GB2466118A - Discharge valve for an airgun - Google Patents

Abstract

A discharge valve especially for an airgun comprises a valve member 1 guided for translatory motion and arranged to be retained by latching means 6 in a closed position wherein the valve member 1 seals an opening 10 in a passage 3 communicating between a reservoir 8 charged with gas at an elevated pressure and a discharge port 9. The arrangement is such that, in use, the valve member 1 is biased towards an open position by the pressure of gas in the charged reservoir 8, whereby upon release of the latching means 6 the valve member 1 is caused to move to an open position in which gas can pass from the charged reservoir 8 to said discharge port 9. In accordance with the invention there is provided a further reservoir 26 containing gas at an elevated pressure and arranged to act upon said valve member 1 in such a manner that, when the valve member 1 is moved to the open position the pressure of gas in said further reservoir 26 provides a restoring force returning the valve member 1 to the closed position upon a reduction of the pressure of gas in said charged reservoir 8.

Description

Discharge Valve This invention relates to an improved discharge valve more especially for an airgun. Tn particular the invention concerns a so-called blow-off valve of the kind wherein a valve member guided for translatoiy motion is arranged to be retained by latching means in a closed position wherein the valve seals an opening in a passage communicating between a reservoir charged with gas at an elevated pressure and a discharge port, the arrangement being such that, in use, the valve member is biased towards an open position by the pressure of gas in said charged reservoir, whereby upon release of said latching means the valve member is caused to move to an open position in which gas can pass from said charged reservoir to said discharge port. Such a valve is described, for example in US

Patent Specification No. 4,163,439.

Such valves are generally referred to as dump valves because once the valve has moved to an open position the valve remains open until the pressure of gas in said reservoir has returned substantially to ambient atmospheric pressure. Thus all of the compressed gas is dumped from the reservoir until the valve can be returned to the closed position, for example by means of a return spring. For this reason, such dump valves are generally only used in airguns of the pump up pneumatic type, wherein all of the air is released from the reservoir at each shot. Between shots the said reservoir is pumped to a high air pressure by means of a manual pump contained within the gun and coupled to the reservoir via a non return valve.

However, there is also known from WO 87/0308 1 an airgun of the so-called precharged pneumatic or PCP type, which has a discharge valve of the kind initially referred to. A PCP airgun has a reservoir which is much larger than that of the pump up pneumatic so that multiple shots can be obtained from a single charge of compressed gas. Conventional PCP airguns use a hammer actuated valve that is biased to the closed position by the pressure of gas in the reservoir so that only a small proportion of the gas contained in the reservoir is released at each shot. However as the pressure of air in the reservoir falls with consecutive shots the power of the airgun varies and exhibits a so-called power curve which detracts from the accuracy of the gun. The arrangement of WO 87/03081 overcame this disadvantage by using a dump valve to discharge gas from a relatively small secondary chamber to which gas is fed from the main reservoir via a regulator providing a controlled pressure in the secondary chamber.

This known arrangement provided a considerable advantage over conventional PCP airguns in that consistency and accuracy of the air rifle were vastly improved. An air rifle using this system and sold as the Sportsmatch 0C2 achieved success as an internationally competitive target rifle.

However this arrangement also had significant disadvantages. II was complicated and expensive to manufacture and was also relatively inefficient so that the number of shots that could be obtained from a charge of compressed air in the main reservoir was lower than that obtainable from a comparable PCP air rifle with a hammer actuated valve. For this reason this known arrangement is no longer manufactured and PCP air rifles currently on the market use hammer actuated valves rather than blow-off valves, even though the more sophisticated rifles also now incorporate pressure regulators in order to improve consistency.

Nevertheless, although hammer actuated valves are now universally used in PCP airguns they do have significant disadvantages. The spring loaded hammer mechanism takes up a significant space within the body of the airgun and requires cocking before each shot. The mechanism is also noisy in operation and exhibits the so-called hammer twang that is unpopular with hunters who require a frilly silenced weapon. Also, in territories where there are legal limits on the power of airguns the hammer actuated valve has the disadvantage that it is too easily modified to increase the power of the airgun, for example by increasing the strength of the hammer spring or the weight of the hammer.

There is therefore a requirement for an improved discharge valve system for an airgun.

