FIELD OF THE INVENTION

This invention relates to a pneumatic or hydraulic mechanism.

BACKGROUND

Pneumatic nail guns and mechanisms can be bulky, heavy, or cumbersome to operate. Some conventional single acting nail guns contain a large void in the housing for holding air pushed out of a piston chamber during the piston drive stroke. The piston must be sized to accommodate this void in the housing, to maintain the usability of the nail gun. This can result in a smaller piston size for a more manageable mechanism. A smaller piston generally results in a lower output force from the gun. Many nail guns lack the power to punch a nail all the way into hardwoods.

Further, many pneumatic mechanisms such as nail guns have complex valve

arrangements that are difficult to access and maintain.

It is an object of at least preferred embodiments of the present invention to address at least one of the abovementioned disadvantages and/or to at least provide the public with a useful alternative.

In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents or such sources of information is not to be construed as an admission that such documents or such sources of

information, in any jurisdiction, are prior art or form part of the common general knowledge in the art.

SUMMARY OF THE INVENTION

A first aspect of the invention broadly comprises a spool valve assembly comprising a housing, a trigger member, and two spools that receive the trigger member. The housing defines four ports, a first one of the ports being a fluid inlet port. The trigger member has a channel and is selectively longitudinally slidable relative to the housing between a first position and a second position. The two spools are slidable relative to the trigger member and relative to the housing, from a first position to a second position. The spool valve assembly is configured such that, upon supply of a fluid to the inlet port: the spools are urged to their first positions when the trigger member is in its first position, to permit fluid communication between the inlet port and a second one of the ports via the channel; and the spools are urged to their second positions when the trigger member is in its second position, to permit fluid communication between the inlet port and a third one of the ports.

In an embodiment, when the trigger member is in its second position and the spools are in their second positions, there is fluid communication between the second port and a fourth one of the ports. For example, to allow fluid to flow into the spool valve assembly through the second port, and out of the spool valve assembly through the fourth port. In an embodiment, the second and fourth ports are configured such that when the trigger member is in its second position, the spools are movable to a transitional position between their first and second positions, wherein one of the spools permits fluid communication between the second and fourth ports, and the other spool blocks fluid communication between the inlet port and the third port. In an embodiment the fourth port is an outlet port.

In an embodiment, the spools are sealingly engaged with an internal surface of the housing, for example by way of a plurality of o-ring type seals or other suitable annular seals. The position of the seals relative to the housing and/or the spools changes as the spools move from their first positions to their second positions, thereby modifying the available flow paths in the spool valve assembly. One or more seals may move in or out of sealing engagement with the housing as the spools move from their first positions to their second positions.

In an embodiment, the spools are sealingly engaged with a surface of the trigger member, for example by way of a plurality of o-ring type seals or other suitable annular seals. The position of the seals relative to the spools and/or the trigger member changes as the spools move from their first positions to their second positions, thereby modifying the available flow paths in the valve.

In an embodiment, the trigger member is sealingly engaged with the housing, for example by way of a plurality of o-ring type seals or other suitable annular seals. The position of the seals relative to the housing and/or the trigger member changes as the trigger member moves from its first position to its second position, thereby modifying the available flow paths in the valve.

In an embodiment, the housing and seals are configured such that in the first position of the trigger member, fluid flow from an interior of the spool valve assembly out of a front of the housing is substantially prevented; and in the second position of the trigger member, a leakage fluid flow from an interior of the spool valve assembly out of a front of the housing is permitted.

In an embodiment, the housing and seals are configured such that in the first position of the trigger member, a leakage fluid flow out of a rear of the housing is permitted; and in the second position of the trigger member, fluid flow out of a rear of the housing is substantially prevented.

In an embodiment, the trigger member is mechanically biased towards its first position, for example with a compression spring acting between the housing and an end of the trigger member.

The trigger member may be an elongate member, for example, a rod. The channel may be internal elongate channel, and may comprise three ports from the channel to an exterior of the trigger member. For example, first and second end ports at or towards opposite ends of the channel, and an intermediate port. The intermediate port is preferably positioned between the two spools when the spools and the trigger member are in their respective first positions. The channel preferably extends substantially coaxially with a longitudinal axis of the trigger member, along a major part of the length of the trigger member.

In an embodiment, a portion of the trigger member extends out of the housing, for example, out of a front wall of the housing, for actuation by an operator.

In an embodiment, the spools are mechanically biased towards their first positions, for example with a compression spring acting between the housing and at least one of the spools.

In an embodiment, the two spools are provided by a plunger that receives the trigger member. In an embodiment, the plunger comprises a through-hole and the trigger member extends through the through-hole, beyond ends of the spools. The plunger may comprise an intermediate portion with an aperture or port configured to be in fluid communication with the intermediate port of the trigger member, when the spools and the trigger member are in their respective first positions. In an alternative embodiment, the spool valve assembly may comprise two separate spools that are spaced apart and independently movable along the trigger member. The spools may be coaxial. In an embodiment, the spools and/or the plunger are concentric with the trigger member. In an embodiment, the housing comprises a sleeve. The sleeve may be concentric with the trigger member and the spools and/or the plunger. In such an embodiment the housing may comprise a stop intermediate the two spools to limit sliding and define the second position of one of the spools.

The spools, trigger member, and sleeve are preferably substantially cylindrical.

However, they may have other shapes.

In an embodiment, the spool valve assembly is a pneumatic spool valve assembly wherein the inlet port is configured to receive compressed air. Alternatively, the spool valve assembly may be a hydraulic spool valve assembly wherein the inlet port is configured to receive a hydraulic fluid.

