Hydraulically Powered Demolition Device

Abstract

A hydraulic hammer for driving a demolition tool is disclosed. The hammer carries a piston which reciprocates in a cylinder. High pressure fluid drives the hammer to a retracted position to compress an air spring. The piston is momentarily held in the retracted position while an annular valve sleeve disposed about the piston is automatically moved downwardly by differential fluid pressure to open an annular passageway around the piston to permit the fluid to freely bypass the piston. The piston is then released so that the stored energy rapidly accelerates the hammer through an impact stroke without significant impedance from fluid and without displacing fluid from the cylinder. Since high pressure fluid is required only on the retraction stroke, the volume of fluid necessary to operate the hammer is essentially reduced by 50 percent, thus permitting either the force or frequency to be doubled for a given high pressure fluid source. A safety shuttle valve is also included which is cooperable with the tool member to bypass pressure fluid to reservoir until a predetermined load is imposed on the tool.

Description

The present invention relates generally to a fluid powered repetitive impact device, and more specifically relates to a hydraulic demolition hammer.

Reciprocating tools for delivering high impact blows to demolish pavement, rock, and the like are well known. These impact tools have heretofore been predominately driven by air pressure and are characterized by the well-known jackhammer. Large versions of the jackhammer have heretofore been mounted on the boom of a backhoe. These devices are characterized by being able to deliver relatively high frequency, but relatively low impact forces. As a result, even the larger of these devices tends to powder the harder materials due to the relatively low force. However, the high frequency to some extent compensates for this deficiency. Additionally, air driven hammers of this type produce a very high noise level as a result of the rapid venting of the air from the cylinder. This is particularly objectionable in metropolitan areas where a major portion of this type of activity is carried out, and the resulting noise pollution is coming under increasingly severe criticism.

A hydraulically driven hydraulic hammer has offered for a long time the potential of increased forces required to fracture concrete, rock and similar materials. Additionally, hydraulically driven devices tend to be much quieter as a result of eliminating the venting noise from an air hammer. However, no hydraulic hammer has heretofore been introduced to the market having sufficient reliability to gain wide acceptance. Additionally, hydraulic hammers of this type have heretofore been relatively inefficient because of the problem of venting the hydraulic fluid from the low pressure side of the piston during the impact stroke. One approach which has heretofore been taken to overcome this deficiency is to drive a hammer against an air spring during a retraction or compression stroke by means of a hydraulic linear actuator including a piston and cylinder, and then by disconnecting the hydraulic actuator from the hammer to allow the energy stored in the spring to accelerate the hammer against the demolition tool. These devices have not only proven to be unreliable, but are also relatively slow in that hydraulic power fluid must return the linear actuator to effect mechanical reengagement with the hammer after each impact stroke in preparation for the next compression stroke.

The present invention is concerned with an impact device of this type which is hydraulically driven and relatively quiet, is capable of delivering an impact stroke of high efficiency because it is substantially unimpeded by fluid an does not require a mechanical disconnect and reconnect during each cycle, and which uses high pressure fluid only during the compression stroke to provide, for a given hydraulic power supply, either twice the impact force, or twice the frequency of a device employing a double acting piston.

More specifically, the present invention is concerned with an impact device in which the shaft of a hydraulic linear actuator is a reciprocating hammer. Hydraulic fluid is applied to one face of the piston of the actuator to drive the hammer through a retraction stroke to compress an air spring. Fluid pressure is then efficiently bypassed from one side of the piston to the other to permit the air spring to accelerate the hammer without the hydraulic fluid materially impeding its motion. Since no hydraulic fluid is displaced from the cylinder during the impact stroke, the volume of hydraulic fluid required is reduced substantially in half. The hammer thus freely impacts an anvil of a tool assembly which transfers the energy to the material to be demolished.

In the preferred form of the invention, the piston and a sleeve valve effectively divide the cylinder into two fluid expansible chambers during the retraction stroke. However, at the end of the retraction stroke, the sleeve is separated from the piston while the piston is retained at the top of the retraction stroke during the downward stroke to permit the hydraulic fluid to bypass the piston.

