US2897782A

US2897782A - Impact tools operated by compressible pressure fluid

Info

Publication number: US2897782A
Application number: US667770A
Authority: US
Inventors: Harold T Kennedy
Original assignee: Individual
Current assignee: Individual
Priority date: 1957-06-25
Filing date: 1957-06-25
Publication date: 1959-08-04
Anticipated expiration: 1976-08-04

Description

' Aug. 4, 1959 H. T. KENNEDY 2,897,782

IMPACT TOOLS OPERATED BY COMPRESSIBLE PRESSURE FLUID Filed June 25, 1957 3, sheeis-sheet 1 ,f2 H 55 53 l 49 Il y 27 INVENTOR. 2] 28 Haro/d Z' kennedy hf-M @n W ATTORNEY 2,897,782 IMPACT Toops OPERATED BY coMPREssIBLE REssuRE FLUID Filed'June 25, 1957 Aug. 4, 1959 H. T. KENNEDY 3 Sheets-Sheet 2 INVNTOR. Haro/a T. Kennedy 14o-MPL M/u( bf' ATTORNEY Aug. 4, 1959 H. T. KENMEDYA 2,897,782

IMPACT TOOLS OPERIATED BY COMPRESSIBLE PRESSURE FLUID Filed June 25, 1957 Sheets-.Shet 5 mimi Nm w S wwwlmww www# Nm n m ihFIl. E

mm mh /M@ X/ l 1km, Lm I l O IMS INVENTOR. Hara/d 7.' Kennedy y 2,897,782 Patented Aug. 4, 1959 l'ice Harold T. Kennedy, Glen Ridge, NJ. Application June 25, 1957, Serial No. `667,770

17 Claims. (Cl. 121-30) This invention relates to improvements in the method of operating impact tools powered by a compressed lluid, such as compressed air, compressed gas, or steam. The invention further provides improvements in the construction of impact tools for more convenient practice of the method, either manually, semi-automatically or fully automatically.

Impact tools of the type to which the invention relates comprise a piston reciprocably movable within a cylinder as their source of power. The piston is normally in a retracted position, which is the rest position, and is driven forward through its Work or power stroke by a burst of compressed uid acting upon the rear surface of the piston. After completion of the work stroke the piston is retracted to the rest position by applying a burst o f compressed uid to the front surface of the piston which then moves through its return stroke.

For the sake of brevity reference will occasionally be made in the description to compressed air as a representative type of pressure fluid, since air-powered impact tools are by far the most numerous, but it is to be understood that other fluids, such as steam or compressed gas, for example, carbon dioxide, may be employed. The same consideration as set forth with relation to operation by compressed air apply to operation by other compressible lluids.

In many instances the size and weight of the impact tool are limited by the fact that the tool must be manageable, must not be unduly heavy, and must not exert an undue recoil on the operator. Also, the pressure of compressed air is limited by the fact that it is normally desirable to operate within a pressure range which can be produced by a single-stage air compressor of the piston type.

These factors limit the power of the impact'which the conventional tool can deliver.

Conditions are occasionally encountered Where the impact power of the conventional impact tool is insutlicient to perform the Work, and where it is not feasible to increase the power by an increase in the size of the tool because the corresponding increase in weight would make the tool unmanageable and tiring for the operator.

There are also conditions Where an increase in the number of the blows is of no avail, as long as each blow is below a required minimum impact. For this reason a great number of blows are in many instances not elective as a substitute for a smaller number of heavier blows.

As a representative example of such a condition may be mentioned the driving of resilient railroad spikes. These spikes comprise basically two straight substantially parallel legs connected by a common resilient head portion. The head portion is produced by bending of the spring steel stock, and is generally of such shape that a blow struck on the head portion causes the head portion to flex slightly, as a result of which only a portion of the blow is transmitted to the legs and effective to drive the legs into the drilled holes of the tie or sleeper. One commercial form of the spring spike is so shaped that United States Patent l the point at which the hammerhits the head is approximately 11A; of an inch (roughly 30 mm.) laterally offset with respect to the plane of the legs. A description of the spike and of its application is found in the United States patent to Tvrzicky, No. 2,287,843, issued lune 30, 1942.

A test was conducted with a conventional pneumatic impact tool, as used by railroads for driving ordinary non-resilient railroad spikes. The tool drove the spring spike about one inch into the holes of the tie or sleeper whereafter it was not possible to drive the spike any farther.