A second aspect of the invention broadly comprises a spool valve assembly comprising : a housing defining ports, one of the ports being a fluid inlet port; a trigger member having a channel and being selectively longitudinally slidable relative to the housing between a first position and a second position; and two spools that receive the trigger member, the spools each being slidable relative to the trigger member and relative to the housing, from a first position to a second position; the spool valve assembly being configured such that, upon supply of a fluid to the inlet port: the spools are urged to their first positions when the trigger member is in its first position, to permit fluid communication between the inlet port and a region between a trigger end of the housing and the spools, and the spools are urged to their second positions when the trigger member is in its second position, to permit fluid communication between the inlet and a cylinder port.

The second aspect may comprise any one or more of the features described above in relation to first aspect.

A third aspect of the invention broadly comprises a cartridge comprising the spool valve assembly described above in relation to the first aspect or the second aspect.

The cartridge may be configured to be removably attach to the housing of a pneumatic mechanism. A fourth aspect of the invention broadly comprises a pneumatic or hydraulic mechanism comprising a housing, a piston, a trigger member, and two spools that receive the trigger member. The housing defines a piston chamber and four ports, a first one of the ports being a fluid inlet port. The piston is slidable in the piston chamber between a first position and a second position. The trigger member has a channel and is selectively longitudinally slidable relative to the housing between a first position and a second position. The spools are each slidable relative to the trigger member and relative to the housing, from a first position to a second position. The mechanism is configured such that, upon supply of a fluid to the inlet port: the spools are urged to their first positions when the trigger member is in its first position, to permit fluid communication between the inlet port and a second one of the ports, thereby urging the piston towards its first position; and the spools are urged to their second positions when the trigger member is in its second position to permit fluid communication between the inlet port and a third one of the ports, thereby urging the piston towards its second position. In an embodiment, the spools are urged to their first positions by the fluid and the spools are urged to their second positions by the fluid.

In an embodiment, the second and third ports are in fluid communication with the piston chamber. In an embodiment, the third port is in fluid communication with a rear side of the piston such that fluid flow through the third port urges the piston forward, and the second port is in fluid communication with a front of the piston such that fluid flow through the third port urges the piston rearward.

In an embodiment, the mechanism is a double acting mechanism, wherein the piston is configured to be automatically moved from its second position to its first position upon release of the trigger member and a supply of fluid to the input port. In an embodiment, the mechanism is configured such that when the trigger member is in its second position and the spools are in their second positions; there is fluid communication between the second port and a fourth one of the ports. For example, to allow fluid to flow from the piston chamber, through the second port, and out through the fourth port. In an embodiment, the fourth port is an outlet port.

In an embodiment, the piston is sealingly engaged with an interior surface of the piston chamber, for example by way of one or more of o-ring type or other suitable annular seals provided on the piston. The seals substantially prevent fluid communication in the piston chamber between a rear side of the piston and a front side of the piston. The piston chamber may comprise one or more resilient stops at end(s) of the chamber for a soft arrest of movement of the piston between its first and second positions.

Alternatively, one or both surfaces of the piston may comprise a resilient stop for a soft arrest of movement of the piston between its first and second positions. In an embodiment, the ports and spools are configured such that when the trigger member is in its second position, the spools are movable to a transitional position between their first and second positions, wherein one of the spools permits fluid communication between the second and forth ports, and the other spool blocks fluid flow between the inlet port and the third port.

In an embodiment, the spools are sealingly engaged with an internal surface of the housing, for example by way of a plurality of o-ring type seals or other suitable annular seals. The position of the seals relative to the housing and/or the spools changes as the spools move from their first positions to their second positions, thereby modifying the available flow paths in the valve. One or more seals may move in or out of sealing engagement with the housing as the spools move from their first positions to their second positions.

In an embodiment, the spools are sealingly engaged with a surface of the trigger member, for example by way of a plurality of o-ring type seals or other suitable annular seals. The position of the seals relative to the spools and/or the trigger member changes as the spools move from their first positions to their second positions, thereby modifying the available flow paths in the valve.

In an embodiment, the trigger member is sealingly engaged with the housing, for example by way of a plurality of o-ring type seals or other suitable annular seals. The position of the seals relative to the housing and/or the trigger member changes as the trigger member moves from its first position to its second position, thereby modifying the available flow paths in the valve.

In an embodiment, the housing and seals are configured such that in the first position of the trigger member, fluid flow from an interior of the spool valve assembly out of a front of the housing is substantially prevented; and in the second position of the trigger member, a leakage fluid flow from an interior of the spool valve assembly out of a front of the housing is permitted.

In an embodiment, the housing and seals are configured such that in the first position of the trigger member, a leakage fluid flow out of a rear of the housing is permitted; and in the second position of the trigger member, fluid flow out of a rear of the housing is substantially prevented.

In an embodiment, the trigger member is mechanically biased towards its first position, for example with a compression spring acting between the housing and an end of the trigger member. The trigger member may be an elongate member, for example, a rod. The channel may be internal elongate channel, and may comprise three ports from the channel to an exterior of the trigger member. For example, first and second end ports at opposite ends of the channel, and an intermediate port configured to be intermediate the two spools when the spools and the trigger member are in their respective first positions.

In an embodiment, a portion of the trigger member extends out of the housing, for example, out of a front wall of the housing, for actuation by an operator.

The mechanism may further comprise an actuator configured to actuate the trigger member. In an embodiment, the spools are mechanically biased towards their first positions, for example with a compression spring acting between the housing and at least one of the spools.

In an embodiment, the two spools are provided by a plunger that receives the trigger member. In an embodiment, the plunger comprises a through-hole and the trigger member extends through the through-hole, beyond ends of the spools. The plunger may comprise an intermediate portion with an aperture or port configured to be in fluid communication with the intermediate port of the trigger member, when the spools and the trigger member are in their respective first positions.

