US2609792A - Distributing valve for percussive tools - Google Patents

Description

Patented Sept. 9, 1952 7 2,609,792 j DISTRIBUTING VALVE FOR PERCUSSIVE TOOLS l r Matthew OFarrell, Detroit, Mich., assignor to Chicago Pneumatic Tool Company, New York, -N. Ya, a corporation of New Jersey Application June 17, 1950, Serial No. 168,737

This invention relates to pneumatically operatedpercus'sive tools such as demolition tools, hammers and rock 'drills and more particularly to a distributing'jvalve therefor which operates with estimated endseating and lapping action. i

Distributing valves of the end seating type are knownto have more effective shut-off characteristics th'aln those ofthe lapo r slip fit type because of the tendency'of the latter to leak especially when'wear'hastaken place. End seating valves however, have a disadvantage occasioned by the fact thatfwhilejthe valve is traveling from one seatteftheother, motive fluid can momentarily now over both ends of the valve to opposite ends of the cylinder at the same time. In addition to being wasteful of air "this simultaneous inflow to bbth's'ides of the piston tends to lessen the toolembo'dyi'ng the invention, with the distrib uting valve and hammer piston in their forward position at the start of the return stroke of the piston; t f t Fig. 2 is a fragme'ntary section similar to Fig. 1

with the valve and piston in their rearward position v at the' 'st'art' of the" power stroke;

Rig. 3 'isan Enlarged longitudinal section of the distributing valve and associated valve chest, the-left sideof the valve being shown in forward position and full-lines, "and the right side of the l valvebeing shown in rearward position in broken linespan'd it q a Fig. 4 isa furtherenlarged longitudinal section of the" right sidej of the distributing valve with associated portions of the .valve chest.

Referring to Fig. 1, the illustrated demolition tool orhammer comprises a cylinder 6 providing piston chamber 1 and hammer piston 8 arranged to deliver impacts to a workingimplement such as a drill steel 9 supported inthe front head 19, either by direct engagement (not shown) or through an anvil block ll mounted in a guide member l2 between cylinder 1 and fronthead Ill. The cylinderis provided with the usual exhaust groove B which is overrun by the piston in each 6 Claims. (01. 121--29) direction and which communicates to atmosphere through exhaust port [4. For supplying live air to the frontend of the piston chamber, the cylinder 6 has a port l5 and a passage 15 extending therefrom to the rear extremity of 'the cylinder.

The rear end of the cylinder is closed by a back cylindrical washer I! which is flanged to fit into the cylinder and into a backhead l8. "The backhead' lll,the cylindrical washer l1, cylinder 6, guide member l2 and fronthead [0 are all rigidly secured together by any suitable means such as theusual bolts (not shown). The backhead is provided with a pair of grip handles [9, a rearwardly open recess 20 for receiving manipulative throttle lever 21, longitudinal bore 22 for receiving the stem of the throttle valve 23, and a counterbore 24 which receives live air under control of the throttle valve. The lower end of the counterbore forms a valve seat engageable with the head of the throttle valve which,' in theinoperative position, is seated by the action of spring 25 mounted in live air passageway 26 formed partly in the back cylinder washer and partly in the cylinder 6. The passageway is supplied through threaded opening 21 which is adapted to receive an air hose connection (not'shown).

At its front face, the backhead is centrally bored to receive a valve block 28, which cooperates with the washer I! to form a valve chest providing a valve chamber 29. A distributing valve 30' is arranged in the valve chamber for controlling the reciprocation of the hammer piston 8. The distributing valve is of ,the spool type or annular in shape and comprises a sleeve portion 3|, an outer portion 32 and a radially disposed portion 33 therebetween. The sleeve portion is mounted with a sliding fit on a cylindrical pin 34 whose front and rear ends are firmly. supported in the washer IT and valve block28 respectively. The outerportion 32 has front and rear ends 36 engageable with corresponding seats on washer I1 and valve block 28 respectively. ,It has a peripheral surface 38 fitting a cylindrical surface 40 in the valve block 28. At each end of the peripheral surface 38 is a peripheral recess 4! in the valve. The cylindrical surface 40 is broken up into a front and a rear portion by an annular recess 42 which is in constant communication with the live air counterbore 24 by means of a port 43. In accordance with this invention, the axial width of the peripheral surface 38 of the valve, although less than the distance between the end seating surfaces 36, is greater than, or at least substantially equal to,

. when the valve is shifting from one seat to the other, live air can not flow from the recess .2 over both ends of the valve 38 at the same time.

