US3245483A

US3245483A - Pneumatic impact tool

Info

Publication number: US3245483A
Application number: US222885A
Authority: US
Inventors: Elmer F Etzkorn
Original assignee: Skil Corp
Current assignee: Skil Corp
Priority date: 1962-09-11
Filing date: 1962-09-11
Publication date: 1966-04-12
Anticipated expiration: 1983-04-12
Also published as: BE637015A; GB1005019A; DE1277770B; CH435161A; GB1005018A; NL288658A

Description

E. F. ETZKORN PNEUMATIC IMPACT TOOL Apri! 12, 1966 2 Sheets-Sheet 1 Filed Sept. ll, 1962 LWQMQ Q mn April l2, 1966 E. F. r-:TzKoRN 3,245,483

PNEUMATICI IMPACT TOOL United States Patent 3,245,483 PNEUMATIC MPACT TOQL Elmer F. Etzkorn, Park Ridge, Ill., assignor to Skil Corporation, Chicago, Ill., a corporation of Delaware Filed Sept. 11, 1962, Ser. No. 222,885 4 Claims. (Ci. 173-137) The present invention relates to a hand operable power tool and, more particularly, to a pneumatically actuated impact tool.

An important object of the present invention is to provide a new and improved pneumatic impact tool of the type which includes a barrel portion having a chamber therein and a striker member which is pneumatically reciprocated in the barrel chamber to deliver -impact blows to the shank end of a tool which is slidably mounted in the forward end of the barrel.

Another important object of the present invention is to provide a new and improved pneumatic impact tool of the character described wherein the barrel is provided with suitable exhaust port means and wherein an airdiverting member, which is disposed in the rear of the barrel chamber i-n communication with both the forward and rear ends thereof, is provided for automatically directing air under pressure first into the rear end of the barrel chamber for propelling the striker member :forwardly therein and then into the forward end of the barrel chamber for propelling the striker member rearwardly therein.

A more detailed lobject of the present invention is to provide a new and improved pneumatic impact tool of Ithe character described wherein the air-diverting member is disposed in a transverse groove formed in a valve block which is mounted in the rear end of the barrel, which airdiverting member is disposed between two air passages which are directed, respectively, into the rear end of the barrel chamber and into the forward end of the barrel chamber, and wherein Igenerally radial slots formed in .the rear end of the barrel are provided to direct air under pressure Ifrom a pressure source to the -groove in which the air-diverting member is disposed.

A yet fur-ther object of the present invention is to provide new and improved air-diverting valve, which valve is of one piece construction, light in Weigh-t, and inexpensive to manufacture, and which valve is quickly responsive to changes in air pressure and less apt to stick or oxidize in place during periods of non-use of the impact tool.

An even further object of the present invention is to provide a new and improved valve block adapted to receive the air-diverting valve, which valve block is of unitary construction thereby having the attendant advantages of easy and low cost manufacture.

Certain other objects of the invention will, in part, be obvious and will in part appear hereinafter.

For a more complete understanding of the nature and scope of the invention reference may now be had to the accompanying drawings wherein:

FIG. 1 is a central vertical section taken through a pneumatic impact tool embodying the invention;

FIG. 2 is an enlarged side elevational view of the valve block of FIG. l;

FIG. 3 is `a top plan view thereof;

FIG. 4 is an enlarged vertical section taken generally on the line 4 4 of FIG. l;

FIG. 5 is a perspective View looking toward the front or rear face of the air-diverting valve member of FIG. 1;

FIGS. 6, 7 and 8 are generally diagrammatic central vertical sections taken through .the barrel portion of the pneumatic impact tool of FlG. 1 and illustrating the operation thereof with the generally radial slots formed in the rear end of the bar-rel for directing air under pressure r, ICC

to the air-diverting valve member in the valve block being rotated approximately into vertical positions for purposes of clarity of description; and

FIG. 9 is a vertical section taken Vgenerally on the line 9 9 of FIG. 1.