In an alternative embodiment, the spool valve assembly may comprise two separate spools that are spaced apart and independently movable along the trigger member. The spools may be coaxial.

In an embodiment, the spools and/or the plunger are concentric with the trigger plunger. In an embodiment, the housing comprises a sleeve. The sleeve may be concentric with the trigger member and the spools and/or the plunger. In such an embodiment the housing may comprise a stop intermediate the two spools to limit sliding and define the second position of one of the spools.

In an embodiment, the mechanism is a pneumatic mechanism and the inlet port is configured to receive compressed air. Alternatively the mechanism may be a hydraulic mechanism wherein the inlet port is configured to receive a hydraulic fluid. In an embodiment, the mechanism is a nail gun, for example, a pneumatic nail gun. In such an embodiment, the piston may comprise a driving ram for driving a nail into an object. The driving ram may be an elongate rod extending from a front of the piston. The housing may comprise a guide channel for receiving and guiding the ram. In one embodiment, the mechanism comprises two coaxial pistons, and the third port is in fluid communication with a rear face of both pistons.

A fifth aspect of the invention broadly comprises a pneumatic or hydraulic mechanism comprising : a housing defining a piston chamber and ports, one of the ports being a fluid inlet port; a piston slidable in the piston chamber between a first position and a second position; a trigger member having a channel and being selectively longitudinally slidable relative to the housing between a first position and a second position; two spools that receive the trigger member, the spools each being slidable relative to the trigger member and relative to the housing, from a first position to a second position; and a spring for biasing the spools; the mechanism being configured such that, upon supply of a fluid to the inlet port: the spring urges the spools to their first positions when the trigger member is in its first position, to permit fluid communication between the inlet port and a region between a trigger end of the housing and the spools, thereby urging the piston towards its first position; and the fluid urges the spools to their second positions when the trigger member is in its second position to permit fluid

communication between the inlet port and a cylinder port, thereby urging the piston towards its second position.

The fifth aspect may comprise any one or more of the features described above in relation to fourth aspect. A sixth aspect of the invention broadly comprises a bidirectional piston drive comprising : a housing defining an inlet and an exhaust; at least one annular plunger; a trigger having a hollow passage and that passes through the at least one plunger; and a piston. The trigger is actuable to port inlet and exhaust fluid to provide bidirectional movement of the piston. In an embodiment, the trigger passes through the centre of the at least one plunger.

In an embodiment, the piston drive comprises a single plunger with two spools. In an alternative embodiment, the piston drive comprises two plungers, each having one spool

A seventh aspect of the invention broadly comprises a cartridge for a bidirectional piston drive comprising : a housing defining an inlet and an exhaust; at least one annular plunger; and a trigger having a hollow passage and that passes through the at least one plunger. The trigger is actuable to port inlet and exhaust fluid.

The sixth and seventh aspects may comprise any one or more of the features described above in relation to the first, second, third, fourth, or fifth aspects. The term 'comprising' as used in this specification and claims means 'consisting at least in part of. When interpreting statements in this specification and claims which include the term 'comprising', other features besides the features prefaced by this term in each statement can also be present. Related terms such as 'comprise' and 'comprised' are to be interpreted in a similar manner.

It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.

To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. Where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

As used herein the term '(s)' following a noun means the plural and/or singular form of that noun.

As used herein the term 'and/or' means 'and' or 'or', or where the context allows both.

The invention consists in the foregoing and also envisages constructions of which the following gives examples only.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Figure 1 is a section view of a pneumatic nail gun mechanism according to an exemplary embodiment of the present invention, showing the mechanism in a starting position with the trigger released; Figure 2 is a section view of the nail gun mechanism of Figure 1, showing the mechanism in a second condition with the trigger immediately depressed and the plunger unmoved;

Figure 3 is a section view of the nail gun mechanism of Figures 1 and 2, showing the mechanism in a third condition with the trigger depressed and the plunger moved slightly to a transitional position;

Figure 4 is a section view of the nail gun mechanism of Figures 1 to 3, showing the mechanism in a fourth condition with the trigger depressed, the plunger in its second position, and illustrating resultant movement of the piston;

Figure 5 is a view corresponding to Figure 4, with the plunger moved to its second position;

Figure 6 is a section view of the nail gun mechanism of Figures 1 to 5, showing the mechanism in a fifth condition with the trigger immediately released and the plunger and piston unmoved from their second positions;

Figure 7 is a section view of a pneumatic nail gun mechanism showing detail of a seal, with the mechanism in a condition between the fifth condition and a sixth condition;

Figure 8 is a section view of the nail gun mechanism of Figures 1 to 6, showing the mechanism in the sixth condition with the trigger released, the plunger returned to its first position, and illustrating resultant movement of the piston;

Figure 9 is a section view of the nail gun of Figures 1 to 6 and 8, showing the mechanism reset to the condition of Figure 1;

Figure 10 is a section view of an alternative embodiment nail gun having two independently movable spools;

Figure 11 is a section view of a further alternative embodiment nail gun having two collinear pistons;

Figure 12 is a cut-away perspective view of an exemplary spool valve cartridge for use in a mechanism such as the embodiment of Figures 1 to 6, 7 and 9;

Figure 13 is an exploded perspective view of the cartridge of Figure 12;

Figure 14 is a section view of a pneumatic nail gun mechanism according to an alternative embodiment of the present invention;

Figure 15 is a section view of an alternative embodiment of a trigger and spool mechanism, showing the mechanism in a starting position with the trigger released;

Figure 16 is a section view of the mechanism of Figure 515, showing the mechanism in a second condition with the trigger immediately depressed and the plunger unmoved; Figure 17 is a section view of the mechanism of Figure 15, showing the mechanism in a third condition with the trigger depressed, the plunger in its second position;

