US3429382A

US3429382A - Devices for applying hammer blows to a body

Info

Publication number: US3429382A
Application number: US657417A
Authority: US
Inventors: Horace Briden
Original assignee: Individual
Current assignee: Individual
Priority date: 1967-07-31
Filing date: 1967-07-31
Publication date: 1969-02-25
Anticipated expiration: 1986-02-25

Description

Feb. 25, 1969 l l`||, BR'lDEN 3,429,382

DEVICES F03v APPLYING HAMMER BLows To A BODY Filed July 31, 19e? sheet of 7 l oknc'e vBfllbel Feb. 25, 1969 H. BRIDEN DEVICES FOR APPLYING HAMMER BLOWS TO A BODY Sheet Filed July 3l, 1967 Y @Qd N SN BN\ w m Vv 4/// N m9 .w L

Feb. 25, 1969 H. BRlDl-:N

DEVICES FOR APPLYING HAMMER BLOWS TO A BODY Sheet Filed July 3l, 1967 Alba...

Q @a i Feb. l25, 1969 H. BRIDEN DEVICES FOR APPLYING HAMMER BLOWS TO A BODY Filed July s1, 1967 Sheet 4 of? v Feb.25,1969 -H.BR|DEN :Y 3,429,382

DEVICES FORAPPLYING HAMMER BLOWS TO A BODY Filed July 51, 1967 Sheet 5 of '7 Xml Feb. 25, 1969 H, BR|DEN DEVICES FOR APPLYING HAMMER BLOWS TO A BODY Filed July 51, 1967 Sheet fNve/Vr-IL ,4 Tr); S.

Habeas, v:BIB/02N MJ )man FIG.- /6

Feb. 25, 1969 H. BRIDEN DEVICES FOR APPLYING HAMMER BLOWS TO A BODY Sheet Filed July 3l, 1967 .l 1 I- f 5 7 1 i I I l IL M w IT# B wlmmg m ..1 H. glwn," w w p f 2 M N m @om f ma w Tl, 1 fO 7 m m .m m f 3,429,382 Patented Feb. 25, 1969 32 Claims ABSTRACT F THE DISCLOSURE A hydraulic breaker, including a hammer connected to a driving piston slidable in a cylinder and valve means which are changed over from a first state to a second state when the hammer has been retracted to a predetermined position and a predetermined quantity of energy has been stored by the compression of a quantity of gas in an accummulator cylinder, wherein when the valve means are in the first state they serve to admit hydraulic fluid to the cylinder containing the driving piston to act on one side of said piston and thus to retract the hammer, whereas when they are in the second state they serve to admit hydraulic uid to the cylinder to act on the opposite side 0f the driving piston and thus to move the hammer in the direction necessary to apply impact forces to a tool.

This invention relates to devices of the kind comprising a hammer and means for causing the hammer to apply a blow or a series of blows to a body.

The invention is intended to provide an improved device of the kind referred to suitable in particular although not exclusively for applying blows to a tool for cutting or breaking rock, minerals, masonry, brickwork or concrete including any metallic reinforcement embedded therein, or to a total for cutting metals or nonmetallic materials or to dies for extruding or forming metals or plastics, or for driving piles.

Many problems arise in the design and construction of devices of the kind referred to, in particular when these devices are required to apply relatively heavy blows. Some of the most difficult problems to solve in this connection result from the facts that the structure supporting the device must absorb the reaction applied to the device by the force used to accelerate the hammer and that the hammer must be decelerated without applying destructive forces to the device itself or to the supporting structure.

It is an object of the present invention to enable a device of the kind referred to to be designed in such a way that at least some of the problems referred to in the preceding paragraph can be solved more easily than in the case of known devices of this kind.

It is a further object of the invention to enable a device of the kind referred to to be designed in such a way that it is simpler and more efiicient than known devices of this kind.

From one aspect, the invention consists in a device for applying impact forces to a body, including a hammer and`spring means, wherein, when the hammer has been retracted to a predetermined position and a predetermined quantity of energy has been stored in the spring means, the stored energy is transmitted to the hammer through a hydraulic transmission system.

From another aspect, the invention consists in a method of applying impact forces to a body, wherein energy stored in spring means is applied to a hammer through a hydraulic transmission system.

Preferably, the energy to be stored is transmitted to the spring means through a hydraulic system and the spring means is in the form of a quantity of gas under pressure acting on an accumulator piston slidable in a cylinder. In such an arrangement, the hydraulic transmission system for transmitting energy to the hammer may be designed in such a way that the hammer moves at a faster rate than the accumulator piston under the inuence of hydraulic duid displaced by the accumulator piston.

Preferably, means are provided for absorbing energy which is transmitted to the hammer but is not absorbed by the body and further means are provided for preventing operation of the device until a predetermined load has been applied to the body.

A device in accordance with the invention may be mounted for axial motion along a mounting and may be provided with at least one hydraulic jack adapted to move the device towards the body. Either the device itself or its mounting may be mounted in bearings at one end of the boom of a movable vehicle, said boom preferably being hydraulically controlled.

