the floating differential piston is forced against the forward face of poppet


147




a


, causing the desired pre-loading to be imposed on the strong spring


108


. This improves retention of compressed air in the storage chamber, thereby providing better overall performance of the gun.




Another advantage of the pump design shown in

FIG. 4

is that it can be quickly disassembled, permitting easy access to the O-ring and U-cup seals used in the check valve, floating differential piston, and firing valve assembly. Unthreading the sleeve


84


from the forward end of the high pressure housing


82


causes the O-ring seal


96


on the check valve housing


90


to clear the high pressure storage chamber and release any pressure in that chamber. The pressure is safely relieved when a number of threads are still in contact, thus allowing air to be expelled safely. The pressure of any air in the firing chamber drops, say to about 75 psi, as the floating differential piston is pushed forward into the high pressure chamber. Firing the gun releases any remaining pressure in the firing chamber so the entire rear end of the assembly shown in

FIG. 4

can be safely disassembled, using only a small allen wrench as described below.




As the pump is operated by swinging the cylinder away from and back toward the gun barrel, the first strokes, say 15 or 20, deliver compressed air only to the storage chamber until the pressure in the storage chamber reaches the value set by the pressure relief valve. Thereafter, further pumping opens the pressure relief valve to admit air into the firing chamber until the pressure in the firing chamber equals the pressure in the storage chamber, less the pressure set by the pressure relief valve. Continued pumping increases the pressure in both the storage chamber and the firing chamber until the force exerted on the rear end of the floating differential piston by the compressed air in the firing chamber exceeds the force exerted on the forward end of the piston by the compressed air in the storage chamber. The piston then slides forward to reduce pressure in the firing chamber and increase pressure in the storage chamber until the forces on each end of the piston are balanced. For example, if the area of the rear end of the floating piston is twice that of the forward end, and the pressure relief valve is set at 600 psi, the forward movement of the piston as just described begins when the pressure in the firing chamber is 600 psi, and the pressure in the storage chamber is 1200 psi. Further pumping increases the pressure in both chambers, causing the piston to move forward to adjust the relative volumes of the storage and firing chambers so the pressure in the storage chamber is twice that in the firing chamber. The forward movement of the piston continues with additional pumping until the forward end of the piston engages the internal shoulder


129


in the high pressure housing. The strong spring


108


is now compressed, and ready to act with the compressed air in the storage chamber to drive the piston forward as described below when the gun is fired. Pumping can be discontinued before the floating differential piston is forced to the full forward position, i.e., with the forward end of the piston engaging the internal shoulder


129


, and the gun can be fired with reduced power. For example,

FIG. 1

shows the gun in firing position with the air pressure in the firing chamber only high enough to force the floating differential piston through only about 75% of the full travel possible.




Flow of compressed air through the pressure relief valve is fairly restricted because of the close fit of sleeve


146


in bore section


138


and around the shank of set screw


140


. The flow path is adequate for charging the firing chamber with compressed air, but sufficiently restrictive to prevent excessive loss of compressed air when the gun is fired. This is important because minimum loss of air from the storage chamber when the gun is fired permits the storage and firing chambers to be recharged for the next is shot with relatively few, say seven to ten, strokes of the pump.





FIG. 5A

shows an alternate, and preferred, embodiment of the floating differential piston


116


. The embodiment shown in

FIG. 5A

is almost identical with that shown in

FIG. 5

, and the same reference numerals are used in

FIG. 5A

to identify identical elements in FIG.


5


. The difference between the two embodiments is that in the one shown in

FIG. 5A

, the rear end of stepped bore


134


includes a first large section


135




a


, which is substantially deeper than the first large section


135


of FIG.


5


. The deeper first large section


135




a


of

FIG. 5A

replaces the second section


136


of

FIG. 5

to accommodate a compression closure spring


148




b


, which makes a loose fit around the rear end of valve cap


139


, and a close fit within deep bore


135




a


. The rear end of compression spring


148




b


engages the forward face of the poppet


147




a


when the gun is fired and the floating differential piston is driven to the rearmost position. Since compression spring


148




b


does not exert any force on the valve cap


139


, the spring can be stiff, and therefore exert a large force on the poppet


147




a


without influencing the setting of the pressure release valve


133


. Moreover, the large force exerted by compression spring


148




b


permits the use of hard rubber as the material for the annular washer


156


against which poppet


147




a


seats. This arrangement causes the poppet to open the firing valve quickly when the gun is fired, and thus improves the efficiency of the firing operation. Preferably, compression spring


148




b


causes the poppet


147




a


to close the firing valve


119


before the rear face of the floating piston contacts the forward face of the firing valve. This retains a small amount of high pressure firing air in the firing chamber, say at a pressure between about 500 and about 800 psi, and therefore retains more compressed air in the high pressure storage chamber. This decreases the number of pump strokes required for subsequent charging for the next firing cycle.