Figure 18 is a section view of the mechanism of Figure 15, showing the mechanism in a fourth condition with the trigger immediately released and the plunger unmoved from its second positions;

Figure 19 is a section view of the mechanism of Figure 15, showing the mechanism in the fifth condition with the trigger released, the plunger returned to its first position;

Figure 20 is a section view of an alternative embodiment of a trigger and spool mechanism, showing the mechanism in a starting position with the trigger released;

Figure 21 is a section view of the mechanism of Figure 20, showing the mechanism in a second condition with the trigger immediately depressed and the plunger unmoved;

Figure 22 is a section view of the mechanism of Figure 20, showing the mechanism in a third condition with the trigger depressed, the plunger in its second position;

Figure 23 is a section view of the mechanism of Figure 20, showing the mechanism in a fourth condition with the trigger immediately released and the plunger unmoved from its second positions; and

Figure 24 is a section view of the mechanism of Figure 20, showing the mechanism in the fifth condition with the trigger released, the plunger returned to its first position; and

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Figures 1 to 8 show an exemplary embodiment mechanism for a pneumatic nail gun 1. For convenience, an arrow marked T' has been inserted into some of the figures to indicate a forward direction of the nail gun mechanism. Accordingly the terms forward, rearward, left side, and right side (or similar) should be construed with reference to the forward direction F. These terms are used for ease of explanation and are not intended to be limiting.

The nail gun 1 comprises a housing 3, a spool valve assembly 5, and a piston 7. The housing 3 defines a piston chamber 9, an integral valve sleeve 11, and a handle 13. The valve sleeve 11 defines four ports 15, 17, 19, 21 internal in the mechanism 1. The piston chamber 9 has two internal ports - a front port 23 and a rear port 24. A first one of the valve sleeve ports 15 is a fluid inlet port for receiving compressed air. The housing 3 may comprise an attachment feature 16 such as a threaded boss or lip at or in fluid communication with the inlet port 15, for coupling the nail gun 1 to a compressed air supply. The inlet port 15 is preferably positioned towards a rear of the valve sleeve, but may be otherwise positioned.

The second and third ports 17, 19 of the valve sleeve 11 are in fluid communication with the piston chamber 9. The second port 17 is in fluid communication with the front port 23 of the piston chamber such that fluid from the second port 17 can enter a forward region of the piston chamber 9 and contact a front surface 7a of the piston 7. The third port 19 is in fluid communication with the rear port 25 of the piston chamber 9 such that fluid from the third port 19 can enter a rear region of the piston chamber 9 and contact a rear surface 7a of the piston 7.

The fourth port 21 is an outlet port for the exhaust of air from the nail gun mechanism 1. In the embodiment shown, the outlet port 21 is through the handle 13. The piston 7 is slidable in the piston chamber 9. The piston 7 has annular seals 27 around its outer surface to seal against the interior surface 9a of the piston chamber 9. The seals 27 substantially prevent fluid flow between the forward portion of the chamber 9 that is in communication with the second port 17 and the rear portion of the chamber 9 that is in communication with the third port 19. In the embodiment shown, the seals are o-ring type rubber seals, but the seals may comprise any other suitable seal.

A front surface 7a of the piston 7 comprises a resilient, compressible stop 29. A second resilient, compressible stop 30 is provided at the rear of the piston chamber 9.

However, alternatively these stops may be provided on a forward facing surface 9b of the piston chamber 9, or on the rear surface 7b of the piston 7 respectively, or the mechanism 1 may not comprise any resilient stops.

An elongate driving ram 31 extends from a front of the piston 9, and has a front surface 31a for contacting the head of a nail (not shown) to drive the nail. In the embodiment shown, the ram is a rod member. Nails may be feed into the nail gun in any suitable manner, as are commonly known. One example is via a nail magazine. The housing 3 has a guide portion 33 with a channel 35 for receiving and guiding the ram 31. The ram has one or more annular seals 37 around its outer surface to seal against the interior surface of guide channel 35. The seals 27 substantially prevent fluid flow from the piston chamber, out through the guide channel 35. The spool valve assembly 5 comprises an integrated trigger and plunger arrangement with a trigger member 39, and a plunger 41. The plunger 41 has two spaced apart spools 43, 44, an intermediate adjoining portion 45, and an axial through-hole 46. The spool valve assembly 5 is positioned in the housing valve sleeve 11. The plunger 41 is slidable forward and rearward in the valve sleeve 11. A plurality of annular seals 47a, 47b, 47c, 47d such as o-ring type seals around the spools 43, 45 seal against the internal surface of the valve sleeve 11. The plunger intermediate portion 45 connects the two spools 43, 44, and comprises a port 48 that is in fluid communication with the through hole 46. A spring 49 acts between a front internal surface of the housing and the plunger to mechanically bias the plunger 41 rearwardly.

The plunger through-hole 46 receives the trigger member 39 (herein 'trigger'). The trigger 39 is an elongate member such as a rod. The trigger member 39 is longer than the plunger and extends beyond front and rear ends of the plunger 41 such that the plunger can slide along the trigger 39.

The trigger 39 is preferably but not necessarily coaxial with the plunger 41 and spools 43, 44. Similarly, the plunger spools 43, 44 are preferably but not necessarily collinear.

The trigger 39 is slidable in the housing valve sleeve 11 relative to the housing 3. A front end 39a of the trigger 39 extends beyond the housing 3 out of a front wall 12 of the valve sleeve 11, such that an operator can push the trigger 39 rearward.

