IMPROVEMENTS IN OR RELATING TO PRESSURE RESPONSE OF HIGH PRESSURE FLUID VALVING, APPARATUS AND METHODS THEREFOR

Abstract

Disclosed is a system, method and apparatus operating on a high-pressure working fluid with high efficiency. The device has a reservoir of high-pressure working fluid. A fluid connection supplies the high-pressure working fluid at a controlled working pressure to a dose chamber to contain a volume of the high-pressure working fluid. A dose valve, biased to close, and able to be triggered open, is present between the dose chamber and a working chamber. A charge of the high pressure working fluid can be released from the dose chamber via the dose valve at a first end of the working chamber, to undergo a first expansion in the working chamber and do work therein to or towards a second end of the working chamber distal from the first end. The dose valve closes again before a pressure front of the charge in the working chamber has travelled less than or equal to halfway between the first end and the second end. This allows a second expansion of the charge to continue doing work. When the work is complete, the working chamber pressure is less than or equal to half the working pressure.

Claims

1. A system to operate on a high-pressure working fluid, comprising or including, A reservoir of high-pressure working fluid, with a fluid connection supplying the high-pressure working fluid at a controlled working pressure to, A dose chamber to contain a volume of the high-pressure working fluid, A dose valve, biased to close, and able to be triggered open, between the dose chamber and, A working chamber, into which a charge of the high pressure working fluid is released from the dose chamber via the dose valve at a first end of the working chamber, to undergo a first expansion in the working chamber and do work therein to or towards a second end of the working chamber distal from the first end, the dose valve closing again before a pressure front of the charge in the working chamber has travelled less than or equal to halfway between the first end and the second end, thereafter allowing a second expansion of the charge to continue doing work, the fluid connection having a flow restriction which is significantly less than a flow capacity of the dose valve, Wherein when the work is completed, the charge in the working chamber is at a pressure less than or equal to half the working pressure.

2. The system of claim 1 wherein the volume of the dose chamber to the working chamber is at a ratio of 1 to 1.

3. The system of either claim 1 or 2 wherein the volume of the dose chamber to the working chamber is between a ratio range of 1 to 2 and 1 to 20.

4. The system of any one of claims 1 to 3 wherein the bias to close the dose valve is derived from either fluid pressure acting on a pressure area, or a mechanical spring.

5. The system of any one of claims 1 to 4 wherein there is a pressure regulator between the reservoir and the dose chamber.

6. The system of claim 5 wherein the pressure regulator and dose valve ensure the dose chamber consistently has at least one specified pressure or energy state, irrespective of the reservoir pressure while the reservoir is between a maximum allowable pressure and the selected or regulated working pressure.

7. The system of any one of claims 1 to 6 wherein the dose chamber is concentric to the working chamber.

8. The system of any one of claims 1 to 7 wherein the dose valve is concentric to the working chamber.

9. The system of any one of claims 1 to 8 wherein the reservoir is a self-contained tank, or a tethered pressure supply from a separate high-pressure fluid source, such as a tank, compressor or the like external pressure supply.

10. The system of any one of claims 1 to 9 wherein the charge expands, pushes against and accelerates, a workload and the pressure front lies behind the workload, in the work chamber in order to extract work from the charge.

11. The system of any one of claims 1 to 10 wherein the dose valve is opened by a trigger which can be mechanical, pneumatic, electrical or any other means of opening the flow between the dose chamber and work chamber via the dose valve, and may be operated by hand, for example a finger trigger or by a machine.

12. The system of any one of claims 1 to 11 wherein the workload is captive, for example a piston or is non-captive for example a projectile.

13. The system of any one of claims 1 to 11 wherein, there is no workload in the chamber as such, but rather the pressure front ejects from the working chamber to cause an effect external to the working chamber.

14. The system of any one of claims 1 to 13 wherein flow from the reservoir to the dose chamber is eliminated when the dose valve is open, for example statically such as a one-way valve, or selectively openable valve, or dynamically such as a restriction.

15. The system of claim 14 wherein such flow elimination is located within the regulator or trigger or is another mechanism.

16. The system of any one of claims 1 to 15 wherein closure of the dose valve is at least in part controlled by an elastic element, such as a spring, whether compressive or extensive.