A second tool was constructed capable of delivering individual blows, one at a time. The tool included a power cylinder of a bore of 11/2 inches permitting a stroke of 12 inches. A hammer head was used of a weight to bring the total movable mass, piston, piston rod and head, to l0 pounds. With this tool it required 45 blows to set the resilient spike. The time required for this operation is far too long to be economically acceptable.

Economy considerations require that the spike should be driven home with no more than a total of 10 blows struck by a tool of conventional size and weight.

The problem was solved by the invention which is based on the consideration that it is possible to increase the output of an impact tool by utilizing the return stroke for the generation -of impact power, storing this power and then adding or superimposing it to the normal power developed during the work stroke.

According to the invention this is accomplished by first driving the piston by application of a burst of compressed fluid against the front of the piston through the return stroke from a normal rest position in which the piston is projected, rather than retracted. The kinetic energy developed during the return stroke is temporarily stored in one or a plurality of springs, which may be of the metallic or pneumatic type. After compression the spring or springs expand, thereby driving the piston through the work stroke. At this moment a burst of compressed uid is applied to the back side of the piston, the burst being so timed as to coincide with the expanding action of the spring or springs to result in a total driving force of the piston in excess of the power imparted by the last applied burst of compressed fluid.

lt is conventional practice to install a resilient buffer in impact tools to absorb and dissipate piston energy at the end of the return stroke at which the piston reaches its rest position in which the piston is retracted. As far as I am aware, the buffers, usually made of rubber, are not suited for the operation contemplated by the present invention, nor does an arrangement in which the piston is retracted in rest position lend itself tovmy improved method. Furthermore, it is desirable to employ spring means capable of absorbing substantial amounts of energy of the order of the energy generated during the Work stroke and then releasing such energy with a minimum of loss.

My method may be practiced by controlling the action of the power piston manually by appropriate manipulation of a valve mechanism for admitting and discharging compressible fluid into, and from, the cylinder chambers in front and in back of the piston. Such manual control requires an appropriate timing or rhythm on the part of the operator.

It is also possible to assist the operator by automatic control mechanism in the timing of the burst of pressure uid which drives the piston through the work stroke.

It is finally possible to provide automatic means for controlling the timing in such a way that a series of blows are struck in automatic sequence one after another.

A test was conducted during which the previously mentioned impact tool Was employed, modified by the addition of two energy storing springs, and fitted with a hammer head of the weight of pounds. The test proved that the spike could be driven with an average of 5 to 6 blows. Such performance is of an entirely diiferent order of magnitude than the performance obtainable by conventional operation.

The various objects, features, advantages and applications of this invention will appear more fully from the detailed description which follows accompanied by drawings showing, for the purpose of illustration, mechanical devices by means of which the invention may be practiced. The invention also resides in certain new and original features of construction, combination of elements, steps, and sequences of steps as hereinafter set forth and claimed.

Although the characteristic features of this invention which are believed to be novel will be particularly pointed out in the claims appended hereto, the invention itself, its objects and advantages, and the manner in which it may be carried out may be better understood by referring to the following description taken in connection with the accompanying drawings forming a part of it, in which:

Figure 1 is a diagrammatic representation of an impact tool with its associated control mechanism capable of practicing the invention;

Figure 2 is a diagram of an impact tool of the type shown in Figure 1 and valve mechanism assembled from commercially available components; and

Figure 3 is a diagrammatic illustration of the valve mechanism of Figure 2.

In the following description and in the claims various details will be identied by specific means for convenience. The names, however, are intended to be generic in their application. Corresponding reference characters refer to corresponding parts in the several figures of the drawings.

The drawings accompanying, and forming part of, this specication disclose certain specific details of the invention for the purpose of explanation of its broader aspects, but it is understood that the details may be modified in various respects without departure from the principles of the invention, and that the invention may be practiced by and applied to other devices than shown.

The pneumatic impact tool L11 in Figure 1 is shown as comprising a yoke or beam 12 to which handles 13 and 14 are attached. The yoke is mounted on the upper end of a power cylinder 15 within which a piston 16 is slidably movable. The piston divides the cylinder into chambers, an upper chamber 17 above the piston and a lower chamber 18 below the piston. In the rest position in which the piston is shown in Figure 1 the lower chamber 18 is volumetrically small and the upper chamber 17 is large. If the piston is in its uppermost position the volumetric relationship is reversed.

