US3403739A

US3403739A - Fluid-actuated impact tool

Info

Publication number: US3403739A
Application number: US591258A
Authority: US
Inventors: Robinson W Brown
Original assignee: Bowen Tools Inc
Current assignee: Bowen Tools Inc
Priority date: 1966-11-01
Filing date: 1966-11-01
Publication date: 1968-10-01
Anticipated expiration: 1985-10-01

Description

Oct.'1, 1968 R. w. BROWN 3,403,739

FLUID -ACTUAT ED IMPACT TOOL Rab/0J a0 l/l/. Bran/f7 INVENTOR.

Oct. 1, 1968 R. w. BROWN 3,403,739l

FLUID-ACTUATED IMPACT TOOL Filed Nov. l, 1966 2 Sheets-Sheet 2 Fa/fara l/V. .Bron/0 INVENTOR.

14 fr0/PNE .VJ

United States Patent O 3,403,739 FLUID-ACTUATED IMPACT TOOL Robinson W. Brown, San Antonio, Tex., assigner, by mesne assignments, to Bowen Tools, Inc., Houston, Tex., a corporation of Texas Filed Nov. 1, 1966, Ser. No. 591,258 11 Claims. (Cl. 173-73) ABSTRACT F THE DISCLOSURE This invention relates to a pneumatically powered impact tool adapted to be coupled to a drill string and lowered into a borehole to effect drilling operations at the bottom of the borehole, more particularly it is directed to a down-the-hole impact tool having a unique construction whereby all springs are eliminated from the operating mechanism and the frequency of the impact strokes is substantially increased.

When a fluid-actuated impact tool is used for drilling boreholes, the impact tool is located in the lborehole at the end of a drill string and, therefore, not subject to adjustment. Moreover, the tool is subject to the hostile environmental conditions often found in borehole operations. Further, impact tools used in such service frequently operate for a continuous extended period of time. Therefore, it is necessary that impact tools used in such service do not require adjustments during operation and that parts subject to fatigue due to continuous extended service are eliminated. Accordingly, it is an object of this invention to provide an improved fluid-operated impact tool for down-the-hole operation, which requires no adjustments and has no springs or other parts likely to be subject to fatigue in its operating mechanism.

Many impact tools used in down-the-hole drilling operations utilize the fluid power to actuate the hammer for both the power and return strokes. In such type of construction, the prevailing fluid pressure has to be rapidly shifted from one side of the hammer to the other. While the mechanical action resulting from the hammer striking the anvil will reverse the direction of movement of the hammer, it is necessary to immediately provide fluid pressure to the downstream end of the hammer to continue the hammer in its upstream or return stroke. However, in order that a drilling blow results from the impact between the hammer and anvil, it is necessary that there be no cushioning effect during the power stroke. Accordingly, it is another object to provide a fluid-actuated impact tool utilizing fluid power to actuate the hammer during both the power and return strokes in which there is rapidly available source of fluid power for the return stroke without any cushioning of the power stroke.

In such impact tools, once the hammer is accelerated upstream on its return stroke, it is necessary to decelerate it, arrest its move-ment and reaccelerate it on its power stroke. All of this takes time and often requires complex valving mechanism. Accordingly, many of the prior art fluid-actuated impact tools operate in the range of several hundred strokes per minute. However, it has been found that if the frequency of operation can be increased so that the frequency of operation will be in the range of thousands of strokes per minute, there will be a substantial increase in horsepower at the bottom of the borehole. Moreover, the increased frequency of operation results in amore even delivery of power to the bit or cutting tool thereby substantially increasing bit life. Accordingly, it is an object of the present invention to provide a down-the-hole percussion impact tool in which the time required for hammer turnaround is greatly reduced.

It is another object to provide a down-the-hole impact ice tool having a val-ving mechanism which improves the frequency of operation obtainable from a delivered amount of fluid.

It is still another object to provide a down-the-hole impact tool in which the push-down area is increased without sacrificing the push-up area.

It is a further object to provide a down-the-hole impact tool using fluid power for both the power and return strokes of the hammer, in which the push-down area is greater than the push-up area near the terminus of the upstream stroke, whereby reversing of the hammer from return to power is greatly accelerated.