The present invention provides a discharge valve of the kind initially referred to which is characterised in that, in use, the said valve member is coupled to a further reservoir containing gas at an elevated pressure, in such a manner that, when the valve member is moved to the open position the pressure of gas in said frirther reservoir acts upon the valve member to provide a restoring force returning the valve member to the closed position upon a reduction of the pressure of gas in said charged reservoir.

The arrangement according to the invention has the advantage that the blow-off valve is not a dump valve, since the valve is closed whilst there is still a residual gas pressure in the said charged reservoir. The valve thus has characteristics that are more similar to those of a hammer actuated valve in that it avoids wastage of gas due to the exhaustion of gas from the charged reservoir after all useful energy has been transferred to the airgun missile. As will become more apparent from the following description the construction of the valve may be such that for any given pressure of gas in the said charged reservoir upon the opening of the valve there will be a corresponding pressure at which the valve closes. Therefore by selecting the size of charged reservoir in accordance with the intended pressure of gas within the charged reservoir and the volume of the airgun barrel the valve can be tuned to give a desired power of the airgun with relatively efficient use of gas. Moreover since this power will be inherent in the valve for any given gas pressure the possibility of unauthorised tampering with the power of the airgun is significantly reduced. Other advantages of the valve are those inherent in known blow-off valves, such as reduced noise of operation, saving in space and faster lock time.

Further preferred features and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawings and the appended claims.

In the drawings: Figure 1 is a sectional elevation in diagrammatic form of a known discharge valve as shown in US Patent No. 4,163, 439.

Figure 2 is a similar view of an airgun incorporating a discharge valve in accordance with the present invention, and Figure 3 is a diagram showing a discharge valve in accordance with another embodiment of the invention.

Referring to Figure 1 of the drawings there is shown a so-called dump valve of known type. For a full description reference may be made to US Patent No. 4,163,439 but features relevant to the present invention will be outlined here. The arrangement illustrated comprises a valve member in the form of a generally cylindrical rod 1 having an intermediate shoulder portion 2. The rod 1 is guided for translatory motion in registering bores 3 and 4 in a valve housing 3A and an end cap 4A respectively, both of which are received in a pressure tube 5. The rod 1 is arranged to be retained by latching means 6 in a closed position wherein it seals an opening in a passage 7 communicating between a reservoir 8 charged with gas at an elevated pressure and a discharge port 9.

The seal is effected by means of an 0-ring 10 defining the opening to be sealed and engaging around the rod 1. The arrangement is such that, in use, the rod 1 is biased towards an open position by the pressure of gas in said charged reservoir 8, whereby upon release of said latching means 6 the rod is caused to move to an open position in which gas can pass from the charged reservoir 8 to the discharge port 9 via the passage 7.

The discharge valve shown in Fig 1 is incorporated in an airgun, the port 9 being coupled to a barrel 11 whereby the discharged gas is effective to propel an airgun pellet. The known arrangement has proved popular in airguns of the pump up pneumatic type, wherein the reservoir 8 is coupled to a manual pump contained within the airgun via a non-return valve. However this arrangement does have disadvantages. Since all of the air is dumped from the reservoir 8 at each shot the system is wasteful of energy, as more air is discharged from the barrel 11 than is necessary to propel the airgun pellet. This also increases the noise of a shot, to the extent that such airguns are normally fitted with sound moderators where this is permitted by local laws. Also the force on the valve member 1 due to the pressure of air in the reservoir 8 is relatively high so that the diameter thereof should be kept as small as possible in order to maintain the trigger pressure of the airgun within acceptable limits.

Referring to Figure 2 of the drawings, an airgun according to one embodiment of the present invention comprises a discharge valve that is similar to the known arrangement shown in Fig 1 to the extent that relevant parts are indicated by the same reference numerals. The airgun comprises a barrel 11 secured in known manner in a breach block 12 that has a loading port 13 and a bolt 14. The bolt 14 is manually actuatable in known manner in order to enable airgun pellets to be loaded into the port 13 and advanced into the barrel 11 by means of a probe 14A of the bolt 14, so that they become located in the barrel 11 in front of a transfer port 9 communicating with the barrel 11 in a conventional manner. The bolt 14 carries a seal 16 such as an 0-ring seal in order to close the barrel 11 in an air tight manner behind the transfer port 9 and is retained in the closed position also in a conventional manner, not shown.

