US3038447A - Distributing valve assembly for pneumatic percussive tools - Google Patents

Description

June 12, 1962 M. O'FARRELL Mm.. Omi,

Filed Feb. 16, 1960 ATTORNEY it tats 1 arent 3,038,447 DISTRlBU'llNG VALVE ASSERELY FR PNEUMATC PERCUSSEVE TLS Matthew Farrell, Utica, NX., assigner to Chicago Pneumatic Tool Company, New York, FLY., a corporation of New Jersey Filed Feb. 16, 1960, Ser. No. 9,023 3 Claims. (Cl. 121-29) This invention relates to an improved pneumatic distributing valve assembly for percussive tools of the demolition type, such as pavement breakers and the like.

ln the demolition type tool pneumatic pressure iiuid :is directed by a distributing valve alternately to opposite ends of a piston chamber so as to reciprocate a heavy slide hammer piston relative to an anvil associated with a work steel. It is the purpose of the tool to forcefully and repeatedly pound by means of pneumatic pressure the hammer piston against the anvil to provide effective action of the Work steel. ln the operation of the tool considerable pneumatic pressure is present in a chamber associated with the distributing valve. Any leakage of pneumatic pressure from this chamber to the return end of the piston chamber during a work stroke of the piston will resist or retard the driving speed of the piston and thereby frustrate or miniF mize its effects upon the anvil and the associated work steel.

It is an object of this invention to provide an improved and efficient pneumatic distributing valve assembly in a percussive tool of the demolition type which avoids such leakage.

At times in the manufacturing of different assemblies or parts for a demolition tool tolerance variations develop which are greater in one run of parts than in another. Where such occur in the housing of the tool or in the casing of the distributing valve assembly there may be leakage of operating pneumatic fluid around the distributing valve assembly to the return end of the piston chamber so as to decrease the efficiency of the tool on a work stroke of the piston.

A further object of this invention is to provide a distributing valve assembly for a percussive tool which is adapted to be effectively assembled in similar chambers of different housings even though such chambers may vary slightly in dimension from one another.

A still further object of the invention is to provide an improved distributing valve assembly in a pneumatic percussive tool of the type mentioned which provides an effective seal between an intake port to the chamber containingr the valve assembly and an outlet port of this chamber associated lwith the return end of the piston chamber.

The invention further lies in the particular construction of its component parts and in their cooperative association with one another to effect the purposes and advantages intended herein.

The foregoing and other objects and advantages of this invention will appear more fully hereinafter from a considcration of the detailed description which follows, taken together with the accompanying drawings wherein an embodiment of the invention is illustrated. It is to be eX- pressly understood, however, that the drawings are for purposes of illustration and description and are not to be construed as defining the limits of the invention.

ln the drawings:

FIG. l is a longitudinal section through a pneumatic percussive tool of the demolition type embodying the invention;

FIG. 2 is an enlarged detail of the distributing valve assembly;

FIG. 3 is a further enlarged sectional detail showing the seal ring in its channel in a normal relaxed condition before the distributing valve assembly has been disposed in the housing of the tool;

FIG. 4 is a detail View showing the seal ring fully compressed into its peripheral channel; and

FIG. 5 shows the distributing valve assembly in a housing Where there exists a variation from that in FIG. 1 in the clearance between the casing of the valve assembly and the surrounding Wall of the housing, and shows an eX- panded condition of the seal ring relative to that shown in FIG. l to provide a seal tight relation between the casing and the surrounding wall of the housing.

For a more detailed understanding of the invention reference is now directed to the several figures of the drawing, wherein there is disclosed a pneumatic percussive tool of the demolition type. It includes a housing generally designated 11 comprising a body portion l2 bolted by the usual side tie-bolts, not shown, to a backhead portion 13. The body portion defines a cylindrical piston chamber 14 in which a heavy slide hammer piston 15 reciprocates to forcefully pound an anvil 16 against a work steel, not shown. The backhead 13 has a recessed inner end which, together with a slightly complementary recessed end in the adjoining body 12, defines a cylindrical pneumatic distribution chamber 17. A trigger operated throttle valve 13A in the housing wall 19` controls iiow of pneumatic perssure iiuid from a supply inlet 21 to an inner passage 22. The latter opens centrally through the cylindrical wall 23 into chamber 17.