17. The system of any one of claims 1 to 16 wherein the dose valve closure is controlled via a mechanism which ties the closure of the dose valve to a specific amount of movement of the pressure front along, or pressure in, the work chamber.

18. The system of any one of claims 1 to 17 wherein the working pressure is above 10%, but below 50% of the maximum pressure of the reservoir.

19. The system of any one of claims 1 to 17 wherein if the reservoir is an external pressure supply, the working pressure may be equal to that of the external pressure supply, such external pressure supply being regulated as part of the supply to the system.

20. The system of any one of claims 1 to 19 wherein the system is portable and is powered by an onboard reservoir.

21. The system of any one of claims 1 to 20 wherein the dose valve closure occurs fully independently of any input via the triggering method.

22. The system of any one of claims 1 to 21 wherein the operating range of the working pressure is regulated between 13 bar and 60 bar.

23. The system of any one of claims 1 to 4 wherein the high-pressure working fluid is non-combustible in use in the system.

24. A device to operate on a high-pressure working fluid, comprising or including, A reservoir of high-pressure working fluid, with a fluid connection supplying the high-pressure working fluid at a working pressure to, A dose chamber to contain a volume of high-pressure working fluid, A dose valve, biased to close, and able to be triggered open, between the dose chamber and, A working chamber, into which a charge of the high pressure working fluid is released from the dose chamber via the dose valve at a first end of the working chamber, to undergo a first expansion in the working chamber and do work therein to or towards a second end of the working chamber, distal from the first end, the dose valve closing again before a pressure front of the charge in the working chamber has travelled less than or equal to halfway between the first end and the second end, thereafter allowing a second expansion of the charge to continue doing work, the fluid connection having a flow restriction which is significantly less than a flow capacity of the dose valve, Wherein when the work is completed, the charge in the working chamber is at a pressure less than or equal to half the working pressure.

25. The device and claimed in claim 24 wherein the working pressure is a controlled working pressure.

26. The device as claimed in either 24 or 25 wherein the volume of the dose chamber to the working chamber is at a ratio of 1 to 1.

27. The device as claimed in any one of claims 24 to 26 wherein the volume of the dose chamber to the working chamber is at a ratio range of 1 to 2 and 1 to 20.

28. The device as claimed in any one of claims 24 to 27 wherein the bias to close the dose valve is derived from fluid pressure, for example pressure acting on a pressure area, or a mechanical spring.

29. The device as claimed in any one of claims 24 to 26 wherein there is a pressure regulator between the reservoir and the dose chamber.

30. The device as claimed in claim 29 wherein the pressure regulator and dose valve ensure the dose chamber consistently has at least one specified pressure or energy state, irrespective of the reservoir pressure while the reservoir is between a maximum allowable pressure and the working pressure.

31. The device as claimed in any one of claims 24 to 30 wherein the dose chamber is concentric to the working chamber.

32. The device as claimed in any one of claims 24 to 31 wherein the dose valve is concentric to the working chamber.

33. The device as claimed in any one of claims 24 to 32 wherein the reservoir could be a self-contained tank, or a tethered supply from a high-pressure fluid source, such as a tank, compressor or the like external pressure supply.

34. The device as claimed in any one of claims 24 to 33 wherein the charge expands, pushes against and accelerates, a workload and the pressure front lies behind the workload, in the work chamber in order to extract work from the charge.

35. The device as claimed in any one of claims 24 to 34 wherein the dose valve is opened by a trigger which can be mechanical, pneumatic, electrical or any other means of opening the flow between the dose chamber and work chamber via the dose valve, and may be operated by hand, for example a finger trigger or by a machine.

36. The device as claimed in any one of claims 24 to 35 wherein the workload is captive, for example a piston or is non-captive for example a projectile.

37. The device as claimed in any one of claims 24 to 35 wherein there is no workload in the chamber as such, but rather the pressure front ejects from the working chamber to cause an effect external to the working chamber.

38. The device as claimed in any one of claims 24 to 237 wherein flow from the reservoir to the dose chamber is eliminated when the dose valve is open, for example statically such as a one-way valve, or selectively openable valve, or dynamically such as a restriction.