It is still a further object to provide an impact tool using fluid power in both the power and return strokes of the hammer, which is provided with an auxiliary ram having limited reciprocatory motion furnishing decelerating force on the return stroke and added'acceleration force for a limited time on the power stroke.

Other objects, advantages and features of this invention will be apparent to one skilled in the art upon a consideration of the detailed specification, the appended claim and the attached drawings wherein:

FIGS. l, 2, and 3 are schematic illustrations of an limpact tool constructed in accordance with the present invention showing various stages of operation;

FIG. 4 is a vertical section through a preferred embodiment of an impact tool constructed in accordance with the present invention;

FIG. 5 is a cross sectional view taken on line 5-5 of FIG. 4.

Like reference characters are used throughout the several views to designate like parts.

Generally, the impact tool of this invention includes a hammer 10 mounted for reciprocation relative to a fluid supply conduit means, designated generally by the reference character 12, to deliver impact blows to an anvil 14 by striking the downstream hammer face 16 against anvil face 18. A passage 20 is provided which, when open, delivers fluid to the downstream side of the hammer 10. A valve 22 cooperates with the passage 20 to restrict flow through the passage 20 during the main portion of the power or downstream st-roke of the hammer 10. The valve 22 is so designed that, prior to the full downstream travel of the -hammer 10, it is operated to open the passage 20 permitting fluid flow therethrough whereby, upon the hammer face 15 striking the anvil face 18, fluid pressure acts on the downstream hammer face 16 to reverse the movement of the -hammer 10` an-d direct it'upstream toward the fluid supply conduit means 12. Positioned between the hammer 10 and fluid supply conduit 12 is a solid ram 24 which is mounted for limited reciprocatory movement. During return stroke or upstream movement of the hammer 10, the valve 22 closes the passage 20, thereby restricting further ffnid flow to the downstream side of the hammer 10. The hammer 10 contacts the ram 24 and the combined area of the ram 24 land the upstream face 26 of the ham-mer 10 are subject to the force from the fluid flowing through fluid supply conduit means 12, thereby the upstream movement of the ram 24 and the hammer 10 is rapidly deaccelerated and speedily arrested. Immediately upon such upstream movement being arrested, the fluid force from the fluid flowing through the fl-uid supply conduit means 12 causes` the ram 24 and the hammer 10 to be reaccelerated downstream toward the anvil for a subsequent stroke. Due to the Iram 24 coming into play during the latter part of the return stroke and being available during initial portion of the power stroke, the turnabout of the hammer is greatly accelerated increasing the frequency of operation.

Accordingly, the impact tool is so designed that there is a maximum frequency of operation and each stroke of 3 the hammer face 16 with the anvil tface 18 results in a drilling blow.

Turning now to a detailed description of the impact tool illustrated in FIGURES 4 and 5, the fluid supply conduit means 12 comprises an upper sub 28 having a central bore 30 therethrough. The sub 28 is provided with la box or other connecting means at its upper end (not shown) for connection with a drill string. Therefore, not only can fluid -be conducted to the impact tool through the drill string to provide fluid power, but the drill string can act to lower the impact tool into the borehole, rotate it and otherwise govern its operation therein.

As illustrated, the impact tool has a tubular housing 32 extending downwardly from the sub 28. The connection between the tubular housing 32 and the sub 28 is by means of tapered threads, as illustrated at 34. Other desirable means well known to those in the art may be used to join the two elements.

As illustrated, the anvil 14 is attached to the lower end of the tubular housing 32 by means of tapered threads 36. However, other means may be used to attach the anvil 14 to the housing 32. For example, as is well known to the art, there may be a sliding spline connection between the anvil 14 and the housing member 32. The lower end of the anvil 14 is provided with a drill bit 37 which does the actual cutting work. The drill bit 37 may be a separate element attached to the anvil 14 or, if desired, the drill bit may be an integral portion of the anvil.

The tubular housing 32 is provided with three cylindrical sections; namely, a first cylindrical section 38 adjacent the anvil 14, a second cylindrical section 40 having a reduced diameter adjacent the first section 38, and a third cylind-rical section `42 of the same diameter Aas the first cylindrical section 38 and located adjacent the fluid con- `duit means 12. It is within these three cylindrical sections that the hammer 10, Valve means 22 and ram 24 are operatively located. In order to dispose of the fluid power used in the operation of the impact tool, the anvil 14 is provided with a passage v44, the construction and function of `which will be described more fully hereinafter.

