US20090145414A1

US20090145414A1 - Pneumatic launcher

Info

Publication number: US20090145414A1
Application number: US12/328,707
Authority: US
Inventors: Giles Russell; Andrew Peter Marshall; Caroline Nola Marshall; Cyril Charles Russell
Original assignee: SNOWTEK SYSTEMS Ltd
Current assignee: SNOWTEK SYSTEMS Ltd
Priority date: 2007-12-05
Filing date: 2008-12-04
Publication date: 2009-06-11
Also published as: CA2645848A1

Abstract

A pneumatic launcher includes a number of chambers for holding a compressed gas and a valve for releasing the compressed gas into a firing chamber to fire a projectile. The firing valve may include a number of surfaces on which pressure acts to slide a sliding valve body between an open position and a closed position. The launcher may include a recess for preventing pressure from acting on one of those surfaces when the valve is in the closed position. A part of the sliding valve body may interact with adjacent parts to form a closed region ahead of the sliding valve body, in order to cushion motion of the sliding valve body. The launcher may have a breech and a breech pin shaped to create a desired gas flow within the firing chamber during firing. The breech may include a breech pin seal which seals between two faces oriented transverse to the axis of the launcher. The launcher barrel may have a number of ribs for improved stability and accuracy.

Description

FIELD OF THE INVENTION

The invention relates to pneumatic launchers for launching projectiles, particularly but not exclusively to launchers for launching projectiles for triggering avalanches.

BACKGROUND TO THE INVENTION

In various circumstances it may be desirable to trigger an avalanche, usually to prevent the build up of material which could form an uncontrolled avalanche at a later time.
Various methods of triggering avalanches have been used. Explosive charges can be placed by hand, although this requires a worker to travel close to the avalanche zone, which is both time consuming and potentially dangerous. Therefore various methods of triggering avalanches from a distance have been developed. Explosive charges can be fired from a distance, for example using some form of launcher such as a Howitzer.
Such launchers include the “Avalauncher”, which delivers a projectile using compressed gas. However, known pneumatic launchers perform poorly in a number of areas. The launchers are generally inaccurate, which leads to poor control of avalanche triggering. The launchers include valves which are prone to wear and are relatively difficult to replace.
It is an object of the invention to provide an improved pneumatic launcher, or at least to provide the public with a useful choice.