39. The device as claimed in claim 38 wherein such flow elimination is located within the regulator or trigger or is another mechanism.

40. The device as claimed in any one of claims 24 to 39 wherein the dose valve closure is at least in part controlled by an elastic element, such as a spring, whether compressive or extensive.

41. The device as claimed in any one of claims 24 to 40 wherein the dose valve closure is controlled via a mechanism which ties the closure of the dose valve to a specific amount of movement of the pressure front along, or pressure in, the work chamber.

42. The device as claimed in any one of claims 24 to 41 wherein the working pressure is above 10%, but below 50% of the maximum pressure of the reservoir.

43. The device as claimed in any one of claims 24 to 41 wherein if the reservoir is an external pressure supply, the working pressure may be equal to that of the external pressure supply, such external pressure supply being regulated as part of the supply to the device.

44. The device as claimed in any one of claims 24 to 43 wherein the device is portable and is powered by an onboard reservoir.

45. The device as claimed in any one of claims 24 to 44 wherein the dose valve closure occurs fully independently of any input via the triggering method.

46. The device as claimed in any one of claims 24 to 45 wherein the operating range of the working pressure is regulated between 13 bar and 60 bar.

47. The device as claimed in any one of claims 24 to 46 wherein the high-pressure working fluid is non-combustible in use in the device.

48. A method of operating on a high-pressure working fluid, comprising or including, supplying a high-pressure working fluid from a reservoir, at a working pressure, containing a volume of the supplied high-pressure working fluid in a dose chamber, Biasing closed a dose valve, from the dose chamber, Triggering open the dose valve to allow a charge of the high-pressure fluid to flow from the dose chamber into a first end of a working chamber, and undergo a first expansion and do work in the working chamber, Closing the dose valve before a pressure front of the charge has travelled half way down the working chamber from the first end, such that the charge undergoes a second expansion in the working chamber and continues to do work therein, toward a second end of the working chamber, distal from the first end, Restricting a flow of high-pressure working fluid from the reservoir to the dose chamber to significantly to less than a flow of the dose chamber to the working chamber via the dose valve, Wherein when the second expansion reaches the second end the charge is at a pressure less than or equal to half the working pressure.

49. The method as claimed in claim 48 wherein the volume of the dose chamber to the working chamber is at a ratio of 1 to 1.

50. The method as claimed in either of claim 48 or 49 wherein the volume of the dose chamber to the working chamber is at a ratio range of 1 to 2 and 1 to 20.

51. The method as claimed in any one of claims 48 to 50 wherein the bias to close the dose valve is derived from fluid pressure, for example pressure acting on a pressure area, or a mechanical spring.

52. The method as claimed in any one of claims 48 to 51 wherein there is a pressure regulator between the reservoir and the dose chamber, whether onboard the tool, or separate if a tethered supply.

53. The method as claimed in any one of claims 48 to 52 wherein the pressure regulator and dose valve ensure the dose chamber consistently has at least one specified pressure or energy state, irrespective of the reservoir pressure while the reservoir is between a maximum allowable pressure and the working pressure.

54. The method as claimed in any one of claims 48 to 53 wherein the dose chamber is concentric to the working chamber.

55. The method as claimed in any one of claims 48 to 54 wherein the dose valve is concentric to the working chamber.

56. The method as claimed in any one of claims 48 to 55 wherein the reservoir could be a self-contained tank, or a tethered pressure supply from a high-pressure fluid source, such as a tank, compressor or the like external pressure supply.

57. The method as claimed in any one of claims 48 to 56 wherein the charge expands, pushes against and accelerates, a workload and the pressure front lies behind the workload, in the work chamber in order to extract work from the charge.

58. The method as claimed in any one of claims 48 to 57 wherein the dose valve is opened by a trigger which can be mechanical, pneumatic, electrical or any other means of opening the flow between the dose chamber and work chamber via the dose valve, and may be operated by hand, for example a finger trigger or by a machine.

59. The method as claimed in any one of claims 48 to 58 wherein the workload is captive, for example a piston or is non-captive for example a projectile.

60. The method as claimed in any one of claims 48 to 58 wherein there is no workload in the chamber as such, but rather the pressure front ejects from the working chamber to cause an effect external to the working chamber.