A pneumatic flow distributing valve assembly is removably disposed in chamber 17. it comprises a cylindrical container or casing 24 slidably received in chamber 17. Centrally about the periphery of the casing is an annular groove 25 which registers with passage 22. Groove 25 communicates through radial ports 26 with an internal annular groove 27 which opens into a valve chamber 28 centrally of the casing. The left end of the valve chamber is closed by a dead end 29 of the casing. A separable partition disc 31 closes over an open right end of the valve chamber, and separates chamber 17 from the piston chamber 14. The partition disc abuts about its inner marginal face against a complementary end wall 32 of the casing, and limits about its opposite marginal area against a recessed internal shoulder 33 of the housing body 12. The dead end 29 of the casing presses against a coned spring washer 34 which abuts the neighboring end wall 35 of chamber 17 and takes up end play or clearance between the valve assembly and the end wall 35.

The valve chamber 28 communicates through a ring of perforations 36 in the partition disc with the rear or driving end 37 of the piston chamber. The valve chamber also communicates through a ring of radial ports 38 in the casing with an annular peripheral outlet groove 39 in the casing. The latter groove or passage is registered with a terminal end of a passage 41 leading through the wall of the kbody 12 to the forward or return end 42 of the piston chamber.

A shaft 43 integral with the partition disc 31 extends axially and freely through the valve chamber 28, and has a slide fit at its free end in an axial hole 44 of the end wall 29 of the casing. A slide valve 45 shiftable along shaft 43 controls iiow of operating pneumatic fluid entering the valve chamber 28, alternately through the perforations 36 and through the peripheral groove 39 to associated ends of the piston chamber.

The slide valve 45 is of T-ring form. It comprises coaxial inner and outer tubular cylinders 46 and 47 integrally connected by an annular web 4S. The inner cylinder 46 has a slide lit for longitudinal movement along the shaft 43. The outer cylinder 47 seats in an internal annular groove 49 of the icasing upon a pair of annular shoulders 51, 52 between which the inner groove 27 opens into the valve chamber 28. roove 49 is a little longer in its end to end dimension than the outer valve cylinder 47. Squared end shoulders 53, 54 limit the extent of shifting of the slide valve in one direction or the other relative to the inner groove 27. When the slide valve is in its left position limited against the left shoulder 53 as in FIGS. l and 2, a ring of radial ports 55 in the valve cylinder 47 are sealed over by the shoulder 51, and a second ring of radial ports S6 in the valve cylinder 47 are registered with the inner groove 27, whereupon operating pneumatic fluid admitted by the throttle valve 18 to groove 27 iiows through ports 56 into the valve chamber to the right side of the valve web 48 and passes through the perforations 36 to the rear end 37 of the piston chamber, thus exerting pressure on the piston and driving the same forwardly. Momentarily before the forward end of the piston pounds the anvil, the rear end of the piston overruns or clears an exhaust vent 16 whereupon 4the spent driving pneumatic fluid -at the rear of the piston exhausts to atmosphere. Residual air in the piston chamber ahead `of the piston is trapped and forced by the moving piston through passages 42 and 41 to the valve chamber where it acts upon the web 48 to shift the valve to its right position where it will limit against the shoulder 54. In the latter position of the valve, the ring of ports 56 will be sealed over by the shoulder 52 and the ring of ports 5S will be registered with groove 27, whereupon pneumatic flow from the latter will be to the valve chamber 28 at the left of web 48, and through the ports 38 and groove 39 to the return end 42 of the piston chamber to cause return of the piston. Atmosphere air trapped in the piston chamber ahead `of the returning piston will pass through the perforations 36 to shift the valve back to the position shown in FIGS. l and 2. This shifting or shuttling ofthe slide valve and reciprocation of the piston continues automatically as long as the throttle valve 1S is held open.

It is obvious from the foregoing manner in which the tool operates that if there is any leakage of pressure air between the casing 24 and the surrounding wall 23 of chamber 17 from the peripheral groove 25 to the peripheral groove 39, the efficiency of the tool on the work stroke of the piston will be impaired. If there is such leakage, pressure air will ow from groove 39 and passage 41 to` the forward end 42 `of the piston chamber where it will cushion and retard pounding of the piston 15 against the anvil 16. A resilient deformable seal ring 57 seated in an annular peripheral channel 53 of the casing in resiliently pressed relation to the iloor 59 of the channel and to the opposed surrounding wall 23 of the housing provides a seal tight relationship between the two which prevents any possibility of leakage of pressure air around the casing from groove 25 to the groove 39 and the associated forward end 42 of the piston chamber.