A rear end 39b of the trigger 39 is guided in a recess 50 in a rear of the housing. A spring 51 in the recess 50 acts between the housing 3 and the trigger 39 to mechanically bias the trigger 39 forward

The trigger 39 is sealingly engaged with the housing 3 by way of a plurality of o-ring type seals 61a, 61b, 61c, 61d or other suitable annular seals on the trigger 39. Not all of the seals are engaged with the housing in all positions of the trigger 39.

The trigger 39 has an internal elongate channel 53 that is closed at its opposing ends, and three apertures 55, 57, 59 that act as ports from the channel to an exterior of the trigger. First and second end ports 55, 57 are positioned at or towards opposite ends of the channel 53. An intermediate port 59 is positioned intermediate the first and second end ports 55, 57 to provide fluid communication between the channel 53 and the plunger through hole 46. A plurality of o-ring type seals 63a, 63b, or other suitable annular seals on the interior of the plunger through-hole 46 provide a sliding sealed engagement between the plunger 41 and the trigger 39.

Operation of the nail gun mechanism 1 will now be described with reference to Figures 1 to 9.

Figure 1 shows the nail gun mechanism 1 in a first, starting condition. In this condition, the trigger 39 is released and compressed air A is supplied to the inlet port 15. The trigger 39 is in a first, forward position; the plunger 41 and spools 43, 44 are in a first, rearward position; and the piston 7 is in a first, rearward position. In this arrangement, the first spool 43 blocks the third port to prevent air entering the piston chamber 9 behind the piston 7. The inlet port 15 is instead in fluid

communication with the second port 17 and a front portion of the piston chamber 9 via the trigger 39.

As illustrated by the arrows in Figure 1, air from the inlet port 15 enters the trigger channel 53 through its rear inlet port 57. Some of the air flows out the trigger channel 53 through its front port 55 and is trapped in a front region 14 of the spool valve assembly 5 between the housing and a front surface of the second spool 44. Seals 61a between the trigger and the housing, seals 47a, 63a between second spool 44 the housing and the trigger 39 substantially prevent leakage of air from this region. The frontal area of the second spool 44 is greater than the rearward area of the first spool 43. Therefore, the pressure on the spool surfaces from the compressed air results in a net rearward force on the plunger 41, maintaining the plunger in its second position as shown.

The remainder of the air flows out the trigger channel 53 through its intermediate port 59. In this configuration, the channel's intermediate port 58 is preferably positioned between the two spools 43, 44. Air from the intermediate port 59 in this configurations passes into the plunger through-hole 46, the plunger aperture 48, and into the piston chamber front port 23. Seals 61a between the trigger 39 and plunger 41 substantially prevent leakage of air from the plunger through hole 46 to the regions forward and rear of the plunger 41.

The resulting pressure differential between the front and rear sides of the piston 7 holds the piston in its first, rearward, position as shown. The piston seals 27 substantially prevent air flow in the piston chamber 9 from the front of the piston 7 to the rear of the piston 7. A rigid stop 65 on the housing 3 limits rearward movement of the piston 7. In this configuration, the rear of the piston chamber 9 is in fluid communication with the external environment through an exhaust passage 67 and aperture 69 in the housing 3. These exhaust features assist with movement of the piston 7 into its first position and are discussed below. The nail gun is actuated by depressing the trigger 39.

Figure 2 shows the nail gun mechanism 1 in a second, instantaneous condition that occurs as the trigger 39 is depressed to a second, rearward position. The trigger 39 may be depressed by an operator directly pressing the front end of the trigger 39a, or it may be indirectly actuated. For example, the nail gun 1 may comprise an actuator, such as a pivoted lever, that acts on the trigger 39.

Pressing in the trigger 39 moves one of the seals 61b towards the rear of the trigger 39 into engagement with the internal surface of the recess 50 in the rear of the housing. This blocks air flow into the trigger channel 53, resulting in increased pressure behind the first plunger spool 43 from the inlet 15. In this manner, the trigger 39 acts in a similar way to a spool valve by changing flow paths through the valve.

Pressing in the trigger 39 also moves the front seal 61a on the trigger 39 out of engagement with the housing 12. This allows a leakage air flow L out of the front of the housing 12 around the trigger 39, depressurising the front region 14 of the valve sleeve 11. The loss of pressure in the front region 14 of the valve sleeve 11 causes the plunger 41 to start moving forward under the air pressure from the inlet 15, compressing the plunger spring 49. Figure 3 shows a first stage of the resulting forward movement of the plunger 41.

Figure 3 shows the plunger in a transitional position in which the first spool 43 is still blocking the third port in the valve sleeve 11, and the first spool seals 47c, 47d are still sealed against the valve sleeve 11 to prevent airflow to the rear of the piston 7.

However, one of the second spool's seals 47b has moved out of contact with the valve sleeve near the fourth port 21.

This permits fluid communication between the second port 17 and the outlet port 21 resulting in air flow from the piston chamber 9 in front of the piston 7, out the outlet port 21, reducing the air pressure in the front part of the piston chamber 9.

The plunger 41 continues to move forward under the air pressure from the inlet port 15, until it reaches a forward, second position shown in Figure 4. In this second plunger position, the first spool 43 is no longer blocking the third port 19, and seals 61b, 63b on the trigger and the first spool 43 are still preventing air flow from the inlet port 15 into the trigger channel 53.

Air from the inlet 15 is now directed through the third port 19 into the piston chamber 9, behind the piston 7. Seals 61c, 61d on the trigger 39 prevent air escaping from the rear of the housing through the leakage passage and aperture 67, 69. Air from in front of the piston 7 is free to flow out of the device through the second and forth ports 17, 21, and through the front of the valve sleeve 12.

As shown in Figure 5, the pressure differential in the plunger chamber 9 causes the piston 7 to rapidly move forward in the piston chamber 9 from the first position shown in Figures 1 to 4, to the second position shown in Figure 5. This forward movement also drives the ram 31 forward in the guide channel 35 to drive a nail into a surface.