Below the breach block 12 is secured, by mounting screws 17 of which only one is shown, a valve block 18. The forward end of the valve block 18 defines a pressure chamber 8 only part of which is shown. This chamber can be charged with compressed air at an elevated pressure of, for example, 80-100 Bar in a manner well known in the art of airguns. For example the airgun could be a so-called multi pump pneumatic in which a manual pump contained in the fore end of the gun is coupled to the chamber 8 via a non-return valve. Alternatively the chamber 8 could be charged with compressed air from a main pressure cylinder or buddy bottle in a manner well known in the art of PCP airguns.

n the latter case means should be provided to enable the chamber 8 to be charged to a predetermined pressure from the main cylinder and then isolated therefrom prior to each shot. For example the chamber 8 may be coupled via a manually actuatable valve to the output of a buddy bottle containing compressed air and provided with a preset regulator at its output. Such buddy bottles are commonly used for paintball guns. The valve block 18 contains a valve member 1 of elongated generally cylindrical configuration, one end 1A of which is received in a bore 3 communicating between the chamber 8 and the transfer port 9. The end 1A of the valve member is sealed within the bore 3 at a point upstream of the transfer port 9 by means of an 0-ring 10 or a similar seal suited to the high air pressures of airguns. The bore 3 extends past the transfer port 9 to a space 22 that is at atmospheric pressure and will be described further below. Therefore a further 0-ring 23 is provided in the bore 3 to provide a seal around the valve member 1 at a point behind the transfer port 9. A coupling member 24 is received within the breach block 12 and clamped between the barrel 11 and the valve block 18 in order to ensure that the transfer port 9 provides a fluid tight conduit between the bore 3 and the barrel 11. The valve member 1 extends from the bore 3 and through the aforementioned space 22 into a further bore 4 that communicates with a pressure chamber 26 at the rear of the valve block 18.

The other end lB of the valve member 1 terminates within the chamber 26. The diameter of a rear portion 1C of the valve member 1 is reduced at a point within the space 22 and thus the bore 4 is of correspondingly smaller diameter than the bore 3. The bore 4 contains an 0-ring 27 that provides a seal around the circumference of the valve member 1. The pressure chamber 26 is closed at the rear by an end plug 28 and is sealed by means of an 0-ring 29 carried by the end plug 28. The end plug 28 has a threaded bore 30 and is secured in place in the valve block 18 by means of fastening screws located in the bore 30. An upper fastening screw not shown passes through the breach block 12 and corresponds to the fastening screw 17. A trigger block 31 is secured below the valve block 18 by means of fastening screws 32 passing through the trigger block and engaging respectively in the valve block 18 and the bore 30. As described in more detail below, the pressure chamber 26 is charged with air at high pressure comparable with that of the normal operating pressure of a PCP airgun, for example 80 to 100 Bar. The valve member 1 has fixed thereto a collar 2 which carries a sear pin 38 and the movement of which is limited by end faces 22A and 22B of the space 22. The sear pin 38 can engage a trigger member 6 that is pivoted about a pivot 40 mounted in the trigger block 31 and urged into engagement with an end stop 41 by means of a compression spring 42 engaging between the trigger member 6 and the trigger block 31.

The system shown in Fig 2 operates as follows. The pressure chamber 26 contains air at the high pressure already mentioned, and thus in conjunction with the valve member 1 it forms a gas spring causing the valve member 1 to be urged to the left as viewed in the drawing until the collar 2 engages the end face 22A. In the idle condition the components thus adopt the positions shown in the drawing, there being a slight play between the sear 38 and the trigger 6 to allow the latter to adopt its rest position under the influence of the spring 42. The chamber 8 is now charged with air at high pressure in the manner described above, in order to bring it to substantially the same pressure as the chamber 26.

Since the diameter of the end 1A of the valve 1 is greater than that of the end lB the force thereon is correspondingly greater and the valve 1 is thus biased to the right as viewed in the drawing. The valve is held against movement by engagement of the sear pin 38 against the trigger 6. When the trigger 6 is pulled it moves anticlockwise against the force of the spring 42 and releases the sear pin 38 so that the valve member 1 can move rearwards to a position in which the end 1A is located between the transfer port 9 and the 0-ring 23 and the collar 2 is arrested by the end face 22B. Air can now pass from the chamber 8 to the barrel 11 via the transfer port 9. The difference in the diameters of the two ends of the valve member 1 is such that at the working pressure of the chambers 8 and 26 the force on the valve member is sufficient to cause it to snap rapidly into the open position. The pressure chamber 8 is isolated as described above and therefore as air is discharged therefrom the pressure drops. However, the pressure in the chamber 26 is maintained and therefore when the pressure in chamber 8 drops to a predetermined value the force acting on the end 1 B will be greater than that acting on the end 1A and the valve 1 will return to the position shown in the drawing. Upon release of the trigger 6 the chamber 8 can be recharged to its working pressure and the system is ready to fire again.