61. The method as claimed in any one of claims 48 to 60 wherein flow from the reservoir to the dose chamber is eliminated when the dose valve is open, for example statically such as a one-way valve, or selectively openable valve, or dynamically such as a restriction.

62. The method as claimed in claim 61 wherein such flow elimination is located within the regulator or trigger or is another mechanism.

63. The method as claimed in any one of claims 48 to 62 wherein the dose valve closure is at least in part controlled by an elastic element, such as a spring, whether compressive or extensive.

64. The method as claimed in any one of claims 48 to 63 wherein the dose valve closure is controlled via a mechanism which ties the closure of the dose valve to a specific amount of movement of the pressure front along, or pressure in, the work chamber.

65. The method as claimed in any one of claims 48 to 64 wherein the working pressure is above 10%, but below 50% of the maximum pressure of the reservoir.

66. The method as claimed in any one of claims 48 to 64 wherein if the reservoir is an external pressure supply, the working pressure may be equal to that of the external pressure supply, such external pressure supply being regulated as part of the supply.

67. The method as claimed in any one of claims 48 to 66 wherein the method includes the step of being portable and powered by an onboard reservoir.

68. The method as claimed in any one of claims 48 to 67 wherein the dose valve closure occurs fully independently of any input via the triggering method.

69. The method as claimed in any one of claims 48 to 68 wherein the operating range of the working pressure is regulated between 13 bar and 60 bar.

70. The method as claimed in any one of claims 48 to 69 wherein the method does not allow combustion of the high-pressure working fluid in use.

71. A system as described herein with reference to any one or more of the accompanying drawings.

72. A device as described herein with reference to any one or more of the accompanying drawings.

73. A method as described herein with reference to any one or more of the accompanying drawings.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0136] Preferred forms of the present invention will now be described with reference to the accompanying drawings in which;

[0137] FIG. 1A shows a schematic view of a prior art system, in this case a nail gun, run with a tether supplying pressurized air from a compressor,

[0138] FIG. 1B shows a stage by stage of operation of the applicant's own prior art device that utilizes a single stage expansion of the high pressure fluid in the working chamber,

[0139] FIG. 2A Shows a performance graph of pressure behind the piston verses travel of the piston of a prior art device as the nail gun of FIG. 1A for delivering an energy of 250 Joules,

[0140] FIG. 2B shows an expansion of the working fluid in the working chamber verses position along the working chamber of the workload of the prior art device in FIG. 1B, the behind piston working fluid pressure verses position for this system is overlaid on FIG. 7,

[0141] FIG. 3 shows a side cross sectional view of a device or system configured to use, and follow the method of the present invention, in this case for a nail gun also,

[0142] FIG. 4 shows the working fluid pressure (behind the piston) verses displacement of the workload or pressure front along the working chamber as a graph for the device shown in FIG. 3,

[0143] FIG. 5 shows the working fluid temperature verses displacement of the workload or pressure front along the working chamber, again behind the piston, as a graph for the device shown in FIG. 3,

[0144] FIG. 6 shows the working fluid volume verses displacement of the workload or pressure front (behind the piston) along the working chamber as a graph for the device shown in FIG. 3,

[0145] FIG. 7 shows a similar graph to that of FIG. 4 of the working fluid pressure behind the piston verses displacement of the work load or pressure front along the working chamber as a graph for the device shown in FIG. 3, overlaid in red and dashed line with the pressure versus displacement for a single stage expansion prior art product (for example that shown in FIG. 1B), to illustrate the improved energy extraction,

[0146] FIG. 8 shows a similar graph to that of FIG. 5 of the working fluid temperature behind the piston verses displacement of the work load or pressure front along the working chamber as a graph for the device shown in FIG. 3, overlaid in red and dashed line with the temperature versus displacement for a single stage expansion prior art product (for example that shown in FIG. 1B), to illustrate the improved energy extraction,

[0147] FIG. 9 shows a similar graph to that of FIG. 6 of the working fluid volume verses displacement of the work load or pressure front along the working chamber as a graph for a device shown in FIG. 3, overlaid in red and dashed line with the volume versus displacement for a single stage expansion prior art product (for example that shown in FIG. 1B), to illustrate the improved energy extraction,

