GB2520038A

GB2520038A - Mechanism for rapid discharge of compressed gas

Info

Publication number: GB2520038A
Application number: GB1319653.0A
Authority: GB
Inventors: Roy Jones
Original assignee: ECS Special Projects Ltd
Current assignee: ECS Special Projects Ltd
Priority date: 2013-11-07
Filing date: 2013-11-07
Publication date: 2015-05-13
Anticipated expiration: 2033-11-07
Also published as: GB201319653D0; GB2520038B

Abstract

A discharge mechanism for pressurised gas comprising a piston 11 slidably mounted in a housing 10. The housing defines a first chamber 14 for the gas to be discharged and the piston 11 is able to slide along an axis within the housing 10 between charging and discharged positions. In the charging position, pressurised gas in the first chamber 14 exerts no force on the piston 11 in the axial direction. The housing may defines a second chamber 19 configured such that pressurised fluid in the second chamber 19 may exert a force on the piston 11 to move it towards the discharged position. The first chamber 14 may be located outside the volume of the piston 11. Pressurised fluid in the second chamber 19 may exert a force on the piston 11 in an opposite direction to the discharge of gas pressurised by the first chamber 14. There may be seals 15, 16, 20 sealing the first 14 and second 19 chambers; a seal in the first chamber 14 in the forward direction may also seal the second chamber 19 in the rearward direction. This mechanism may be used in a gun, cannon or launcher.

Description

Mechanism for Raiid Discharge of Comrressed Gas The present invention relates to a mechanism for the rapid discharge of compressed gas.

Such mechanisms are used for tiring tethered or untethered projectiles for example. The mechanism is suitable for many applications including rescue and recovery at sea or from buildings and any other situations where it is desired to fire a projectile instantaneously. The mechanism of the invention also has broader applications and can simply be used to rapidly discharge a compressed gas such as air, e.g. for an air cannon, or some other gas.

Many mechanisms for the rapid discharge of compressed gas have been proposed. A large number of these comprise a control chamber containing air or other gas under pressure to balance the holding of the main pressure that is to be discharged. This pressure is then released in order to fire the mechanism and release the compressed gas. A disadvantage of such mechanisms is that they are susceptible to unscheduled activation due to leakage of this balancing pressure.

In one example mechanism according to the invention, to be described in more detail below, high pressure gas to be discharged is held around a piston such that a small amount of force acting on the piston is sufficient to cause the piston to move so as to enable the high pressure fluid to escape from around the piston. The pressure on the piston could be achieved through the use of fluid, i.e. liquid or gas, as described in more detail below. With the high pressure gas being held around the piston it can be arranged that the high pressure gas does not exert any force on the piston in its direction of travel. Indeed in the preferred embodiment there is no pressure on the piston from any source. It is preferred but not essential for the high pressure gas to surround the piston in order to achieve this. With this configuration no biasing elements such as springs are needed in order for example to resist pressure on the piston from fluid to be discharged. Also, only a small force is needed to move the piston in order to enable the discharge of the high pressure gas.

The high pressure gas could be in liquid form and therefore references in the following to pressurised gas include liquid gas, i.e. a liquid that will change state to become gas under the prevailing ambient conditions.

Thus in one aspect there is provided in the following a discharge mechanism for pressurised gas. The mechanism comprises a piston slidably mounted in a housing. The housing defines a first chamber for the gas to be discharged, also called the high pressure chamber. The piston is slidable along an axis within the housing between charging and discharged positions to effect the discharge of gas from the first (high pressure) chamber. The piston and chamber are so arranged that in the charging position pressurised gas in the first chamber exerts no force on the piston in the axial diiection. Indeed in the preferred embodiment of the invention in the charging position there is no force on the piston in the charging direction from the pressurised gas or anything else.

Such a mechanism is less susceptible to unscheduled activation since no air or other gas that might leak is required to hold the piston in place.

In the preferred embodiment of the invention one or more stops are provided to retain the piston in the charging position and prevent accidental firing of the mechanism. The purpose of such stops is not to resist any torce but simply to prevent the piston from sliding along its axis.

The first chamber may be provided with a gas inlet, preferably having a non-return valve, to permit the first chamber to be charged with high pressure gas.

It will be noted that the mechanism does not rely on decompression to discharge the gas as is required in some existing mechanisms in which a pressurised volume is relieved in order to achieve the discharge.