Still more specifically, the piston moves into a retaining cavity at the top of the retraction stroke as the valve sleeve is mechanically separated from the piston. The valve sleeve is then shifted to the end of the impact stroke by differential pressure at which time an exhaust port is opened to release the piston from the retaining cavity to start the impact stroke.

Additional details and features of the preferred embodiments of the invention are set forth in the appended claims. The invention itself, however, as well as other objects and advantages thereof, may best be understood by reference to the following detailed description of illustrative embodiments, when read in conjunction with the accompanying drawings, wherein:

FIG. 1 shows a side view of the hammer of the present invention mounted on the end of a conventional backhoe boom;

FIG. 2 is a longitudinal sectional view illustrating the details of the present invention;

FIG. 2A is an enlarged view of the center portion of the sectional view of FIG. 2;

FIG. 3 is a sectional view taken along lines 3--3 of FIG. 2; and

FIGS. 4 through 7, in simplified schematic form, illustrate the operation of the hammer.

Referring now to the drawings, a demolition device in accordance with the present invention is indicated generally by the numeral 10 in FIG. 1. The demolition device 10 is mounted on a pair of bracket plates 14 which are connected to the end of boom 11 of a typical construction machinery unit such as a backhoe, not shown. As is conventional with such machinery, boom 11 may be swung horizontally or raised vertically to hold the device 10 against any desired object with considerable force. A hydraulic cylinder 15 is associated with the boom 11 and is employed to pivot the hammer structure 10 about pinned construction 12. Hydraulic lines 84 and 64 connect the hammer to a source of fluid pressure and to a reservoir. The demolition or breaking of hard objects such as pavement, roadbeds, rocks and other materials is accomplished by chisel tool 20 which engages the material.

In operation the device will generally assume a position as seen in FIG. 1 and therefore throughout the specification the relative terms "upper" and "lower" refer to a unit positioned as in FIG. 1. The device is shown in FIG. 2 in a horizontal position with the upper end to the left-hand side of the drawing for purposes of illustration. The hammer 10 includes upper end chamber 22 which houses the air spring or other similar energy storage device. Chamber 22 is generally rectangular and is defined by a frame including upper cover plate 23 and side members 25 which are joined at their lower ends to base plate 24. Base plate 24 is provided with a central circular opening 26 which receives the axial shaft portion 27 of hammer member 28. Hammer 28 diverges at the upper end to enlarged head 29 which is disposed within chamber 22. A cushion plate 30 is interposed between tapered head 29 of the hammer and base plate 24. Cushion plate 30 has a conical bore 32 which receives generally frusto conical dampening member 34. A similarly shaped hardened steel ring 35 is provided at the upper surface of the dampening member 34 to abut the tapered underside of head 29 when the hammer is in the extended position. Typically, cushion plate 30 would be formed of steel and cushion ring or dampening member 34 of a suitable resilient material such as an elastomer or rubber. Bearing plate 38 is secured to the upper end of hammer head 29 and approximately corresponds in diameter to the cushion plate 30. The upper surface of bearing plate 38 has circular cavity 39 which receives metal bumper pad 40. Pad 40 is an integral part of air spring device 45 comprised of a compliant air chamber 42 having a central retaining ring 43. Another bearing pad 44 is provided between the surface of upper end of air chamber 42 and the inside of cover plate 23 of the chamber 22.

The chamber 42 of air spring 45 is formed of a compliant material such as fabric and rubber and iis inflatable to a predetermined pressure with a compressible fluid such as air by means of a suitable valve, not shown. As hammer 28 is restricted, the air spring will be compressed, storing energy which is utilized to drive the hammer downwardly on the impact stroke. The bearing pads 40 and 44 serve to distribute the thrust load of the hammer over the area of the chamber and the cushion plate 30 absorbs energy if for any reason the tool 20 is not in position to stop the travel of the hammer before the head 29 reaches the plate 30. It will be obvious to those skilled in the art that energy storing devices, other than the air spring device shown could also be utilized. For example, pneumatic air spring assembly 45 could be replaced with a conventional compression spring and give similar results.