To prevent possible damage to the gun or seals in the gun due to over pumping, the pump piston can be provided with a pump piston pressure relief valve, such as that shown in U.S. Pat. No. 5,617,837 to Momirov.




The firing valve


119


at the rear end of the high pressure housing includes a longitudinal firing pin


150


disposed in a longitudinal stepped bore


152


extending through the firing valve. The forward end of the firing pin is threaded into the cylindrical poppet


147




a


, the rear face of which seats on an annular washer


156


of hard rubber on a forwardly facing shoulder


158


in the stepped bore. The forward face of the poppet


147




a


is contacted by the rear end of closure spring


148




a


or


148




b


(

FIGS. 5 and 5A

) on the rear face


154


of the pressure relief valve


133


in the floating differential piston when the piston is urged against the forward face of firing valve


119


by the strong compression spring


108


and the compressed air in the storage chamber, as described above. The poppet


147




a


is prevented from rotating relative to the firing valve housing by a stop pin


160


press fitted in a lateral bore


162


extending through a forward portion of the firing valve housing. The inner end of stop pin


160


fits loosely in one of four identical longitudinally extending and outwardly opening grooves


163


(only two grooves are shown in

FIGS. 4 and 6

) spaced at equal intervals around the poppet. The rear end of the firing pin carries an alien head


161


, which permits the firing pin to be removed from poppet


147




a


(after all compressed air is released from the high pressure housing as described above) so the firing valve can be disassembled with an allen wrench for servicing.




The firing valve housing


119


is secured in the rear end of the high pressure housing by a transverse retaining pin


164


, which extends down through a pair of collinear bores


166


through the rear end of the high pressure housing, and through transverse stepped bore


167


through the firing pin housing. An oversize bore


168


extending longitudinally through the forward side of a lower portion of the retaining pin receives the shank of the firing pin


150


, which makes a close sliding fit through a bore


170


extending through the rear side of the retaining pin. An O-ring seal


172


makes a sliding seal around the firing pin shank and a section


173


of stepped bore


152


extending through the firing valve housing. The retaining pin


164


is locked against transverse movement with respect to the high pressure housing by the firing pin extending through bore sections


170


and


173


. An O-ring


174


around a lower portion of the retaining pin seals that part of the pin against the firing valve housing. O-ring


176


around an upper portion of the retaining pin seals that portion of the pin against the adjacent portion of the firing valve housing. A cylindrical recess


180


in the retaining pin extends down from the upper end of the retaining pin to just below longitudinal bores


168


and


170


in the retaining pin to form a firing conduit


181


for transferring compressed air from the firing chamber to the breech of the gun, as described in detail below. The upper end of the recess


180


is sealed by an elastomeric plug


182


. A longitudinally extending pellet bore


184


through the upper end of the retaining pin traverses the firing conduit


181


, and receives a pellet or projectile


186


, which is held in the bore


184


by friction contact with elastomeric plug


182


and the surrounding surface of bore


184


.




When the pumping cylinder and high pressure housing are moved up to the firing position shown in

FIGS. 1 and 6

, the upper end of the retaining pin


164


nests in a downwardly opening cylindrical recess


188


(

FIG. 2

) in an upper block


189


of a breech assembly


190


(which includes a lower block


191


secured to the upper block as described below) so that the pellet


186


is in longitudinal alignment with the breech end


194


(

FIG. 2

) of an elongated rifled barrel


196


coaxially mounted in the steel outer barrel


22


. The upper surface of the elastomeric plug


182


bears against the inner end of recess


188


in the upper block. The breech end of the rifled barrel makes a snug fit in the forward end of an elongated longitudinally extending bore


199


extending through the upper block (

FIGS. 6 and 9

.)




As shown in

FIGS. 4

,


4


E and


4


F, the rear end of the firing valve housing includes a rearwardly extending vertical tang


197


, which makes a snug sliding fit in a vertical slot


198


(

FIG. 2

) in the forward end of the lower breech block


191


. The upper end of tang


197


on the rear end of the firing valve assembly tapers upwardly and forwardly at an angle of about 5° from vertical to facilitate the movement of the tang into and out of the vertical slot


198


in the forward end of the lower breech block. An O-ring


192


around retaining pin


164


, just below pellet bore


184


, facilitates the pin making a releasable sealed fit into the downwardly opening recess


188


in the upper breech block


189


.