Preferably the movement of the piston towards the discharge position is in a direction opposite to a firing direction or discharge direction.

In a preferred embodiment of the invention the first chamber is located outside a volume in which the piston travels. The first chamber may extend parallel to the direction of travel of the piston. As noted above the first chamber preferably comprises an annular volume in which the piston is held.

The piston may form at least one wall of the high pressure chamber. In the case that the high pressure chamber is an annular space the piston may form the interior cylindrical wall of the annular space. Either way, one way to ensure that the gas does not exert a force to cause the piston to travel is to arrange that within the first chamber the piston has only surfaces which are parallel to the sliding direction or axis. In other words preferably there are no transverse surfaces of the piston within the high pressure chamber in the charged position.

In one possible configuration in the charging position the piston protrudes forwardly and rearwardly from the high pressure chamber.

In the following expressions such as "forward" and "rear" and "in front" and "behind" refer to the discharge direction, i.e. "forward" is downstream in the discharge direction.

In the specific embodiment described below, the housing further defines a second chamber, also called the low pressure chamber. The second chamber is configured such that fluid in the second chamber exerts a force on the piston to move the piston towards the discharged position. Given the very low pressure that is required to move the piston, the second chamber could be supplied with gas at low pressure or a liquid.

The second chamber may be provided with an inlet permitting lower pressure gas or liquid to t5 enter the second chamber and thereby cause the discharge of the high pressure gas.

The second or low pressure chamber is preferably in front of the piston. With this arrangement it can be ensured that pressurised gas in the second chamber exerts a force on a forward face of the piston.

The second chamber is preferably located in front of the first chamber. The second chamber may comprise an annular volume surrounding a part of the piston. The piston may form at least one wall of the second chamber. This may be a shoulder formed in the outer surface of the piston, preferably an annular shoulder. The second chamber may be defined between respective surfaces of the piston and the housing.

In the preferred configuration, the components of the mechanism are so arranged that pressurised gas escapes from the first chamber into the second chamber to cause an increase in pressure in the second chamber which accelerates the piston to the discharged position. Ideally there are no intervening volumes between the first and second chambers, i.e. they are in direct communication.

The mechanism preferably comprises seals sealing either or both of the first and second chambers. In a preferred embodiment, a seal which seals the first chamber in the forward direction also seals the second chamber in the rearward direction. Thus, when this seal is breached gas is able to escape directly from the first chamber to the second chamber.

With the use of seals to contain gas in the first chamber, if the gas were to leak past the seals the mechanism would vent without firing and therefore not present a safety risk.

As noted above the first chamber is preferably defined between an annular recess formed in the wall of the cylinder and the cylindrical surface of the piston. Preferably there are no protrusions on the piston surface within the high pressure chamber.

The second chamber is preferably defined between respective surfaces on the piston and cylinder, for example cylindrical surfaces on the piston and cylinder and annular surfaces formed on the piston and cylinder respectively. The annular surfaces are defined by respective shoulders formed on each of the cylinder and the piston.

The second chamber may be defined between a forward portion of the piston and the t5 cylinder. The first chamber may be defined between a rearward portion of the piston and the cylinder. The second chamber may include a forward facing surface of the piston.

In a preferred mechanism the piston has a wide rear section which serves to close the annular volume which is the high pressure chamber and a narrower front section. The narrower front section may partially define the second chamber. When the piston moves in the direction opposite to the firing direction the narrower front section enters the high pressure chamber. This causes the venting of the high pressure chamber to the low pressure chamber to exert further force on the piston to drive the piston to fully open the second chamber to atmosphere thereby ensuring a rapid discharge of the gas.

In the foregoing and the following "pressurised" should be understood to mean above-ambient pressure. Examples of high and low pressures that may be used are given in the

following detailed description.

It will be appreciated from the foregoing that the mechanism is constructed such that the pressure required to move the piston to the discharge position is lower than the pressure of the gas to be discharged.

It will be appreciated from the foregoing and what follows that the mechanism is in the form of apparatus and therefore mechanism may be interpreted as "apparatus". The term "mechanism" is used since it will usually be supplied to form part of other apparatus such as an air gun or cannon for example. More generally the apparatus may be used in launchers of many kinds.

The invention therefore also provides apparatus comprising the mechanism.