The main shaft portion 27 of hammer 28 extends axially within intermediate cylindrical housing section 50. Housing section 50 is provided with a stepped axial bore having upper major diametral section 52 and reduced diametral section 53 at the lower end which define annular expansible chambers 60 and 90, respectively, around hammer section 27. The upper chamber 60 is closed by bearing member 55 which is generally annular and held in place by engagement at interior shoulder 56 and abutting exterior snap ring 57. Concentric bore 59 in member 55 bears against hammer shaft 27 and, along with appropriate packing or sealing members 58, prevents fluid leakage from annular cylinder chamber 60. An extension 62 of bearing 55 extends axially into chamber 60 and serves as an abutment for the reciprocating internal valve sleeve. Exhaust port 61 communicates with chamber 60 through bearing portion 62. Lower chamber 90 is closed by bearing member 65 which similarly engages the housing bore at shoulder 66 and is held in place against axial movement by snap ring 67 engaging the bore and the end face of bearing member 65. Similar sealing members 68 engage the surface of shaft 27 at concentric bore 69 to prevent leakage along the hammer shaft 27. The inner end of member 65 is provided with interior circular groove 92 extending adjacent bore 53.

Piston 70 in the form of a generally annular ring is affixed to hammer shaft 27 by snap rings 72 and 73 which abut opposite faces of the piston. The piston is provided with a frustro conical surface 71 exposed to chamber 90 tapering from peripheral sealing surface 74.

Reciprocation of the hammer is automatically effected by sequencing valve 75. The valve 75 is in the form of a differential area cylindrical sleeve 76 which is in sliding, sealed with bores 52 and 53. The differential area is provided by the difference in diameters of the cylinder bores 52 and 53, the latter being the smaller. Annular metal piston rings 88 and 78 provide sliding fluid seals with the bores 52 and 53, respectively. In the position shown in FIG. 1, valve sleeve 75 seals off outlet port 79 which is connected to the low pressure reservoir. The upper end 80 of sleeve 76 is provided with a slight taper 81 to admit the piston 70 more easily on the downstroke. An annular recess 82 extends around the exterior of sleeve 76 at upper end 80 and one or more radial notches 87 (see FIG. 3) provide fluid communication with the recess 82 when the sleeve abuts the lower end of bearing 55. As mentioned, end 80 of valve 75 has a larger effective area than the opposite end as a result in the difference in diameters of the bores 52 and 53, and thus will be rapidly shifted downwardly when high pressure is applied to both ends of the sleeve as the piston 70 leaves the sleeve on the upstroke.

Inlet port 91 communicates with chamber 90 at undercut groove 92 in bearing member 65. The inner end 93 of the bearing serves as an abutment to engage the end of sleeve valve 75 when the sleeve assumes its lowermost position adjacent the tool end.

An anvil 120 is reciprocable in sleeve 95 below the terminal end of the hammer. The anvil has an enlarged shoulder portion 121 which slides within sleeve 95. Stub shaft 122 is impacted by the lower end of hammer member 28.

Hammer 10 also incorporates a shuttle valve 100, which makes the hammer inoperative by diverting high pressure fluid to a reservoir until at least a predetermined load has been placed on the unit at chisel 20. By virtue of the safety feature, the hammer cannot be inadvertently actuated until the hammer is positioned in an operative position. Shuttle valve 100, having a body member in the form of a generally cylindrical sleeve 101, is positioned in chamber 102 defined in sleeve 95. Chamber 102 has cylindrical exterior walls 103 which enlarge at shoulder 108 to bore portion 104. High pressure port 106 and low pressure port 112 intersect the chamber wall adjacent opposite sides of shoulder 108.