The rear portion of bore


199


in the upper breech block includes an outwardly and rearwardly tapered section


200


, which connects to a longitudinal extension of bore


199


to hold a cylindrical bronze bearing sleeve


202


in which a cylindrical bolt


204


is mounted to slide back and forth to drive the pellet into the breech end of the rifled barrel as shown in

FIG. 6. A

pair of longitudinally spaced O-rings


205


around the rear end of the rifled barrel seal the barrel against the interior of bore


199


in the upper breech block.





FIG. 6A

shows an alternate embodiment for sealing the breech end of the rifled barrel


196


in bore


199


in the forward end of upper breech block


189


. The rear end of a cylindrical plug


206


is threaded into the forward end of bore


199


to compress an O-ring


207


against the exterior of rifled barrel


196


and the interior of bore


199


.




A bolt compression spring


210


in a rearwardly opening longitudinal cylindrical recess


212


in the bolt urges the bolt toward the forward or firing position shown in FIG.


6


. The rear end of the bolt compression spring fits over a forwardly extending guide


214


formed integrally at its rear end with a rear retaining fitting


218


, which is held in place by a rear vertical screw


220


extending down through a barrel upper guide and scope mount


222


, the upper block


189


, the bronze sleeve


202


, a vertical bore


224


in the rear retaining fitting


218


, and a pair of vertically spaced collinear bores


226


in the lower block


191


.




A longitudinally extending cylindrical hammer


230


makes a sliding fit within a cylindrical bronze firing piston sleeve


232


press fitted into a longitudinal bore


234


extending through the lower block. A compression firing spring


236


in a longitudinal stepped bore


238


extending through the hammer


230


fits around a longitudinal and forwardly extending cylindrical guide


240


formed integrally with a rear retaining fitting


242


held in the rear end of the bronze firing piston sleeve by vertical screw


220


. The firing compression spring is held in a compressed condition by a pawl


244


engaging the forward end of the hammer. The pawl is on a trigger


246


mounted in a lower portion of the lower breech block. A compression trigger spring


248


in a downwardly opening recess


250


in the lower block urges the trigger in a clockwise (as viewed in

FIG. 6

) direction around a trigger pivot


252


so the hammer holds the firing spring in the compressed condition. When the trigger is pulled, the hammer is released so the compression spring drives the hammer forward to strike and drive forward a firing piston


260


, which drives the firing pin and poppet forward to open the firing valve and release compressed air from the firing chamber through the firing conduit


181


and into the breech end of the rifle barrel to drive the pellet forward.




A forward vertical retaining screw


262


secures the bronze firing piston sleeve within the lower block, and secures the forward portion of the lower block to the upper block, which projects a substantial distance forward of the lower block.




Once the gun is fired, the bolt is returned to the loading position shown in

FIG. 2

by operation of a bolt handle


270


(

FIGS. 7

,


8


and


9


), which is secured to the bolt


204


by a screw


272


which extends through a compression spring


274


mounted in a stepped bore


276


in the bolt handle


270


. The inner end of the screw


272


is threaded into the bolt. The head of the screw


272


bears against the outer end of compression spring


274


, the inner end of which bears against an internal shoulder


278


in the bolt handle. The inner end of the bolt handle is cylindrical and shaped to fit in either a forward or firing detent bore


280


or in a rear or loading and safety detent bore


282


formed in the left (as when sighting down the barrel of the gun) side of the upper block housing of the breech assembly. The two detent bores are connected by a longitudinal slot


284


in the upper block and a slot


286


in the bronze sleeve


202


.




The forward detent bore


280


holds the bolt in place against back pressure when the gun is fired. The rear detent bore holds the bolt in the rear position shown in

FIG. 2

so the gun can be loaded, but not fired, as explained below. A pair of longitudinally spaced O-rings


205


around the bolt at its forward end make a sliding seal between the bolt and the longitudinal bore in the upper block of the breech assembly. Another pair of longitudinally spaced O-rings


205


around the rear end of the rifled barrel seal that portion of the barrel against the longitudinal bore extending through the upper block of the base assembly. A gun stock (not shown, and which may be conventional) is secured to the breach assembly by a hold-down bracket


300


welded to the rear of fitting


218


, and by a stock screw


302


, which also secures the rear end of a trigger guard


304


to the stock. The forward end of the trigger guard is secured to the stock and the underside of the lower block of the breech assembly by a screw


306


.