Having a transitional position such as the one shown in Figure 3, that allows a decrease in the pressure in front of the piston 7 before increasing the pressure behind the piston, decreases the resistance to forward piston movement provided by air in front of the piston 7. This advantageously increases the speed of the piston movement. For example, in one embodiment the piston moves at about 26ms ¹ .

The resilient stop 29 on the front of the piston 7 contacts a forward stop 9b in the piston chamber to arrest forward movement of the piston 7. The resilient stop 29 provides a soft arrest, absorbing some of the impact energy to reduce sound and damage to components. Alternatively, a resilient stop may be provided on the housing stopping surface 9b. The resilient stops 29, 30 may comprise any suitable material that resiliently deforms to absorb energy, for example an elastic material such as rubber, or a spring.

The ports 15, 17, 19, 21 on the valve sleeve 11 and the piston chamber ports 23, 35 are preferably sized so that air flow out of the piston chamber 9 and mechanism 1 can at least match the air flow into the mechanism and piston chamber 9, to minimise any 'bottlenecks'.

This porting arrangement of air out of the piston chamber enables a larger piston to be accommodated by the housing than in traditional nail guns. A larger piston provides a greater driving force for the same air pressure. For example, in one example

conventional nail gun, the piston has a diameter of 55 mm and area of 2376 mm ² . In an embodiment according to the present invention with a comparable housing size to the conventional nail gun, the piston has a diameter of 77.8 mm and area of 4754 mm ² . This corresponds to a 1473 N force produced by the conventional gun at 90 psi and 2947 N force for the embodiment according to the present invention. The mechanism 1 is a double acting, bidirectional piston drive that automatically moves the piston 7 from its second (forward) position back to its first (rearward) position to reset the mechanism 1 for reuse, when the trigger 39 is released. Figures 6 to 9 illustrate the reset process. Figure 6 shows the nail gun mechanism 1 in an instantaneous condition that occurs immediately when the trigger 39 is released . Upon release of the trigger 39, the trigger spring 51 returns the trigger 39 to its first position. This in turn unseals the leakage passage 67 and aperture 69 in the rear of the housing, reducing the pressure in the rear of the piston chamber 9 as air escapes through the passage 67 and aperture 69. Releasing the trigger 39 also seals off the front 12 of the valve sleeve 11 via the front trigger seal 61a, and moves the trigger's internal channel rear port 57 back into fluid communication with the spool inlet port 15. Air flows into the channel 53 and out of the channel's front and intermediate ports 55, 59.

Figure 7 shows detail of an O-ring type seal 61e or other suitable annular seal between the trigger 39 and the plunger 41. Although it is not specifically shown or described, the O-ring type seal 61e will typically be present in the other figures shown and described in this specification. The O-ring type seal 61e reduces or eliminates leakage of air through the port 48, which would then escapes through the fourth port 21. That path is sealed by the O-ring type seal 61e until the plunger 41 has moved to seal the fourth port 21. The plunger sealing the fourth port is shown in Figure 8. Figure 7 also shows port 48 is narrower than as it is shown in the other figures. The port may have either a relatively narrow or wide width.

The air that flows out the trigger channel 53 through its front port 55 is trapped in the front region 14 of the spool valve assembly 5, between the housing and the second spool 44. Together with the plunger spring 49, the air pressure urges the plunger 41 rearwardly back to its first position as shown in Figure 8.

The air that flows out the channel's intermediate port 59 flows into the front of the piston chamber 9 via the plunger port 59 and the valve sleeve second port 17. The increased pressure in front of the piston 7 and the reduced pressure behind the piston 7 creates a pressure differential that urges the piston 7 back to its first, rearward, position as shown in Figure 9. As the piston 7 moves rearward, air from behind the piston 7 vents to atmosphere through the leakage passage 67 and aperture 69 in the rear of the housing. The resilient stop 30 on the housing's rear rigid stop 65 in the piston chamber 9 arrests rear movement of the piston 7. The resilient stop 30 provides a soft arrest, absorbing some of the impact energy to reduce sound and damage to components. Alternatively, a resilient stop may be provided on the rear of the piston 7. Figure 10 shows an alternative embodiment nail gun 101 that operates substantially as described above in relation to the embodiment of Figures 1 to 9, but has two independently movable coaxial spools 143, 144 in place of the plunger member 41. Like parts are labelled with like reference numerals, with the addition of 100. Each spool 143, 144 is independently movable and biased rearwardly to its first position by a respective spring 149a, 149b. Radially directed stops 145 in the valve sleeve 111 limit rearward movement of the first spool 143.

When the trigger 139 is released, as shown, the trigger channel's intermediate port 159 is in fluid communication with the valve sleeve second port 117 and the front of the piston chamber 109, and with a region 115 in front of the rear spool 143. Figure 11 shows a further alternative embodiment nail gun 201 that has two attached collinear pistons 207, 208. Each piston 207, 208 slides in a respective piston chamber 209, 210. Components in the embodiment of Figure 11 are labelled with like reference numerals to the embodiment of Figures 1 to 9, but with the addition of 200.

In this embodiment, the valve sleeve third port 219 is in fluid communication with a rear port 25a of the forward piston chamber 209, and a rear port 25b of the rear piston chamber 210. The nail gun 201 operates substantially as described above in relation to the embodiment of Figures 1 to 9. However, on the piston drive stroke, air enters the rear of both piston chambers 209, 210 to drive both pistons 207, 208 forward. The two pistons 207, 208 provide an increased surface area compared to the single piston embodiment, thereby increasing the force acting on the pistons 207, 208.