The seal ring is circular in cross section in its normal relaxed condition externally of the tool, las appears in FIG. 3. It is of soft elastic or live rubber which is readily deformable under pressure, and is adapted to resiliently restore upon relaxing of such pressure. The channel S in which the seal ring is seated extends about the periphery of the casing. It is isquared in cross section having a flat annular floor 59 and vertical side walls 6l. The cross sectional diameter of the seal ring corresponds to the width of the channel, and is slightly greater than the depth of the channel so that lthe seal ring projects in part out of the channel in its fully relaxed condition, as in FIG. 3. In this fully relaxed condition of the seal ring, the adjacent annular corners 62 of the channel are vacant. As peripheral pressure is applied to the seal ring the latter will, according to the degree of the pressure, be compressed and deformed so as to spread out in its channel and till the vacant side corners 62. The cross sectional diameter of the seal ring relative to the channel 58 is such that the seal ring may be resiliently compressed into the latter and so deformed as to fully l occupy the channel substantially level with the peripheral surface of the casing, as in FIG. 4. When relieved of such pressure the seal ring will resiliently restore to normal.

The structural arrangement of the seal ring and its channel to each other provides various advantages. It enables the valve assembly to be effectively used in different housings though these may vary slightly from one another in the diameter of the chamber 17. Such dimensional variations may occur in different manufacturing runs of the housings. In some cases, as in FIGS. l and 2, the casing 24 of the valve assembly has a slide or close lit in the housing chamber 17, and the seal ling in such cases will be deformed under the pressure of the surrounding wall 23 as to substantially fill the channel. `In other cases, as in FIG. 5, because of dimensional variations the tit between the casing 24 and the surrounding wall 23 of the housing is not as close as that in FIGS. l and 2, as indicated by the clearance 63. In each of the cases exempliiied in FIGS. l and 5, the seal ring 57 will nevertheless press resiliently against the oor 59 of its channel and against the opposed surrounding wall 23 of the housing to provide a fluid tight relation between the latter wall and the casing so as to prevent leakage around the casing from groove 25 to the groove 39. The dimensional relation of the seal ring 57 to its channel 58, as mentioned above, permits the seal ring according to the pressure thereon to be deformed to a degree wherein it is fully contained in the channel. This avoids overflow of any portion of the seal ring laterally upon the periphery of the casing which, if allowed to occur, would prevent a very close or slide lit of the Valve assembly in a housing.

The extent of such dimensional variations between the housing and casing that may be taken up by the seal ring will be limited substantially to the extent of the normal projection of the seal ring from its channel.

The valve assembly is restrained against longitudinal play in the housing by means of the coned spring washer 3d which is loaded between the dead end 29 of the valve casing and the opposed wall 3S of the housing. The stationary condition given to the valve assembly by the spring washer avoids undesirable slight back and forth movement of the seal ring and consequent Wear of the latter that might otherwise occur during the operation of the tool were the spring Washer omitted. Chattering of the valve assembly is also prevented by this arrangement of the spring washer.

While an embodiment of the invention has been illustrated and described in detail, it is to be expressly understood that the invention is not limited thereto. Various changes can be made in the design and arrangement of the parts without departing from the spirit and scope of the invention, and it is my intent, therefore, to claim the invention not only as shown and described but also in all such forms and modifications thereof as may be reasonably construed to fall within the spirit of the invention and the scope of the appended claims.

What is claimed is:

l. A valve assembly unit disposable in a cylindrical flo'w distributing chamber of a pneumatic percussive tool having a piston reciprocable in a piston chamber, wherein the distributing chamber has a dead head closing its rear end, has a pneumatic supply inlet port and has an outlet port located between the inlet port and the dead head and connected to a return end of the piston chamber, the valve assembly comprising an outer closed ended cylindrical container having a uniform outer diameter less than that of the distributing chamber whereby the container is receivable into the latter, a valve chamber defined by the interior of the container, a peripheral inlet groove in the surface of the container communicating with the valve chamber, a peripheral outlet groove in the surface of the container communicating with the interior of the container, the inlet and outlet grooves being registrable respectively with the inlet and outlet ports of the distributing chamber upon reception of the container into the latter, valve means in the valve chamber for peiodically communicating the inlet groove through the valve chamber with the outlet groove, a peripheral channel in the surface of the Container separating the inlet groove from the outlet groove, a resilient compressihle 'seal ring seated in the channel having its periphery projecting from the latter and having a greater outer diameter than the diameter of the distributing chamber; and the seal ring being compressible into the channel to the eX- tent of the greater difference of the outer diameter of the seal ring over the diameter of the surrounding wall of the distributing chamber and adapted to provide a seal tight relation between the two upo-n reception of the container into the distributing chamber.