SUMMARY OF THE INVENTION

In a first aspect the invention provides a pneumatic launcher having:
a firing chamber configured to hold a projectile to be fired, a wall of the firing chamber having one or more apertures therein forming a flow path;
a gas chamber for holding gas under pressure, the gas chamber communicating via the flow path with the firing chamber; and
a firing valve having an open position and a closed position, and being configured to block the flow path in the closed position and, in the open position, to allow gas under pressure to flow from the gas chamber via the flow path into the firing chamber, the firing valve including: a sliding valve body having one or more operating surfaces angled with respect to a movement direction of the sliding valve body, such that pressure acting on the operating surfaces forces the valve body to slide; and
a recess configured to receive, when the firing valve is in the closed position, a part of the sliding valve body including at least a first operating surface such that pressure in a region outside the recess is prevented from acting on the first operating surface.
In a second aspect the invention provides a pneumatic launcher having:
a firing chamber configured to hold a projectile to be fired, a wall of the firing chamber having one or more apertures therein forming a flow path;
a valve chamber between the firing chamber wall and an outer valve chamber wall, the valve chamber communicating via the flow path with the firing chamber;
a gas chamber for holding gas under pressure and communicating with the valve chamber; and
a firing valve positioned within the valve chamber, the firing valve having an open position and a closed position, and being configured to block the flow path in the closed position and, in the open position, to allow gas under pressure to flow from the valve chamber via the flow path into the firing chamber, the firing valve including: a sliding valve body having: an inner surface which engages with an outer surface of the firing chamber wall to close the flow path when the firing valve is in a closed position; one or more operating surfaces angled with respect to a movement direction of the sliding valve body, such that pressure acting on the operating surfaces forces the valve body to slide; and a protrusion extending outwards; and a valve wall positioned to the outside of the valve body and engaging with the protrusion, such that a pressure difference can be maintained between the regions on each side of the protrusion.
In a third aspect the invention provides a pneumatic launcher having:
a firing chamber configured to hold a projectile to be fired, a wall of the firing chamber having one or more apertures therein forming a flow path;
a gas chamber for holding gas under pressure, the gas chamber communicating via the flow path with the firing chamber; and
a firing valve having an open position and a closed position, and being configured to block the flow path in the closed position and, in the open position, to allow gas under pressure to flow from the gas chamber via the flow path into the firing chamber, the firing valve including: a sliding valve body having a range of movement and cooperating with a part of the launcher to form a substantially closed region ahead of the moving sliding valve body near an extremity of the range of movement, thereby cushioning the motion of the sliding valve body.
In a fourth aspect the invention provides a pneumatic launcher having:
a firing chamber configured to hold a projectile to be fired, a wall of the firing chamber having one or more apertures therein forming a flow path;
a gas chamber for holding gas under pressure, the gas chamber communicating via the flow path with the firing chamber;
a firing valve having an open position and a closed position, and being configured to block the flow path in the closed position and, in the open position, to allow gas under pressure to flow from the gas chamber via the flow path into the firing chamber; and
wherein the firing valve is held in place by a fastening mechanism at one end of the valve and can be removed from the pneumatic launcher by releasing the fastening mechanism and sliding the firing valve from the launcher.
In a fifth aspect the invention provides a pneumatic launcher having:
a breech; and
a breech plug configured to be inserted to close the breech during firing and to be removed from the breech to allow a projectile to be loaded into the launcher;
wherein the breech plug extends into a firing chamber of the launcher and is shaped so as to produce a desired gas flow profile during firing, or is adapted to support an insert shaped so as to produce a desired gas flow profile during firing.
In a sixth aspect the invention provides a pneumatic launcher having:
a breech;
a breech plug configured to be inserted to close the breech during firing and to be removed from the breech to allow a projectile to be loaded into the launcher; and
a breech seal configured to seal between the breech and the breech plug, when inserted;
wherein the breech seal seals between a first face on the breech and a second face on the breech plug, the first and second faces being substantially transverse to an insertion direction of the breech plug.
In a seventh aspect the invention provides a pneumatic launcher configured to project a projectile using gas pressure and having a barrel with one or more longitudinal ribs.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a pneumatic launcher;

FIG. 2 is a cut away view of a valve section in a pneumatic launcher, showing the valve in an intermediate position;

FIG. 3 is a cut away view similar to FIG. 2, showing the valve in a closed position;

FIG. 4 is a cut away view similar to FIG. 2, showing the valve in an open position;

FIG. 5 is a cut away perspective view of the sliding valve body of the valve section in FIG. 2;

FIG. 6 is a cut away perspective view of the valve wall of the valve section in FIG. 2;

FIG. 7 is a cut away view of a pneumatic launcher breech assembly;

FIG. 8 is a perspective view of the breech assembly of FIG. 7;

FIG. 9 is a perspective view of one embodiment of a breech plug;

FIG. 10 shows the breech plug of FIG. 9, carrying a replaceable insert;

FIG. 11 is an enlarged view showing the breech plug seal;

FIG. 12 is a cut away perspective view showing the valve section and breech assembly;

FIG. 13 is a cross-section of the pneumatic launcher barrel; and

FIG. 14 is a schematic diagram showing external valves and conduits used to operate the launcher.