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a part sectional view of a discharge mechanism according to the invention in the charging position with a cock lever in the de-cocked position; Figure 2 is a sectional view corresponding to figure 1 with the mechanism in the charging position showing the cock lever in the cocked position; and t5 Figure 3 is a sectional view corresponding to figure 1 showing the position of the components in the discharged position.

The illustrated discharge mechanism comprises a pressure housing 10 in which a piston 11 is slidably retained so as to be able to travel in an axial direction between a charging or loading position and a discharged position. Pressure housing 10 defines an interior space which is preferably in the form of a cylinder having portions or sections of different diameter along its length. The functions of the pressure housing portion will be explained below.

Pressure housing 10 may have a cylindrical outer surface and be generally in the form of a cylinder. Piston 11 is likewise preferably cylindrical in cross section with different diameter portions along its length. The pressure housing 10 and piston 11 preferably have a common cylinder axis, not shown, which defines the firing direction of the mechanism. Other cooperating cross sectional shapes of piston 11 and pressure housing 10 are possible.

For the sake of clarity the sections of the piston are labelled on figure 1 only and the sections of the pressure housing are labelled on Figure 2 only.

Referring to figure 1, the illustrated mechanism the piston comprises, from the rear: a shaft ha extending to the outside of the pressure housing 10, a rear face 11 b surrounding the shaft 11 a, preferably oriented perpendicular to the direction of travel of the piston and preferably annular in shape, a maximum diameter portion llc, a forward portion lid having a diameter less than the diameter of portion lib; and a circular front face lie, preferably oriented perpendicular to the direction of travel of the piston. As illustrated the edges of the front face lie are slightly rounded to the rear.

The diameter of forward portion 1 ic is preferably larger than the diameter of the shaft ii a.

Referring to figure 2, the pressure housing comprises, from the rear: a first cylindrical portion ending at annular shoulder lOa shaped to receive a closure 12, first piston-guiding portion lOb having a diameter dimensioned to receive maximum diameter portion lic of piston 11, maximum diameter portion bc having a diameter larger than the maximum diameter portion of piston 11, second piston-guiding portion lOd having the same diameter as first piston guiding portion 1 Ob, tS third piston-guiding portion 1 Oe having a diameter to receive forward portion lid of piston 11, and front cylindrical portion lOf of wider diameter than portion iDe thereby forming an annular shoulder log to receive a cylindrical barrel 13. The barrel 13 is shown cut away.

Preferably the portions of the pressure housing 10 and the piston ii have concentric cross sections.

Pressure housing portion lOc defines with piston portion lic a first annular chamber 14 also referred to in the following as the high pressure chamber. This chamber is provided for receiving gas to be discharged, and is formed between opposing annular interior surfaces 14a and 14b and cylindrical interior surface 14c of pressure chamber 14, and outer cylindrical surface of piston maximum diameter portion lic. The piston guiding portions lOb, lOd, and be of the pressure housing 10 and the cooperating outer surfaces of the piston portions llc and lid are manufactured to close tolerances in order to minimise leakage of gas between their respective surfaces. Such leakage is further prevented by annular seals and 16. Seals 15 and i6 are positioned between the respective surfaces of the piston and the high pressure housing ii. In the charging position shown in figures 1 and 1 seal 16 is positioned at the front of the high pressure chamber 14 and seal 15 is positioned at the rear of the high pressure chamber 14.

In this illustrated embodiment of the invention the high pressure chamber 14 surrounds the piston 11. In other words the piston extends through the high pressure chamber. Preferably the piston protrudes from the front and rear of the high pressure chamber 14 in the charging position shown in figuies 1 and 2. This is not essential. However in this embodiment of the invention it is preferred that the chamber 14 extends parallel to the piston. It will be understood that the piston 11 slides within a cylindrical volume defined within the pressure housing 11, termed the volume ot travel. It should be noted that the high pressure chamber 14 is outside the volume of travel of piston 11. All of the foregoing alternatives may be configuied such that high piessure gas in the piston exerts no axial force on the piston. Thus no biasing elements such as springs are needed in order for example to resist pressure on the piston from gas to be discharged.

In the illustrated preferred embodiment of the invention the piston has a constant diameter section that extends beyond the high pressure chamber in the forward and rear directions in the chaiging position of the mechanism. The charging position may also be ieferred to as the rest position.