As best illustrated in FIG. l, a pneumatic impact tool 10 embodying the invention and in the form of a hammer includes a generally hollow handle portion 11 which is provided at its upper end with a transverse socket or recess 12 with only the outer end portion thereof being provided with an internal or fem-ale thread 13. The handle portion 11, which is characterized by an internal chamber 14, is provided at its lower en-d with a standard adapter 15 for connection to a source of air pressure to place the chamber 14 in communication with the source of -air pressure. A ringer-operable plunger valve 17 is mounted in a transverse bore 13 formed in the handle portion 11, which bore 18 is connected to the chamber 14 by a passage 19 .and to the inner end of lthe socket 12 by a passage 20 whereby, when .the plunger valve 17 is actuated, air runder pressure is directed into the inner end of the socket 12.

vThe pneumatic impact tool 1d is further characterized by a barrel 22 mountable in Ithe socket 12 in the handle portion 11 and having a cylindrical barrel chamber 23 for-med therein which is open at the rear end of the barrel 22. The outer surface at the rear end of the barrel 22 is provided with an external or male thread 24 which terminates a short distance forwardly of the rear end of the barrel 22 'for a purpose which will be m-ade cle-ar hereinafter. The Irear end of the barrel 22 is adapted 4to be threadedly tightened into the socket 12 `formed in the handle portion 11 of the pneumatic impact tool 10 with the rear end surface of the barrel 22 being spaced a subst-antial distance forwardly of the inner end of Ithe socket 12, as illustrated in FIG. l. The outer surface at the forward end of the barrel 22 is provided with round-bottomed threads 26 for tool .retaining purposes to be described hereinafter. An axial through bore 27 formed in the front end of yt-he barrel 22 and opening into the front end of the barrel chamber 23 is adapted to slidably receive a rearwardly disposed shank portion 28 of an impact tool 29 of knownrtype. A free piston or striker -member 30 is pneumatically reciprocal within the barrel chamber 23, in a manner to be described, for delivering continuous impact blows to the rear end ofthe shank portion 28 of the impact tool 29 as long as the plunger valve 17 is actuated.

For pneumatic actuation of the striker member 30,`

the barrel 22 is provided with a pair of longitudinally spaced

exhaust ports

32 and 33 which

exhaust ports

32 and 33 extend through the wall of the barrel 22 from the atmosphere and open into the barrel chamber 23 with the exhaust port 32 being disposed forwardly of the exhaust port 33 for purposes which will be evident hereinafter. A shield or detiector 34 is mounted on the barrel 22 outwardly of the

exhaust ports

32 and 33 to deflect the air exhausted therethrough. An air passage 35 extends from the rear end of the barrel 22 into communication with the barrel chamber 23 at the forward end thereof whereby to provide passage means for directing air under pressure into the forward end of the barrel chamber 23. As illustrated, the air passage 35 includes a longitudinally extending blind bore portion 35 which is disposed radially outwardly of the barrel chamber 23 and parallel to the axis thereof. The bore portion 36 is open at the rear end of the barrel 22 and terminates at its inner end at a point which is generally in alignment with the forward end of the barrel chamber 23. The air passage 35 also includes a generally transverse bore portion 37' which extends into the forward portion of the barrel chamber 23 from the inner or forward end of the longitudinally extending bore portion 36. It is noted that the generally transverse bore portion 37 of the air passage 35 and the forwardmost exhaust port 32 are co-axially aligned with a common axis x-x thereof being inclined to the longitudinal axis of the barrel chamber 23 in a manner such that the exhaust port 32 is disposed rearwardly of the generally transverse bore portion 37 of the air passage 35.

One novel feature of the present invention is a new and improved method for forming a barrel for a pneumatic impact tool such as the barrel 22 -for the tool 10 of FIG. 1. 1n the past, it has been the practice lin forming a generally transverse internal air passage, such as the generally transverse bore portion 37 of the air passage 35, to drill a vhole through the wall of the barrel 22 from the lower surface thereof (as viewed in FIG. 1) through the inner end of the longitudinal bore portion 36 of the air passage 35 and then into the barrel chamber 23. It has then been necessary to weld over or provide a plug for the portion of this generally transverse bore which extends between the outer surface of the wall of the barrel 22 and the inner end of the longitudinal bore portion 36. The obvious disadvantages of the foregoing method have been overcome by the novel method which has been developed for forming the generally transverse bore portion 37 of the air passage 35 in the barrel 22 of the pneumatic impact tool of FIG. 1.