DETAILED DESCRIPTION

FIG. 1 shows a pneumatic launcher 1. The pneumatic launcher 1 may include a base 2 which allows adjustment of the direction and elevation of the launcher 1. Adjustment of the direction may be achieved, for example, using a turntable 3 driven by a handle 4 via a suitable gear mechanism 5. Adjustment of the elevation may be achieved, for example, using a hydraulic ram 6. The base 2 includes a number of supports 7, which support the main part of the pneumatic launcher 1. Thus, the base 2 functions to support and direct the launcher 1. Many different types of base or support may be used, or indeed the launcher may be used without a base or support.
The pneumatic launcher 1 includes a number of gas chambers 10, 11, 12 for holding a compressed gas before the launcher is fired. These chambers may be formed in any suitable manner, so long as they are capable of withstanding the required pressures. Before firing, the chambers receive compressed gas from an external source and hold the compressed gas until firing.
The chambers 10, 11, 12 communicate via conduits 13, 14, 15 with a valve section 16, which is described in detail below. The valve section 16 in turn communicates with a barrel 17. The back of the valve section 16 receives a breech assembly 18, which again is described in detail below.
In use, a projectile is loaded into a firing chamber in the valve section 16, through the breech assembly 18. The breech is then closed. The valve contained in the valve section 16 is operated to release compressed gas from the chambers 10, 11, 12 into the firing chamber, forcing the projectile from the firing chamber through the barrel 17.
FIG. 2 is a cutaway view of the valve section 16. The valve section 16 is of generally cylindrical construction. The valve section 16 includes a barrel end 20 and a breech end 21. The breech end 20 is configured to receive the barrel 17 (see FIG. 1), while the breech end 21 receives the breech assembly 18 (see FIG. 1).
The valve section 16 includes a number of apertures 23, 24 which communicate with the conduits 13, 15 shown in FIG. 1. A further aperture which communicates with the conduit 14 of FIG. 1 is also provided but is not shown in FIG. 2. The valve section 16 also includes a valve chamber 25 communicating with the apertures 23, 24 formed in an outer wall of the valve chamber. The valve chamber 25 also communicates via apertures 26, 27 with a firing chamber 28. The firing chamber 28 holds a projectile before firing and, in the assembled pneumatic launcher, communicates with the barrel 17.
Thus, a flow path is established from the chambers 10, 11, 12 through conduits 13, 14, 15 and apertures 23, 24 to the valve chamber 25. The flow path extends from the valve chamber 25 via apertures 26, 27 to the firing chamber 28.
A firing valve operates to open and close this flow path and may be situated within the valve chamber. In a closed position, the firing valve obstructs the apertures 26, 27, such that compressed gas cannot flow from the valve chamber 25 into the firing chamber 28.
The firing valve may be formed as follows. A sliding valve body 30 may be arranged with its inner surface 31 against the outer surface of the wall 32 of the firing chamber 28. The sliding valve body 30 slides along the length of the valve section 16 between a closed position (shown in FIG. 3) and an open position (shown in FIG. 4).
In the closed position (see FIG. 3) the sliding valve body 30 obstructs the apertures 26, 27, preventing flow of compressed gas from the valve chamber 25 to the firing chamber 28. In the open position (see FIG. 4), the sliding valve body is positioned out of the way, such that compressed gas can flow freely from the valve chamber 25 to the firing chamber 28.
The sliding valve body 30 may be shaped to include a number of operating surfaces 33, 34, 35, 36, 37. Each operating surface is oriented at an angle to the direction of motion of the sliding valve body 30 (i.e. each operating surface is non-parallel to the direction of motion). Therefore pressure acting on each operating surface 33-37 creates a force tending to cause sliding motion of the sliding valve body 30. Motion of the sliding valve body 30 may be controlled entirely by the action of gas pressure on these operating surfaces 33-37, as described below.
The firing valve also includes a valve wall 40, which may be positioned to the outside of the sliding valve body 30. The sliding valve body 30 includes a protrusion 41, an outside surface of which engages with an inside surface of the valve wall 40. This means that a pressure difference can be maintained between a region 42 on a first side of the protrusion 41 (where pressure acts on the operating surface 33) and a trigger chamber 43 on a second side of the protrusion 41 (where pressure acts on the operating surface 34). The chamber 43 communicates with the outside of the valve section 16 via a flow path 44.
FIG. 5 is a perspective cut away view of the sliding valve body 30, while FIG. 6 is a similar view of the valve wall 40. Note that the L-shaped end section 45 of the valve wall 40 consists of a number of protrusions 46 as shown in FIG. 6, rather than the continuous wall which could be incorrectly inferred from FIGS. 2 to 4.
The operation of the firing valve over a complete firing cycle will now be described with reference to FIGS. 2 to 4.
The valve chamber 25 begins in an unpressurised state. Pressure is introduced via the flow path 44 into the trigger chamber 43, acting on the operating surfaces 34, 35 to force the sliding valve body 30 into the closed position.
The valve section 16 includes a recess 50, which is configured to receive part of the sliding valve body 30, when the firing valve is in the closed position. FIG. 3 shows a part 51 of the sliding valve body 30 situated within the recess 50. In the closed position, pressure in the valve chamber 25 does not act on a first operating surface 37, situated at an end of the sliding valve body. Preventing pressure from acting on this surface contributes to the stability of the closed position, since the pressure acting to force the sliding valve body 30 towards the open position is lessened.