The outer surface of the valve sleeve 101 has a peripheral sliding seal 109 within bore 104. In FIG. 2, valve 100 is shown in its uppermost position with the lower end 116 of sleeve 101 engaging shoulder 121 of anvil 120. Peripheral groove 105 extends in sleeve 101 defined by opposite ends 114 and 115. It will be observed that end 115 is of greater cross-sectional area than end 114 due to the increased bore diameter at 103.

Chisel or tool member 20 is reciprocable within lower bearing member 126 and has an appropriately shaped blade end 130. Chisel 20 is formed having a flat face 127 extending longitudinally within bearing 126. A removable pin 129 in bearing 126 engages the flat face 127 to hold the chisel 20 in predetermined rotational position and to retain the chisel 20 within the bearing but is permitted axial movement as determined by the length of flat face 127. The upper end 132 of chisel 130 abuts the lower end 131 of anvil 120.

The hammer 10 is held together by tie rods 145 which extend longitudinally between recesses 144 in plate 24 at upper chamber 22 and recesses 141 in lower bearing member 126. It will be obvious that the hammer can be easily disassembled by simply removing the tie rods to permit bearing 126 to be removed, thus releasing intermediate body section 50. Anvil 120 can then be removed and removal of appropriate snap rings 57 and 67 will permit access to the valving and piston components.

Bracket plates 14 are provided with inwardly depending plates 137 which receive bolts 139 to secure the brackets to the underside of hammer plate 24. Bottom plate 150 secured between the bottom of the brackets defines a socket 151 which receives a portion of tool bearing member 126. The hammer 10 can be separated as a unit from bracket plates 14 by removing bolts 139.

Ideally, the combined mass of hammer 28 and plate 38 is approximately equal to the combined mass of anvil section 120 and chisel 20. In this way, the unit is dynamically balanced and when the compacting blows are dellivered by the hammer 28, undue vibration and rebound of the unit is avoided and maximum energy transfer is achieved.

The construction and operation of the hydraulic hammer of the present invention will be better understood from the following description of operation as shown schematically in FIGS. 4 to 7. The unit initially is in an inactive mode as shown in FIG. 4 with hammer 10 positioned by boom 11 so that chisel 20 engages the material to be broken. The hammer is connected having inlet port 91 in communication with a source of fluid pressure 83 via line 84. A bypass line 107 connects line 84 to inlet port 106. Port 112 is connected to a low pressure reservoir 63 by line 113. Outlet or exhaust ports 61 and 79 are similarly connected to a low pressure reservoir 63 by line 64.

Referring to FIG. 4, when high pressure fluid is introduced into chamber 105, the differential area between ends 114 and 115 results in a net pressure force acting to urge valve 100 and the anvil 120 downwardly. As valve 100 moves downwardly, chamber 105 is placed in communication with low pressure port 112, causing high pressure fluid to be directed to reservoir 63. In this position the unit is inoperable as high pressure fluid is bypassed directly to reservoir, and accordingly, chamber 90 will not be pressurized to actuate the hammer. When valve 100 is moved upwardly by virtue of upward movement of anvil 120, due to the force exerted at chisel 20, chamber 105 will again be moved out of communication with outlet port 112 with peripheral land 109 closing off port 112. Supply fluid will again be directed via port 91 permitting discharge pressure to build up in chamber 90. For typically operating pressures, approximately 600 pounds of force will be required at chisel 20 to overcome the differential hydraulic bias forcing the sleeve valve 100 downwardly. Thus, the hammer cannot be inadvertently actuated until a sufficient load is placed on the hammer to insure that operation of the hammer is intended and that the anvil is in position to prevent the hammer from striking plate 30.