After the longitudinal bore portion 36 has been formed in the barrel 22 by drilling the same from the rear end of the barrel 22, the generally transverse forwardmost exhaust port 32 is drilled through the wall of the barrel 22 from a point on the periphery of the barrel 22 which is generally diametrically opposite from the forward end of the longitudinal axis of the longitudinal bore portion 36 and on the opposite side of the barrel chamber 23 therefrom with the drilling then being continued throu-gh the barrel chamber 23 and through the inner wall thereof until the inner end of the longitudinal bore portion 36 is intersected whereby to provide the generally transverse bore portion 37 of the air passage 35 which opens into the forward end o-f the barrel chamber 23. With the foregoing method, the generally transverse bore portion 37 of the air passage 35 is co-axial with the exhaust port 32 with the angle at which Ithese two

co-axial bores

37 and 32 are drilled relative 4to the axis of the barrel chamber 23-being chosen so as to ylongitudinally position the inner end of the exhaust port 32 at the proper point on the inner surface of the barrel chamber 23 for pneumatic reciprocal actuation of the striker member 30.

To direct air under pressure alternately into the rear and forward ends of the barrel chamber 23, a novel valve block and air-diverting valve arrangement is provided. As best illustrated in FIG. 1, a valve block 40 is mountedy on the barrel 22 at the rear end thereof and is adapted to be received in the space dened between the rear end of the barrel 22 and the inner end of the socket 12. The valve block 40, as illustrated in FIGS. 2 4, is characterized by a rearward portion 42 which is adapted to be fitted against the rear end of the barrel 22 and which has an outer diameter which is slightly less than the bore diameter of the socket 12 at the inner end thereof whereby to define an annular passage 41 which is in communication with the air inlet passage 2t) from the plunger valve 17. The valve block 40 is further characterized by a reduced-in-diameter forward portion 43 which is integral with the rearward portion 42 and which is adapted to be tted in the rear end of the barrel 22 to provide a closure fo-r .the same. A forwardly projecting guide pin 44, which is provided on the front face of the portion 42, is receivable in a mating recess formed in the rear end surface of the barrel 22 whereby to properly angularly position the lvalve block 40 relative to the rear end of the barrel 22.

A transversely extending semi-circular slot or groove 46 is formed in the upper half of the forward portion 43 of the valve block 40 a slight distance forwardly of the rearward portion 42 thereof. An air passage 48 extends forwardly from the front face of the groove 46 through the forward portion 43 of the valve block 40 and opens into the rear end of the barrel chamber 23 at 4the front surface of the forward portion 43. An air passage 5i) extends rearwardly from the rear face of the groove 46 and then downwardly and forwardly within the rear portion 42 with the opposite end thereof being open at the front face of the portion 42 of the valve block 40 and aligned for communication with the rear open end of the longitudinal bore portion '36 of the air passage 35 formed in the rear endV surface of the barrel 22. The air passage 5i) is characterized by an upper rearwardly extending portion 50a, by a downwardly extending portion 50b, and by a lower `forwardly extending portion 50c. The groove 46 is therefore in communication with the forward end of the barrel chamber 23 through

lthe air passages

50 and 35 and with the rear end of the barrel chamber 23 through the` air passage 48.

As set forth earlier herein, the male or external thread .Z4-on the rear end of the barrel 22 terminates forwardly of the rear end of the barrel 22. The non-threaded rear end peripheral portion of the barrel 22 is slightly less in diameter than 4the bore diameter of the inner end of the socket 12 whereby an annular passage 51 is defined therebetween, which annular passage 51 is in communication open into the groove 46 through the opposite front and Y rear faces thereof.