In one embodiment of the invention, a device of the kind referred to consists of an outer casing which at one end supports a shaft in bearings which allow the shaft to move axially. The shaft either forms part of the body to which the blow or blows are delivered, or serves to transmit the blow to the body. The hammer lies lies within the outer casing adjacent to this shaft and can slide axially relative to the outer casing so as to impact on the end of the shaft. Two chambers are formed an a block joined to the outer casing. The first chamber connects with a first cylinder fixed to this block, the axis of this first cylinder being parallel to the axis of the outer casing. The yfirst cylinder is provided with a first piston which has a piston rod which protrudes through seals from the end of the first cylinder remote from the first chamber, and this piston rod is connected to the hammer. The volume enclosed by the first cylinder and the rst piston together with its piston rod is connected by ports to the second chamber which in turn connects with a second cylinder provided with a second piston which has a piston rod which passes from the second chamber through seals into the first chamber. Preferably the diameter of the second piston is at least twice that of the piston rod of the first piston. Movement of the second piston in the second cylinder into the second chamber is limited by stops. A third cylinder is formed in the piston rod of the second piston and a third piston moves within this third cylinder. The third piston has a piston rod which protrudes without seals from the third cylinder further into the first chamber, the movement of this third piston being limited by stops in the piston rod of the second piston. The third cylinder is connected by ports to the second chamber at all times. Preferably the hammer the shaft and the first second and third cylinders are arranged co-axially. The end of the second cylinder remote from the second chamber is connected to a volume of gas under pressure so that the second piston can form the piston of a hydraulic accumulator. Alternatively the gas may be replaced by precompressed springs bearing on the face of the second piston.

The proportions of the first and second pistons and their respective piston rods are chosen with respect to the mass of the hammer and the load applied to the face of the second piston by gas pressure or springs to be such that the fluid pressure in the second chamber needed to move the first piston and thereby the hammer in a direction away from the shaft is less than that needed to move the second piston against the gas or spring load applied to it.

A series of valves are provided which are interconnected in such a way that when the device is supplied with uid under pressure the settings of all valves are determined by the setting of the first valve. The rst valve can be set in either of two positions and has a position of unstable equilibrium between these positions, that is to say, as the valve is operated it passes through a position from which it will complete its movement unaided. The energy to do this may conveniently be provided by a spring or springs or by magnetic or by hydraulic means. Means are provided to cause the `first valve to operate when the hammer reaches a predetermined position when moving away from the end of the device carrying the shaft, and to reset the valve to its first setting when the hammer reaches a second predetermined position when moving back towards the shaft. When the first valve is in its first setting, the other valves in the series move to settings which connect the first chamber to exhaust, the second chamber to a source of fluid under pressure and isolate the first chamber from the second chamber. When the first valve is in its second setting, the other valves in the series move to settings which first completely isolate the first chamber from exhaust and the second chamber from the source of pressure except for a small by-pass port, then connect the first and second chambers. When the first valve moves from its first to second setting the other valves in the series moves rapidly to their second settings. When the first valve moves from its second setting to its first setting means are provided to delay the movement of the other valves in the series to their first setting for a period of time longer than that taken by the hammer in moving forward to impact on the shaft.

In brief the action of the device when supplied with fluid under pressure is as follows. With the first valve in its first setting the first piston moves drawing the hammer away from the impact position until the piston rod of the third piston engages with the face of the first piston, movement of the third piston in the third cylinder cushioning the impact. This engagement brings the assembly of the first piston and the hammer to rest relative to the assembly of the second and third pistons. The latter assembly now starts to move and the two assemblies remain in contact and move together, taking the hammer further away from the shaft, until the hammer trips the -tirst valve which moves to its second setting thereby changing the setting of the other valves in the series as previously described. Because the valves move rapidly from their first to second positions, the position of the hammer at which the first valve trips also determines the total movement of the second piston against the gas or spring loads applied to it.

Both assemblies now start to move in the reverse direction, but the duid discharged from the second chamber into the first chamber and the iiuid displaced in the first chamber by the movement into it of the rod of the second piston cause the first piston to move much faster than the second piston and to drive the hammer forward to impact on to the shaft. As the hammer moves forward the first valve is reset to its first position and when the other valves in the series reach their first settings and the hammer has come to rest the cycle is repeated.

For applications of this invention in which the energy of the blow may not always be completely absorbed by the body to which it is delivered, the shaft and if necessary the hammer may be brought to rest by the engagement of a shoulder on the shaft with la thrust member through which the shaft passes. This thrust member is preferably conical in shape and serves to transmit the thrust exerted by the shoulder on the shaft to the pistons of a series of cylinders fixed to the outer casing and disposed around the shaft with their axes parallel to that of the shaft. Movement of the shaft out of the outer casing causes 4fluid to be discharged from the cylinders and this discharge is arranged to be against a fluid pressure that absorbs the energy of the moving parts.