With the firing valve in the closed position shown in FIG. 3, pressurised gas is introduced into the chambers 10, 11, 12 and therefore into the valve chamber 25. This pressurised gas may be drawn from the same source used to pressurise the trigger chamber 43. Even though the pressure in the valve chamber increases, acting on the operating surface 33, the combined area of the surfaces 34, 35, 36 is sufficient to create a force holding the sliding valve body 30 in the closed position.
When the chambers 10, 11, 12 and the valve chamber 25 have been sufficiently pressurised, and an operator wishes to fire the pneumatic launcher, the pressure in the chamber 43 is released (preferably suddenly) to the outside of the valve section 16 via the flow path 44. The pressure in the trigger chamber 43 is now much lower than the pressure acting to force the sliding valve body 30 towards the open position. The sliding valve body 30 therefore moves rapidly from the closed position to the open position, allowing compressed gas to flow from the valve chamber 25 and chambers 10, 11, 12 into the firing chamber 28 to fire a projectile.
The motion of the sliding valve body is rapid. This is beneficial for the firing of the pneumatic launcher 1, since it allows a rapid release of pressurised gas into the firing chamber 28. However, such rapid motion tends to damage the mechanism of the firing valve, resulting in a short lifetime of these components and/or a lack of reliability. Therefore, the valve section 16 is designed to cushion the motion of the sliding valve body 30 so as to reduce any damage caused to the valve components.
During firing, the sliding valve body 30 moves from the closed position of FIG. 3 through the intermediate position shown in FIG. 2 to the open position shown in FIG. 4. In the position of FIG. 4, the end 53 of the sliding valve body 30 enters a narrowed passage 54 and the passage 54 is dimensioned to cooperate with the end 53 of the sliding valve body 30. This creates a substantially closed region 55 ahead of the protrusion 41 of the advancing sliding valve body 30, near the end of its range of movement. This closed region 55 cushions or slows the motion of the sliding valve body 30, since the air within that region cannot escape, or cannot escape fast enough to allow the sliding valve body 30 to reach the end of its range of motion unchecked.
A similar effect may be used to cushion motion of the sliding valve body 30 from the open position to the closed position at the start of the firing cycle. For example, a similar closed region could be created using the recess 50. Alternatively, the pressure introduced through the flow path 44 could initially be fairly low, so that motion of the sliding valve body 30 into the closed position is relatively gentle.
The outer wall 57 of the valve chamber 25 is formed with an end plate 58 for mounting of the firing valve into the valve chamber. A fastening mechanism, which may be a top plate 59 is used to secure the valve wall 40 to the end plate 58. A number of fasteners, for example threaded screws, engage with cooperating apertures 60 in the top plate 59, valve wall 40 and end plate 58. The top plate may also be shaped to support the barrel in the assembled launcher.
Other fastening mechanisms may also be suitable. However, it is preferred that the fastening mechanism should be situated at one end of the valve section 16, such that when the fastening mechanism is removed the firing valve (including the sliding valve body 30 and the valve wall 40) can be removed by sliding it from the end of the valve section 16.
The valve section 16 also includes a bottom plate 62 situated at the breech end 21 and configured to receive a breech assembly as described below.
Finally, the valve section 16 includes a number of seals positioned to prevent the undesired flow of gas within the valve section. FIGS. 2 to 4 show the grooves provided to receive the seals, which may be o-rings formed from rubber, composite material or any other suitable material.
Thus, referring to FIG. 4, a groove 63 is provided in the outer surface of the projection 41. The seal contained in this groove restricts gas flow between the first side 42 and the second side 43 of the projection 41. A seal 64 is provided between the outer surface of the firing chamber wall 32 and the inner surface of the sliding valve body 30.
A further seal 65 is provided near the end 51 of the sliding valve body 30, in order to seal within the recess 50, preventing pressure in the valve chamber 25 from acting on the first operating surface 37. This seal is carried on the sliding valve body, for ease of replacement. However, a similar seal could be provided in or near the recess 50. Two or more seals could be used to perform this function.
The above seals are all seals provided between moving components.
Furthermore, seals are provided between fixed components where those components lie against each other in the assembled valve section 16. These include a seal 67 between the outer wall 57 of the valve chamber and the bottom plate 62; and seals 68, 69, 70 at the joins between the outer wall 57 of the valve chamber, valve wall 40 and top plate 59.
FIG. 7 shows the breech assembly 18 mounted to the bottom plate 62. The breech assembly 18 includes a backplate 75 which is secured to the bottom plate 62 by a number of fasteners. In the embodiment shown, the backplate 75 and bottom plate 62 include a number of apertures 76 for receiving threaded screws.
The breech assembly 18 also includes a locking ring 77 which rotates about the axis of the breech assembly 18. A locking handle 78 is mounted to the locking ring 77 to enable a user to operate the locking ring.