To direct air under pressure from the groove 46 into either the rear end of the barrel chamber 23 through the air passage 48 to propel the striker member 30 forwardly so that same delivers an` impact blow to the end of the shank portion 28 of the impact tool 29 or into the forward end of the barrel chamber 23 through the

air passages

50 and 35 to return the striker member 30 to a rearward position in the barrel chamber 23, a generally planar or se-mi-disc-like air-diverting valve member 55 is freely disposed in the semi-circular groove 46 formed in the valve block 40 with the thickness of the valve member 55 being less than the width of the groove 46. The valve member 55 is preferably non-ferrous and more preferably formed of a phenolic laminate characterized, for instance, by a canvas or linen base which is impregnated with a phenolic resin.

This construction of the valve 55`from a phenolic laminate, or other suitable non-ferrous material forms an inexpensive and light valve which is quickly responsive to changes in air pressure and vacuum. Heretofore, ferrous valves have been used and they have beenV known to oxidize or rust dueto moisture in the air lines.` During a period of non-use' of the' pneumatic tool, ferrous valves frequently rust or freeze in the valve block making the tool inoperative until disassembly of the same and manual freeing of the valve.

When the valve member 55 Vis disposed against'the rear face of the groove 46, the'air pasage 5U, which connects with the air passage 35 and thus the forward end `of the barrel chamber 23, is closed and lair under pressure which is directed into the groove 46 through the generally radial slots 53 is thus directed through the air passage 48 into the rear end of the barrel chamber 23 to propel the striker member 39 forwardly therein. When the valve member 55 is disposed against the forward face of the groove 46, the air passage 48 to the rear end of the barrel chamber 23 is closed and the air under pressure which is directed into the groove 46 through the generally radial slots 53 is directed through the air passages 5G and 35 into the forward end of the barrel chamber 23 to return the striker member 30 to a rear position in the barrel chamber 23. To facilitate movement of the air-diverting valve member 55 between its positions against the front and rear faces of the groove 46, side portions of the front and rear faces of the groove 46 outwardly `of the

air passages

48 and 50a are arcuately cut away, as at 57, and the air inlet slots 53 to the groove 46 are provided with a width suicient for extending fully across the arcuately cutaway portions 57.

Reciprocal operation of the striker member 30 may best be described with reference to FIGS. 6, 7 and 8. With the valve member 55 initially in its position against the rear face of the groove 46, as in FIG. 6, air under pressure is directed through the passage 48 into the rear end of the barrel chamber 23 to propel the striker member 43 forwardly, with the forward exhaust port 32 being open and the rear exhaust port 33 being closed bythe striker member 30 during the rst portion of the forward movement thereof. Prior to the striker member 30 reachingl its forwardmost tool shank impact position, the forwardmost exhaust port 32 is closed by the striker member 30, whereby the air trapped in the forward end of the barrel chamber 23 becomes compressed as a result of the continued forward movement of the striker member 30l under its own momentum. By the time the striker member 30 reaches its tool shank impact position (FIG. 7), the rearmost exhaust port 33 is open and the pressure increase at the forward end of the barrel chamber 23 which is communicated to the rear face of the valve 55 by means of the

passages

35 and 50 in combination with a partial vacuum formed attheI front face of the Valve 55 by the increased iiow of air across the same and out through the port 33 is suicient to shift the valve to its position against the forward face of the groove 46, as illustrated in FIG. 7. The lightness of the air-diverting valve 55 and its resulting lack of inertia permit a more rapid response to these pressure and vacuum effects thereby providing a more positive valve movement which increases the operating eiciency of the impact t-ool. This action closes olf the air passage 4,8 to the rear end of the barrel chamber 23 and directs air under pressure through the

air passages

50 and 35 into the forward end of the barrel chamber 23 to propelthe striker member 30 rearwardly in the barrel chamber 23, as illustrated in FIG. 8. Before the striker member 30 reaches its rearwardmost position in the barrelchamber 23, the rearwardmost exhaust port 33 is closed whereby the air trapped behind the striker member 30 is compressed as -a result of the continued rearward movement thereof. This increase in pressure in the rear end of the barrel chamber 23 in combination with the partial vacuum formed rearwardly of the valve 55 by the air ow therepast serves to shift the valve member 55 into its initial position against the rear face of the groove 46, as illustrated in FIG. 6, with air under pressure -again being directed into the rear end of the barrel chamber 23 to propel the striker member 39 forwardly for its next cycle of lreciprocal operation. In FIGS. 6, 7 and 8, the air ow through the various parts and passages is indicated by -a series of arrows. This reciprocal cyclic operation continues automatically as long as the plunger valve 17 is depressed and -air under pressure is directed into the groove 46.