An inlet port 17 is provided for the high pressure chamber 14. This is formed in pressure housing maximum diameter portion bc. Inlet permits high pressure chamber 14 to be filled with gas to be dischaiged. Inlet poit 17 is closed by a non-letuin valve 18. In the illustrated arrangement gas enters the high pressure chamber 14 in a direction transverse, preferably perpendicular, to the firing or discharge direction, i.e. the direction of travel of the piston 11 towards the dischaiged position. Thus the inlet is positioned such that gas enteis via a cylindrical interior surface of the high pressuie chamber.

A second annular chamber 19, also referred to in the following as the low pressure chamber, is foimed between the outer suiface of piston portion lid and the innel surface of piessure chamber piston guiding portion be. In contrast with chamber 14, chamber 19 is formed between outer annular and cylindrical surfaces of the piston 11 and annular and inner axial surfaces of the pressure chamber 10. Thus whereas the high pressure chamber 14 includes only surfaces of the piston 11 extending parallel to the axis or firing direction, the low piessure chambei 19 includes transveise surfaces of the piston. Thus, when the low pressure chamber is filled with fluid to a pressure above atmosphere, an axial pressure is applied to the piston via the annular surface which foims part of the chambei. This surface is forwaid facing.

As with the high pressuie chamber 19, the respective cylindrical surfaces of the piston forward portion lie and the piston guiding portion be are manufactured to close tolerances to minimise leakage. This is further prevented by seal 20 between the respective surfaces. It will be noted that seal 16 seives to seal the low pressure chambei 19 from the reai as well as serving to seal the high pressure chamber 14 from the front.

Low pressure chamber 19 is provided with an inlet 21 for fluid. This is formed in pressure housing section lOd. Fluid enters the low pressure chamber 19 in a direction transverse, pieferably perpendicular, to the direction of tiavel of the piston. Thus fluid enters the low pressure chamber 19 via a cylindrical interior surface of the high pressure chamber.

Closure 12 comprises a circular plate with a through hole through which shaft 1 la passes.

This seives as a ieai stop foi the tiavel of the piston as will be explained below.

A cock lever 25 with offset cam disc 26 is mounted at the rear of the pressure housing 10, by means not shown, so as to be pivotable with respect to housing 10. The lever is pivotable between a de-cocked position shown in figure 1 and a decocked position shown in figures 2 and 3. In the de-cocked position, the cam disc 26 abuts the shaft 11 a of piston 11 and limits the leftward, or rearward, travel of the piston as shown. The lever 25 may be rotated to the de-cocked position, in this example through a half turn, in which position the cam disc is rotated away from the shaft 11 a and shaft 11 a is permitted to travel towards the rear of pressure housing 10.

Bairel 13 is provided to channel the discharge of gas using the mechanism. It may be loaded with a projectile to be ejected, depending on the implementation of the mechanism. In some implementations of the mechanism the barrel 13 may not be required.

The operation of the mechanism will now be described.

In the charging or loading position shown in figure 1, the lever 25 is in the upward position such that the disc 26 holds the piston in place on the seals 15, 16 and 20. Pressurised gas, e.g. air, to be dischaiged is added to the high piessure chamber 14 via the high piessure inlet 17 from a cylinder or compressor. The gas is prevented from escaping by non-return valve 18.

To discharge the pressurised gas, the lever 25 is moved into the downward position shown in figure 2. Then pressurised fluid, e.g. air, at a lower pressure than the fluid to be discharged, is added through the low pressure inlet or firing port 21. This fluid may be comprise gas bled from the high pressure chamber via a reducer and valve, not shown, or may be added from any external source either adjacent or remotely. Initially the lower pressure fluid is contained in the low pressure chamber 19 which is at the front of the piston 11 and between the two seals 16 and 20. When sufficient pressurised fluid has been introduced to chamber 19, the pressure overcomes the friction caused by the seals 15, 16 and 20 and causes the piston 11 to begin to move to the right.

Figure 3 shows the piston having moved sufficiently for the gas in chamber 14 to escape past the seals 16 and 20 into the region in front of the piston. This causes a rapid equalisation of pressure moving the piston rapidly and fully to the right, and a rapid discharge of the gas via the barrel 13, if provided. Once the seal 16 to chamber 14 is released, the high pressure gas escapes to the region in front of the piston and exerts additional force on the piston in the rearward direction thereby speeding up the release of the high pressure gas in the forward direction. The high pressure gas contributes to the rapid movement of the piston.