In an advantageous construction the cylinders are connected at all times through a restrictor to the source of fluid under pressure which operates the device, and this fluid pressure causes the pistons to extend and hold the thrust member against stops in the outer casing which are positioned so that the shaft has a limited unrestricted stroke. The cylinders are connected to a hydraulic accumulator through a valve which allows free flow out of the cylinders but restricts any flow in the reverse direction. This accumulator is constructed so that it will not begin to charge until the fluid pressure acting on it rises above that of the source supplying the device. When fluid is discharged from the cylinders by the movement of the shaft most of the fluid is unable to pass through the restrictor back into the main pressure circuit and is stored in the accumulator. When the shaft comes to rest the reverse flow from the accumulator supplies the majority of the fluid used in returning the thrust member back against its stops.

Preferably the hydraulic accumulator into which the discharged fluid tlow will be formed by a fourth cylinder coaxial with the second cylinder and so arranged that the fluid to be stored acts on only part of the fourth piston while the other face of this piston is in contact either with the gas under pressure or the other end of the springs, whichever are used, which bear on the face of the second piston as previously described. Conveniently movement of the fourth piston will limit the movement of the second piston so that a further blow cannot be delivered until most of the iiuid stored by the movement of the fourth piston has been discharged.

Control of the functioning of the device may be effected directly by opening a valve between the device and the source of fluid under pressure. Alternatively and preferably functioning may be made subject to a predetermined load being applied to the body to which the blow is to be delivered before the device starts to function. Advantageously, the device may be mounted so that it can slide axially in its mounting and operation of the control valve arranged to cause hydraulic jacks to thrust the device against the body to be struck. The preload on the body is measured by measuring the fluid pressure in the thrusting jacks or alternatively the defiection of some part of the structure resisting the thrust, and means are provided to cause a second valve to open to admit iiuid under pressure to the device as soon as the required preload is applied.

So that the invention may be clearly understood, one example of a device in accordance with the present invention will now be described by way of example with reference to the accompanying drawings. This embodiment of the invention which will be described is a device in which a hammer is cau-sed to deliver a blow or blows to a cutting tool after the cutting tool has first been brought to bear with some predetermined loading against the body to be struck. The machine in which such an embodiment is incorporated would be used for example in demolition work.

The cutting tool is carried by the device and the device is carried in a cradle in which it can be caused to slide. The cradle may conveniently be carried in bearings at one end of an arm in such a manner that the cradle can be caused to rotate relative to the arm, while the arm tself is attached at its other end to a turntable in such a way that the arm can be caused to rotate relative to the turntable. The turntable is mounted on a self-propelled base. The axes about which the cradle and the arm rotate are parallel and are horizontal when the turntable axis is vertical.

FIGURE l shows a side elevation of a machine such as has been described in the previous paragraph.

FIGURE 2 shows a partly diagrammatic sectional elevation of the forward portion of a device in accordance with the invention.

FIGURE 3 shows a partly diagrammatic sectional elevation of the rear portion of the device.

FIGURE 4 is a section of the device on the line IV-IV in FIGURE 2.

FIGURE 5 is a partly diagrammatic section of the device substantially on the line V--V in FIGURE 3.

FIGURES 6, 7 and 8 are par tly sectional side elevations of FIGURE S.

FIGURE 9 shows a sectional elevation to a larger scale of part of the hammer, the piston which moves the hammer and the cylinder in which the piston moves.

FIGURE is a section on the line X-X in FIGURE 9 showing one stage of the assembly of the joint between the hammer and the piston.

FIGURE 11 is a partly sectional plan of the device assembled in its cradle.

FIGURE 12 is a side elevation of the device assembled in its cradle.

FIGURE 13 is a cross-section on the line XIII-XIII in FIGURE 12.

FIGURE 14 is a section on the line XIV-XIV in FIGURE 12.

FIGURE is a part sectional elevation on the line XV-XV in FIGURE 1l.

FIGURE 16 shows an underneath plan of the device.

FIGURE 17 is a diagram of a suitable hydraulic circuit for the control and operation of the device.

Reference will rst be made to FIGURE 2, from which it will be seen that the forward end of an outer casing 1 is provided with bearings which carry a shaft 2 one end of which protrudes through dirt excluding seals (not shown) from the end of the outer casing 1 and terminates in a llange to which can be bolted one of a variety of cutting or breaking tools of which the tool 3 is a specific example. The method of attachment is such that the tool can readily be removed for sharpening or repair or can be replaced by a. different tool ori site Without exposing any part of the mechanism to the entry of foreign matter.

The bearings in the end of the casing act to maintain the shaft 2 co-axial with the casing and movement of the shaft 2 into the casing is limited by a shoulder 201 on the shaft 2 which engages with stops 202 inside the outer casing 1.