The pneumatic impact tool of this invention also includes a novel tool retainer which is illustrated in FIGS. 1 and 6 through 9. At present, retainers consist of a coil or beehive retainer threadable over the front end of the barrel of an impact tool. The shank portion of a standard working tool is inserted in the barrel of the tool for contact by the striker. The extent to which the shank may be inserted in the tool is controlled by an integral annular shoulder provided on the shank intermediate the ends thereof, which shoulder is adapted to engage the nose of the barrel. After the Working tool is inserted, the beehive retainer is slid over the working end of the tool and threadingly engaged with the front end of lthe impact tool barrel which is usually provided with a number of threads on the outer surface thereof. The working tool is held in place and its accidental removal is prevented since the shoulder on the shank of the tool has a diameter larger than the diameter of the opening in the front end or nose of the beehive retainer. Today there is a great and evergrowing demand for working tools having working portions of considerable size. The working portions of such tools are too large to pass through the nose of conventional beehive retainers thereby making a tool retainer of the type described useless for retaining these newer working tools. Consequently, the industry Vhas |been presented with a problem of retaining these large size working tools in impact tools.

The tool retainer of this invention, which is adapted to hold a working tool to an impact tool regardless of the size of the working portion of the tool, includes a split collar retainer 60 and la beehive or coil retainer 62. The coil retainer is for-med of a series of interconnected coils 70, and it is generally cylindrical in configuration. The rear end portion of the coil may be threadingly mounted on the forward end of the lbarrel 22 by engagement of the Icoils of the retainer with the round-'bottomed external threads 26 formed on the barrel of the impactv -tool for holding the entire retainer assembly to the impact tool. The forwardmost -coils 72 of the coil retainer 62 progressively decrease in diameter in a forward direction for retaining engagement with the split collar 6G. The forwardmost coils 72 dene an opening 68, which opening is of a diameter large enough to receive an annular shoulder 67 formed on the shank 28 of a working tool 29. The coil retainer, therefore, retains only the split collar member 60 in place on the barrel of the tool and not the working tool :itself -as will be shown hereinafter.

The split collar retainer is characterized by a generally cylindrical body member 63 having an axially extending opening 64 formed in the wall thereof, with the rear end of the body mem'ber 63 being adapted to -abut the front end surface of the Ibarrel 22. The forward or nose end of the body member is tapered inwardly as at 65 on the outer surface thereof and on the inner surface thereof is Iformed an inwardly extending flange-like portion 66 dening an opening having a diameter less than the diameter of the major portion of the body member 63 and less than the diameter of the shoulder 67 formed on the shank 28 of the working tool.

The working tool member 29 is insertedthrough the coi-l retainer 62 before this retainer is attached to the impact tool. If the working portion of the t-ool 29 is too large to pass through the opening 63 in the nose of the coil retainer, the shank 2S of the working tool is passed through the opening 68 from left to right, as shown in the drawings. It will be recalled that this opening 68 has a diameter larger than the diameter of -the annular shoulder 67 on the shank of the working tool. The coil retainer is slid to its forward-most position on the working tool and the split collar retainer 60 is tted downwardly or dropped over the shank of the tool forward of the shoulder 67 thereon. The opening 64 in the split collar has a width greater than the diameter of the -tool shank.

thereby permitting the collar member to be dropped into position in this manner. The split collar 60 will be received within the coil 62 with the tapered portion 65 of the collar in engagement with the inside of the reduced p0rtion 72 of the coil retainer. The shank 28 of the working tool is then inserted within the bore 27 of the barrel 22 for actuation by the striker 30. The coil retainer with the split collar held therein is threaded over the roundedbottom threads 26 on the barrel 22. Thus in place on the impact tool the retainer assembly permits limited reciprocal movement of the working tool 29 in a longitudinal direction, but the working tool will be retained to the irnpact tool Iby engagement of the shoulder 67 on the shank of the working tool with the inwardly extending flangelike portion 66 formed on the split collar 60. The split `collar 60 is, in turn, resiliently held to the barrel 22 by the coil spring retainer 62. The spring 62 is provided at its rear end with `an outwardly projecting end portion 74 which serves as a manually grippable handle for rotatably mounting the coil retainer 62 `and the split collar retainer 60 associated therewith on the forward end of the barrel 22.