A hollow cylindrical cage 46 having a spider 48 at its upstream end is mounted in the third cylindrical section 42 and extends into and through the second cylindrical section `40. The spider 48 has a central passage S8 to receive a portion of the valve member 22. The spider 48 also has `a number of longitudinal passages 52. The remainder of the hollow cage 46 forms a cylindrical section 54 in which is positioned the upstream portion of the hammer 10. To prevent fluid flow between the cage member 46 and the interior wall of the housing 32, the exterior wall of the spi-der `48 is provided with a groove S3 in which is positioned O-ring 55 forming a seal with the wall of the cylinder 42.

The reciprocating hammer is formed of a first cylindrical portion 56 which is in sliding engagement with the wall of the rst cylindrical section 38 and `a second cylindrical portion 58 which is in sliding engagement with the wall of the cylindrical section S4 of the cage member 46. Both

piston portions

56 and 58 may have a plurality of labyrinth grooves 60l around their peripheral surface to aid in limiting flow of fluid past the hammer 10. The downstream end 16 of the hammer 1i) has projections 62 formed by channels 64 crossing at 90 degrees with respect to each other to assure the passage of air or other fluid to the lower end of the cylinder 38, particularly during the initial starting up of the impact tool.

Abutting against the top of the spider 48 and extending upstream thereof is `a second static hollow cylindrical cage member 66 in which is operatively located the reciprocatory ram 24 and the upper end of the valve member 22.

The upstream end of the second cage member 66 has a reduced diametrical exterior section to provide an external shoulder 68 against which a coil spring 70 abuts. The coil spring 70 will take up any manufacturing tolerances in

cage members

46 and 66 filling the space between the bottom of the sub 28 and the shoulder formed at the juncture of the second and third cylindrical sections. The downstream end of the member 66 is provided with an internal axial cylindrical section 72 into which the upper end of the valve member 22 extends. The upstream end of the member 66 is provided with an internal axial cylindrical section 74 in which is positioned the ram 24. The internal cylindrical section 74 terminates at its downstream end with a shoulder 76 which acts as a stop to limit the downstream movement of the ram 24. A coaxial passage 77 provides communication between the two

cylindrical sections

72 and 74. The member 66 is also provided with a plurality of longitudinal fluid passages 78, whereby fluid from the conduit 30 may flow through to the upstream end of the hammer 10, thereby constantly transmitting fluid force to the top of the hammer 10. Cage 66 is also provided with a number of laterally extending passages 80 which communicate with a circumferential groove 82 mating with lateral passages 84-84 in the housing 34. The passages 78, groove 80 and passages 84- exhaust the fluid from the downstream side of the cylindrical section 74 to atmosphere upon downstream movement of the ram 24. The outer peripheral surface of the cage 66 is provided with a pair of circumferential grooves 86-86, one on each side of the circumferential groove 80 and an O-ring 88 is positioned in each groove 86 and cooperates with the wall of the cylindrical section 42 to prevent fluid flow between the outer peripheral wall of cage 66 and the wall of the cylindrical section 42.

As mentioned, the valve 22 is located between the hammer 18 and the ram 24.. The valve 22 has a downstream cylindrical portion 90 located in the passage 50, which cooperates with a valve seat 92 located on the upstream end of the passage 20. The valve member 22 has a shoulder 94 adjacent to the cylindrical portion 90, which will be hereinafter more fully explained, and an upstream cylindrical portion 96 which extends into the cylindrical portion 72 of the member 66. The upstream end of the cylindrical portion 96 of Athe valve member 22 contacts the downstream end of the ram 24 through the passage 77 in the cylindrical cage member 66. A hollow metal cylinder 98 is positioned in the cylindrical portion 72. The cylinder 98 acts as a guide for the upper portion 96 of the valve member 22. Although the fit between the guide 98 and upper portion 96 is loose, the guide 98 tends to restrict flow therethrough.

The impact tool now having been described in detail, attention is now directed to the schematic drawings, FIGS. 1, 2 and 3, for the purpose of explaining the operation of the impact tool.