A cap 4 is firmly fixed to the inner end of the shaft 2 and a generally conical thrust member 5 is provided with a cylindrical bearing surface 206 which co-operates with three ribs 6 on the casing 1 to hold the member S concentric with the casing and hence with the cap 4 (FIGURES 2 and 4). The conical thrust member 5 can slide along the ribs 6, but is normally held against stops 203 at the inner end of the ribs 6 by three pistons 7. Each piston 7 lies in a cylinder 8 which itself together with its piston 7 forms the piston of a respective one of three cylinders 9 formed in the outer casing 1 and disposed symmetrically around the shaft 2. Stops 204 on the cylinders 8 prevent their being ejected from the cylinders 9 when the cylinders are Supplied with uid under pressure.

The three cylinders 9 are interconnected and are joined by a pipe 10 to an annular chamber 11 (FIGURE 3). The chamber 11 is connected at all times to a source of fluid under pressure 205 through a restrictor. This restrictor is shown diagrammatically at 12 but may conveniently be provided by the use of small-bore tubing for the connection to the pressure source.

A ring of ports 13 connected the c-hamber 11 to au intermediate chamber 206 which is itself in communication with the annular area fomring the underside of a piston 15 through a further ring of ports 14. The face of this piston 15 is in Contact with a volume of gas under pressure stored in a chamber 16 formed in the outer casing 1. The piston rod of the piston 15 includes a portion 207 which is provided with a seal 208 and extends into a chamber 17 at atmospheric pressure. The diameter of the portion 207 is chosen wit-h respect to the pressure of the gas in the chamber 16 and the maximum circuit pressure of the source of tluid under pressure which operates the device to be such that the piston 15 is held against the stops 209 by the pressure of the gas until the pressure of the fluid acting on the underside of the piston 15 rises to a predetermined pressure which is greater than the maximum circuit pressure. When uid flows from the chamber 11 towards the chamber 206, a plate valve 18 lifts to allow free flow through the ports 13, but when flow is in the reverse direction, the plate 18 moves to cover most of these ports leaving only a restricted path through which uid can pass.

The hammer 19 slides on ribs 20 inside the outer casing 1 in a manner which allows the air to ow freely from one end of the hammer to the other when the hammer moves. The hammer 19 is connected to a piston 21 which moves in a cylinder 22; this cylinder opens into a chamber 23. Substantial ports 24 (one only shown) connect the annular volume underneath the piston 21 to a second chamber 25.

The piston 21 and the means by which it is connected to the hammer 19 are shown diagramatically in FIGURE 3, an actual practical construction being shown in, and described with reference to, FIGURE 9.

Chamber 25 is in communication with a cylinder 210 which is provided with a piston 26. The gas under pressure in chamber 16 bears on the face of the piston 26 tending to force it against a shoulder 27 which can engage with the piston 26 to prevent it from moving into the chamber 25. The piston rod 211 of the piston 26 passes through a seal 212 from the chamber 25 to the chamber 23. A cylinder 213 is formed in this piston rod and this cylinder is provided with a piston 28; ports 29 allow uid in the chamber 25 to bear on the piston 28. When the uid pressure in chamber 25 is greater than that in chamber 23, the piston 28 is forced against stops 214 formed in the piston rod 211. A piston rod 215 extends from the piston 28 through the chamber 23 and into the cylinder 22, but there is no seal between the

piston rods

215 and 211.

T-he part of the outer casing 1 containing the cylinder 210 `has a smaller cross-section than the parts on either side of it and around the part of smaller diameter is disposed the assembly shown in FIGURES 5, 6, 7 and 8. Parts of this assembly are omitted from FIGURE 3. The assembly comprises a valve 30 and a mechanism which serves to move the spool 31 of the valve 30. A cover, not shown, protects the assembly.

The mechanism includes a lever 35 which can be moved in one direction by a piston 32 working in a cylinder 33 which is directly connected to a line 66 and hence to the source of uid under pressure, and which can be moved in the other direction by the movement of the hammer 19 acting through a push rod 34 which the hammer 19 engages as it moves away from the impact position.

The lever 35 is held in bearings so that it can turn about an axis 36. It carries three

rollers

37, 38 and 39; t-he piston 32 bears against the roller 37 while the push rod 34 engages the roller 38. When the lever 35 is held against a stop 40 by the thrust of the piston 32, the device operates to cause hammer 19 to separate from the push rod 34. The roller 39 lies in the forked end of a lever 41, and this lever is joined rigidly to one end of a tube 42 which is supported in bearings so that it can rotate about an axis 43. A lever 44, joined rigidly to t-he other end of tube 42, has two projections 45 and 46 which can engage with a lever 47.

The lever 47 pivots in bearings about the axis 43, but its movement is independent of that of tube 42 except when one of the projections `4S and 46 on the lever 44 engage with it. A lever 48 pivots about an axis 49 and carries a roller 50. A spring 51 causes a plunger 52 to bear against the roller S0. A link 53 is pivotally connected to levers 47 and 49 so that these three members, together with the outer casing 1 constitute a four-bar chain. In the contiguration shown in FIGURE 8, the lever 47 is in contact with a block 54 and the mechanism constituting the chain is held locked in this position. The spool 31 which is connected through bearings to the lever 48 by a link 55 is thus locked in its inner end position.