The piston 16 has a piston rod 19 attached thereto, and

the piston rod carries a head 20 whose total mass may be chosen by attachment thereto of a hammer mass 21 of suitable size. Bolts 22 are shown for this purpose. The head 20 has two

lateral bearings

23 and 24 for guiding the head along

guide columns

25 and 26. The lower ends of the columns are secured to a base 27 having an aperture 28 therethrough through which the hammer mass 21 may extend. The upper ends of the columns are secured to the yoke 12 at 29 and 30.

A pair of power springs 31 and 32 are mounted on the

columns

25 and 26 by means of

clamp collars

33 and 34. The collars are recessed at the bottom at 35 and 36 to engage and hold the upper ends of the

springs

31 and 32. The lower ends 37 and 38 of the springs may be adjusted to assume a predetermined distance above the base 27 by sliding the

collars

33 and 34 into an appropriate vertical position and then clamping them by means of handles 39 and 40.

An air duct 41 leads to the lower chamber 18 to introduce compressed air into the chamber or vent air therefrom, and a corresponding duct 42 leads to the upper chamber `17.

A rnain control valve 43 for the power cylinder 15 comprises a housing 44 within which a valve member 45 is movable. The housing has a total of five ports, three of which are directly controlled by the valve member.

An inlet port 46 receives compressed air from a line 47 and the admitted air passes into

ducts

41 or 42 through

control ports

48 and 49, respectively, depending on the position of the valve member 45. In the illustrated position air entering through port 46 is directed into duct 42 through port 49. Simultaneously, air is vented from the lower chamber 18 through duct 41 to pass into the atmosphere through a Vent port 50. If the valve member is in the other extreme position, air passes from inlet port 46 through control port 48 into duct 41, and the upper chamber 17 is vented through duct 42 and a further vent port 51.

The control valve member 45 may be manually controlled, but preferably a servo mechanism is provided for remote control of the valve member from a pilot or relay valve.

As shown in the illustratedembodiment, a servo motor 52 comprising a servo piston 53 on an extension rod or stem 54 of the valve member 45 moves the valve member into one or the other of its two control positions, depending on whether pressure fluid is admitted into the space above the servo piston through a control line 55 or to the underside of the piston through a control line 56.

A pilot or relay valve 57 is provided which is of similar construction as the main control valve but may incorporate a retarding device, as will presently be described.

r[he pilot valve 57 comprises a housing 58 within which a valve member 59 is movable. The housing 58 has an inlet port 60, two control ports 61 and 62 and two vent ports `63 and 64. A pressure line 65 extends to the inlet port60.

In the position in which the valve member 59 is shown, pressure liluid supplied through the line 65 passes into control line 56 to the underside of the servo piston 53. At the same time the chamber above the servo piston 53 is vented through line 55, control port 62 and vent port 64.

If the valve member `59 is moved into its other extreme position, pressure uid passes from pressure line 65 through control port 62, control line 55 to the chamber above the servo piston 53, and the chamber below the servo piston is vented through control line 56, control port 61 and vent port 63.

The pilot valve member A59 has an upper extension 66 carrying a control knob 67 and a lower extension or rod 68 whose end 69 may be engaged by a bracket 70 on the head 20 for actuation of the valve by the head. The pilot valve housing 58 is vertically adjustable on the column 26 by a clamp 7'1 to permit the end 69 of the rod 68 to be brought into any desired vertical position, so as to permit presetting of the point of reversal of the piston 16.

The handle 14 is shown as being hollow to serve as an air duct, `and a hose coupling 72 is provided in order to connect the tool to the pressure line 73 of a suitable source of compressed air indicated in Figure 1 as being an air compressor 74.

The rate at which the pilot valve 57 may be actuated may be controlled by a single-acting retarding device shown in Figure 1 as being a dash pot. The dash pot comprises a cylinder 75 within which a dash pot piston 76 on the rod `68 is movable. A spring 77 normally biases the valve member 59 towards its upper end position in which the valve is arrested by a collar 78 abutting the housing 58. The collar has a set screw 79. An adjustablevent valve 80 and a check valve 80 control the escape of air from and entry of air into the dash pot in such a way that air leaves the dash pot only slowly when the dash pot piston 76 is depressed, but is admitted readily when the dash pot piston is raised.

As a result, the downward movement of the pilot valve member 57 is retarded, whereas the upward movement is not retarded.

My method may be practiced either manually, semiautomatically or fully automatically.