[0148] FIG. 10 shows the device of FIG. 3 and the pressure versus displacement graph of FIG. 6 at each stage for (A) prior to opening the dose valve and the workload at the first end, (B) the dose valve opening after triggering and the workload starting movement down the working chamber, (C) the dose valve closing before the workload has moved to half the length of the working chamber, and (D) the workload reaching the end of the work,

[0149] FIG. 11 shows a device that uses the present invention showing its layout in a tether-less nail gun, and,

[0150] FIG. 12 shows a graph of working fluid pressure (behind the piston in the working chamber) verses time for the device as shown in FIG. 11, the blue line showing the distinct knee of the two stage expansion, and in comparison the orange line shows the pressure behind the piston of the prior art product in FIG. 1B, the data being gathered from physical measurement of a test device configured as per FIG. 11 running the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0151] Preferred embodiments will now be described with reference to FIGS. 3 through 11, and discussions on the prior art with reference to FIGS. 1A,B and 2A, B.

Thermodynamic Efficiency

[0152] At a certain operating pressure, a measure of energy can be extracted from each shot volume or charge of a high-pressure operating fluid. A simple benchmark is the amount of energy that is liberated by a traditional pneumatic piston, assuming idealised flow, friction, and we ignore ambient pressure.

[0153] Work extracted from such a system, assuming ideal conditions as is at most:

[00001]$\begin{array}{c}\mathrm{Energy}=\mathrm{Force}?\mathrm{Distance}\\ =\left(\mathrm{Pressure}?\mathrm{PressureArea}\right)?\mathrm{Distance}\\ =\mathrm{Pressure}?\left(\mathrm{PressureArea}?\mathrm{Distance}\right)\\ =\mathrm{Pressure}?\mathrm{Volume}\\ =\mathrm{PV}\end{array}$

[0154] Now, providing a Single Stage Adiabatic expansion system with that same amount of pressure and volume to use in one cycle, how much energy can it possibly liberate? The ratio will give the relative efficiency of this system compared to the Traditional system above, that traditional system liberating 100% at any given pressure, and with other systems liberating either <100% if less efficient, or >100% if more efficient.

[0155] If we set V.sub.USED=1.0 for simplicity, and allow the gas to expand down to ambient pressure P.sub.FINAL=1.0 also for simplicity and to show the ideal expansion case, we can find that a single stage adiabatic system can liberate:

[00002]$\mathrm{Energy}=\frac{P\left[{\left(P^{\frac{1}{?}}\right)}^{1-?}-1\right]}{1-?}$$??1.4\mathrm{for}\mathrm{air},\mathrm{nitrogen},\mathrm{oxygen}$$??1.3\mathrm{for}{\mathrm{CO}}_2$

[0156] For any gas, when comparing this idealised version of a single stage adiabatic system to a traditional E=PV system. The adiabatic system has an efficiency below 100% at very low pressures, but efficiencies significantly above 100% at high pressures.

[0157] How does the double expansion of the present invention allow access to efficient operation?

[0158] Double expansion is achieved by closing the dose valve 4 shown in FIG. 3 during the expansion event, which truncates the expanding volume to only the working chamber 6 and allows pressure of the charge 7 to drop extremely fast as the pressure front 11 or workload 19 (for example the piston) moves down the working chamber 6, such as shown in FIG. 3 in a ready to trigger or ready to work state. The operation of such a system, its method and a device utilising these is explained shortly.

[0159] One of the assumptions presented above was that P.sub.FINAL is low (1.0), when a system has a high operating or working pressure (e.g. 15-60 atmospheres) the expansion ratio required to bring the gas down to (or close to) ambient pressure, for example atmospheric (1.013 bar) is very high.

[0160] One way to achieve this large expansion ratio is to use a large working chamber in comparison to the volume of the dose chamber to allow for this large expansion ratio, however this is often not feasible within the allowable space/weight envelope for a given system, for example in hand held tools.

[0161] Double expansion allows for very high expansion ratios (and therefore >100% relative efficiencies) to be achieved in small, compact, and lightweight systems which don't require large working chambers.