Finally, the breech assembly 18 includes a breech plug 79, which can be removably inserted and locked into the breech by the locking ring 77. The breech plug can be removed for loading of a projectile into the firing chamber and then inserted to close the breech during firing.
FIG. 8 is a perspective view of the breech assembly 18 mounted to the bottom plate 62. This view shows the cooperating shapes of the breech plug 79 and backplate 75. In use, the breech plug 79 can be inserted such that the lugs 80 situated on shoulders 81 pass through the cooperating aperture 82 in the backplate 75. The inner surface (not shown) of the locking ring 77 is shaped to allow the lugs 80 to pass beyond the locking ring 77 when the locking ring is in an open position. The locking ring can then be rotated to a locked position, in which the inner surface of the locking ring 77 engages with the lugs 80, locking the breech plug in place.
The breech plug 79 includes a protrusion 85 which sits within the firing chamber 28, in order to position a projectile for firing. The breech plug 79 may also be shaped appropriately, so as to achieve desired flow characteristics within the firing chamber 28. This may be achieved either by shaping the breech plug 79, or by use of a shaped insert.
FIG. 9 is a perspective view of an alternative breech plug which includes a shaft 90 having a removable collar 91. FIG. 10 shows the breech plug of FIG. 9, with a removable, shaped insert 92 arranged on the shaft 90 and held in place by the collar 91 and fastener 93.
The shape of the breech plug 79, or the shape of the removable insert 92 can be adapted for any desired purpose, such as altering the range of the pneumatic launcher, or adapting the pneumatic launcher for different types of projectiles.
Furthermore, the breech plug operates to close or seal the breech during firing. For this purpose, a seal 95 may be provided, preferably between the breech plug and the bottom plate 62. Preferably, the seal 95 is situated between two surfaces which lie against each other in a plane substantially transverse to the axis of the breech assembly 18 (where the axis of the breech assembly lies along an insertion direction of the breech plug). This orientation of the seal 95 provides improved performance over prior systems, in which a seal has been provided between circumferential faces. The seal 95 may be formed from rubber, composite or any other suitable material.
FIG. 11 is an enlarged view of the breech plug 79 and bottom plate 62 (in which the backplate 75 and locking ring 77 are not shown). This view clearly shows the position of the seal 95.
FIG. 12 is a cutaway perspective view of the valve section 16, with the breech plug 79 in place. Again, the backplate 75 and locking ring 77 are not shown in this view.
FIG. 13 is a cross-section of the barrel 17. The barrel 17 includes a generally cylindrical bore 100, through which the projectile is fired. However, the barrel also includes a number of ribs 101, which provide greater rigidity to the barrel 17 without requiring a great deal of additional weight. The ribs may be external ribs. This improved rigidity provides significantly increased accuracy.
FIG. 14 is a schematic diagram showing the various external valves and conduits used to operate the launcher. Pressurised gas, preferably dry nitrogen, is held in a tank 105. This tank is connected by a conduit 106 with a three-way valve 107. In one position this valve 107 operates to feed pressurised gas into the trigger chamber 43 in the valve section 16 through conduit 108 in order to close the firing valve. In a second position this valve 107 operates to feed gas through conduit 109 into the three gas chambers 10, 11, 12 to pressurise those chambers. A one-way check valve 110 allows gas to flow from the conduit 109 into the conduit 108 but does not allow gas to flow in the opposite direction.
The chamber 43 is also connected via conduit 112 with a safety valve 113 and a trigger valve 114. The safety valve is to be closed whenever the breech is open, and sensors and the like may be used to ensure that this is the case. When the breech is closed, the safety valve 113 may be opened and the launcher may be fired by opening the trigger valve 114 to release the pressure in the trigger chamber 43 to the atmosphere.
Finally, various sensors and safety devices may be provided. Pressure release or safety valves 115, 116 may be provided, and pressure gauges 118 may be connected as required.
The gas chambers may be pressurised for firing to a pressure in the range about 40 to 600 pounds per square inch (psi), preferably in the range 100 to 400 psi. the pressure chosen may depend on the desired range as well as the nature of the projectile to be fired.
The firing chamber wall, sliding valve body, valve wall and the outer wall of the valve chamber may all be of generally cylindrical construction. This provides for ease of manufacture and alignment of the parts. In the assembled launcher, these parts may be arranged substantially coaxially.
The outer valve chamber wall, bottom plate, top plate, valve wall, firing chamber wall, sliding valve body, breech assembly, breech plug and barrel may all be formed from steel or any other suitable material.
The pneumatic launcher 1 has been described in general terms. However, while the launcher is likely to have many and varied applications, it is expected to be particularly applicable to launchers used for triggering avalanches. Such launchers generally fire a projectile having an explosive charge which detonates on or near a slope to trigger an avalanche.
The design of the valve section 16 provides improved reliability and a longer lifetime for the various components. Furthermore, the valve section 16 is easily disassembled for removal or replacement of the firing valve.
While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the spirit or scope of the Applicant's general inventive concept.