Thus it will be seen that the tool retainer of this invention permits the easy and rapid engagement of a working tool to an impact tool, and it will be apparent that the retainer is adapted to retain working tools in place regardless of the size of the working end of such tools.

While the invention is shown `in but one form it will be obvious to those skilled in the art that it is not to be so limited, Ibut rather it is susceptible of various changes and modifications without departing yfrom the spirit and scope of the yappended claims.

I claim:

1. in a pneumatic impact device comprising a barrel having a cylinder-like chamber therein `and adapted to have the shank of an impact tool slidably inserted into the forward end of the chamber therein, a striker member pneumaticaflly reciprocable within said barrel chamber for imparting impact blows to the end of a tool shank extending into the forward end of same, said lbarrel having a generally longitudinally extending passage with its forward end communicating with the forward end of said barrel chamber, and said barrel having exhaust port means arranged to be opened and closed by the striker member upon reciprocation of the same, the improvement c-omprising, a valve `block mounted in the rear end of said barrel and characterized Iby a generally cylindrical forward portion fitted within and closing the rear end of said barrel chamber and by an enlarged diameter rear portion fitted against the rear end of said barrel, said valve block having a generally vertically disposed transverse groove Iformed in the upper portion of said -forward portion thereof, which groove cooperates with the inside wall of said barrel to define an enclosed space, said valve vblock having iirst passage means extending from the forward face of said groove land communicating with the rear end of said Ibarrel chamber, said valve block having second passage means extending lfrom the rear face of said groove and communicating with the rear end of said generally longitudinal passage formed in said barrel, said barrel having passageway means adjacent the rear end thereof and communicating with the periphery of-said groove to allow fluid yunder pressure from a pressure source to be admitted to said enclosed space, a pressure actuated valve loosely disposed in said enclosed space and having athickness less than the distance between the forward and rear -faces of said groove, said valve being shiftable between positions against the rear and front faces of Vsaid groove-for 'alternately closing said second and lirst passage means thereby to direct air under pressure into the rear and front ends of said barrel` chamber, respectively, to reciprocably propel vsaid striker member forwardly land rearwardly in said barrel chamber whereby same delivers impact blows to a tool shank extending into the forward end of the barrel, said valve being contained in said enclosed space solely lby'reason of the engagement of said forward portion ofthe valve block with the rear end of said `barrel chamber.

2. The improvementv according to claim 1 wherein said groove is generally in the form -ofa semi-disk thereby to define an enclosed Vspace of corresponding shape, andwherein said lvalve is generally in the formy 'of a semi-disk with its arcuate periphery generally conforming to the curvature of said forward portion of the valve block.

3. The improvement according to claim 1 wherein said forward and rear faces of they groove `are cut-away adjacent the periphery ofthe latter there-by to facilitate the admission of fluid to opposite yfaces of said valve.

4. The improvement according to `claim y1 wherein said valve member is formed of a phenolic laminate.

References Cited by the Examiner UNITED STATES PATENTS 1,485,010 2/1924 Ash et al. 279-19 1,796,487 3/1931 Stevens 279-19 2,275,102 3/1942 Fitz Simmons 173-73 2,478,818 8/1949 Geiger etal 29-156.4 2,500,036 3/1950 Horvath 173-162 2,699,153 1/1955 Russell 137-625.48 2,717,613 1/1955 Conrad 137-62548 2,752,664 7/1956 Brown 29-156.4 `3,086,501 4/1963 Nielsen 173-137 3,137,483 6/1948 Zinkiewicz 173-137 BROUGHTON G. DURHAM, Primary Examiner.