As pressure builds up in chamber 90, valve 75 will be caused to move rapidly upward into engagement with the inner end of upper bearing member 55 as seen in FIG. 5. Intermediate exhaust port 79 will be sealed from communication with chamber 90 at groove 77 by sealing ring 78. Fluid pressure in chamber 90 acting against the area of piston 70, will cause piston 70 to move upwardly, displacing the hammer. As hammer 28 moves upwardly, bearing plate 38 will compress air spring 45, storing energy in the spring. During upward movement of the piston and hammer, cylinder chamber 90 expands in volume with pressure fluid being admitted at port 91. Opposite cylinder chamber 60 contracts in volume with fluid being exhausted through port 61 to reservoir.

When the piston 70 has reached the fully retracted position shown in FIG. 6, the piston is within the interior surface of the inner extension 62 of bearing 55. High pressure fluid behind piston 70 will then pass through radial notches 87 to act on the upper end 80 of valve 75. Since the end 80 of valve 75 has a larger effective surface area than does the opposite end, the differential force will rapidly move valve 75 downwardly into engagement with lower bearing member 65. The piston 70 will be retained in the end of bearing sleeve 62 until seal 88 passes discharge port 79 as is seen in FIG. 7, chamber 90 is placed in communication with exhaust port 79 via recess 85 in the upper end of sleeve 76 and chamber 90 will rapidly depressurize. Once pressure in chamber 90 is vented, the piston 70 leaves the end of bearing 62 and the energy stored in air spring 45 is released, forcing hammer 28 rapidly downwardly to impact the anvil and in turn chisel 20.

It should be noted that once the piston 70 leaves the end of the bearing 62, it is free to move almost unimpeded by the fluid in the cylinder chamber until it again enters the valve sleeve 75. Thus, the energy of the air spring is not dissipated in moving fluid. It is also important to note that no fluid is displaced during the downstroke, i.e., impact stroke of the hammer.

The hammer 28 normally impacts the anvil just before it reaches the downward limit of the stroke where the hammer head engages the cushion plate 30. In this position, the piston 70 is within the upper end of sleeve valve 78 so tha the lower expansible chamber is again sealed as shown in FIG. 4. Thus, as long as sufficient force is applied at chisel 20, the hammer will cycle at a rate determined by the fluid flow rate from the power source.

The hydraulic hammer of the present invention provides a high impact device which can cycle at a relatively high, but controllable rate. Previous hydraulically actuated hammers which are double acting, that is, driven hydraulically in both the retraction and actuation strokes, can cycle at only approximately half the rate at which the hammer of the present invention can cycle for the same fluid supply flow rates annd pressures. This is because the speed of operation of a hydraulic linear device is limited by the rate of flow to the device, the double acting unit requiring pressure flow to be directed to both sides of the piston. Further, the hammer operates at a relatively low noise level with no high frequency sounds due to exhausting or venting of air pressure. The simple valving is highly efficient as most of the energy stored in the air spring is transferred to the hammer to impact and cause the demolition of materials.

It will be obvious that the hammer device of the present invention has broad application to other types of impact tools. For example, the reciprocating hammer could be used for drilling, hand held demolition hammer, as a nail gun, cutting or stamping device and the like. Also, modifications and changes will suggest themselves to those skilled in the art. It is intended that the scope of the present invention be limited only by a fair interpretation of the appended claims.

Claims

What is claimed is:

1. A hydraulic impact device for applying impact forces to a tool assembly comprising:

a housing having an axial bore,

a hammer member slidable in the housing and defining with said bore a cylinder chamber,

energy storage means adapted when compressed to accelerate the hammer in a first direction to deliver an impacting blow to the tool assembly when the hammer is released,

piston means carried on the hammer dividing the cylinder chamber into first and second pressure chambers and movable between first and second positions, the first chamber being that which when pressurized causes the piston to move the hammer in a second direction to the second position to compress the energy storage device,

a high pressure inlet port in the housing communicating with the first chamber,

a first outlet port communicating with the second chamber, and

valve means in slidable contact with the bore and in sealing contact with the piston to cooperate with the piston and selectively isolate the first chamber from the first outlet port whereby the piston and valve are moved in the second direction, the valve being shiftable in the first direction when the piston reaches the second position to provide open communication between the first chamber and the second chamber and thus the first outlet port to permit the storage device to accelerate the hammer by permitting relatively unrestricted return of said piston in said first direction without significant displacement of fluid from the housing.