The system as described above has the advantage that it can provide a pulse of high pressure air to fire a pellet from the barrel 11 without discharging all of the air from the chamber 8 so that lower pressure air that would be ineffective in driving the pellet is not wasted. Thus the system has characteristics similar to those of a hammer actuated valve whilst retaining the advantageous characteristics of the known dump valve. Moreover, for any given working pressure of the airgun the pressure at which the valve closes and the volume of air discharged through the transfer port 9 will be determined by the relative dimensions of the ends 1A and lB of the valve 1 and the volume of the chamber 8. This enables the power of the airgun to be determined at the design stage by matching the volume of air to be discharged to the volume of the barrel 11. Furthermore, since the force on the end 1A of the valve 1 is partly balanced by the force on the end 1B, the force on the trigger 6 is less than that of the known arrangement shown in Fig 1 so that a relatively low trigger pressure can be achieved in a simple arrangement.

The arrangement shown in Fig 2 may be modified in various respects without departing from the scope of the invention. If the chamber 26 is charged to a working pressure that is lower than that of chamber 8 then the two ends of the valve member 1 could be the same diameter. Instead of the valve member 1 extending into the chamber 26, the chamber 26 could be provided in a mechanically separate gas strut or gas ram mechanically coupled to the valve member 1. Such a separate unit may be made interchangeable in order to enable the characteristics of an airgun to be modified. In an arrangement in which the working pressures of the chambers 8 and 26 are to be substantially the same, the valve 1 or the valve housing 18 may incorporate an air bleed passage coupling the chambers 8 and 26 via a non-return valve. The chamber 26 may then derive its pressure air from the chamber 8. Alternatively the chamber 26 could simply be connected directly to the preset regulator of a buddy bottle as mentioned above at a point upstream of the manually actuatable valve referred to.

Fig 3 shows another embodiment of the invention which is adapted for use with a gun having a discharge port in line with the barrel. The discharge valve comprises a generally cylindrical valve housing 58 which contains a valve member 51 of elongated generally cylindrical configuration, one end 51A of which is received in an outlet port 53 and is sealed within the port 53 by means of an 0-ring 4 or a similar seal suited to the high air pressures of airguns. The valve member 51 has at the other end a stem portion SiB, of larger diameter than the end 51 A, which is received in a bore 55 that extends through the valve housing 58 to atmosphere. The bore 55 is sealed by means of an 0-ring 56 located around the stem 51B within the bore 55. An inlet port 57 opens into the housing 58 adjacent the bore 55.

An end of the stem portion SiB engages a latch or sear 52 that is mounted on a pivot 59 fixed with respect to the housing 58 for example in the frame of an airgun not further illustrated. The sear 52 is biased in an anti-clockwise direction as viewed in the drawing by means of a compression spring 60 located between the sear 52 and an abutment face 61 of the airgun frame and movement thereof in an anti-clockwise direction is limited by a stop indicated diagrammatically by the arrow 62. The stop 62 may be adjustable. The sear 52 is shaped to provide a recess 52A for a purpose to be described below.

A two-armed lever 63 forming a trigger is also mounted on a pivot 64 fixed within the airgun frame. One arm of the lever 63 carries a pawl 65 that is pivoted at 66 and is biased in an anti-clockwise direction as viewed in the drawing by means of a compression spring 77 engaging between the lever 63 and the pawl 65, so that an end of the pawl 65 rests on the end 51B of the valve member 51.

The trigger 63 is biased in a clockwise direction by a compression spring 68 located between it and an abutment face 69 of the airgun frame and a stop 70 of the airgun frame determines the rest position of the trigger 63. An adjusting screw indicated diagrammatically by the arrow 71 limits the travel of the trigger 63.