[0162] This is the key utility of the application of a high pressure, double expanding adiabatic systemit is able to generate high efficiency and high energy density systems, and high specific energy systems.

[0163] A device, system and method in keeping with the present invention will now be described with reference to FIGS. 3 through 12.

[0164] The device 22 shown in FIG. 3 operates on a high-pressure working fluid provided from a reservoir 2, in this case shown as a tank, via a fluid connection 15. However, the device 22 could equally be tethered via the fluid connection 15 to an external reservoir 2 supply such as, but not limited to a compressor, directly, or indirectly via a manifold (not shown).

[0165] The fluid connection 15 leads to a trigger 20, and optionally, though preferably there is a regulator 18 between the reservoir 2 and the trigger 20, either at some point along the fluid connection 15, or directly connected to the reservoir 2 and from which the fluid connection 15 then extends, or the fluid connection. Alternatively the fluid connection 15 extends from the source (and may well be the tether where the source is a compressor, manifold or similar) to the regulator 18 which then connects into the trigger 20.

[0166] The regulator 18 reduces the pressure from the source or reservoir 2 down to the working pressure. For example the reservoir may be at 310 bar and the regulator reduces this to 40 bar working pressure. In the preferred form the regulator 18, or elsewhere in the supply into the device, possibly even up to the dose chamber 3 there also may be a flow restriction that throttles the flow of high-pressure working fluid from the reservoir 2. The flow restriction has a maximum flow rate that is much less that the maximum flow rate of the dose valve 4 when open.

[0167] Further controlling the flow of high-pressure working fluid from the source 2 is the trigger 20. When in a standby, or ready to fire position, such as shown in FIG. 3 the trigger allows a fluid connection, throttled, restricted or otherwise, between the reservoir 2 and the dose chamber 3, and fills the volume of the dose chamber 3 with high pressure fluid 1 at the working pressure.

[0168] In the device 22 shown there is a workload 19 in a working chamber 6 at rest at a first end 8 of the working chamber 6. The workload 19 in this case is a piston, that is captive within the working chamber 19, and the device may be for example, but not limited to, a nail gun, or pest control trap. In other configurations, the workload 19 may be ejected, such as for example, but not limited to, a ballistic application, launching an item, or similar. In other configurations, there is no physical workload, but rather a pressure wave issues from the working chamber 6 and may act to disturb or otherwise something externally, for example dust control or clearance, snow clearance, pressing one item against another or similar. The working chamber has a length X, 12 within which expansion can occur, this may be the swept path of the workload, such as the piston, projectile, or the length of working chamber within which the pressure wave is confined.

[0169] A dose valve 4, bias closed, in this case by a spring 23, prevents the high-pressure working fluid from exiting the dose chamber 3 and thus from entering the working chamber 6. The high pressure working fluid also acts on a hammer 24 on a front side first area thereof and biases this into a ready to fire position as shown, against an equal pressure back side second area thereof, the second side of lower area than the first area.

[0170] When actuated, either manually by a user, directly or indirectly, or by, or via, a mechanism, remotely or automatically or controlled by a separate system, the trigger 20 (in this case a sliding spool valve), closes supply of high pressure fluid from the reservoir 2, and then allows the high pressure working fluid acting on the first area of the hammer to vent to reference or atmosphere. This allows the hammer to fire towards the second end 9 and impact the dose valve 4. This impact opens the dose valve 4 and allows a charge of working fluid in enter the working chamber 6 behind, in this case, the workload 19. When the dose valve 4 first opens there is an equalization between the dose chamber 3 and the working chamber 6 as the charge expands into the working chamber, but no work is initially done in this very short time period. The working fluid then undergoes a first expansion 10 and the pressure front 11 of expanding fluid sends the workload, in this case, down the working chamber 6 toward the second end.

[0171] As the high-pressure working fluid is undergoing its first expansion from the dose chamber 3 into the working chamber 6, and the pressure front 11, and thus workload 19 move down the working chamber, the dose valve 3 begins to close under action of a bias 5. The dose valve 3 closes before the pressure front 11 reaches at most, half the length of the working chamber 6, that is X/2. At this point no more high-pressure working fluid can enter the working chamber 6 from the dose chamber 3. At this point the charge of working fluid in the working chamber 6 undergoes a second expansion 14, extracting further energy from the charge.