FIG. 2 shows the position of the various elements in the impact tool as the tool is being lowered into a borehole before commencing drilling operations. As can be noted, the hammer 10 has fallen by gravity to the bottom of the cylinder 38. The valve 22 also has moved downstream; however, its downstream movement has been arrested by the spider 48 and, accordingly, the valve 22 is no longer in contact with the valve seat 20 on top of the hammer 10. Therefore, the passage 20` is open. The ram 24 has likewise moved downstream until its movement was arrested by the shoulder 76 of the cylinder 74. As can be seen, there is space between the top of the hammer 10 and the downstream end of the valve member 22 and between the upstream end of the valve member 22 and the -downstream end of the ram 24.

In order to begin operation of the tool, air under pressure -is pumped down the drill string. The air flows through the fluid supply conduit means `12, through the 1ongitudinal passages '78 in the cage 66 and through the longitudinal passages 52 in the spider 48 until it reaches the top of the hammer 18 where it ows down through the passage 2t). Upon reaching the bottom of the passage 20 in the hammer 10 the air flows through the channels 64 in the downstream face 16 of the hammer 10 into the cylindrical section 38 and through the passage 44 in the anvil 14. However, as can be seen, in FIG. 4, the passage 44 has a restricted orifice 102 at the bottom of a counterbore 104. The restricted orifice 102 limits the passage of air causing pressure to be built up in the counterbore 104 and underneath the downstream face 16 of the hammer 10. As the ow of air continues, pressure builds up suiciently to cause a differential force between the downstream end 18 of the hammer `10 and the upstream end 26 which is smaller in area than the downstream side. Accordingly, the hammer moves upstream.

The high-pressure air acts on the downstream surface of the cylindrical portion 90 of the valve 22 causing the valve 22 to move upstream. As can be seen, the downstream portion 90` of the valve 22 is of larger diametrical area than the upstream portion 96. Further, the downstream end of the cylindrical portion 74 in which the upstream portion 96 of the valve 22 extends is vented to atmosphere through the passages 80. Therefore, the upstream movement of the valve 22 is very rapid. No springs are required to effect such movement.

After a very short travel, the valve 22 contacts the downstream end of ram 24. The incoming air pressure is on the upstream `side of the ram 24 and, since the area of the ram 24 is much greater than the area of the downstream portion 90 of the valve member 22, the upstream movement of the valve 22 is immediately decelerated.

As the hammer 10 starts to move upstream and gain momentum from the fluid pressure acting on its downstream face 16, it contacts the downstream end of the portion 90 of the valve 22. Such contact causes the valve 22 to seat against the valve seat 92 restricting the ow of air through the passage 20. This can be seen in FIG. 1. Accordingly, although the hammer 10 is moving upstream under a certain amount of momentum generated by the pressure on its downstream yface 16, continued upstream movement of the hammer 10 is opposed by the incoming air pressure acting on the upstream face of the ram 24 plus the Iincoming air pressure acting on the upstream face 26 of the hammer 10. Accordingly, although there is a slight amount of over-travel, the upstream movement of the ram, valve and hammer will be rapidly decelerated and very shortly completely arrested. The upstream movement of the ram, valve and hammer is shown in FIG, 3.

Immediately upon the arresting of the upstream movement of the ram, valve and hammer, the incoming air pressure will cause the ram, valve and hammer to be reaocelerated downstream toward the anvil. By the time the movement of the ram, valve and hammer has been reversed, the pressure on the downstream face 16 of the hammer will have been reduced by flow of fluid through the restricted orifice 102. Therefore, the pressure opposing the downstream movement of the hammer, valve and ram `will not impair the movement. As can be seen by comparing FIGS. 3 `and 1, the ram 24 has very limited reciprocatory movement; hence, after only a limited amount of downstream movement, the ram 24 is arrested by the shoulder 76. Incoming air pressure on the valve 22 and hammer 10 continue to move them downstream toward the anvil 14 until the shoulder 94 of the Valve 22 contacts the spider 48, at which time the downstream movement of the valve 22 toward the anvil 14 is arrested. By this time, the hammer 10 has built up momentum and will continue downstream toward the anvil 14, striking the anvil a sharp blow. The arresting of the valve 22 will disengage the downstream portion 90 of the valve 22 from its engagement with the valve seat 92 and will permit air to ow through passage 20, again commencing the return cycle.