During the drive stroke, air from the front piston chamber 209 is vented in the same manner described above. Air from the second piston chamber 210 is vented through an opening 204 in the wall of the rear piston chamber 210. Resilient stops 229, 230 on the front of the two piston chambers 209, 210 arrest forward movement of the respective pistons 207, 208.

The pistons 207, 208 are returned from their second positions to their first positions, as described above. Only the front piston 207 is driven by air entering the second port 217. The rear piston 208 is driven back by movement of the front piston 207. Air from behind the pistons 207, 208 vents through the vent passage 267 and aperture 269 in the rear of the housing. The opening 204 in the wall of the rear piston chamber 210 allows for the ingress of air into the rear piston chamber 210 as the rear piston 208 is moved to its first position.

In the embodiments above, the valve sleeve 11, 111, 211 is integral with the housing 3, 103, 203. However, the valve sleeve may be a separate component and/or may be removable from the housing 2, 103, and 203. For example, the spool valve assembly 5, 105, 205 may be provided in the form of a removable cartridge containing the plunger 41 and/or spools 43, 44, 143, 144, the trigger 39, 139, 239, and the respective springs 49, 51, 149, 152, 249, 251. An exemplary cartridge 305 is shown in Figures 12 and 13. The cartridge 305 is suitable for use with a mechanism such as the one shown in Figures 1 to 9. The components are labelled with the same reference numbers as for the first embodiment of Figures 1 to 9, but with the addition of 300.

The cartridge comprises a sleeve 311 housing the spool valve assembly. The cartridge sleeve 311 is shaped to be received in a complementary bore in the mechanism housing 3 of the pneumatic mechanism. The front end of the sleeve has a flange 311a with bolt holes 372 for bolting the cartridge to the housing 3. However, the cartridge may be otherwise removably secured to the housing 3. In this manner, the valve assembly from the pneumatic mechanism may be readily removed for maintenance or replacement.

Holes 315, 317, 319, 321 in the cartridge sleeve 311 provide ports and are positioned to align with the first 15, second 17, third 19 and forth 21 ports respectively in the mechanism housing 3. O-ring type seals 371a, 371b 371c, 371d positioned in grooves on the exterior of the valve sleeve 11 are configured to seal against an interior of the bore in the housing 3 in which the cartridge 305 is received. The seals 371a, 371b 371c, 371d isolate the various sections and prevent leakage flow between adjacent ports, for example seal 371b prevents fluid flow between the second and third ports 17, 19 between the housing bore and the cartridge sleeve 311. In a similar manner, a cartridge could be provided for use with the double piston embodiment 201 of Figure 11, or with the independently movable spools 143, 144 of Figure 10.

Figures 15 to 19 show an alternative embodiment of a trigger and spool mechanism. Components in the embodiment of Figures 15 to 18 are labelled with like reference numerals to the embodiment of Figures 1 to 9, but with the addition of 400. The features and operation of the embodiment of Figures 15 to 18 are the same as the features and operation of the embodiment of Figures 1 to 9, unless described below. The cylinder, piston and other associated components of the nail gun are not shown in figures 15 to 18, but it will be appreciated that trigger and spool mechanism may be used with the cylinder, piston and other associated components shown and described in relation to Figures 1 to 9.

In this embodiment, the trigger and spool mechanism comprises a compression spring 471. The compression spring 471 mechanically urges the spools 443, 444 to their first positions when the trigger member 439 is in its first position. The spools 443,444 of this embodiment are provided by flanges 443a, 443b, 444a, 444b, 444c of the plunger 441.

Figure 15 shows the trigger and spool mechanism in a first, starting condition. In this condition, the trigger 439 is released and compressed air A is supplied to the inlet port 415. The trigger 439 is in a first, forward position; the plunger 4541 and spools 443a, 443b, 444a, 444b, 444c are in a first, rearward position; and the piston (not shown) is in a first, rearward position.

In this arrangement, the first spool 443a, 443b blocks the third port 419 to prevent air entering the rear of piston chamber. The inlet port 415 is instead in fluid communication with the second port 417 and a front portion of the piston chamber via the trigger 439. As illustrated by the arrows in Figure 515, air from the inlet port 415 enters the trigger channel 4553 through its rear inlet port. Seal substantially prevent leakage of air from air exiting the channel 453.

The nail gun is actuated by depressing the trigger 439. Figure 16 shows the nail gun mechanism 401 in a second, instantaneous condition that occurs as the trigger 439 is depressed to a second, rearward position.

Pressing in the trigger 439 exposes the front port 455 of the channel 453. Some of the air flows out the trigger channel 4553 through the front port 455 and is trapped in a front region 414 of the spool valve assembly 405 between the housing and a front surface of the second spool flange 444c. Seals 461a between the trigger and the housing, seals 47a, between second spool's third flange 444c and the housing

substantially prevent leakage of air from this region. The front region 414 begins to fill with air, resulting in increased pressure the front region 414.

The remainder of the air flows out the trigger channel 453 through its intermediate port. In this configuration, the channel's intermediate port is preferably positioned between the two spools 443, 444.

The increased pressure in the front region 414 of the valve sleeve 411 causes the plunger 441 to start moving forward under the air pressure from the inlet 415, compressing the plunger spring 471. Figure 16 shows a first stage of the resulting forward movement of the plunger 441.

Figure 16 shows the plunger in a position in which the first spool's second flange 443b is still blocking the third port 419, to prevent airflow to the rear of the piston. There is fluid communication between the inlet 415 and the second port 417.

The plunger 441 continues to move forward under the air pressure from the inlet port 415, until it reaches a forward, second position shown in Figure 17. In this second plunger position, the first spool 443a, 443b is no longer blocking the third port 419. Additionally air flow from the inlet port 415 continues to flow into the trigger channel 453 to the front region 414.