Using this mechanism a projectile in barrel 13 can be ejected from the barrel with the full force of the high pressure gas. The proximity of the high and low pressure chambers ensures that the high pressure gas is rapidly discharged as soon as gas begins to escape from the high pressure chamber. In particular there are no intermediate chambers that might slow or otherwise hinder the equalisation of pressure between the high pressure chamber and the atmosphere.

The high pressure gas can be used to fire a variety of projectiles. It should be noted that these are not limited to solid objects and may include liquids such as water.

The closure 12 serves as a stop to limit the rearward travel of the piston 11.

The dual function of seal 16 in sealing both high and low pressure chambers 14 and 19 assists in the rapid discharge of gas from the high pressure chamber. Further seals may be provided in addition to seals 15, 16 and 20.

It will be appreciated that the low pressure only has to overcome the friction of the seals to move the piston since the piston is under no axial force from any other source. The piston does not need to be biased, for example by means of springs or a pressure chamber, against pressure from the gas in chamber 14.

The cam disc 26 simply defines the lest or loading position of the mechanism as well as ensuring that it cannot be knocked so as to accidentally discharge the gas, which is a real possibility given the small pressure that is required to do this. It is not resisting any pressure applied to the piston 11.

It will be appreciated that it is not essential for the first and second piston guiding portions lOb and 10d of the pressure housing to have the same diameter. For example it would be possible for the maximum diameter portion of the piston 11 to be replaced by one or more portions of different diameter. However a single portion of constant diameter is preferred for ease of construction and speed of operation.

It will be appreciated from the foregoing explanation that the mechanism described is able to achieve near-instantaneous release of the high pressure gas. Experiments have achieved satisfactory discharge of pressures up to 200 bar with application of only 1 bar low pressure.

It is expected that similar mechanisms could be used to discharge gases at pressures far in excess of this amount.

The mechanism has been tested to eject a tennis ball and has succeeded in sending this over a kilometre away. For this only 70 bar pressure was actually needed. The appropriate volume for the high pressure chamber 14 will depend on a number of factors including the diameter of the barrel, if present, and the nature of the projectile, if present. In the tennis ball experiment a 60mm diameter barrel was used and a high pressure chamber of approximately 180cm3.

A number of modifications to the mechanism described above are possible including the following: It is not essential for the pressure chamber to surround the piston as noted above. Where it is desired for the high pressure gas to be contained around the piston, the annular chamber 14 could be replaced by radial bores formed in the pressure housing 10.

Different sealing arrangements might be used. In particular the seal 20 could be omitted.

Since only a very small force is required to move the piston 11 towards the discharged position, it may not be critical to achieve a good seal in the chamber 19.

In fact the chamber 19 could be omitted altogether and instead of using fluid pressure to move the piston towards the discharge position, some other means could be provided. Any means for applying a mechanical force to the piston in the rearward direction could be used.

Thus an optional embodiment of the invention could comprise an actuator for applying a force to move the piston towards the discharged position. This force need not act on the front face of the piston and could act on the rear. For example the shaft 1 la could be pulled in the rearward direction to "tire" the mechanism. Indeed such means may not be required. With the cock lever released simply dropping the mechanism could cause the release of the high pressure gas.