Claims

1. A pneumatic launcher having:

i. a firing chamber configured to hold a projectile to be fired, a wall of the firing chamber having one or more apertures therein forming a flow path;

ii. a gas chamber for holding gas under pressure, the gas chamber communicating via the flow path with the firing chamber; and

iii. a firing valve having an open position and a closed position, and being configured to block the flow path in the closed position and, in the open position, to allow gas under pressure to flow from the gas chamber via the flow path into the firing chamber, the firing valve including:

a) a sliding valve body having one or more operating surfaces angled with respect to a movement direction of the sliding valve body, such that pressure acting on the operating surfaces tends to force the valve body to slide; and

iv. a recess configured to receive, when the firing valve is in the closed position, a part of the sliding valve body including at least a first operating surface such that pressure in a region outside the recess is prevented from acting on the first operating surface.

2. A pneumatic launcher as claimed in claim 1 wherein the first operating surface is situated at an end of the sliding valve body.

3. A pneumatic launcher as claimed in claim 1 including one or more seals arranged to seal the recess around the part of the sliding valve body, when the firing valve is in the closed position.

4. A pneumatic launcher as claimed in claim 3 wherein the one or more seals are positioned on the sliding valve body.

5. A pneumatic launcher as claimed in claim 1 wherein, when the firing valve is in the closed position, pressure acting on the operating surfaces except the first operating surface, maintains the firing valve in the closed position and wherein, on release of pressure from a trigger chamber, pressure acting on the operating surfaces causes the firing valve to open.