Assuming that the impact device 11 is fitted only with a main control valve 43, it is evident that the valve 43 may be manipulated lirst to admit compressed air into the chamber 18 of the power cylinder 15. The burst of air causes the piston y16 to move upwardly, thereby compressing the

springs

31 and 32. When the power piston reaches its upper reversal point at which the kinetic energy: of the upwardly moving piston and hammer

head assembly

16, 19, 20 and 21 is substantially fully absorbed and stored in the power springs 31 and 32, the point is reached at which the compressed springs move the piston downwardly through its work stroke, the valve 43 is manipulated to admit a brust of air into chamber 17 whereby the piston '16 and its head 20 are driven downwardly by a force greatly in excess of the force of the compressed air acting on the piston, and also at a rate in excess of the rate at which the compressed air would move the piston in the absence of the springs.

As a second mode of operation, it may be assumed that the pilot valve is adjusted sufficiently high on the column 26 as to be beyond reach of the bracket 70. In that case manipulation of the pilot valve member 59 produces the same result via the servo motor 52 as would direct manual operation of the valve member 45.

In manipulating the control button 67, two conditions may be provided for.

It may rst be assumed that the vent valve `80 is open so as to permit unrestricted discharge of the air from the dash pot chamber 77. Under this condition a sense of timing is required on the part of the operator in order to time the reversal of the valve member 59 properly.

Assuming now that the vent valve 80 is tightened to resist rapid venting of the dash pot chamber, the sequence of operating cycles is automatically controlled by preventing initiation of the cycle before the power piston y16 has returned to its rest position. The dash pot resists rapid depression of the control button and the valve member 69 is moved into its lower depressed position only after a certain lapse of time, the duration of which depends on the resistance of the dash pot valve 80.

It may next be assumed that the position of the pilot valve is adjusted, by an appropriate vertical setting of the valve housing 58, to cause engagement of the reversing rod `68 by the bracket 70. This makes the timing of the valve reversal automatic and not dependent on a sense of timing of the operator.

Depression of the control knob 67 causes delayed or immediate actuation of the valve 58, as may be desired. As a result, air is admitted into the lower chamber 118 of the power cylinder and the upper chamber 17 is vented, as previously described. During the upward stroke of the piston the

springs

31 and 32 are compressed to store the energy of the upwardly moving hammer head 20. At the desired reversal point for which the valve 57 is set by vertical adjustment, the `bracket 70 strikes the reversing rod, whereupon the power piston is driven through its power stroke by the joint action of the `springs and of the burst of air entering the upper chamber y17 through the previously described valve mechanism.

Assuming that the operator continuously pushes the control valve downwardly, for which purpose a spring may also be employed, the downward deilection of the pilot valve member 59 is temporarily and periodically overruled by the bracket 70 striking the reversing rod, and the impact tool will continue to perform one cycle after another, until the actuating force depressing the control knob 67 ceases.

Test I .-An impact tool was constructed capable of delivering individual blows, one at a time. The piston diameter was l1/2 inches land 'its stroke was l2 inches. The operating pressure averaged 90 pounds. 'With a hammer head of a size to bring the' total movable mass, piston,

scarse piston rod and head, to 10 pounds, 45 blows were required to set the spike.

Test [L -The mass of the head was then increased to a total of 15 pounds, resulting in a slight improvement reducing the required number of blows to 30.

Test IIL- The movable mass was further increased by a larger head to a total of 40 pounds. With this arrangement 14 blows were necessary to set the spike. However, the tool became too heavy to be handled by a single operator and also the recoil at the end of the upstroke was so hard as to be painful.

Test I V.-Two springs of a modulus of 15 pounds per inch and a length of 12 inches were then installed on the columns, and the operation was modified to start each cycle from a rest position in `which a piston is projected, according to the present method. At the end of the upstroke the springs were compressed approximately 6 inches corresponding to approximately 18() pounds of spring power and a burst of air was admitted against the back of the piston to drive the piston down in timed relationship with the action of the springs. The total weight of the movable mass was l7 pounds. With this arrangement 4 to 5 blows rwere suilicient to drive the spike home.

Figure 2 is a diagrammatic illustration of a control mechanism assembled from commercially available valve or control components. The arrangement of the control mechanism is best seen in Figure 3 showing the operating parts of the various components.