MILTON KAUFMAN, Examiner.

Claims

1. IN A PNEUMATIC IMPACT DEVICE COMPRISING A BARREL HAVING A CYLINDER-LIKE CHAMBER THEREIN AND ADAPTED TO HAVE THE SHANK OF AN IMPACT TOOL SLIDABLY INSERTED INTO THE FORWARD END OF THE CHAMBER THEREIN, A STRIKER MEMBER PNEUMATICALLY RECIPROCABLE WITHIN SAID BARREL CHAMBER FOR IMPARTING IMPACT BLOWS TO THE END OF A TOOL SHANK EXTENDING INTO THE FORWARD END OF SAME, SAID BARREL HAVING A GENERALLY LONGITUDINALLY EXTENDING PASSAGE WITH ITS FORWARD END COMMUNICATING WITH THE FORWARD END OF SAID BARREL CHAMBER, AND SAID BARREL HAVING EXHAUST PORT MEANS ARRANGED TO BE OPENED AND CLOSED BY THE STRIKER MEMBER UPON RECIPROCATION OF THE SAME, THE IMPROVEMENT COMPRISING, A VALVE BLOCK MOUNTED IN THE REAR END OF SAID BARREL AND CHARACTERIZED BY A GENERALLY CYLINDRICAL FORWARD PORTION FITTED WITHIN AND CLOSING THE REAR END OF SAID BARREL CHAMBER AND BY AN ENLARGED DIAMETER REAR PORTION FITTED AGAINST THE REAR END OF SAID BARREL, SAID VALVE BLOCK HAVING A GENERALLY VERTICALLY DISPOSED TRANSVERSE GROOVE FORMED IN THE UPPER PORTION OF SAID FORWARD PORTION THEREOF, WHICH GROOVE COOPERATES WITH THE INSIDE WALL OF SAID BARREL TO DEFINE AN ENCLOSED SPACE, SAID VALVE BLOCK HAVING FIRST PASSAGE MEANS EXTENDING FROM THE FORWARD FACE OF SAID GROOVE AND COMMUNICATION WITH THE REAR END OF SAID BARREL CHAMBER, SAID VALVE BLOCK HAVING SECOND PASSAGE MEANS EXTENDING FROM THE REAR FACE OF SAID GROOVE AND COMMUNICATING WITH THE REAR END OF SAID GENERALLY LONGITUDINAL PASSAGE FORMED IN SAID BARREL, SAID BARREL HAVING PASSAGEWAY MEANS ADJACENT THE REAR END THEREOF AND COMMUNICATING WITH THE PERIPHERY OF SAID GROOVE TO ALLOW FLUID UNDER PRESSURE FROM A PRESSURE SOURCE TO BE ADMITTED TO SAID ENCLOSED SPACE, A PRESSURE ACTUATED VALVE LOOSELY DISPOSED IN SAID ENCLOSED SPACE AND HAVING A THICKNESS LESS THAN THE DISTANCE BETWEEN THE FORWARD AND REAR FACES OF SAID GROOVE, SAID VALVE BEING SHIFTABLE BETWEEN POSITIONS AGAINST THE REAR AND FRONT FACES OF SAID GROOVE FOR ALTERNATELY CLOSING SAID SECOND AND FIRST PASSAGE MEANS THEREBY TO DIRECT AIR UNDER PRESSURE INTO THE REAR AND FRONT ENDS OF SAID BARREL CHAMBER, RESPECTIVELY, TO RECIPROCABLY PROPEL SAID STRIKER MEMBER FORWARDLY AND REARWARDLY IN SAID BARREL CHAMBER WHEREBY SAME DELIVERS IMPACT BLOWS TO A TOOL SHANK EXTENDING INTO THE FORWARD END OF THE BARREL, SAID VALVE BEING CONTAINED IN SAID ENCLOSED SPACE SOLELY BY REASON OF THE ENGAGEMENT OF SAID FORWARD PORTION OF THE VALVE BLOCK WITH THE REAR END OF SAID BARREL CHAMBER.