When the lever 35 is caused to rotate about the axis 36 in a clockwise direction when viewed as shown in FIGURE 6 by the rearward movement of the hammer 19 transmitted by the push rod 34, the corresponding movement of the lever 41 and hence the tube 42 and lever 44 with which it forms a rigid assembly, is `clockwise about the axis 43 when viewed as shown in FIGURE 8.

Continued movement of the hammer 19` causes the pro jection 46 on the lever 44 to engage with the lever 47 and to cause the lever 47 to rotate about the common axis 43. The lever 47 remains in contact with the projection 46 on the lever 44 until the four-bar chain formed by levers 47 and 48 the links 53 and the outer casing 1 reaches a point of instability which occurs when the lever 47 has moved through a small angle past the position when the centres of the bearings in the link 53 and the lever 47 lie on a common straight line. The value of the angle depends on the friction opposing the movement of the mechanism and of the spool 31 attached to it, and the design should be such as to reduce this friction to a practical minimum.

When the lever 47 has moved through the point of instability, the movable members of the four-bar chain move under the action of the spring-loaded plunger 52 until the lever 48 engages a resilient stop 56 against which it is held by the action of the springr 51. The link S causes the spool 31 to move with the lever -48 to its outer end position and the four-bar chain together with the spool 31 are now locked in a second conguration.

The distance between the projections 45 and 46 on the lever 44 is suicient to allow the lever 47 to move from the position of instability to its position of rest in the second configuration of the four-bar chain without coming into engagement `with the projection 45. f

The arrangement of the valve .and the link 55 are such that, when the four-bar chain is being moved from the rst configuration to the second configuration, the spool 31 reaches its neutral position after the point of instability of the four-bar chain has been passed and the characteristics of the spring 51 with respect to the geometry of the four-bar chain and the masses of the various members and parts which are attached is such that the time taken for the spool 31 to move from its neutral position to its outer end position is substantially independent of the speed of the lever 44 for such speeds as the lever 44 will move.

Movement of the hammer 19 towards the shaft 2 allows the push rod 34 to move to the right in FIGURE 6 so that pressure on the piston 32 can reverse the movement of the lever 35 and hence that of the tube 42. The lever 44 moves until its projection engages with the lever 47, and the two levers then move together until a second position of instability is reached when the lever 47 moves under the iniluence of the spring 51 on to the stop 54, and the movable members of the four-bar chain are now back to their position shown in FIGURE 8 with the spool 31 in its inner end position. Continued movement of the hammer 19 allows the lever 35 to engage the stop 410 and the hammer 19 separates from the push rod 34. The stop 40 is engaged before the projection 45 on lever 44 can re-engage with the lever 47.

The valve 30 acts as a pilot valve to control the position of the spool 57 of a larger valve 255 (FIGURE 3). The setting of a poppet 58 of a further valve 216 is determined by that of the spool 57. The two

valves

255 and 216 are housed in a block 217 which forms the part of the outer casing 1 in which the chambers 23 and 25 are formed. In FIGURE 3, for clarity, these valves are shown outside the main body of the device and the valve 30 is shown to a larger scale than that used for the other two valves.

Spool 57 is urged in opposite directions by two

pistons

59 and 60, The smaller of these tWo pistons 59` is connected permanently to the line 66 and hence to the source of fluid under pressure. The pressure applied to the larger of the two pistons 60 is determined by the setting of the spool 31 in the valve 30.

When the spool 31 is in the inner end position shown in FIGURE 3 the cylinder in which the piston 60 moves is connected to exhaust by a restricted passage 218, and the smaller piston 59 moves the spool 57 to the left to the position shown in FIGURE 3 and holds it there. In this setting the chamber 23 is connected to exhaust through

ports

22,1 and 222 0f the valve 255 and a line 223, While the chamber 25 is connected to pressure through a main 8 passage 225,

ports

226 and 227 of the valve 25S and a line 228. There will also be a parallel connection between the chamber 2S and the line 228 through a small by-pass passage 62. Further, the chamber 61 will be connected t0 the line 66 through

ports

229 and 230 of the valve 255.

When the movable members of the four-bar chain previously described move to their second configuration, the spool 31 moves to its outer end position to connect the piston 60 freely to the line 66 and hence to the source of uid under pressure and the spool 57 moves to the right (FIGURE 3) to engage a second stop. In this setting the chamber 23 is sealed from exhaust by the land 231 of the spool 57, the chamber 61 is connected to exhaust through a passage 232 which extends along the length of the valve spool 57 and the chamber 25 is cut off from the source of fluid under pressure except for the small by-pass passage 62.