To exhaust fluid on the downstream side of the ram 24, and to maintain the downstream end of the cylinder 74 and upstream side of the valve 22 at a reduced pressure, the downstream terminus of the ram cylinder 74 is provided with radial ports 78 which communicate through circumferential groove 80 in the member 66 under the radial ports 82 in the housing 32. Accordingly, the downstream side of the ram 24 and the upstream end of the valve 22 will be at the pressure of the environment in which the impact tool is operating. When operating in a borehole, there will be some pressure above atmospheric due to the air flow used in cleaning the borehole of cuttings. The housing 32 is provided with

lateral ports

106, 106 to exhaust fluid during the upstream movement of the hammer 10. n

As can be seen from the foregoing the present invention is so designed that there is an increase in the area subjected to pressure during push-down without any sacrifice of the push-up area. In other words, the areas which are subject to the pressure from the fluid conduit supply means for the acceleration of the hammer 10 toward the anvil 14 is not only the entire upstream area of the hammer 10, but also the upstream area of the ram 24. Accordingly, it can be seen that the ram 24 adds a considerable amount of area subject to pressure for the acceleration of the hammer 10 toward the anvil 14.

On the other hand, the ram 24 acts to rapidly decelerate the upstream movement of the valve 22 toward the conduit supply means. The rapid deceleration results from the ram 24 having a much greater upstream area subject to incoming uid pressure than the valve member 22 has in downstream area subject to the same pressure. Accordingly, the upstream movement of the valve member almost instantly is arrested. Therefore, the amount of upstream movement of the hammer 10 prior to its contacting the valve member 22 and shutting off the flow of air through the passage 22 is kept to a minimum. This aids in decelerating the upstream movement of the hammer 10 since the ow of high pressure iiuid to the downstream side of the hammer 10 is more rapidly terminated. The area of the ram 24 subject to upstream pressure also aids in decelerating the upstream movement of the hammer 10. Accordingly, a faster turnaround of the ram, valve, hammer assembly results. Moreover, the ram 24 serves an additional purpose, i.e., it aids in reaccelerating the hammer in its downstream movement. After the upstream movement of the assembly is arrested, there is immediately available to the incoming huid pressure the area of ram 24 as well as the area of the upstream face 26 of hammer 16. The additional area of the ram 24 greatly assists in rapid reacceleration of the hammer 10 downstream. It has been found that an impact tool constructed in accordance with the present invention can be operated with a frequency in the neighborhood of 7000 to 8000 strokes per minute with 500 lbs. of air pressure.

In order that the striking of the hammer 10 against the anvil 14 will not be cushioned by air trapped between the bottom of the hammer and the anvil, it has been found desirable to form the counterbore 104 in the anvil. The counterbore 104 will accept the initial volume of air from the passage 22 and allow a sharp blow to be struck by the striking face 16 of the hammer 10. HOW- ever, the counterbore 104 is of limited capacity so that immediately after the hammer 10 strikes its sharp blow and the direction of the hammer 10 is thereby reversed, a back pressure will be built up to act upon the downstream end 16 of the hammer 10 to immediately start the hammer 10 moving upstream toward the conduit 12.

It has been found that by increasing the frequency of blows the horsepower delivered is correspondingly increased. It has also been found that by utilizing the increased frequency of operation the life of bits has been greatly extended. It has been found that the inclusion of the independent ram 24 having limited reciprocatory movement has made the increased frequency of operation possible. The ram 24 limits initial upstream movement of the valve member 22 and, therefore, shortens the time when the valve member is disengaged from the valve seat 92 on the passage 20. Moreover, when the hammer l contacts the valve 22 and ram 24, the upstream area of the ram 24 instantly comes into play in assisting in the deacceleration of the upstream movement of the assembly. Moreover, immediately upon the arresting of the upstream movement, the upstream area of the ram is instantly available to assist in reaccelerating the assembly downstream. Therefore, there is instantaneous turnaround greatly aiding in increasing the frequency of operation.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by yand is within the scope of the claims.

As many possible embodiments may be made of the invention without depa-rting from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in ra limiting sense.