Claims

Claims 1. A discharge mechanism for pressurised gas comprising a piston slidably mounted in a housing, the housing defining a first chamber for the gas to be discharged, the piston being slidable along an axis within the housing between charging and discharged positions to effect the discharge of gas from the first chamber, the piston and chamber being arranged such that in the charging position pressurised gas in the first chamber exerts no force on the piston in the axial direction.
2. A discharge mechanism as claimed in claim 1 in which the first chamber is located outside the volume of travel of the piston.
3. A discharge mechanism as claimed in claim 1 in which the piston forms at least one wall of the first chamber.
4. A discharge mechanism as claimed in claim 1, 2 or 3, in which the first chamber comprises an annular volume which encircles the piston in the charged position.
5. A discharge mechanism as claimed in claim 4 in which the piston comprises a rear section which serves to close the annular volume of the first chamber and a forward section of lower diameter than the first section.
6. A discharge mechanism as claimed in any preceding claim arranged such that the first chamber is in immediate contact with atmospheric pressure in the discharge position.
7. A mechanism as claimed in any preceding claim in which, within the first chamber, the piston has only surfaces which are parallel to the axis.
8. A discharge mechanism as claimed in any preceding claim wherein the housing further defines a second chamber configured such that pressurised fluid in the second chamber exerts a force on the piston to move the piston towards the discharged position.
9. A discharge mechanism as claimed in claim 8 in which the second chamber is located in front of the first chamber.
10. A discharge mechanism as claimed in claim 8 or claim 9 in which pressurised fluid in the second chamber exerts a force on the piston in a direction opposite to the direction of discharge of gas under pressure from the first chamber.
11. A discharge mechanism as claimed in claim 8, 9 or 10, in which the second chamber is in front of the piston in the discharge direction.
12. A discharge mechanism as claimed in any of claims 8 to 11 in which the second chamber comprises an annular volume surrounding a part of the piston.
13. A discharge mechanism as claimed in claim in any of claims 8 to 12 in which the piston forms at least one wall of the second chamber.
14. A discharge mechanism as claimed in claim 13 in which the at least one wall is a shoulder formed in the outer surface of the piston.
15. A discharge mechanism as claimed in any preceding claim in which the first chamber opens into the second chamber in the discharged position.
16. A discharge mechanism as claimed in any preceding claim comprising seals sealing the first and second chambers, wherein a seal which seals the first chamber in the forward direction also seals the second chamber in the rearward direction.
17. A mechanism as claimed in any preceding claim in which the piston has a constant diameter section that protrudes from the first chamber in the forward and rear directions in the charging position.
18. A gun or cannon or other launcher comprising a mechanism as claimed in any preceding claim.
19. A discharge mechanism substantially as hereinbefore described with reference to the accompanying drawings.Amendments to Claims have ben filed as follows Claims 1. A discharge mechanism for pressurised gas comprising a piston slidably mounted in a housing, the housing defining a first chamber for the gas to be discharged and a second chamber located in front of the first chamber and in front of the piston in the discharge direction, the piston being slidable along an axis within the housing between charging and discharged positions to effect the discharge of gas from the first chamber, the piston and first and second chambers being arranged such that in the charging position pressurised gas in the first chamber exerts no force on the piston in the axial direction, and pressurised fluid introduced to the second chamber exerts a force on the piston to move the piston towards the discharged position.2. A discharge mechanism as claimed in claim 1 in which the first chamber is located outside the volume of travel of the piston.3. A discharge mechanism as claimed in claim 1 in which the piston forms at least one wall of the first chamber.4. A discharge mechanism as claimed in claim 1, 2 or 3, in which the first chamber comprises C\J an annular volume which encircles the piston in the charged position. rC"J 5. A discharge mechanism as claimed in claim 4 in which the piston comprises a rear section which serves to close the annular volume of the first chamber and a forward section of lower diameter than the first section.6. A discharge mechanism as claimed in any preceding claim arranged such that the first chamber is in immediate contact with atmospheric pressure in the discharge position.7. A mechanism as claimed in any preceding claim in which, within the first chamber, the piston has only surfaces which are parallel to the axis.8. A discharge mechanism as claimed in any preceding claim in which pressurised fluid in the second chamber exerts a force on the piston in a direction opposite to the direction of discharge of gas under pressure from the first chamber.9. A discharge mechanism as claimed in any preceding claim in which the second chamber comprises an annular volume surrounding a part of the piston.10. A discharge mechanism as claimed in claim in any preceding claim in which the piston forms at least one wall of the second chamber.11. A discharge mechanism as claimed in claim 11 in which the at least one wall is a shoulder formed in the outer surface of the piston.12. A discharge mechanism as claimed in any preceding claim in which the first chamber opens into the second chamber in the discharged position.13. A discharge mechanism as claimed in any preceding claim comprising seals sealing the first and second chambers, wherein a seal which seals the first chamber in the forward direction also seals the second chamber in the rearward direction.14. A mechanism as claimed in any preceding claim in which the piston has a constant diameter section that protrudes from the first chamber in the forward and rear directions in the charging position.15. A gun or cannon or other launcher comprising a mechanism as claimed in any preceding claim. (416. A discharge mechanism substantially as hereinbefore described with reference to the CJ accompanying drawings.