When the chambers 25 and 61 are connected to pressure, hydrostatic forces together with the thrust of a spring 65 hold the poppet 58 against its seating 63, thereby sealing the chamber 25 from the cham-ber 23. When the chamber 61 is connected to exhaust, the uid pressure in chamber 25 overcomes the thrust of the spring '65 and moves the poppet 58 away from its seat 63 and holds it against stops. This movement connects the chamber 23 to the chamber 25. A piston 64 serves to balance the valve 216 so that its action is substantially independent of the pressure of fluid in chamber 23. Thus the rate at which the poppet moves away from its seat is determined by the pressure in the chamber 25 and the rate at which Huid can flow to exhaust from the chamber 61 through the valve 255, but is independent of the rate at which fluid can be supplied from the source 205 through the line 66.

The device is brought into operation when a control valve 219 in the line 66 connects the

valves

30 and 255 and the Icylinder 33 to the source of uid under pressure. When the device is not required to operate, the control valve connects the line 66 to exhaust through a restrictor. The line 67 is connected directly to the source of fluid under pressure.

When the line 66 is connected to exhaust, the piston 26 is moved by the gas loads acting on it to bear against the shoulder 27. The spool 31 will normally be held in the end position shown in FIGURE 3.

The action of the device will now be described from the moment the control valve 219 admits pressurised fluid to the line 66.

With the spool 31 in the inner end position shown in FIGURE 3, the spool 57 and the poppet S8 will also be in the positions in which they are shown in this figure or will at once move to them. Fluid will ow from the line 66, through the line 228, the

ports

227 and 226, the passage 225, the chamber 25 and the ports 24 to the underside of the piston 21 which will move to the left taking the hammer 19 with it until it engages with the piston rod 215 of the piston 28. The Huid pressure needed to move the piston 21 until it engages with the piston rod 215 is less than that needed to move the piston 26 against the gas loads acting on it, so until

pistons

21 and 28 engage the piston 26 will normally remain against the shoulder 27. The cross-sectional area of the piston 28 on which the pressure in the chamber 25 acts is greater than the area of the annulus below the piston 21 on which it also acts, so that when hydrostatic forces only are acting, the piston 23 remains on its stops.

When the

pistons

21 and 28 engage, the piston 28 moves momentarily into its cylinder in the rod 211 of the piston 26 to cushion the movement of the Piston 21 and the hammer 19 and then return to its stops. The fluid pressure in the chamber 25 is initially only that necessary to retract the hammer but it will now rise to that needed to move the piston 26 into the chamber 16, against the gas loads acting on it, and the hammer 19 and the

pistons

21, 26 and 28 all move together to the left (FIGURE 3) though at a much slower speed than the hammer 19 moved before the

pistons

21 and 28 engaged.

At this stage of the operating cycle, the push rod 34 comes into contact with the hammer 19 moving the linkage which ultimately trips the spring-loaded four-bar chain to move the spool 31 to its outer end position as has previously been described. The mechanism is set to trip when the hammer 19 has moved the required distance away from the impact position and at this position the design is such that sui'licient uid has been stored in the chamber 25 by the movement of the piston 26 into the chamber 16, to deliver the blow.

The thrust of the spring 51 (FIGURE 8) is such as to cause the four-bar chain and hence the spool 31 to move rapidly from its rst position of rest to the second, and the time elapsing between the spool 31 passing through its neutral position and reaching its fully open position is very short. In consequence the piston 60 is fed almost from the beginning of its stroke through a fully open valve which has large ports relative to the size of the piston 60, and as the ports relative to the piston 59 are of proportional size, the spool 57 also moves rapidly to the right (FIGURE 3) to its second stop.

In this direction of travel the spool 57 cuts off the main pressure supply to the chamber 25 before isolating the chamber 23 from exhaust and connecting the chamber 61 to exhaust. For this last operation the movement of the spool 57 between opening and unrestricted connection to exhaust is short and the time taken equally short for example two milliseconds. 'Ihe poppet 58 immediately starts to lift thereby connecting the chambers 23 and 25. The uid pressure in these chambers and in the volume under the piston 21 is now approximately the same as that of the gas in the chamber 16.

The piston 26 now starts to move to the right (FIG- URE 3) causing iiuid to fiow through the poppet valve from chamber 25 to chamber 23, and this fluid together with that displaced by the piston rod of piston 26 entering the chamber 23 causes the piston 21 and the hammer 19 to accelerate to the right, the inertia of the moving parts being the only resistance to movement other than comparatively minor frictional restraints in seals and bearings. The fluid displaced from under the piston 21 flows through the ports 24, the chambers 25 and 224, and the poppet valve 216 and the chamber 220 into the chamber 23.

The rate of flow through the poppet valve increases from zero as the hammer 19 accelerates. The sizes of the ports connecting the chamber 61 to the spool '57 are suiciently large as to ensure that the poppet valve reaches its fully open position during the early stages of the forward movement of the hammer 19, and in this fully open position the valve can pass fluid at a rate of fiow corresponding to the maximum hammer speed with only a small pressure drop.