Air from the inlet 415 is now directed through the third port 419 into the piston chamber. Seals 61c, 61d on the trigger 439 prevent air escaping from the rear of the housing through the leakage passage and aperture 67, 69.

Figure 18 shows the nail gun mechanism 1 in an instantaneous condition that occurs immediately when the trigger 439 is released. Upon release of the trigger 439, the trigger spring (not shown) returns the trigger 439 to its first position. This in turn unseals the leakage passage 467 and aperture 469 in the front of the housing and closes the front port 455 of the channel 453, reducing the pressure in the front region 414 as air escapes through the passage 473 and aperture 475. The plunger spring 471 urges the plunger to return to the first, starting condition. As the piston moves rearward, air from behind the piston vents to atmosphere through an aperture 469 in the rear of the housing.

Figures 20 to 24 show an alternative embodiment of a trigger and spool mechanism. Components in the embodiment of Figures 20 to 24 are labelled with like reference numerals to the embodiment of Figures 1 to 9, but with the addition of 500. The features and operation of the embodiment of Figures 20 to 24 are the same as the features and operation of the embodiment of Figures 1 to 9, unless described below. The cylinder, piston and other associated components of the nail gun are not shown in figures 20 to 24, but it will be appreciated that trigger and spool mechanism may be used with the cylinder, piston and other associated components shown and described in relation to Figures 1 to 9.

Figure 20 shows the trigger and spool mechanism in a first, starting condition. In this condition, the trigger 539 is released and compressed air A is supplied to the inlet port 515. The trigger 539 is in a first, forward position; the plunger 541 and spools 543, 544 are in a first, rearward position; and the piston is in a first, rearward position.

In this arrangement, the first spool 543 blocks the cylinder port 519 to prevent air entering the piston chamber behind the piston. As illustrated by the arrows in Figure 20, air from the inlet port 515 enters the trigger channel 553 through its rear inlet port 557. Some of the air flows out the trigger channel 553 through its front port 555 and is trapped in a front region 514 of the spool valve assembly 505 between the housing and a front surface of the second spool 544. Seal 561a between the trigger and the housing, seal 47a, 63a between second spool 544 the housing and the trigger 539 substantially prevent leakage of air from this region. The pressure of the air in the front region 514 is equal to the pressure between the spools and the spring 549 biases the plunger towards its first position.

The nail gun is actuated by depressing the trigger 539.

Figure 21 shows the nail gun mechanism 1 in a second, instantaneous condition that occurs as the trigger 539 is depressed to a second, rearward position. Pressing in the trigger 539 moves the front seal 561a on the trigger 539 out of engagement with the housing 512. This allows a leakage air flow L out of the front of the housing 512 around the trigger 539, depressurising the front region 514 of the valve sleeve 511. When the trigger 539 is in the second, rearward position the rear inlet port 557 of the channel is blocked.

The loss of pressure in the front region 514 of the valve sleeve 511 causes the plunger 541 to start moving forward under the air pressure from the inlet 515, compressing the plunger spring 549. Air is now able to transfer from the inlet port 515 to the cylinder port 519. The plunger 541 continues to move forward under the air pressure from the inlet port 515, until it reaches a forward, second position shown in Figure 22. In this second plunger position, the first spool 543 is no longer blocking the cylinder port 519, and he rear inlet port 557 of the channel is still blocked, preventing air flow from the inlet port 515 into the trigger channel 553. Air from the inlet 515 is now directed through the cylinder port 519 into the piston chamber.

With reference to Figure 23, the trigger is released, resuming transfer of air through the trigger channel 553 through its front port 555 to front region 514. The pressure of the air in the front region 514 is equal to the pressure between the spools and the spring 549 biases the plunger towards its first position. Air from the inlet port 515 is blocked from entering the cylinder port 519. Air from the cylinder port 519 is now vented to atmosphere through the outlet 521. Figure 14 shows an alternative embodiment having a reservoir 400 in fluid

communication with the inlet port 15. Although it is not specifically shown or described, the reservoir 400 may be present in the other embodiment shown and described in this specification.

The reservoir 400 is useful when the compressed air A is supplied to the inlet port 15 via a relatively thin hose and coupling. When the compressed air is supplied using such a relatively thin hose and coupling, the volume of air supplied by the compressed air supply A does not match the amount of air required behind the piston 7.

The reservoir 400 acts to store compressed air for the inlet port 15. In particular, the air in the reservoir 400 has already passed through the bottleneck that the relatively thin hose creates. In this embodiment, the reservoir 400 provides a volume of air that is ready to be used, rather than 'waiting' for the air to pass through the bottleneck in the thin hose. In a preferred embodiment, the volume of air that is ready to be used is the same volume as volume required by the stroke of the piston 7.

Preferred embodiments of the invention have been described by way of example only and modifications may be made thereto without departing from the scope of the invention.

For example, the spool valve assembly has been described as having three or four main ports 15, 17, 19, 21. In an alternative embodiment, the spool valve assembly may have more than four ports. For example, rather than a pneumatic mechanism the mechanism may be a hydraulic mechanism with the inlet port configured to receive a hydraulic fluid. In a hydraulic mechanism, rather than the fluid being vented to atmosphere, the housing ventilation ports would be otherwise configured to capture and direct 'vented' fluid.

Rather than being oriented forward -rearward, the piston chamber 9, 109, 209 could be otherwise oriented, for example, it could have an angled or upright orientation. The mechanism is not limited to a gun-type mechanism, but could have another shape such as an inline mechanism. The mechanism has been described above in relation to a nail gun. However, other applications are envisaged. For example, in staple guns, air powered guns, paintball guns, high pressure water pumps, compressed air brake systems, compressed air engines, and firearms.