The invention having lbeen described, what is claimed is:

1. In a fluid-actuated impact tool for forming a borehole including a hammer mounted for reciprocation relative to a fluid supply conduit and a cutting tool having an anvil, said hammer being provided with a rst area exposable to :lluid pressure from the conduit to urge the hammer toward the anvil and a second area which, when exposed to pressure from said conduit, is effective to urge the hammer away from the anvil, passage means for placing second area in fluid communication with the conduit, valve means cooperable with the hammer restricting ilow through the passage means upstream of the second area prior to the hammer moving to la predetermined distance from a point in the conduit upstream of the hammer and permitting flow through such passage means after the hammer has moved 'said predetermined distance from such point, fluid ilow through the passage means developing a pressure on the second area of the hammer to move the hammer toward the conduit, means to controllably bleed ol the iluid pressure from the second area of the hammer, a solid ram mounted for limited reciprocation between the conduit and hammer, the hammer in moving toward the conduit contacting the ram, fluid pressure from the conduit acting on the ram and the first area of the hammer to cause movement of the hammer toward the conduit to 'be arrested, reversed and reaccelerated toward the anvil, the travel of the ram toward the anvil being arrested prior to the hammer moving said predetermined distance.

2. In a uid actuated impact tool including a hammer mounted for reciprocation relative to a uid supply conduit and an anvil, said hammer being provided with a first area exposable to fluid pressure vfrom the conduit to urge the hammer toward the anvil and a second area which, when exposed to pressure from said conduit, is elfective to urge the hammer away from the anvil, passage means for placing second area in fluid communication with the conduit, valve means cooperable with the hammer to restrict ow through the passage means upstream of the second area prior to the hammer moving to a predetermined distance from a point in the conduit upstream of the hammer and to permit ow through such passage means after the hammer 'has moved a predetermined distance from such point, uid flow through the passage means developing a pressure on the second area of the hammer whereby after the hammer strikes the anvil and its movement is reversed, the pressure moves the hammer toward the conduit, means to controllably bleed off the fluid pressure from the second area of the hammer, means operable to move the valve means toward the conduit after the hammer has moved said predetermined distance, a ram mounted for limited reciprocation between the conduit and valve means, the valve means contacting the ram on its movement toward the conduit and being decelerated thereby, the hammer in moving toward the conduit cooperating with the valve means to restrict flow through the passage means, uid Ipressure from the conduit acting on the ram and the first area ofthe hammer to cause movement of the hammer toward the conduit to be arrested, reversed and reaccelerated toward the anvil, the travel of the ram toward the anvil being arrested prior to the hammer moving the predetermined distance to operate the valve means.

3. A fluid-actuated impact tool which comprises:

a tubular housing having at one end a fluid supply conduit and at the other end an anvil;

a hammer mounted in said housing for reciprocatory movement relative to said anvil;

passage means directing fluid ow to the anvil end of the hammer, one end of the passage being located in the conduit end of the hammer and provided with a valve seat;

a valve member disposed in the housing between the hammer and the fluid conduit;

the valve member cooperating with the valve seat on the hammer to restrict uid flow through the hammer whereby fluid from the lluid supply conduit transmits a uid force to the valve member and hammer, in the direction of the anvil;

means arresting the movement of the valve member toward the anvil prior to the hammer striking the anvil;

means to move the valve member toward the fluid conduit;

the disengagement of the valve member from the valve seat on the hammer opening the passage means permitting fluid to flow through said passage means toward the anvil end of the hammer;

means in the anvil cooperating with the hammer to discharge the fluid pressure in a limited manner to provide an upward fluid force on the hammer after the hammer strikes the anvil to move the hammer toward the conduit;

a ram mounted for limited reciprocatory movement between the uid supply conduit and the valve member, the valve member contacting said ram and being decelerated thereby;

the hammer contacting the valve member and ram on its movement toward the conduit, said contact restricting flow through the passage means, the movement of the hammer, valve member and ram being decelerated by the action of the force developed by the fluid owing through the uid supply conduit, upon arrestment of such movement, the uid force causing the tool to recycle and the ram, valve member and hammer to he reaccelerated toward the anvil, the movement of the ram toward the anvil being arrested prior to the movement of the valve member being arrested.