The air line 73 irst leads to an air lter 81 having two chambers 82 and 83 divided by a bronze screen 84 for removing mechanical impurities from lthe compressed air. Theiiltered air then passes through a lubricator 85 comprising an oil chamber 86 from which a sintered porous bronze wick 87 extends into the throat 88 of a Venturi passage 89. The oil chamber has communication with the upstream portion of the Venturi passage 89 through a port '90. Air rushing through the throat of the Venturi passage takes a certain amount of vaporized oil with it which then lubricates the various elements of the control mechanism and the power cylinder 15.

The air line 73 is divided into

branches

91 and 92. Branch '91 leads to a manual operating valve 93 having a valve element 94 cooperating with two valve seats 95 and `96. The valve element 94 is under the action of a spring 97 biasing the valve element towards the right, whereas depression of an operating handle 98 moves the valve element in the opposite direction. In the illustrated position the handle 98 is depressed, thereby allowing air entering the chamber 99 to pass through the valve into a further air duct 100.

When the handle 98 is released, the spring 97 moves the valve element to the right closing the seat 95, and opening the seat 96 whereby the air duct 100 is vented to the atmosphere.

The air duct 100 leads to a single-stroke Ivalve 101 having two

chambers

102 and 103. The air duct 100 terminates in the lowest chamber 103, and a further air duct 104 extends from the lower chamber 103. Passage of air from the chamber 103 into duct 104 is controlled by a main valve element 105 having a lower valve seat 106. The valve element 105 is hollow and carries a check valve 107 in its central bore. The check valve is loaded by a spring 108 mounted within the valve element 105, and the valve element itself is normally maintained closed by a biasing spring 109.

A second check valve 110 biased by a spring 111 permits air to pass from chamber 102 into chamber 103.

The single-stroke valve operates as follows:

Assuming that

chambers

102 and 103 were previously vented so that substantially equal pressure of the order of atmosphere pressure prevails therein, a burst of cornpressed air passing through the duct 100 produces an increase in pressure within the chamber 103. The main valve element 105 responds to this increase in pressure and is lifted up as soon as the pressure acting on the underside of the element produces a lifting forceY in excess ofthe force of the spring 109 andthe pressure prevailing in the chamber 102. Lifting` of the valve element 105 from its seat 106 admits compressed air into. line 104. Compressedair also passes into the upper chamber 102 through the check valve 107. As a result pressure balance between

chambers

102 and 103 is restored and .the main valve element 105 moves back into closing position under the action of the spring 109. It subsequently the lower chamber 103 is vented to the atmosphere, the upper chamber 102 is vented likewise through the check valve 110.

The air duct -104 has two

branches

112 and 113. Branch 112 leads to an operating valve 114. This valve has an upper chamber 115 anda lower chamber 116. Two valve elements 117 and 118 are provided, biased by springs 119 and 120, respectively. The Valve element 117 is operated by a servo piston 121 and the valve element 118 is operated by a servo piston 122. The valve element 117

controls seats

123 and 124 and the valve element 118 controls seats 125 and 126. A vent passage 127 extends between the valve element and leads to a vent port 128.

The lower chamber 116 receives compressed air through the branch line 92. An increase in pressure in the chamber 115 causes the servo pistons 121 and 122 to move the valve elements into the position in which they are shown, opposed by the springs 11'9 and 120. In this position compressed air passes from the branch line 92 through the chamber 116 past the valve element 117 to an outlet port 129 from which the line 41.1eads into the lower chamber of the power cylinder 15. At the same time the upper chamber of the power cylinder is vented through the line 42 past the valve element 118 and out through the vent port 128.

Subsequent venting of the upper chamber 115 in the manner about to be described causes the valve elements 117 and 118 to move upwardly under the action of their respective springs 119 and 120. When this happens the valve element 117 seats on the seat 124, thereby shutting off the supply of compressed air to the duct 41. The valve element 118 is lifted off the seat 126 to close valve seat 125. This admits compressed air past the valve element 118 into line 42, thereby driving the power piston 16 downwardly. At the same time the lower` chamber of the power cylinder is vented through line 41, port 129, vent passage 127 and vent port 128.

The device for venting the chamber 115 is the reversing valve 130. This valve has an element 131 cooperating with a seat 132. The valve element 131 is biased by a spring 133 tending to close the valve. A lever 134 pivoted at 135 carries a roller 136. The roller cooperates with the cam surface 137 on the hammer head. Deflection of the roller 136 to the left causes the valve 130 to open, thereby venting line 113 past the element 131 and a vent port 138 to the atmosphere.