6. A pneumatic launcher as claimed in claim 1 further including a valve chamber between the firing chamber wall and an outer valve chamber wall, the valve chamber communicating via the flow path with the firing chamber and also communicating with the gas chamber, the firing valve being positioned within the valve chamber.

7. A pneumatic launcher as claimed in claim 6, wherein the sliding valve body includes:

a) an inner surface which engages with an outer surface of the firing chamber wall to close the flow path when the firing valve is in a closed position; and

b) a protrusion extending outwards;

and wherein the launcher includes a valve wall positioned to the outside of the valve body and engaging with the protrusion, such that a pressure difference can be maintained between the regions on each side of the protrusion.

8. A pneumatic launcher as claimed in claim 7 configured to enable a sudden reduction in pressure on one side of the protrusion, such that pressure acting on the operating surfaces on the other side of the protrusion moves the sliding valve member to the open position.

9. A pneumatic launcher as claimed in claim 1 wherein the sliding valve body has a range of movement and cooperates with a part of the launcher to form a substantially closed region ahead of the moving sliding valve body near an extremity of the range of movement, thereby cushioning the motion of the sliding valve body.

10. A pneumatic launcher as claimed in claim 1 wherein the firing valve is held in place by a fastening mechanism at one end of the valve and can be removed from the pneumatic launcher by releasing the fastening mechanism and sliding the firing valve from the launcher.

11. A pneumatic launcher as claimed in claim 10 wherein the fastening mechanism is a top plate which also supports a barrel.

12. A pneumatic launcher as claimed in claim 1 wherein the sliding valve body and the firing chamber wall are formed as substantially cylindrical coaxial elements.

13. A pneumatic launcher as claimed in claim 1 including a plurality of seals for sealing between the sliding valve body and adjacent elements to prevent undesired flow of gas.

14. A pneumatic launcher as claimed in claim 1, including:

i. a breech; and

ii. a breech plug configured to be inserted to close the breech during firing and to be removed from the breech to allow a projectile to be loaded into the launcher;

wherein the breech plug extends into the firing chamber of the launcher and is shaped so as to produce a desired gas flow profile during firing, or is adapted to support an insert shaped so as to produce a desired gas flow profile during firing.

15. A pneumatic launcher as claimed in claim 1, including:

i. a breech;

ii. a breech plug configured to be inserted to close the breech during firing and to be removed from the breech to allow a projectile to be loaded into the launcher; and

iii. a breech seal configured to seal between the breech and the breech plug, when inserted;

wherein the breech seal seals between a first face on the breech and a second face on the breech plug, the first and second faces being substantially transverse to an insertion direction of the breech plug.

16. A pneumatic launcher as claimed in claim 1, including:

i. a breech;

iii. a locking ring configured to rotate between a first position in which the breech plug can be removed or inserted into the breech and a second position in which the breech plug is locked into the breech for firing.

17. A pneumatic launcher as claimed in claim 1 having a barrel with one or more longitudinal ribs.

18. A pneumatic launcher as claimed in claim 1 configured to fire an avalanche-triggering projectile.

19. A pneumatic launcher having:

ii. a valve chamber between the firing chamber wall and an outer valve chamber wall, the valve chamber communicating via the flow path with the firing chamber;

iii. a gas chamber for holding gas under pressure and communicating with the valve chamber; and

iv. a firing valve positioned within the valve chamber, the firing valve having an open position and a closed position, and being configured to block the flow path in the closed position and, in the open position, to allow gas under pressure to flow from the valve chamber via the flow path into the firing chamber, the firing valve including:

c) a sliding valve body having:

i. an inner surface which engages with an outer surface of the firing chamber wall to close the flow path when the firing valve is in a closed position;

ii. one or more operating surfaces angled with respect to a movement direction of the sliding valve body, such that pressure acting on the operating surfaces tends to force the valve body to slide; and

iii. a protrusion extending outwards;

d) a valve wall positioned to the outside of the valve body and engaging with the protrusion, such that a pressure difference can be maintained between the regions on each side of the protrusion.