2. In a pneumatic percussive tool, a housing, a piston chamber in the housing, a pneumatically powered hammer piston reciprocable in the piston chamber, the latter having `an exhaust vent to atmosphere located so as to be overrun by the hammer piston in either direction, a cylindrical pneumatic ow distributing chamber in the housing having a dead head closing one end and having an opposite end in axial extension of the rear end of the piston chamber, an annular shoulder in the housing dividing the two chambers from one another, an intake passage through the housing opening centrally into the distributing chamber adapted to supply the latter constantly with pneumatic pressure fluid, an outlet passage from the distributing chamber opening into the return end of the piston chamber, a valve unit of uniform outer diameter comprising a cylindrical valve casing disposed in the distributing chamber providing an internal valve chamber, a dead end closing one end of the casing, a disc seated against the shoulder and closing over the opposite end of the casing, the disc having perforations communicating the valve chamber with the driving end of the piston chamber, a peripheral inlet groove in the casing registered with the intake passage, an annular internal groove in the wall of the valve chamber having radial communication With the inlet groove, an outlet peripheral groove in the casing in spaced relation to the inlet groove and registered with the outlet passage, the outlet groove having radial communication with the valve chamber, a slide valve means reciprocable in the valve chamber relative to the internal groove of the lat-ter adapted to alternately communicate the internal groove through the valve chamber with the perforations in the partition disc to supply driving power to the driving end of the piston chamber and to communicate the internal groove through the valve chamber with the outlet groove to supply driving power to the return end of the piston chamber, a peripheral seal ring channel in the casing separating the inlet groove from the outlet groove, and a resilient seal ring seated in the channel providing a fluid tight seal between the casing and the surrounding wall of the distributing chamber whereby leakage of pneumatic fluid from the inlet groove around the casing to the outlet groove and the associated return end of the piston chamber is blocked, and spring means between the dead end of the distributing chamber and the dead end of the casing exerting a pressure through the casing holding the disc seated against the annular shoulder.

3. In a pneumatic percussive tool including a housing having a piston reciprocable in a piston cylinder in response to pressurized air admitted alternately to opposite ends of the cylinder, a cylindrical valve chamber in the housing in axial alignment with the cylinder opening at one end into the cylinder and having a back wall closing over the opposite end, the valve chamber being of greater diameter lthan the cylinder whereby an annular shoulder is defined between the valve chamber and the cylinder, an inlet port in the housing connectable to a source of pressure air and communicating centrally through the cylindrical wall of the valve chamber to the latter, the valve chamber having `an outlet port which opens through a marginal back end area of its cylindrical wall and communicates through the housing with a forward end of the cylinder; a valve assembly unit including a casing of uniform outer diameter having a close slide fit in the valve chamber, the casing having a front head seatable against the shoulder and having a rear head spaced by a close clearance from the back wall of the valve chamber, spring means interposed in this clearance pressing the front head of the casing fluid tight against the shoulder, an annular peripheral groove in the casing communicating with the interior of the casing and registering with the inlet port', an annular pcripheral outlet groove in the casing communicating with the interior of the casing, axial holes in the front head of the casing communicating the interior of the casing with the cylinder, valve means in the interior of the casing controlling pneumatic flow from the interior of the casing alternately to said holes and to the outlet groove, a U-shaped annular peripheral channel in the wall of the casing between the inlet and outlet grooves, and a resiliently compressible G-ring seated in the channel having a diameter when fully relaxed greater than the height of the channel, and having a depressed condition completely lilling the channel and exerting a pressurized contact of its outer surface with the closely tting opposed surface of the valve chamber.

References Cited in the le of this patent UNITED STATES PATENTS 2,090,031 Curtis Aug. 17, 1937 2,201,431 Douglass May 2l, 1940 2,604,072 Beckett et al. July 22, 1952 2,609,792 OFarrell Sept. 9, 1952 2,613,646 Gillerstrom Oct. 14, 1952 2,888,679 Peterssen et al. June 2, 1959

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