The valve chest i7, 23 provides space in the valve chamber 29 forwardly and rearwardly of the radial portion 33 of the distributing valve. The forward space of the valve chamber is conn cted through ports id to the rear end of the piston chamber 2'. heated, through ports iii in the valve block 23 to a passageway it in the backhead It, which communicates with the passage l5 leading to the front end of the piston chamber. 1 i

In operation, let it be assumed'the distributing valve 39 and the hammer piston 8 are in the Fig.'

2 position at the start of a power stroke. Live air enters the pneumatic tool through the inlet passages 27, 25, 24, 43 (Fig. 1) to the'annular recess 42 in the valve chest which constantly supplies live :air to the valve chamber 29 as long as the throttle valve 23 is held open. With the distributing valve 38 in the rearward position, as shown in Figs. 2 and 4 and on the right side of Fig. 3, the live air passes from the annular recess 42 into valve chamber 2t, around the front end of the outer portion 32 of the valve, thence through ports it to the rear end of piston chamber T to drive piston i forwardly on its working stroke. The forward recess ti in the periphery of the distributing valve 3t forms a part of the live air passageway, and the metering of the motive fluid for the power stroke is calibrated by the depth of the forward recess t i. By increasing the difference in diameters between the peripheral surfaces 33 and the forward surface il, the designer of the valve may increase the supply of air on the power stroke and accordingly the speed of the piston and force of the blow. During the first part of the forward stroke of the hammer piston 8, the distributing valve 39 is held in its rearward position with the rear end 36 firmly held against its associated seat in valve block 28, thereby preventing any flow of live air through ports &5 toward the end of the piston hammer. The engagement between the rear part of the peripheral surface 38 of the valve 3c and the rear cylindrical surface it on the valve block 28 also inhibits flow of live air toward the ports 55, but

even if these cylindrical surfaces should become worn, the rear and seating surface on the valve will continueto be effective. The valve is held in its rearward position at this time due to the fact that the rear part of the valve chamber 29 is vented to atmosphere through ports d5, passageway 55, passage It, port l5, the front end of the piston chamber 1 and exhaust port i l; whereas the surfaces at the front of the valve 38, and especially along the radial portion 33 are exposed to live air. As the hammer piston 8 advances, the pressure on the front faces of valve 39 decreases rapidly because of the increasing velocity of the motive fluid in the rear end of piston chamber i.

'The air in front of the advancing piston 8 is vented through exhaust groove l3 and exhaust port :4 until such time as the exhaust groove is covered by the piston. Thereafter the residual air in the front end of the piston chamber 7 is trapped and becomes compressed by the advancing piston to increase the pressure in passage l6 and on the rear surface of the distributing valve 30. During the interval when the pressure is falling at the rear end of the piston chamber and rising at the forward end, the preponderance of pressure shifts to such extent. as to trip the valve The rearward space is con-" suddenly from the Fig. 2 to the Fig. 1 position. Immediately thereafter, the piston uncovers the exhaust groove l3 thereby suddenly causing a still further drop in the pressure at the rear end of the piston chamber 1. The piston completes its forward stroke by delivering a powerful impact 'to an anvil block I I.

Fig. 1 shows the piston at the start of its return stroke and with the valve held in its forward position by the action of live air against the rear surfaces of the valve while the forward surfaces are vented through ports 44, the rear end of piston chamber i and exhaust port M. The seated forward end '36 on the valve, and to a lesser degree the. forwardjpart of the lapping surface 33, prevent escape of live air around the front end of the valve to the rear end of the piston chamber.