When the gun is fired the hammer compression spring


236


drives the hammer forward so the longitudinal bore


238


in the hammer slides over a rearwardly extending cylindrical boss


310


on the rear end of the firing piston until the forward end of the hammer slams into a rearwardly facing annular shoulder


312


surrounding the projection


310


. The firing piston then drives the firing pin forward to force the firing valve open and released compressed air from the firing chamber into the breech end of the rifled barrel behind the projectile. As shown in

FIG. 6

, the forward end of the bolt


204


includes a section


314


of reduced diameter to permit compressed air to flow freely around the bolt and into the breech end of the rifled barrel.




As also shown in

FIG. 6

, before the gun is fired, the forward end of the firing piston


260


extends forward of the front face of the firing piston sleeve


232


and the forward end of the lower block


191


into the rearwardly opening bore


152


in the rear face of the firing valve housing so the forward end of the firing piston bears against the rear end of the firing pin, and also locks the pumping cylinder and high pressure housing in the firing position shown in

FIGS. 1 and 6

.




To prepare the gun for another firing, the bolt handle


270


(

FIGS. 7 and 8

) is pulled out slightly away from the breech assembly so the inner end of the bolt handle clears the forward (firing) detent bore


280


. The bolt handle and bolt screw


272


are free to slide rearwardly through slot


284


in the breech assembly upper block and slot


286


in the bronze bearing sleeve


202


. A vertical cocking pin


330


(

FIG. 6

) is threaded at its upper end into the bolt just forward of the bolt handle. The lower end of the cocking pin extends down into an upwardly opening longitudinal slot


332


in the upper surface of the firing piston


260


. When the gun is in the firing position, the lower end of the cocking pin is at the forward end of slot


332


, which is long enough to permit the firing piston to move forward and open the firing valve when the gun is fired. When the bolt handle is pulled out and the bolt slid to the rear position so that bolt handle can snap into the rear detent bore


282


, the lower end of the cocking pin travels rearwardly through slot


332


until it engages a forwardly facing shoulder


334


at the rear end of the slot. Thereafter, the cocking pin pushes the firing piston and hammer rearwardly to the position shown in

FIG. 2

, compressing hammer spring


236


to the condition shown in FIG.


6


. The trigger spring


248


forces the trigger to rotate in a clockwise direction around the trigger pin


252


so the trigger pawl locks the hammer in the cocked position. With the firing piston retracted to the position shown in

FIG. 2

, and the bolt locked in the rear (safety) detent, the firing valve housing and pumping cylinder are free to swing away from the gun barrel, as shown in

FIG. 2

, and a pellet can be inserted into bore


184


of retaining pin


164


(FIG.


4


). Moreover, with the bolt locked in the rear detent, the locking pin


330


locks the firing piston


260


in the rear position shown in

FIG. 2

so the hammer cannot be driven forward by compression spring


236


, even if the trigger is pulled. Thus, the gun is locked in a “safety” condition.




Once the firing chamber is recharged with compressed air as described above, and a pellet is inserted in the pellet chamber as shown in

FIG. 2

, the pump and high pressure housing is returned to the position shown in FIG.


1


. The bolt handle can then be pulled outwardly from the rear detent, and slid forward to the forward detent so the forward end of the bolt pushes the pellet into the breech end of the rifle barrel, and the cocking pin pushes the firing piston forward to the locking position shown in

FIGS. 2 and 6

. A downwardly opening and longitudinally extending slot


340


(

FIGS. 6 and 9

) in the upper block, and an upwardly opening and longitudinally extending slot


342


in the upper surface of the lower block permits the cocking pin to slide back and forth as just described.




An intermediate portion of the rear barrel stiffener


222


is secured to the top surface of the upper block


189


by a pair of longitudinally spaced screws


350


. The forward end of the rear barrel stiffener


222


rests in a rearwardly opening notch


354


of an elongated and longitudinally extending forward barrel stiffener


356


welded to the top of the outer barrel


22


. The rear and forward barrel stiffeners provide the stiffness required because of the large mechanical advantage developed by the pump linkage.




Referring to

FIGS. 11-14

, a pressure relief fitting


370


includes an elongated and longitudinally extending cylindrical body


372


which has a uniform longitudinal cylindrical bore


374


extending through it and making a snug sliding fit over the muzzle end of the rifled barrel


196


. As shown in

FIG. 2

, the forward ends of the rifled barrel and the pressure relief fitting are substantially coterminous, and each are tapered forwardly and outwardly. The pressure relief fitting is welded to the rifled barrel in the position shown in

FIGS. 2 and 11

. The forward end of the steel outer barrel


22


makes a snug sliding fit over the rear end of the pressure relief fitting, which includes a section


378


of reduced external diameter to receive the outer barrel, the forward end of which abuts against a rearwardly facing annular shoulder


380


at the forward end of section


378


. The steel outer barrel is welded to the pressure relief fitting. The forward end of the pressure relief fitting has four elongated and longitudinally extending slots


382


, which open radially outwardly through the pressure relief fitting with equal angles between adjacent slots. Four sets of three longitudinally spaced and circular vents


390


extend radially through the forward end of the rifled barrel so that each set of three vents is centered within a respective slot


382


, as shown in

FIGS. 2 and 11

.