2. The device of claim 1 wherein said energy storage device comprises a compliant chamber containing a compressible fluid.

3. The device of claim 1 wherein said energy storage device is an air spring.

4. The device of claim 1 further including second valve means for bypassing fluid from said first chamber until at least a predetermined load is applied to said hammer.

5. The impact device comprising:

a housing defining a cylindrical chamber,

a compressible energy storage means attached to the housing at one end of the cylindrical chamber,

a hammer reciprocally disposed in the cylindrical chamber to leave an annular cavity therein and positioned to compress the energy storage device when moved in a first direction and to impact a tool assembly disposed at the other end of the housing when moved in a second direction,

a piston mounted on the hammer and disposed within the annular cavity, the piston being sized to leave a substantial annular opening between the piston and the housing,

a low pressure exhaust port in fluid communication with the end of the annular cavity near the energy storage means,

a high pressure inlet port in fluid communication with the other end of the annular cavity, and

a valve sleeve reciprocally disposed in the housing and sealingly engaging the piston and the housing to divide the annular cavity into first and second expansible fluid chambers when in contact with the piston whereby the piston will move the hammer through a compression stroke to compress the energy storage means, and, alternatively, to freely pass fluid around the piston when separated from the piston to permit the energy storage means to freely accelerate the hammer through an impact stroke to impact the tool assembly,

both ends of the valve sleeve being entirely exposed to hydraulic fluid and pressure shiftable in the direction of the impact stroke when the valve sleeve is separated from the piston as a result of only the supply and return hydraulic pressures.

6. A hydraulic impact device for applying impact forces to a body comprising:

a housing having first, second and third housing sections,

a hammer member having a head in said first housing section and having an axial shaft section extending into a bore in said second section, said hammer shaft and said bore defining an annular cylinder chamber,

said third section housing an anvil and chisel, said chisel adapted to be impacted by said hammer through said anvil,

energy storage means contained in said first section and engagable with said hammer head and adapted when activated to transmit stored energy to said hammer to move said hammer in a first direction to deliver an impacting blow,

piston means carried on said hammer dividing said cylinder chamber into first and second pressure chambers, said first chamber when pressurized causing said piston to move said hammer in a second direction against said energy storage device to activate same,

a first outlet port housing communicating with said second chamber,

a second outlet port in communication with said first chamber,

a supply port in communication with said first chamber, and

sequencing valve means in slidable contact with said bore and said piston, said valve movable in the second direction to isolate said first chamber from said second outlet port and from said second chamber whereby said hammer is moved in said second direction to activate said energy storage means, said valve shiftable in the first direction upon predetermined movement of said piston to separate the valve from the piston and openly communicate said first chamber with said second outlet

across said valve thereby initiating transfer of energy from the storage means to the hammer by permitting relatively unrestricted return of said piston in said first direction.

7. A hydraulic impact device for applying impact force to a body comprising:

a housing having upper, intermediate and lower sections,

said upper section including a frame having an upper bearing plate and a lower bearing plate,

a hammer member having an enlarged head in said upper section and an axial shaft portion extending through said lower bearing plate into a bore in said intermediate section,

an anvil and blade member reciprocable in said lower section adapted to be impacted by said hammer,

air bag means contained in said upper section and engagable with said hammer and adapted when compressed to expand transmitting stored energy to said hammer to move said hammer in said first direction,

said bore in said intermediate section having an axial section of a first increased diameter and a second section of reduced diameter, said bore defining with said hammer shaft a cylinder chamber enclosed at the ends by bearing members,

piston means carried on said hammer shaft dividing said cylinder chamber into first and second pressure chambers, said first chamber when pressurized causing said piston to move said hammer in a second direction against said air bag to compress same,