An intermediate portion of the valve member 51 carries a piston shaped baffle 72 that is slideable relatively thereto and to the internal circumference of the valve housing 58. The baffle 72 may have a peripheral seal, such as an 0-ring not shown, although this may not be necessary if the baffle 22 is of a material that engages the housing 1 in a relatively fluid tight manner. The valve housing 58 is provided with an abutment portion 73 defining the rest position of the baffle 72 and the baffle 72 is biased into engagement therewith by a compression spring 74 engaging between the baffle 72 and a shoulder portion SiC of the valve member.

The operation of this arrangement will now be described. The inlet 57 of the valve housing 58 is intended to be coupled to a source of gas at elevated pressure. This source may be the main reservoir of a PCP airgun, in which case a pressure regulator is preferably arranged to control the pressure at the inlet 57 in a known manner not shown.

The source could also be a carbon dioxide cylinder as is also known for airguns. The outlet port 53 is coupled to the barrel of the airgun via a suitable loading mechanism that allows the insertion of pellets in the barrel. For example the port 53 may be in line with the barrel like the transfer port of a spring airgun and have a similar loading mechanism.

Since the valve has a semiautomatic action, as will be described below, it could be associated with a self-loading mechanism similar to that of a paintball gun.

When the valve is in the idle condition the compression spring 74 biases the valve member 51 towards the port 53 and the baffle 72 towards the abutment 73. Thus the end 51A engages within the port 53, its limit position being defined by a shoulder 51D which engages the rim of the port 53 under the pressure of the spring 74. Gas applied at the inlet 57 initially passes to a space 75 within the housing 58 between the baffle 72 and the bore 55. As the pressure of gas rises within this space the gas passes through the clearance between the valve member 51 and the baffle 72 and enters a space 76 between the port 53 and the baffle 72. Thus the housing 58 becomes charged to a uniform gas pressure corresponding to that at the inlet 57. n the idle condition there is a small clearance between the end SiB of the valve member 51 and the sear 52 to allow the components of the trigger mechanism to adopt their idle positions under the return spring loading.

However, when the housing 58 is fully charged the gas pressure will bias the valve member 51 into engagement with the sear 52 owing to the difference in the diameters of the respective ends of the valve member 51. The components thus adopt the positions shown in the drawing, in which the shoulder 51D is slightly spaced from the port 53.

When the trigger 13 is pressed and rotates anticlockwise as viewed in the drawing the pawl 15 is pushed upwards to release the sear 52 from the end SiB of the valve member 51. The upward movement of the paw! 65 is limited by the stop 71. The valve member 51 is thus free to move to the right as viewed in the drawing and the shoulder portion SiC compresses the spring 74 sufficiently to release the end 51A from the port 53. It will be understood that the force on the valve member 51 due to the gas pressure within the housing 58 is sufficient that the valve is fully opened to discharge gas from the port 53.

As the valve member 51 moves to the right it carries with it the pawl 65 which pivots clockwise until it enters the recess 52A. The sear 52 is thus released to return anticlockwise until it engages the top of the valve member 51. As gas escapes from the port 53 the pressure in space 76 drops whilst the pressure in space 75 is substantially maintained as the flow of gas therefrom is obstructed by the baffle 72. The baffle 72 is thus driven to the left as viewed in the drawing, carrying with it the spring 74 and valve member 51, which is thus returned to the closed position. As the valve member 51 returns the upper end of the pawl 65 remains trapped within the recess 52A and thus the sear 52 can return into the latching position as soon as the valve member 51 has returned to the closed position. Thus gas can now bleed from the space 75 to the space 76 through the clearance between valve 51 and baffle 72 to equalise the pressures in the housing 58 whilst the valve remains closed and the compression spring 74 can return the baffle 72 to its rest position. When the trigger 63 is released it returns in the clockwise direction and releases the pawl 65 from the recess 52A so that the mechanism returns to the state shown in the drawing and the valve is again ready to fire.

II will be appreciated that in order for the valve to operate in the semiautomatic mode described the clearance between the valve 51 and the baffle 72 must be such as to allow gas to bleed between the two spaces in the housing 1 at the appropriate rate. Too fast and the valve does not have time to return to the closed position, too slow and the valve will not be ready to fire again fast enough.