[0172] The trigger 20 plays no further role in actuating the device once it has dumped the high-pressure working fluid from the front side first area of the hammer. Its only purpose is to initiate the dose valve 4 opening and it has part to play in how long or far the dose valve 4 opens. The trigger is returned to the ready to fire state (shown in FIG. 3) and the hammer is reset, and the dose chamber 3 if necessary is recharged from the reservoir 2. The pressure front 11, and in this example the workload 19 continues down the working chamber 6. Where the workload 19 is a piston, for example, it compresses gas or fluid in front of it which then aids in returning the workload from the second position back to the first position and the device is ready to fire again.

[0173] The pressure, temperature and volume of the charge 7 of working fluid acting in the working chamber 6 will now be described with reference to FIGS. 4 through 10.

[0174] It is clear from each of the FIGS. 4 through 10 there are two expansion events occurring, the first expansion 10 and the second expansion 14. The transition of these, seen as the cusp 26 in FIGS. 4, 5, 7, and 8, showing the pressure and temperature denotes where the dose valve 4 closes. This is also visible as a step in FIGS. 6, 9 and 10.

[0175] The timing of the closing of the dose valve 4 is important here, as it allows an initial charge of high-pressure working fluid to leave the dose chamber and enter the working chamber. The charge then undergoes an initial expansion and its pressure front, representing the movable, or unconfined boundary within the working chamber, moves along the working chamber 6. By restricting the open time of the dose valve 4 to less than or equal to the time it takes for the pressure front 11 to travel to half the length 12 of the working chamber 6 then the charge 7 is able to under go two expansion events and release more energy and therefore do more work, than the single expansion event, such as shown in FIGS. 2A and B for prior art systems. The prior art system in FIG. 9 reaches expansion to near 100 cubic centimetres when the pressure front 11 reaches about 75 mm down the working chamber. In contrast the present invention performance reaches about 75 cubic centimetres expansion when it has travelled 110 mm down the working chamber.

[0176] Comparing the typical prior art system from that in FIG. 1B and its expansion performance in FIG. 2B to that of the present invention and its expansion performance in FIG. 6, and the overlay of the prior art performance and the present invention in FIG. 9 it is clear the present invention has continued expansion occurring over the full movement of the pressure front 11 (and therefore any workload 19) in the working chamber 6.

[0177] Comparing the pressure and temperature graphs of the single stage expansion of the prior art being the single curve, and the two-stage expansion of the present invention, being the double curve with the cusp 50, in FIGS. 7 and 8 over the length of the working chamber. The use of the pressure in the prior art at the end of the working chamber is about 11-12 bar. In comparison the present invention is much closer to 0 bar (relative to atmospheric), and is about 1 to 2 bar. It is clear the present invention, in this application, uses approximately 10 bar more of the pressure in the charge released into the working chamber. This shows there is a much greater proportion of available energy used, or released, in the present invention over the prior art for the same charge in the working chamber.

[0178] Likewise, the temperature graph in FIG. 8 comparing the prior art single stage expansion, being a single curve, and the two stage expansion of the present invention, being the double curve with the cusp 50, shows an energy use advantage in the present invention's favour. For the same geometry the single stage expansion ends at about 175 degrees Kelvin, at full travel. In comparison the present invention with two stage expansion ends at about 75 degrees Kelvin, 100 degrees Kelvin lower. Since temperature is a measure of energy in the charge, then more energy has been used in the present invention, than in the single stage prior art. Thus more energy is extracted from the charge by the present invention for the same gas charge and geometry.

[0179] Looking at FIG. 9 we see that the prior art single stage expansion system expands to its maximum well before the full length of the working space. In contrast the present invention undergoes the first expansion 10 and then with the dose valve closing, the second expansion 14, at the knee or cusp 50. The two-stage expansion then goes on to its just under its full expansion at or near the full length of the working space.

[0180] This indicates that for the same geometry as the prior art the present invention is more efficient as it extracts more energy for a given charge. Thus, for a given reservoir volume the present invention will allow more cycles, for example more fasteners driven, more pest control cycles, more projectiles discharged, or more pressure waves emitted.