The piston S is returned by the action of live air delivered through valve block recess 42 into valve chamber 22, around the rear end of the valve 38 through ports 45, passageway 46, passage :5 and port 15. The live air thus delivered flows through the rear peripheral recess 4|, the depth of which can be varied to regulate the supply of live air on the return stroke as in the case of the forward recess 4| which serves as a passageway during the forward stroke. During the initial part of the return stroke of the piston, the

air at the rear end of the piston chamber 1 is vented through exhaust port M. After the piston has covered exhaust groove l3 it compresses the air entrapped in the rear end of the piston chamber thereby building up pressure against the forward faces of the distributing valve 3! The building up of pressure against the rear faces of the valve combine with the reduction in pressure on the front face thereof to trip the valve back to the'Fig. 2 position shortly prior to the time that the piston uncovers the exhaust groove l3. With the valve tripped to its rearward position and the piston at the completion of its return stroke the parts are in their Fig. 2 position to start a new cycle of operation.

From the foregoing description it is apparent that the present valve retains the advantages of an end seating valve because the end seats are effective during the stationary positions of the valve without reliance upon the lapping surfaces 38 and 411, whereas the lapping surfaces are effective during the tripping movement of the valve when neither of the end surfaces 38 is seated. The contact between the rear extremity 36 and the rearseat in the-valve chest is broken.

as soon as the valve starts to move forward, but the supplementary seal at the rear portion peripheral surface 38 prevents escape of live air to the space-in back of the valve until such time as the front portion of the peripheral surface 3 attains lapping engagement with the front cylindrical surface in valve block 28, whereby the front lapping surfaces prevent the escape of live air to the space in front of the valve until such time as the front end 36 is seated. In short, the present invention prevents admission of live air to both ends of piston chamber at the same time by the combinedaction of end seating and lapping surtion having a cylindrical surface adapted to enage a valve chest with a lapping action and having extremities adapted to provide end seating surfaces engageable with said valve chest.

2. In a pneumatic tool, a distributing valve according to claim 1 in which the cylindrical surface is bounded between tw annular recesses, one at each end of the outer portion of the valve.

3. A pneumatic percussive tool comprising a cylinder providing a piston chamber, a hammer piston reciprocable therein, a valve chamber at the end of the cylinder having ports connecting the ends of the valve chamber to the opposite ends of the piston chamber, the periphery of the valve chamber being defined by a pair of lapping surfaces arranged one toward each end, said lapping surfaces being separated by a recess adapted to be constantly supplied with live air during tool operation, and a distributing valve of the spool type reciprocably mounted in the valve chamber and responsive to pressure variations within the valve chamber to cause alternate flow of air from the live air recess to the valve chamber ports to effect automatic reciprocation of the hammer piston, said valve having lapping surfaces fitting the lapping surfaces of the valve chamber and end seating surfaces at its front and rear extremities and having a peripheral recess arranged between each lapping surface and end seating surface, said valve chamber having seating surfaces which are engaged by the valve end seating surfaces to cut off flow of live air past the corresponding end of the distributing valve.

4. A pneumatic percussive tool according to claim 3 wherein the peripheral recesses regulate the flow of live air past the ends of the distributing valve.

5. A pneumatic percussive tool according to claim 4 wherein a cylindrical pin is arranged Within the valve chamber for support and guidance of the distributing valve.

6. A pneumatic percussive tool according to claim 5 in which the lapping surfaces have sufficient width in an axial direction to continue the sealing effect on one side of the valve until a sealing engagement is established by the lapping surface on the other end of the valve, whereby flow of live air over both ends of the valve at the same time is prevented.

MATTHEW OFARRLELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,852,724 Pearson Apr. 5, 1932 2,090,031 Curtis Aug. 17, 1937 FOREIGN PATENTS Number Country Date 397,106 Great Britain Aug. 1.1, 1933

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