20. A pneumatic launcher as claimed in claim 19 configured to enable a sudden reduction in pressure on one side of the protrusion, such that pressure acting on the operating surfaces on the other side of the protrusion moves the sliding valve member to the open position.

21. A pneumatic launcher as claimed in claim 19 wherein the sliding valve body has a range of movement and cooperates with a part of the launcher to form a substantially closed region ahead of the moving sliding valve body near an extremity of the range of movement, thereby cushioning the motion of the sliding valve body.

22. A pneumatic launcher as claimed in claim 19 wherein the firing valve is held in place by a fastening mechanism at one end of the valve and can be removed from the pneumatic launcher by releasing the fastening mechanism and sliding the firing valve from the launcher.

23. A pneumatic launcher as claimed in claim 19 wherein the sliding valve body, the valve wall and the firing chamber wall are formed as substantially cylindrical coaxial elements.

24. A pneumatic launcher as claimed in claim 19, including:

v. a breech; and

vi. a breech plug configured to be inserted to close the breech during firing and to be removed from the breech to allow a projectile to be loaded into the launcher;

25. A pneumatic launcher as claimed in claim 19, including:

v. a breech;

vi. a breech plug configured to be inserted to close the breech during firing and to be removed from the breech to allow a projectile to be loaded into the launcher; and

vii. a breech seal configured to seal between the breech and the breech plug, when inserted;

26. A pneumatic launcher as claimed in claim 19, including:

V. a breech;

vii. a locking ring configured to rotate between a first position in which the breech plug can be removed or inserted into the breech and a second position in which the breech plug is locked into the breech for firing.

27. A pneumatic launcher as claimed in claim 19 having a barrel with one or more longitudinal ribs.

28. A pneumatic launcher as claimed in claim 19 configured to fire an avalanche-triggering projectile.

29. A pneumatic launcher having:

a) a sliding valve body having a range of movement and cooperating with a part of the launcher to form a substantially closed region ahead of the moving sliding valve body near an extremity of the range of movement, thereby cushioning the motion of the sliding valve body.

30. A pneumatic launcher as claimed in claim 29 wherein the sliding valve body has one or more operating surfaces angled with respect to a movement direction of the sliding valve body, such that pressure acting on the operating surfaces tends to force the valve body to slide; and wherein the launcher includes a recess configured to receive, when the firing valve is in the closed position, a part of the sliding valve body including at least a first operating surface such that pressure in a region outside the recess is prevented from acting on the first operating surface.

31. A pneumatic launcher as claimed in claim 30 wherein, when the firing valve is in the closed position, pressure acting on the operating surfaces except the first operating surface, maintains the firing valve in the closed position and wherein, on release of pressure from a trigger chamber, pressure acting on the operating surfaces causes the firing valve to open.

32. A pneumatic launcher as claimed in claim 29 wherein the sliding valve body and the firing chamber wall are formed as substantially cylindrical coaxial elements.

33. A pneumatic launcher as claimed in claim 29 configured to fire an avalanche-triggering projectile.

34. A pneumatic launcher having:

ii. a gas chamber for holding gas under pressure, the gas chamber communicating via the flow path with the firing chamber;

iii. a firing valve having an open position and a closed position, and being configured to block the flow path in the closed position and, in the open position, to allow gas under pressure to flow from the gas chamber via the flow path into the firing chamber; and

wherein the firing valve is held in place by a fastening mechanism at one end of the valve and can be removed from the pneumatic launcher by releasing the fastening mechanism and sliding the firing valve from the launcher.

35. A pneumatic launcher having:

i. a breech; and

wherein the breech plug extends into a firing chamber of the launcher and is shaped so as to produce a desired gas flow profile during firing, or is adapted to support an insert shaped so as to produce a desired gas flow profile during firing.

36. A pneumatic launcher having:

i. a breech;

37. A pneumatic launcher configured to project a projectile using gas pressure and having a barrel with one or more longitudinal ribs.

38. A pneumatic launcher as claimed in claim 37 wherein the ribs include one or more external ribs.