The hammer head is shown during its upward stroke in a position just prior to striking the roller 136. At this moment the power piston 16 has not quite reached its top position within the cylinder 15.

The operation of the control mechanism is now readily understood. Y

Depression of the control handle 98 admits compressed air from line 91 through valve 93 into line100. Pressure is built up within the lower chamber 103 of the single-stroke valve 101 with the result that its main valve element 105 is temporarily lifted off its seat 106. Cornpressed air is thus admitted into line 104. Simultaneously compressed air also passes into the upper chamber 102, past the check valve 107, whereafter the valve element 105 closes again to shut off further supply of compressed air. Compressed air entering the line 104 passes into its

branches

112 and 113. The air cannot leave the branch 113, as long as the valve 130 is closed. v

Compressed air passing through the branch 112 causes the pressure in the chamber of the component 1 14 to increase, thereby moving the two pistons 121 and 122 downwardly against the action of the biasing springs 119 and 120. Compressed air supplied throughfthe branch line 92. into the lower chamber `116 now flows past the valve element 117 through line 41 into the power cylinder, thereby driving the power piston towards the top.y During'this-stroke the upper chamber of the power cylinder is vented through the line 42 and the vent port 128.

Shortly before the piston 16 reaches its top position, the cam surface 137 strikes the roller 136 to actuate the reversing valve 130. Opening of the valve vents the upper chamber 115 of the control unit 114 through

lines

112 and 113 which are now in communication with the vent port 138 leading to the atmosphere.

The biasing springs 119 and 120 of the control unit now reverse the position of the valve elements 117 and 118. Compressedair flows from the chamber 116 past the valve element 118, line 42, into the upper chamber of the power cylinder 15 driving the piston 16 downwardly. The lower chamber of the power cylinder 15 is vented through line 41, vent passage 127 and vent port 128. When the hammer head approaches its bottom position, it delivers its blow and then comes to rest. No further. action results and the mechanism remains at rest even though the actuating lever 98 may still be held in a depressed position.

Release of the actuating lever causes reversal of the position of the valve element 94. When the valve element 94 is lifted off its seat 96, both

chambers

102 and 103 of the single stroke valve 101 are vented to the atmosphere,.the upper chamber 102 being vented past the check valve 110. The venting prepares the mechanism for the start of another cycle. Subsequent depression of the handle 98 results in the repetition of the cycle during the first portion of which the power piston 16 is driven upwardly thereby compressing the

springs

31 and 32. Compression of the springs is followed by the reversal of the control mechanism which then admits a blast of compressed air against the top of the piston `16 thereby driving the head 20 downwardly by the joint action of the compressed air and the power stored in the

springs

31 and 32.

What is claimed is:

1. A pneumatic hammer comprising, in combination, a cylinder; a piston reciprocably movable in said cylinder; a piston rod on said piston; a hammer head connected to said piston rod for movement thereby into a projected and into a retracted position; a spring xedly held at one end with respect to said cylinder in a position t0 be engaged at its other end and compressed by said head within the end portion of the retraction stroke; and control means for admitting, in sequence, compressed air rst against one side of the piston to retract said hammer and compress the spring, and then against the other side of the piston to project said head by the joint power of the admitted air and of said expanding spring.

2. A pneumatic hammer comprising, in combination, a cylinder; a piston reciprocably movable in said cylinder; a piston rod on said piston; a hammer head on said piston rod, said piston rod and hammer head constituting a reclprocable unit projectible to perform a work stroke and retractable to perform a return stroke; a spring fixedly held at one end with respect to said cylinder in a position to be engaged at its other end and compressed by said unit within the end portion of the return stroke; and control means for admitting, in sequence, compressed air first against one side of the piston to retract said unit and compress said spring, and then against the other side of the piston to yproject said unit by the joint power of the admitted air and of said expanding spring. Y 3. A pneumatic hammer comprising, in combination, a cylinder; a piston reciprocably movable in said cylinder; a piston rod on said piston; a hammer head connected to said piston rod for movement thereby into a.

projected and into a retracted position; a spring tixedly held at one end with respect to said cylinder in a position to be engaged at its other end and compressed by said head Within the end portion of the retraction stroke; a 'valve mechanism for admitting compressed air into the cylinder to one side of the piston and to the other side, respectively; land manual control means for operating said valve mechanism.