The pressure relief fitting and rifled barrel vents improve the accuracy of the gun because the force of the discharged air behind the pellet is so great that if the venting and pressure relief were not provided, the compressed air emerging from the muzzle of the gun would tend to overrun the pellet and cause it to wobble or tumble. With the venting just described, some of the compressed air behind the pellet is released laterally from the muzzle as the pellet leaves the gun, thereby avoiding the pellet being overrun with the charge of compressed air. The longitudinally spaced vents


390


provide progressive venting of the compressed gas behind the pellet so that venting can take place rapidly, yet not prematurely, which would decrease the kinetic energy imparted to the pellet.




With the embodiment of the invention just described, a shooter of ordinary strength can easily operate the pump to charge the firing chamber with sufficient compressed air to impart a force of more than 40 foot-pounds to the pellet. This is sufficient to give a 22 caliber pellet weighing 25 grains a muzzle velocity of more than 850 feet per second.



Claims
  • 1. An apparatus for storing and discharging gas, the apparatus comprising:a housing having an inlet and an outlet; a floating differential piston mounted to reciprocate in the housing and divide the housing into a storage chamber adjacent the housing inlet and a discharge chamber adjacent the housing outlet; a check valve in the housing inlet for admitting gas to the storage chamber; a conduit extending through the piston from the storage chamber to the discharge chamber; a pressure relief valve in the conduit and set to maintain a higher pressure in a storage chamber than in the discharge chamber; a first sliding seal between the housing and an end of the piston adjacent the housing inlet; a second sliding seal between the housing and an end of the piston adjacent the housing outlet, the cross-sectional area of the housing sealed by the second seal being larger than that of the first seal, so that when gas pressure in the storage chamber exceeds the differential pressure set by the pressure relief valve, gas flows through the conduit from the storage chamber and into the discharge chamber and forces the piston to move toward the inlet end of the housing to reduce the volume of gas in the storage chamber and increase the volume of gas stored in the discharge chamber; and a discharge valve in the housing outlet.
  • 2. Apparatus according to claim 1 which includes a spring in the housing for urging the piston toward the housing outlet.
  • 3. Apparatus according to claim 1 which includes a compression spring in the storage chamber for urging the piston toward the discharge chamber outlet.
  • 4. Apparatus according to claim 1, in which the pressure relief valve is adjustable.
  • 5. Apparatus according to claim 1, in which the floating differential piston is of a generally elongated cylindrical shape with one end of the piston having a diameter larger than an intermediate portion of the piston, and the other end of the piston having an outside diameter larger than that of the first-mentioned end of the piston.
CROSS REFERENCE TO RELATED APPLICATION

This patent application is a divisional application of U.S. patent application Ser. No. 09/990,908, filed Nov. 16, 2001, now U.S. Pat. No. 6,581,585.

US Referenced Citations (18)
Number Name Date Kind
1486215 Zerbee Mar 1924 A
2119441 Price May 1938 A
2145277 Reardon Jan 1939 A
2652821 Fitch Sep 1953 A
4304213 Jereckos Dec 1981 A
4472794 Chelminski Sep 1984 A
4572152 Olofsson et al. Feb 1986 A
4709686 Taylor et al. Dec 1987 A
4771758 Taylor et al. Sep 1988 A
4844046 Straub Jul 1989 A
4850329 Taylor et al. Jul 1989 A
4928661 Bordt et al. May 1990 A
5193517 Taylor et al. Mar 1993 A
5224465 Milliman Jul 1993 A
5341790 Ebert Aug 1994 A
5617837 Momirov Apr 1997 A
5813392 McCaslin Sep 1998 A
6343598 Pshenychny Feb 2002 B1
Foreign Referenced Citations (1)
Number Date Country
4419680 Aug 1995 DE
Non-Patent Literature Citations (1)
Entry
Internet papers: B. Saltzman, “Three Basic Types of Airguns”, Beeman Precision Airguns, http://beeman.com/types.htm, four pages, retrieved on Jul. 11, 2001.