[0181] The stages of the present method are illustrated in FIG. 10 with the movement of the parts of the device aligned with the volume changes of the charge over the length of the working chamber, and the timing of the system.

[0182] The device, as shown from FIG. 3 and in FIG. 10A is ready to fire. The same integers apply here as in FIG. 3 but are omitted for clarity. The dose chamber 3 is full of high-pressure working fluid at the working pressure of about 40 bar, the dose valve 4 is closed and the workload 19, a piston in this case is at the first end 8.

[0183] The trigger is actuated in FIG. 10B, and the pressure in front of the hammer 24 is dumped, allowing the hammer 24 to impact the dose valve 4 and open it to allow the charge to enter the working chamber 6 and the pressure front 11 begins to expand down the working chamber 6, in this case acting on the piston to drive it from the first end 8 toward the second end 9. The system's pressures and areas and biases are designed such that the dose valve 4 closes to cut the dose chamber 3 off from the working chamber 6, before the pressure front 11 reaches half the length 12, X of the working chamber 6. In this case the dose valve 4 closes well before this at 20 mm in FIG. 10C. This removes a portion of volume the charge of working fluid could otherwise expand in, that portion of volume being the dose chamber 3, and keeps it confined to the working chamber. This effectively resets the volume available for the charge once the first expansion 10 has occurred.

[0184] Once the trigger is actuated, it again has no bearing on the speed or time the dose valve 4 is open and when it closes again, and therefore the rate at which the pressure front will move down the working chamber. This is predetermined and the trigger plays no part in it, other than starting the sequence. This applies independent of the speed with which the trigger is actuated, and whether the trigger is actuated again prior to the cycle being completed.

[0185] From 20 mm onward in the example shown the charge expands in the working chamber only as the pressure front moves from the first end 8 toward the second end 9 in FIG. 10D.

[0186] Once the pressure front 11, in this case acting on the piston reaches the second end 9 of travel of the working chamber 6 the piston returns due to the pressure in front of it, moving it back to the first end 8. The cycle is complete and the device and system, using this method is ready to actuate again.

[0187] A device 22 further encompassing this method and system is shown in FIG. 11, this time as a hand held nail fastener with onboard storage or reservoir 2. This on-board reservoir 2 can be topped up from a separate system, by temporary connection, for example to a tank of compressed air. The device 22 can then be disconnected and used until the reservoir empties to below the working pressure at which point the device will no longer fire. In the image shown the red portion is at storage pressure, the yellow at working pressure, and the blue the pressure as the charge expands.

[0188] The pressure performance of the device in FIG. 11 is shown in FIG. 12 for pressure (behind the workload 19) verses workload 19 displacement. In this case the workload 19 is the piston the working fluid acts on. The first expansion 51 is as the dose valve 4 is opened, and the working fluid enters the working chamber 6, the piston 19 is moving down the working chamber 6. The dose valve 4 then closes before the pressure front in the working chamber 6 in this case as the workload 19 (the piston) has moved halfway down the work chamber 6 and the second expansion 52 begins. The expansion volume for the working fluid for the second event 52 is therefore reduced to only the working chamber 6, and the workload 19 continues to be driven down the working chamber losing pressure as it does so. At the end of the working stroke, when the work of the charge of working fluid in the working chamber is complete the residual pressure in the working chamber 19 (that is behind the workload 19) is shown as about 4 bar, which is well below the working pressure of, in this case, about 40 bar. In contrast the prior art product, with a working pressure of 40 bar also (shown in the orange line) has a working chamber pressure of about 25 bar and sees little reduction in that pressure before reaching the end of the stroke when the work is done, as can be seen, as it is still sitting at about 25 bar. Therefore, the present invention has used about 21 bar more of pressure for the same stroke length and energy delivery. The prior art product dumping the energy from that 21 bar difference to atmosphere and therefore wasting it the energy in that pressure.

[0189] Surrounding the device is atmospheric or reference pressure. If the device is intended to operate at a higher or lower reference pressure, then that is the pressure surrounding the device.

[0190] The foregoing description of the invention includes preferred forms thereof. Modifications may be made thereto without departing from the scope of the invention.