In operation of a conventional kind of pneumatic gun, pulling a trigger of the gun causes a tensioned hammer mechanism to be released.

A hammer is so caused to strike the stem of a valve closure element, so as to move the element from its seating and cause compressed gas to leave an associated pressure chamber.

After the hammer has impacted with the operating member, it usually remains in contact with the closure element. This can give rise to two disadvantages.

Firstly, following recharging of the pressure chamber a shock loading on the gun, for example through banging the gun end on the ground, can give sufficient energy to the hammer to cause a momentary opening of the exhaust valve. This results in a slight discharge of air to the gun breech, which can plainly be with undesirable consequences.

Secondly, the mass of the hammer mechanism serves to increase the inertia of the valve closure system. As a consequence, crisp shut-off of the valve is to an extent impeded by the hammer mechanism.

It is an object of the invention to provide an improved exhaust valve arrangement which overcomes the disadvantages referred to.

The invention provides, in or for an air gun of pneumatic type, an exhaust valve assembly arranged to be opened to permit gas to be discharged from a pressurised chamber into a breech of the gun in response to release of a tensioned hammer mechanism in firing the gun, the exhaust valve assembly comprising a closure element, an operating member which extends from the closure element to enable the element to be displaced to open the valve, a movable shuttle which in a rest position is held out of operative engagement with the operating member but which is arranged to be engaged by a hammer of the hammer mechanism in order to become driven from its rest position into engagement with the operating member whereby to displace the operating member and open the valve, and restoring means arranged to return the shuttle to its rest position in closure of the valve.

Since in its rest position the shuttle is held out of engagement with the operating member, no ordinary shock to the gun will cause it to displace the operating member and open the valve. Also, operation of the restoring means to separate the shuttle from the operating member, slightly prior to closure of the valve by engagement of the closure element on the seating, can provide that the valve is able to close without the movement of the closure element being influenced by the mass of the shuttle.

In a preferred arrangement, the shuttle-restoring means is operative to urge the shuttle to return to its rest position only from a position closely by the rest position (but in which it is still in operative engagement with the operating member). In this way, any adverse influence of the restoring means over the behaviour of the shuttle in operation of the valve can be avoided or at least minimised.

In a preferred construction, the shuttle-restoring means comprises a sprung restoring element arranged to engage in a recess in the rest position of the shuttle and shaped to co-operate with a surface bordering the recess to draw the shuttle into its rest position, whereby to separate the shuttle from the operating member. A suitable element can be a ball which is urged by a spring to draw the shuttle and enter the recess.

There now follows a detailed description, to be read with reference to the accompanying drawing, of an exhaust valve assembly which illustrates the invention by way of example.

The accompanying drawing is an axial cross-section through an exhaust valve assembly in a closed condition.

An exhaust valve assembly suitable for use in an air gun, to release doses of compressed gas from a pressurised chamber in operation of the gun, comprises a valve body 10 from which a tubular housing 12 extends forwardly (i.e. forwardly of the valve, which may be rearwardly of the gun).

The valve body 10 comprises a cylindrical tubular inlet portion 14 which is open-ended at its rear end 16 of the gun. An internally frusto- conical intermediate portion 18 of the body, leading from the front end of the inlet portion 14, forms an exhaust orifice 20 surrounded by a conical valve seating surface 22. The orifice 20 provides communication through to a radially-extending outlet passage 24 provided by a forward-end portion 26 of the valve body. In use of the valve, the passage 24 is connected up to the breech of the air gun.

A cylindrical valve closure element 28 is located within the inlet and intermediate portions of the valve body and urged forwardly by a closure spring 29 for sealing engagement of a circular leading edge 30 of the element with the seating surface 22. An operating member in the form of a valve stem comprising a thin rod 32 is secured centrally to the closure element and extends axially forwards through the orifice 20 (with a large clearance). The rod extends forwardly beyond a front end 34 of the valve body, there being a bushing 36 inserted into the valve body from its front end and bearing internally an O-ring 38 for support of the rod; the rod is free to slide through the O-ring and the bushing.

The tubular housing 12, which extends from the front end of the valve body 10, forms a slide tube to guide movement of a shuttle block 40. The block 40 may conveniently be formed from a piece of hexagonal bar, so as to leave air vents 42 between the surface of the block and the housing 12. A hard insert 44 may be introduced into a front end face 46 of the block.

The shuttle block 40 is shown in the drawing in a rest position, with a steel ball 48 of a ball catch arrangement accommodated in a recess formed by an orifice 50 in the wall of the housing 12. The ball is urged into the recess by means of a compression spring 52 which is accommodated in a radially extending bore 54 in the shuttle block; the bore 54 is of such diameter as to permit the ball 48 to slide freely into it upon the ball being forced radially inwards against the action of the spring.

The shuttle block 40 is held in its rest position by engagement of the ball 48 of the ball catch in the orifice 50 of the surrounding housing.

In its rest pOsition, as shown in the drawing, a plain rear face 56 of the

block is separated from an opposing front end face 58 of the operating rod 32 by a short distance.

In use of the valve, should the gun be subjected to a shock the shuttle block 40, being held in place separated from the operating rod 32, cannot dislodge the closure element 28 and cause an accidental release of gas into the outlet passage 24. Upon operation of the gun, a tensioned hammer mechanism is released, by pulling a trigger, to cause a hammer to impact with the front end of the shuttle block. The block so becomes driven rearwards, the retaining ball becoming depressed into the spring- accommodating bore 54, and drives the operating rod 32 rearwards to open the valve and release a charge of compressed air through the outlet orifice 20.

The block, the operating rod and closure element can thereafter move forwards to close the valve under the influence of the closure spring 29 and residual air pressure within the inlet portion 14 of the valve body. The combined closure element and operating rod push the shuttle block forwards until shortly before the closure element engages the seating surface 22, at which point the ball catch takes over to draw the shuttle block rearwards to assume its rest position. The block so becomes separated from the operating rod prior to the closure element engaging the seating surface, whereby the behaviour of the closure element is not influenced by the mass of the shuttle block and hammer and a particularly crisp closure of the valve is achieved.

The free-floating shuttle block 40, interposed between (but movable independently of) the hammer and the valve stem 32, so provides an anti- bounce device which protects the valve stem from any influence from the hammer other than when the gun is fired; the spring 52 is of sufficient strength to prevent displacement of the shuttle block from its rest position except when the block is hit by the hammer with full force upon firing.

The shuttle, therefore, cannot transmit any energy to the valve stem until the gun is properly fired. After firing, the shuttle and hammer retreat from the valve stem until the shuttle reaches its rest position, the hammer thereafter being prevented from influencing the valve stem; any residual energy in the hammer is absorbed by the shuttle block.