US2070299A - Valve for percussive tools - Google Patents

Description

Feb. 9,

Filed May 16, 1934 Patented Feb. 9, 1937 UNITED STATES PATENT OFFISE VALVE FOR PERCUSSIVE TOOLS Application May 16, 1934, Serial No. 725,835

2 Claims.

This invention relates tol a valve arrangement for fluid `pressure percussive tools and more particularly to a valve for that type of tool which is provided with inlet passages near the ends of the cylinder and one or more intermediate exnaust ports, the tripping of the valve in one direction being effected or assisted by compression created by the piston.

Among the objects of the invention are the provision of a fluid pressure tool that requires no separate valve actuating ports in the cylinder, the tripping of the valve being responsive directly to the pressure in one of the iiuid supply passages. Another object is to reduce the movement of the valve to a minimum. A further objectis the prevention of waste of live air or pressure iiuid which is attained by so proportioning the areas of the valve that the latter is thrown prior to the time that the piston uncovers the exhaust port.

A feature of this invention resides in a relatively small trip area of the valve exposed to fluid compressed by the piston as compared with the opposed area subjected to line pressure. Preferably the areas are so proportioned that compression by the piston must exceed-or at least be equal to-line pressure to trip the valve on the return stroke of the piston. As a result, the holding eiiect of the trip area after the valve is thrown rearwardly is not suiciently great to delay the forward movement of the Valve too long. Consequently, the drop in pressure due to expansion in the cylinder during the forward stroke of the piston is suiiicient to again trip the valve before the piston has moved far enough to uncover the exhaust port.

A still further object of the invention is the provision of a valve suitable for rock drills, the valve being hollow to receive therein a riiie bar.

Still another object of the invention is the provision of a percussive tool whose parts are simple in construction, easy to assemble, and inexpensive to manufacture.

Other objects and features of the present invention will appear more clearly from the following descriptiontaken in connection with the accompanying drawing and appended claims.

In the drawing:

Fig. 1 is a longitudinal sectional View of a percussive tool embodying the present invention, showing the piston beginning its working stroke;

Fig. 2 is a similar view showing the piston beginning its return stroke; and

Fig. 3 is a detail view on an enlarged scale showing the valve and valve chest.

In the embodiment of the invention chosen for the purpose of illustration the cylinder 5 of the percussive drill has an atmospheric exhaust port 6 intermediate its length arranged to be overrun and controlled by the hammer piston l which is reciprocated within the piston chamber of the cylinder to impart blows to a suitable Working tool, such as a drill steel (not shown). The drill steel may be supported in a suitable manner in a chuck of any known or desired type by which rotation imparted to piston l may be transmitted thereto. Since the chuck and the details of the front end construction of the drill form no part oi the present invention, further description is omitted.

The rearward end of cylinder 5 is counterbored to receive and to support in line with the piston chamber a valve assembly which comprises valve cap i0, valve block ll and sleeve valve it slide-bly mounted on the bushing i3. These valve 2O parts are all annular inl shape, as indicated. Valve cap i8 also serves as a closure for the rear end of the piston chamber. Valve block H is engaged by a ratchet ring i6, which is also inserted within the counterbore of cylinder E, and supports the head of a rille bar l5, the bar portion of which extends through the bore of bushing i3 and is journaled in the same. The outer end of the counterbore is closed by a back head I5 secured to the drill cylinder in any suitable manner to retain the parts within the counterbore in assembled relation.

Motive fluid such as compressed air for operating the drill is admitted through a throttle valve 5 8 in the back head, through passage I9 to annular groove 2B and through a series of passages 2| in the ratchet ring I 4 and valve block H and thence to the annular lluid` chambers 2li and 25 formed within the valve block and valve cap respectively.

The parts constituting the valve assembly are best shown in Fig. 3. The valve i2 is generally in the shape of a. sleeve having a flange 2l at one end whose outermost diameter is slightly less than the diameter of the fluid chamber 25 whereby to provide a restricted annular passage 28 for live` air from the chamber 2t to the chamber 25. One face of the liange may be bevelled,` as shown.

The valve I2 is adapted to reciprocate between an annular seat 3i! on the valve cap I il and a similar seat 3l on the valve block Il. Seat 3| separates the live air chamber 24 from an annular outlet chamber 32 which in turn is connected through passages 33 and 34 with the front end of the piston chamber. The inner edge of the seat 3l is larger than the valve l2 whereby live air may be admitted to chamber 32 when the flange 2l is away from the seat 3l as indicated in Figs. 2 and i3. In this position of the valve, seat separates chamber 25 from outlet chamber 38 having ports 31 leading to the rear end of the piston chamber. The eXtreme rear end of the sleeve portion or the valve is vented by a passage 38 extending through the valve block and cylinder respectively.

