US2398992A - Pneumatic tool - Google Patents

Description

Patented Apr. 23, 1946 UNITED ESTATES. PATENT OFFICE John Arthur, Camborne, England Application August 5, 1942, Serial No. 453,653 In Great Britain December 171, 1941 This invention relates to pneumatic and like tools and has reference particularly to riveting and chipping hammers of the general kind having a free piston whose movement is controlled by a valve mechanism comprising a main oscillating distributing valve and an auxiliary oscillating controlling valve; the arrangement being such that compressed air or other elastic fluid, hereinafter referred to as compressed air, is alternately admitted from a source of supply alternately to the two-ends of the cylinder in which the free piston reciprocates.

The invention is indre particularly related to tools of this kind as described in U. S. `Patent No. 1,969,539, and it has for its object tov simplify and improve the `valve mechanism so as to reduce the numbers of angled passages and thus secure entry of the air into the working cylinder, at a higher velocity, with the result that higher piston speeds are attained with a lower air consumption.

The invention consists broadly of a pneumatic pressure tool of the foregoing character having an annular disc main valve so arranged that the compressed air from the source of supply passes directly in the radially inward direction into the end of the cylinder across the valve face to effect the forward movement of the piston.

In order that the invention may be readily understood reference is now made to the accompanying drawing, wherein:

Figure 1 is a longitudinal section of the main portion of the complete tool, with the valve mechanism and piston shown in elevation,vand in the positions which they occupy at the commencement of the operative movement of the piston.

Figure 2 isa sectional view to an enlarged scale of the valve end of the tool, same being taken on line II-II of Figure 3 with the valve elements shown in section.

Figure 3 is a cross-section on the line III- III of Figure 2.

Figure 4 is a view similar in all respects to Figure 2, taken on line IV-IV of Figure 5, but with the valve elements in the position they occupy to eiect the return stroke of the piston, and

Figure 5 is a cross-section on the line V--V of Figure 4.

Referring tothe drawing, and adopting as far as practicable the nomenclature used in the specification of Patent No. 1,969,539, the numeral I designates the main distributing valve, 2 is the auxiliary valve, 3 is the freely moving piston, 4 is the cylinder, 5 is the valve box, 6 is the cylinder cover, which ts in an enlargement of the cylinder end,` 'I is the valve box cover, and B-is the handle of the tool, which is screwed on to the cylinder end and maintains the Whole assembly positioned.

With the parts in the positions shown in Figures 1 and 2, the piston 3 being at the upper end of the stroke, air enters through the passage 9 in the handle, and filling the space IIJ within cover 8, passes directly into the cylinder 4 through ports Il in the wall of the valve box 5, across the face of the disc Ia of the valve I and the adjacent face of the valve box cover l. Air under pressure also passes through ports I2 to the passages I3 beneath the valve disc la, and by way of the passages I4, I5 and I6 to the annular space I 'I at the back of the skirt Ib of the valve I. By vreason of the greater area of the disc Ia the valve I is maintained in the position shown, so that the compressed air can pass freely into the cylinder across the valve face Ia as above stated.

The piston 3 thereupon moves along the cyl- .inder 4 and until it reaches the port I8, the air i in front of the piston can escape freely to atmosphere through port I8 and passage I9, On the piston reaching and closing port I 8, thus preventing exhaust to atmosphere, compression in the front end of the cylinder during continued movement of piston 3 is prevented by the action of the auxiliary valve 2 as hereinafter explained.

When the piston passes port I8 it drives air through port 26, passage 25 and port 24 into arcuate grooves 28 milled in the cylinder cover 6, which lie below the auxiliary valve 2. 'Ihe valve 2 is consequently raised to create an annular f space between it and the flange of the cylinder cover 6 on which it rests, as shown in Figure 2, which allows the air to exhaust through ports 23 and passage I9.

Also, when the piston 3 passes the port I8, the upper end of the cylinder is connected to atmosphere through passage I9. The sudden escape of air causes a pressure drop on valve face Ia, so that the forwardpressure on the valve I is overcome by the rearward pressure on the end of the skirt I b in annular space II added to the pressure in passages I3. Consequently, the valve I moves rearwardly into the position shown in Figure 4, in which the valve ange Ia is pressed against valve box cover 1, so that the supply of air to the cylinder 4 behind the piston 3 is shut oft by valve I. At the same time a space is created round the valve I beneath the flange Ia, and the uncovering of ports I3 and 20 permits air to pass from ports I3 to ports 20, and thence through passages 2l into the annular groove 22 behind the auxiliary valve 2. The area of this groove 22 is greater than the combined areas of the arcuate grooves 28.

The auxiliary valve 2 is therefore forced from the position shown in Figure 2 to that shown in Figure 4, in which it closes the port 23 communieating with the atmosphere through passage I9. At the same time air from groove 22 passes through holes 33 in the auxiliary valve 2 into the arcuate grooves or slots 281, whence it. passes through passage 24 along passage 25 in the cylinder wall to the front end of the cylinder via port 26. The piston 3 is in consequence driven in the reverse direction on its return stroke.

In performing its return stroke -the piston closes port I8 and then compresses the air trapped in the cavity 2'I. of the valve box cover 1; until at the end of the stroke the pressure has risen sufiiciently for the pressure on the edge of valve face Id, projecting beyond the edge of the cavity 21 (the internal diameter of the valve beingslightly less than thediameter of the cavity2I) to overcome the pressure on the valve skirt `Ib in annular space I'I, added to the pressure on the underside of the valve flange Ia, the pressure below the valve ange Ia having in the meantimebeen reduced by the connection of the forward cylinder space to atmosphere through port I8 and passage IS, said cylinder space `being connected to the space belowvalve annulus Ia through ports 20, passages 2|, valve holes 33,' arcuate grooves 28, passages 24, 25 and port 25.

The valve I is consequently forced back into the position shown in Figure 2 ready for repetition of the operating cycle.

I claim:

1. A pneumatic percussive tool comprising a hollow substantially cylindrical casing, a reciprocating hammer slidable in said casing, a cylindrical valve guide tted into a recess at the rear end of said casing, said guide having an axially ported radial flange lat the end thereof seated in said recess with its opposite end projecting from said recess, an annular disc valve having a sleeve portion slidable onthe projecting endof saidvalve guide, an axially and radially yfported sleeve' encircling said valve guide between its radial flange and the wvalve disc, which seats in a recess in said sleeve,

and having a radially ported skirt portion extendning rearwardly beyond the valve disc, said axially land radially ported sleeve having passages therein providing communication between its end faces :and being recessedto lt over the valve sleeve, a false inner cover member fitted into said skirt portion and having an annular projection approaching the rear face of the valve disc and annularlyi spaced.v fromy said skirt portion to form a cavity which Y encircles :saidgannular projection andlthe rear 4partof the'valveclisc, and an outer cover 'member `forasaid casing adapted -to enclose theaforesaid parts, said outer cover-member having an inlet connection `for vthe compressed air for operating thetooLiwhich communicates With'its interior spacesurrounding said ported sleeveand its skirt.

1 2. A tool accordingtofclaim 1J vwherein said axially and radially ported sleeve has 4internally communicating: ports@ opening axially vat its rear end adjacent .the valve dscand radially through theV outer wall of saidvsleeve into `the interiorrof said outer .cover member.

JOHN'ARTHUR.

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