The arrangement in accordance with the invention has significant advantages over the conventional hammer actuated valve currently used in pneumatic airguns. The valve mechanism takes up significantly less space than a hammer mechanism and is less mechanically noisy in operation. The mass of the valve member is relatively low and thus the system can operate very rapidly with a fast lock time. The force acting on the latch mechanism need only be sufficient to enable rapid movement of the valve member against the frictional forces acting thereon and thus the airgun may have a relatively light trigger pressure with a simple latch mechanism. The power characteristics of the valve for any given pressure of the gas supply are inherent in its dimensional design and thus the only effective variable for any given gun is the pressure of the gas supply. This can be set by means of a regulator that is not easily tampered with. The manufacturer is thus able to determine the maximum power of the airgun prior to sale.

Claims (10)

1. Claims 1. A discharge valve system wherein a valve member guided for translatory motion is arranged to be retained by latching means in a closed position wherein the valve seals an opening in a passage communicating between a reservoir charged with gas at an elevated pressure and a discharge port, the arrangement being such that, in use, the valve member is biased towards an open position by the pressure of gas in said charged reservoir whereby upon release of said latching means the valve member is caused to move to an open position in which gas can pass from said charged reservoir to said discharge port characterised in that the arrangement is further such that, in use, the said valve member is coupled to a further reservoir containing gas at an elevated pressure, in such a manner that, when the valve member is moved to the open position the pressure of gas in said further reservoir acts upon the valve member to provide a restoring force returning thc valve member to the closed position upon a reduction of the pressure of gas in said charged reservoir.
2. 2. A system as claimed in claim 1, in which the said valve member comprises an elongate member one end of which extends into a passage communicating between a first gas reservoir and said discharge port and is exposed to gas within said first reservoir whereby the pressure in said first reservoir tends to bias the valve member along said passage in a first direction away from said first reservoir towards a position opening said discharge port, and the other end is coupled to a second gas reservoir in such a manner that gas pressure in said second reservoir biases the valve member in a second direction opposite to the first.
3. 3. A system as claimed in claim 2 in which the arrangement is such that, in use, both reservoirs contain gas at substantially the same pressure, and the said other end of the valve member is exposed to the pressure of gas within said second reservoir and is of smaller cross section than the said one end whereby the force due to gas pressure on said one end is greater than that due to gas pressure on the other.
4. 4. A system as claimed in claim 3, including a main source of gas incorporating a pressure regulator, the said second reservoir being coupled directly to an output of said regulator and the first reservoir being coupled to an output of said regulator via a manually actuatable valve.
5. 5. A system as claimed in claim 1, wherein said valve member is an elongate valve member that is rectilinearly slideable to and fro within a valve housing, one end of the valve member serving to open and close a discharge port of the valve housing and a stem portion of the valve member being received within a seal closing an opening in communication with the valve housing, the arrangement being such that in use when the valve housing is subjected to an elevated internal gas pressure the valve member is biased in a direction tending to cause opening of said discharge port, there being provided, between said one end and said stem portion of the said valve member, an intermediate baffle of greater cross sectional area than that of said stem portion, said intermediate baffle being slideably received in said valve housing and dividing the valve housing into two gas receiving spaces one of which communicates with said discharge port, the said baffle also being slideable relatively to said valve member and being biased in a direction away from said discharge port to a rest position in which an abutment formed on said valve member is spaced from said baffle to allow said valve member to open said discharge port before said abutment engages said baffle, said system further comprising means for charging both of the gas receiving spaces with gas from a source at an elevated pressure, whereby upon release of said latching means when an elevated gas pressure has been established in said spaces the valve member moves in a direction to open said discharge port and release gas from said one space until a restoring force due to the pressure of gas retained in the other space and applied via said baffle is effective to return the valve member into a closed position.
6. 6. A system according to claim 5 in which the means for charging said spaces with gas comprises an inlet coupled to said other space, and a gas bleed passage extending from said other space to said one space and bypassing said baffle.
7. 7. A system according to claim 6 in which the said gas bleed passage is formed by a clearance between the periphery of said valve member and said baffle.
8. 8. A system according to any one of claims 5 to 7 in which the said latching means comprises a pivoted sear for engaging a portion of said valve member, said sear being being movable out of engagement with said valve member by a trigger mechanism including a release member located in the path of movement of said valve member, the arrangement being such that opening movement of said valve member is effective to move said release member out of engagement with said sear and allow said sear to return into latching engagement with said valve member on completion of its closing movement.
9. 9. A system as claimed in any one of claims 5 to 8 in which the said means for charging the said spaces with gas is coupled to said source via a gas pressure regulator.
10. 10. An airgun including a discharge valve system according to any one of claims 1-9.