The hammer 19 continues to accelerate towards the right until it impacts on the cap 4 of the shaft 2 which is held in the impact position by a pre-load applied to the tool 3 which forces the assembly of tool 3, shaft 2 and cap 4 into the outer casing 1 until the shoulder 261 on shaft 2 engages its stops 202. A control circuit, which will be described later, ensures that this preload is applied before the device is brought into operation.

During the forward movement of the hammer 19 the spool 31 is reset to its first or inner end position, that is to the position shown in FIGURE 3, in a manner Which has already been described, and the spool 57 at once begins to move to the left, but the restrictor 218 in the spool 31 of the valve 30 ensures that the spool iniluence of the spring 65, and finally connects the chamber 25 to pressure. Although the spool 57 moves relatively slowly, the time during which the pressure line 66 is connected to exhaust via the poppet valve is very short and the loss of fluid is negligible.

As a safety precaution against the malfunctioning of any valve or any part of the valve operating mechanism, the piston 15 is provided with an extension 233 which engages with the piston 26 to prevent it from entering too far into the chamber 16, while a resilient annular pad 68 rst engages the hammer 19 to limit its rearward movement.

In normal conditions the spool 31 will not be in its second 0r outer end position at the moment when the line 66 is connected to pressure but, should this be the case by some accident, the by-pass port 62 enables fluid to enter the chamber 25, to open the poppet valve 58 against its spring 65 and to move the piston 21 and the hammer 19 forward until the valve 31 is reset to its first position when the action will proceed as has already been described.

After impact the shaft 2 can move forward without restraint from the device until the shoulder on the cap 4 engages with the lconical thrust member 5, when further movement forces the three pistons 7 back into their cylinders 8. Some of the fluid displaced by this movement flows back into the main pressure circuit, but the restrictor 12 limits the flow and the pressure of the fluid in the chamber 11 rises until the piston 15 lifts oi its stops and the displaced fluid is stored in the annular volume under the piston 15.

The first stage of restraint lasts until the shoulder on the piston 7 engages with its cylinder 8 and then both 7 and 8 move together into the cylinder 9. At this point the restraining force increases to approximately twice that exerted during the first stage of restraint. The available movements of the

pistons

7 and 8 are suicient to absorb all the energy of the blow, should this be necessary.

Engagement of the hammer with the shaft 2 limits the movement of the hammer 19.

When the shaft 2 cornes to rest, the piston 15 begins to move back on to its stops 209, the plate valve 18 closes and the iiuid stored under the piston 15 Hows back into the chamber 11 at a controlled rate. This uid, together with the required make-up fluid passing through the restrictor 12 moves the shaft 2 back into the outer casing 1 at a controlled speed until the conical thrust member 5 engages its stops 203 on the ribs 6.

When the piston 15 has rnoved a short distance away from its stops, its extension 233 prevents the piston 26 from moving far enough for a further blow to be delivered, thereby ensuring that whenever a blow is struck the device can always re-'absorb the whole of the energy of the blow should this be necessary.

In FIGURE 3 the difference between the diameter of the piston 21 and its piston rod has been shown exaggerated for clarity, the actual difference being only a small fraction of the diameter of the piston 21.

siderations of wear, for use with piston 21 although they are suitable for other pistons in the device.

FIGURE 9 shows in detail one method of avoiding this diiculty, in which sealing of the piston is effected primarily by the closeness of the tits between the moving parts. This necessitates articulation between the close-litting piston and the hammer which will accommodate the normal measure of inaccuracies in manufacture, working clearances, wear and elastic deflections of the bearings supporting the hammer, without exerting undue side loads on the piston. Provision is also made to cushion the close-fitting parts which move with the hammer against the shock of impact.

The piston 21A and the piston rod 21B 4are integral parts of a light tubular member. Piston 21A is ya close lit in the cylinder 22 while a close-fitting sleeve 69 seals the piston rod 21B. The sleeve 69 includes an annular portion 234 which registers with some measure of clearance in a bore in the casting containing cylinder 22. It is sealed by a rubber seal 70 and is supported against the hydraulic thrust acting on it by a cylinder 71 of resilient material, for example, nylon. A drain line 72 takes any leakage past the sleeve 69 to exhaust. The piston rod 21B is sealed against this oil at exhaust pressure, by a rubber seal 73,(shown diagrammatically), and passes out of cylinder 22 through a hole in an end cap 235 providing a generous clearance around the rod 21B.

The tubular member formed by piston 21A and piston 21B is joined to the hammer 19 by `a hollow connecting rod 74 which has a form of spherical joint at each end.

At the hammer end member 74 has a part-spherical cap 76 which fits into a part-spherical recess formed in an impact block 19B while a part-spherical surface on a ring 77 surrounding the member 74 bears against a sirnilar surface on a ring 78 located in the main body of the hammer 19A. Any axial thrust exerted by the ring 78 on the ring 77 is transmitted to the member 74 by three segments 79 which are held in position by a sleeve S0. This sleeve `S has a ii-ange Whose outer surface is part-spherical and of the same diameter as that of the cylinder in which it lits. The part-spherical surfaces in

parts

76, 77, 78, 80 and 19B have a common centre at the point 75.