a first outlet port communicating with said second chamber,

a second outlet port communicating with major diametral bore section adjacent said reduced diametral section,

an inlet port communicating with said first chamber, and

sequencing valve means having a generally annular body having an inner surface adapted to slidably contact said piston and with a first outer end portion in slidable contact with said minor bore and a second outer portion in slidable contact with said major bore, said valve means slidable from a first position abutting said lower bearing to a second piston abutting said upper bearing, said valve caused to reciprocate from said first position to said second by inlet pressure and caused to move from said second position to said first by fluid pressure at said second spool end when said piston reaches a predetermined position thereby venting said first chamber through said second outlet permitting expansion of said air bag and relatively unrestricted return of said piston.

8. The device of claim 7 further including second inlet means and third outlet means adjacent said second inlet means and shuttle valve means having a groove therein, said shuttle valve being biased to a position communicating said second inlet and third outlet across said groove to bypass fluid from said first chamber and movable to terminate communication therebetween by predetermined movement of said anvil in said second direction.

9. The impact device comprising:

a housing defining a cylindrical chamber,

a compressible energy storage means attached to the housing at one end of the cylindrical chamber,

a hammer reciprocally disposed in the cylindrical chamber to leave an annular cavity therein and positioned to compress the energy storage device when moved in a first direction and to impact a tool assembly disposed at the other end of the housing when moved in a second direction,

a piston mounted on the hammer and disposed within the annular cavity, the piston being sized to leave a substantial annular opening between the piston and the housing,

a low pressure exhaust port in fluid communication with the end of the annular cavity near the energy storage means,

a high pressure inlet port in fluid communication with the other end of the annular cavity, ane

a valve sleeve reciprocally disposed in the housing and sealingly engaging the piston and the housing to divide the annular cavity into first and second expansible fluid chambers when in contact with the piston whereby the piston will move the hammer through a compression stroke to compress the energy storage means, and, alternatively, to freely pass fluid around the piston when separated from the piston to permit the energy storage means to freely accelerate the hammer through an impact stroke to impact the tool assembly,

The valve sleeve having area such as to be being pressure shiftable in response to high hydraulic pressure on each end thereof as a result of being separated from the piston, and being mechanically separated from the piston when the piston has reached a predetermined position in the annular cavity.

10. The impact device comprising:

a housing defining a cylindrical chamber,

a compressible energy storage means attached to the housing at one end of the cylindrical chamber,

a hammer reciprocally disposed in the cylindrical chamber to leave an annular cavity therein and positioned to compress the energy storage device when moved in a first direction and to impact a tool assembly disposed at the other end of the housing when moved in a second direction,

a piston mounted on the hammer and disposed within the annular cavity, the piston being sized to leave a substantial annular opening between the piston and the housing,

a low pressure exhaust port in fluid communication with the end of the annular cavity near the energy storage means,

a high pressure inlet port in fluid communication with the other end of the annular cavity,

a valve sleeve reciprocally disposed in the housing and sealingly engaging the piston and the housing to divide the annular cavity into first and second expansible fluid chambers when in contact with the piston whereby the piston will move the hammer through a compression stroke to compress the energy storage means, and, alternatively, to freely pass fluid around the piston when separated from the piston to permit the energy storage means to freely accelerate the hammer through an impact stroke to impact the tool assembly,

the valve sleeve being pressure shiftable in response to high pressure on each end thereof as a result of being separated from the piston, an being mechanically separated from the piston when the piston has reached a predetermined in the annular cavity,

means forming an annular seal with the piston when the piston has reached the predetermined position in the annular cavity to hold the piston at the end of the compression stroke, and

a second low pressure exhaust port placed in fluid communication with the first fluid chamber only when the sleeve valve is in a predetermined position near the tool assembly end of the housing to release the piston to start the impact stroke.