4. A pneumatic hammer comprising, in combination, a cylinder; a piston reciprocably movable in said cylinder; a piston rod `on said piston; a hammer head connected to said piston rod for movement thereby into a projected and into aV retracted position; a spring xedly held at one end with respect to said cylinder in a position to be engaged at its other end and compressed by said head within the end portion of the retraction stroke; manual control means for admitting compressed air against one side of the piston to retract said hammer and compress said spring; and automatic means operable by the movement of the piston relatively to the cylinder for admitting compressed air against the other side of the piston to project said head in the direction of action of the eX- panding spring.

5. A pneumatic hammer comprising, in combination, a cylinder; a piston reciprocably movable in said cylinder; a piston rod on said piston; a hammer head on said piston rod, said piston rod and hammer head constituting a reciprocable unit projectible to perform a Work stroke and retractable to perform a return stroke; a spring xedly held at one end with respect to said cylinder in a position to be engaged at its'other end and compressed by said unit within the end portion of the return stroke; manual control means for admitting compressed air against one side of the piston to retract said unit and compress said spring; `an automatic means operable by the movement of the unit relatively to the cylinder for admiting compressed air against the other side of the piston to project said unit in the direction of action of `the expanding spring.

6. `A pneumatic hammer comprising, in combination, a cylinder; a piston reciprocably movable in said cylinder; a piston rod on said piston;'a hammer head on said piston rod, said piston rod and hammer head constituting a reciprocable unit projectible to perform a Work stroke and retractable to perform a return stroke; a spring tixedly held at one end with respect to said cylinder in a position to be engaged at its other end and compressed by said unit Within the end portion of the return stroke; a valve mechanism for admitting compressed air into the cylinder to one side of the piston and the other, respectively; manual control means for operating said valve mechanism in one sense to admit air to one side of the piston and retract said unit; and automatic means operable by the position of the unit relatively to the cylinder for operating the valve mechanism in the opposite sense to admit air against the other side of the piston to project said unit in the direction of action of the expanding spring.

7. A pneumatic hammer comprising, in combination, a cylinder; a piston reciprocably movable in said cylinder; a piston rod on said piston; a hammer head on said piston rod, said piston rod and hammer head constituting a reciprocable unit projectible to perform a Work stroke and retractable to perform a return stroke; a spring tixedly held at one end with respect to said cylinder in a position to be engaged at its other end and compressed by said unit Within the end portion of the return stroke; a reversible Valve lfor admitting compressed air into the cylinder to one side of the piston and to the other, respectively; manually operable control means for moving said valve in one direction to admit air to one side of the piston and retract said unit; and automatic means operable by the position of said unit relatively to the cylinder for reversing said valve.

8. A pneumatic impact tool of the reciprocating type,

the tool comprising, in combination, a cylinder; a piston reciprocably movable in said cylinder to perform a work `stroke in one direction and a return stroke in the opposite direction; a spring xedly held at one end with respect to said cylinder in a position to be engaged at its other end and compressed by said piston within the end portion of the return stroke; and control means `for admitting, in sequence, compressed air iirst against one side of the piston to retract said piston and to compress said spring, and then against the other side of the piston to project said piston by the joint power of the admitted air and of said expanding spring.

9. A pneumatic impact tool of the reciprocating type, the tool comprising, in combination, a cylinder; a piston reciprocably movable in said cylinder to perform a work stroke in one direction and a return stroke in the opposite direction; a spring -tixedly held at one end with respect to said cylinder in a position to be engaged at its other end and compressed by said piston within the end portion of the return stroke; a valve mechanism for admitting compressed air into the cylinder to one side of the piston and to the other side, respectively, and manually operable control means for operating said valve mech-- anism, said valve and said control means being so arranged that the piston is first retracted and then projected and comes to rest at the end of a work stroke in projected position.

l0. A pneumatic impact tool of the reciprocating type, the tool comprising, in combination, a cylinder; a piston reciprocably movable in said cylinder to perform a work stroke in one direction and a return stroke in the opposite direction; a spring rixedly held at one end with respect to said cylinder in a position to be engaged at its other end and compressed by said piston Within the end portion of the return stroke; manual control means for admitting compressed air against one side of the piston to retract the piston and compress said spring; and automatic means operable by the movement of the piston relatively to the cylinder Vfor admitting compressed air against the other side of the piston to project said head in the direction of action of the expanding spring.