4. The impact tool set forth in claim 3 characterized in that the passage means is a longitudinal passage through the hammer.

5. The impact tool set forth in claim 4 characterized in that the means in the anvil to discharge the fluid owing through the passage means is formed of a counterbore which will accept Isufcient uid so that the blow of the hammer against the anvil will not be cushioned and a restricted orifice to develop fluid pressure to accelerate the hammer toward the conduit.

6. The impact tool set forth in claim 4 characterized in that the valve member is a reciprocating member having a largerdownstream end than an upstream end and a shoulder separating the two, the shoulder having the means by which the downstream movement of the valve member is arrested, whereby fluid pressure in the housing moves the valve member upstream when its downstream movement is arrested.

7. A fluid actuated impact tool which comprises:

,a tubular housing having at one end a uid supply conduit and at the other end an anvil,

the anvil having a longitudinal passage which has a restricted Orifice therein, the housing having a first cylindrical section adjacent the anvil, a second reduced cylindrical section adjacent the first section and a third cylindrical section adjacent the fluid conduit;

a first hollow cylindrical cage having a spider at its upstream end mounted in the third cylindrical section and extending through the second cylindrical section, the spider having a central passage, the cage having an internal cylindrical section;

a cylindrical hammer having a first cylindrical section in the first cylindrical portion and a second cylindrical section in the cylindrical section of the cage, the first cylindrical section having a greater diameter than the second cylindrical section;

a longitudinal passage through the hammer with a valve seat at its upstream end;

a valve member in the cylindrical passage of the spider,

the valve member having a first area opposing the cylindrical hammer and a second area upstream of the spider, and 4a shoulder therebetween, the first area being of a greater diameter than the second area,

the spider limiting movement of the valve member toward the anvil prior to the hammer striking the anvil;

arresting of movement of the valve member by the spider, opening the longitudinal passage in the hammer whereby after the hammer strikes the anvil fiuid from the conduit flows through the longitudinal passage of the hammer into the longitudinal passage of the anvil, the anvil passage, prior to the restricted orifice being of sufiicient area to prevent cushioning of the contact between the hammer and the anvil, however, in `combination with the restricted orifice building up a pressure to move the hammer upstream toward the conduit;

a second hollow cylindrical cage in the third cylindrical section, the second cage having an upstream cylindrical section, a coaxial downstream cylindrical section, a coaxial communicating passage therebetween and a plurality of longitudinal fluid passageways;

a ram positioned in the upstream cylindrical section of the second cage, the ram being of substantially greater diametrical area than the valve member,

the valve member extending through the downstream cylindrical section of the second cage and into the communicating passage between the two cylindrical sections of the second cage,

disengagement of the valve member from the valve seat on the hammer exposing the downstream portion of the valve to pressure causing the valve member to move upstream toward the conduit, the upstream movement being decelerated upon contacting the ram,

the upstream movement of the hammer contacting the valve member and ram causing the valve member to seat and restrict fiow through the passage in the hammer, the combined area of ram and hammer to the fluid presenting an area to the fiuid from the conduit causing the movement of the valve member, ram and hammer to be arrested and then reversed and reaccelerated toward the anvil;

means in the second cage arresting movement of the ram toward the anvil prior to the arresting of movement of the valve member toward the anvil.

8. The impact tool specified in claim 7 characterized in that a spring is disposed in the body to maintain the first and second cage members in position.

9. The impact tool specified in claim 7 characterized in that there is packing in the downstream cylindrical section of the second cage surrounding the valve member.

10. The impact tool specified in claim 9 characterized in that there are radial passages extending from the terminus of the upstream cylindrical section in the second cage to exhaust fiuid downstream of the ram to atmosphere.

11. The impact tool specified in claim 6 characterized in that the anvil portion terminates in a cutting portion.

References Cited UNITED STATES PATENTS 2,800,884 7/1957 Mori 173--138 X 2,859,733 11/1958 Bassinger et al. 173-73 X 2,979,033 4/ 1961 Bassinger 173-73 3,101,796 8/1963 Stall et al 173-136 X 3,162,251 12/1964 Bassinger 173-73 3,180,434 4/ 1965 Vincent 173-73 DAVID H. BROWN, Primary Examiner.