11. A hydraulic impact device for applying impact forces to a body comprising:

a housing having first, second and third housing sections,

a hammer member having a head in said first housing section and having an axial shaft section extending into a bore in said second section, said hammer shaft and said bore defining an annular cylinder chamber,

said third section housing an anvil and chisel, said chisel adapted to be impacted by said hammer through said anvil,

energy storage means contained in said first section and engagable with said hammer head and adapted when activated to transmit stored energy to said hammer to move said hammer in a first direction to deliver an impacting blow,

piston means carried on said hammer dividing said cylinder chamber into first and second pressure chambers, said first chamber when pressurized causing said piston to move said hammer in a second direction against said energy storage device to activate same,

a first outlet port housing communicating with said second chamber,

a second outlet port in communication with said first chamber,

a supply port in communication with said first chamber,

sequencing valve means in slidable sealing contact with said bore and said piston, said valve movable in the second direction to isolate said first chamber from said second outlet port and from said second chamber whereby said hammer is moved in said second direction to activate said energy storage means, said valve shiftable in the first direction upon predetermined movement of said piston to openly communicate said first chamber with said second outlet across said valve thereby initiating transfer of energy from the storage means to the hammer by permitting relatively unrestricted return of said piston in said first direction, and

said sequencing valve having a first surface disposed in said first chamber and an opposite second surface, said second surface having greater cross-section area than said first and cooperable with said piston whereby upon said piston reaching said predetermined position fluid pressure acting at said second surface will shift said valve.

12. The device of claim 11 further including shuttle valve means having a first position bypassing fluid from said first chamber to a low pressure reservoir and a second flow blocking position, said shuttle valve being biased to said first position and adapted to be moved to said second position by a predetermined force being applied to move said hammer in said second direction.

13. The impact device for applying repetitive impact forces to a tool assembly comprising:

a housing having a bore,

an axially slidable hammer member in the bore for impacting the tool assembly,

energy storage means adapted to transmit energy to accelerate the hammer to impact the tool assembly,

piston means carried on the hammer in the bore defining opposite first and second fluid chambers, and

valving means for limiting high pressure fluid to the first chamber to move the hammer against the energy storage device, and for placing the first chamber in fluid communication with the second chamber when the piston has reached a predetermined position to thereby permit the energy storage device to accelerate the hammer to impact the tool assembly as the fluid moves from the first chamber to the second chamber, and for again limiting high pressure fluid to the first chamber when the piston has reached a predetermined second position to repeat the cycle,

the valving means including a sleeve forming a peripheral fluid seal between the piston and the cylinder, the sleeve being shifted away from the piston to place the first chamber in fluid communication with the second chamber, the opposite ends of the valving means being exposed entirely to hydraulic fluid in either the first or second fluid chambers and being pressure shiftable toward the second position of the piston when separated from the piston and being maintained in sealing engagement with the piston by fluid pressure as the piston moves from the second position to the first position.

14. The impact device for applying repetitive impact forces to a tool assembly comprising:

a housing having a bore,

an axially slidable hammer member in the bore for impacting the tool assembly,

energy storage means adapted to transmit energy to accelerate the hammer to impact the tool assembly,

piston means carried on the hammer in the bore defining opposite first and second fluid chambers,

valving means for limiting high pressure fluid to the first chamber to move the hammer against the energy storage device, and for placing the first chamber in fluid communication with the second chamber when the piston has reached a predetermined position to thereby permit the energy storage device to accelerate the hammer to impact the tool assembly as the fluid moves from the first chamber to the second chamber, and for again limiting high pressure fluid to the first chamber when the piston has reached a predetermined second position to repeat the cycle,

the valving means including a sleeve forming a peripheral fluid seal between the piston and the cylinder, the sleeve being shifted away from the piston in the direction of the impact stroke to place the first chamber in fluid communication with the second chamber, and

means for momentarily retaining the piston against the force of the storage means until the sleeve has separated from the piston a distance sufficient to prevent the piston from overtaking the sleeve until the hammer has closely approached the point of impact with the tool assembly.