1l. A pneumatic impact tool of the reciprocating type, the tool comprising, in combination, a cylinder; a piston reciprocably movable in said cylinder to perform a Work stroke in one direction and a return stroke in the opposite direction; a spring xedly held at one end with respect to said cylinder in a position to be engaged at its other end and compressed by said piston within the end portion of the return stroke; a valve mechanism for admitting compressed air into the cylinder to one side of the piston and the other, respectively; manually operable control means for operating the valve mechanism in one sense to admit air to one side of the piston and retract said piston; and automatic means operable by the pos-ition of the piston relatively to the cylinder for operating the Valve mechanism in the opposite sense to admit air against the other side of the piston to project said piston in 4the direction of action of the expanding spring.

l2. A pneumatic impact tool of the reciprocating type, the tool comprising, in combination, a cylinder; a piston reciprocably movable in said cylinder `to perform a work stroke in one direction and a return stroke in the opposite direction; la spring xedly held at one end With respect to `said cylinder in a position to be engaged at its other end and compressed by said piston within the end portion of the return stroke; a reversible Valve for admitting compressed air into the cylinder to one side of the piston and to the other, respectively; manually operable control means for moving said valve in one direction to admit Iair to one side of the piston and retract said piston; land `automatic means operable by the position of the piston relatively to the cylinder for reversing said valve.

13. A pneumatic hammer comprising, in combination, a cylinder; a piston reciprocably movable in said cylinder; a piston rod on said piston; a hammer head connected to said piston rod for movement thereby into a projected and into a retracted position; a spring xedly held at one vend-with respect to said cylinder in a position to be engaged at `its other end and compressed by said head within the end portion of the retraction stroke; control valve means for admitting in sequence, compressed `air first against-one side ofthepiston to retract said hammer and compress the spring, and then against the other side of the piston toy project said head by the joint power of the admitted air and of said expanding spring; and means operable inresponse to the movement of the piston relatively to the cylinder for reversing said control fvalve means.

14. A pneumatic impact tool of the reciprocating type, the tool comprising, in combination, a cylinder; a piston reciprocably movable in said cylinder to perform a work stroke in one direction and a return stroke in the opposite direction; `a spring ixedly held at one end with respect to said ,cylinder in a position to be engaged at its other end and compressed by said piston within the end portion of the return stroke; control valve means for admitting, in sequence, compressed air rst against one side of the piston to retract said piston and compress said spring, and then against the other side of the piston to project said piston by the joint power of the admitted air and of said expanding spring; and means operable in response to the movement of the piston relatively to the cylinder for reversing said control valve means.

15. The method of operating a double acting pneumatic impact tool comprising a head powered by a piston reciprocable within a cylinder, the method comprising, rst, by a burst lof compressed air against one side of the piston retracting said head from a normal rest position in which the head is projected; then compressing by the action of the piston a `spring within the end portion of the retraction stroke, thereby converting kinetic energy of the head into stored spring energy; and then assisting the action of the expanding spring projecting the head by a further timed burst of compressed air applied to the other side of the piston to drive the head in the direction of the expanding spring.

16, The method of operating a pneumatic impact tool of the reciprocating type comprising a pneumatic cylindirecting a burst of compressed `air against the other side of the piston, the last named burst being so Itimed as to drive the piston through its work stroke substantially simultaneously withthe expanding action on the piston of the drive spring.

17. The method of operating a pneumatic impact tool of the reciprocating type comprising a pneumatic cylinder and a piston mounted thereon for reciprocating movement to perform a work stroke in one direction and a return strokein the opposite direction, the method comprising, first driving said piston through `its return stroke by a burst of compressed air directed against one side of the piston, the intensity ofthe burst exceeding the power required to return said piston; converting the eX- cess energy of the returning piston into spring power by compressing a spring within the terminal portion of the return stroke; and then driving the piston through its -work stroke by a burst of compressed air directed against the opposite side of the piston, said last named burst being so timed as to coincide with the expanding action of said spring to result in a total driving force of the piston in excess of the power imparted by said last named burst of compressed air.

References Cited in the tile of this patent UNITED STATES PATENTS 1,163,715 Upson et al Dec. 14, 1915 1,379,225 Smith May 24, 1921 2,087,321 Hilke July 20, 1937 2,105,074 Eppens Ian. 11, 1938 2,107,495 Otto et al Feb. 8, 1938 2,429,780 Terhune Oct. 28, 1947 2,612,868 Fitzgerald Oct. 7, 1952 FOREIGN PATENTS 284,515 Great Britain Feb. 2, 1928