In operation the bevelled portion RC on the rear face of the flange 21 is continuously exposed to live air of substantially constant pressure tending to hold the valve against its forward seat 3d. The front face of the flange comprises an annular balancing area FB within chamber 25 and surrounding the seat 3i). The front face also comprises a trip area FT inwardly of the seat 3d and defining one end of the outlet chamber Se. When the front face is away from its seat, as in Fig. 1, the entire face acts as a holding area. Conversely, when the rear face is away from its associated seat, as in Figs. 2 and 3, the entire area of this face constitutes the holding area for retaining the valve in forward position.

Assuming the parts are in the Fig. 1 position, live air or other expansible motive iluid passes from the supply chamber 24 around the peripheral edge of the valve to the chamber 25, over the edge of the seat 3) to the outlet chamber 35 which delivers the air through the passages 3i to the rear end of the piston chamber, thereby driving the piston forwardly. Due to the iicw of the air in a stream through the restriction isurrounding the valve ange, the front face oi the valve is subjected to a lower pressure per unit area than the constantly exposed surface RC on the rear face. Since the front face has a greater area than RC this lower unit pressure is. sufficient to hold the valve in the Fig. 1 position until expansion of air behind the piston reduces the holding pressure sufficiently to permit the constant pressure on area RC to trip the valve to the Fig. 2 and Fig. 3 positions. Movement or the valve to its forward position perf mits admission of air past the seat 3l into outlet chamber 32 connected to the front end of the piston chamber for driving the piston rearwardly.

When the valve rests against its front seat iii?, there is no appreciable ow through the annular restriction 28 and hence unit pressure on the area FB is substantially the same as on the larger holding area on the rear face of the valve flange. When the piston 'I has moved rearwardly to cover the exhaust S, the air in the rear end of the piston chamber becomes trapped and further movement of the piston compresses this air which transmits a corresponding pressure to the trip area FT. The areas of the respective surfaces on the valve are preferably so proportioned that compression due to the piston must exceed, or at least be equal to, line pressure before the valve is kicked to the Fig. 1 position, after which the valve and piston commence a new cyclerof operation.

The area FT exposed to compression by the piston should not be appreciably greater than the unbalanced holding area of the valve exposed to line pressure. Such an area would result in the dubious advantage of tripping the valve rearwardly before the piston compression equalled line pressure but being unnecessarily large would increase the holding surface on the front face of the valve to retard the next valve movement as the piston is being forced forwardly. This holding surface should be reduced in area so that the valve trips before the exhaust 6 is uncovered by the forward movement of the piston. Otherwise live air may nd its way through the rear piston chamber direct to the exhaust port.

The relative areas of the surfaces of the valve constituting the present invention are important since they cause the valve to trip instantly and at the proper time without requiring the use of separate passages leading from the piston chamber to the valve which were found necessary in similar prior devices in order to provide proper balancing of pressures on the valve.

While the invention has been herein disclosed in what is now considered to be a preferred form, it is to be understood that the invention is not limited to the specic details thereof but covers all changes, modifications and adaptations within the scope of the appended claims.

What I claim is:

1. In a fluid actuated rock drill, a cylinder having a central exhaust and pressure fluid supply passages leading to opposite ends of the cylinder respectively, a piston reciprocating in the cylinder, a valve chest at the rear end of the cylinder, said passages being connected to said valve chest, a bushing centrally mounted within said chest, a cylindrical valve sleeved over the bushing and adapted to reciprocate thereon, a of axially spaced annular seats on the chest, a ange on the valve disposed between said seats and alternately engageable therewith, said chest providing a valve chamber in front of the flange and a valve chamber in back of the flange, said chambers communicating with each other through a restricted passageway around the outer edge of the flange, means for admitting live pressure iiuid to the rear valve chamber thereby tending to hold the valve against its front seat, said valve chambers having communication over the seats with the respective passages in the cylinder, the front face of the valve having a balancing area which surrounds the front valve seat and which opposes the holding pressure on the rear face of the valve, and having a trip area which lies between the front seat and the bushing and which is exposed to compression by the piston at the rear end of the cylinder to overcome the holding pressure, said trip area being no greater than the unbalanced area exposed to live pressure uid, whereby live pressure iiuid may force the valve to its front seat prior to the time the piston uncovers the exhaust on its forward stroke.

2. A iiuid actuated rock drill according to claim l, in which said trip area is less than the unbalanced area exposed to live pressure fluid.

ALFRED G. SLATCHER.

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