The method of assembly of the three segments 79 is shown in FIGURE 10.

The end of the member 74 remote from the hammer 19 terminates in a piston 236 carrying an O ring seal 81. A short length of the piston is part-spherical with its centre at point 82 and this piston lies in a cylinder 237 formed in the piston 21. A sleeve 83 of resilient material, for example nylon, is pressed on to the member 74 yand this bears on an annular pad 84 pressed into the piston 21. The contact surfaces of

parts

83 and 84 are part-spherical with their centres at S2, and these surfaces are normally held together by an assembly comprising a sleeve 85 of resilient material, for example nylon and

light alloy members

86 and 87. The sleeve 85 is a close fit in the piston rod 21B but has clearance with the member 74.

At impact the

parts

83 and 84 separate and the piston 21 (comprising the parts 21A and 21B) is cushioned by the compression of the resilient sleeve 85. This compression causes the outer diameter of the sleeve 85 to increase and to bear with increasing pressure against the inside of the piston rod 21B as the compression increases. During the cushioning 'action energy is stored elastically in the sleeve 85 but it is also adsorbed and dissipated by the frictional forces which oppose the relative movement of these sur- `faces in loaded contact, during both the compression and subsequent expansion of the cylinder 85.

The resilience of the part 33 and ofthe long member 74 cushions the rc3-engagement of the piston 21 and the hammer 19.

The device described may be carried in a mounting cradle in the form of a. trough or open channel, stifened near its centre by members which form a closed box section around the channel, and provided with widely spaced stub axles 8S which have thrust faces such that the cradle can be held in bearings which allow rotation 4about the axis of the axles but which restrain lall other movement (FIGURES 11 to 15 inclusive).

Parts

89, 90 and 91 are fixed rigidly to the device. Part `89 is provided with a tongue which fits into a channel 92, and with thrust faces which can bear against this channel. The part 90 and a channel 93 are respectively similar to the part 89 and the channel 92 but of opposite hand. The part 91 has two tongues and two thrust faces and lits in and bears against

channels

94 and 95.

The

channels

92, 93, 94 and 95 are xed rigidly to the cradle and are aligned parallel to each other. The clearance between the tongues on the part 91 and the

channels

94 and 95 is greater than that provided between the tongues on

parts

89 and 90 and the channels 92 vand 93. All tongues and thrust faces are relatively short.

The

parts

89 and 90 in their respective channels prevent displacement of the device at this point in directions normal to the longitudinal axis of the device and also prevent the device from rotating about Aan axis parallel to its own longitudinal axis; the part 91 engaging with the

channels

94 and 95 also prevents the displacement of the device at this second point in these normal directions, but the greater clearances provided between the tongues and the channels avoid the introduction of a redundant constraint against the rotation of the device around an axis parallel to its longitudinal axis.

This arrangement will be seen to provide the device with one degree of freedom, namely that of movement parallel to its own axis, by means which approximate to the kinematic ideal of providing sufficient constraints to prevent other movements without introducing a redundancy of constraints. The cradle can therefore accommodate some measure of distortion without causing the device to jam in the channels.

The device is moved in its cradle by two hydraulic jacks 96 which are attached one to the part 89 the other to part A90. Two cylinders 97 are mounted on the cradle parallel to the longitudinal axis of the device so that the

parts

89 and 90 will engage simultaneously with the protruding piston rods of the cylinders 97 when the device is at a distance from the end of its stroke approximately equal to the maximum stroke of the cylinders 97.

A valve 98 is provided with a lever 99 which when rotated clockwise (FIGURE 15) opens the valve 98. This valve 98 is fixed to the cradle and a cam 100 is xed to the device and is so positioned that it engages with a roller on the lever 99 and thereby rotates the lever 99 to open the valve 98 shortly before the piston rods of the cylinders 97 engage with the

parts

89 and 90. Continued forward movement of the device causes the valve 98 to open fully and the cam 100 is shaped so as to hold the valve 98 open for the remainder of the stroke available to the device.

The power supply to the device and the means of controlling its operation will now be described with reference to the hydraulic circuit diagram shown in FIGURE 17.

The control circuit is arranged so that the device cannot be brought into operation until it has been 'brought to bear against the body to be struck with a predetermined thrust. Control is exercised by moving a lever 101 to one of three positions.

When the level 101 is in position A, the jacks 96 extend to move the device forward out of the cradle. When the tool 3 comes into contact with the -body to be struck and the thnust on this body exceeds the critical value, the device automatically comes into operation and remains in operation until either the thrust falls below the critical value or the device reaches the end of its working stroke out of the cradle.

lIn position B the jacks 96 are held stationary but the device will come into operation if a thrust is applied to the tool 3.

In position C the jacks 96 contract and the device is drawn back into the cradle. When fully back the device cannot come into operation.

The circuit is fed by two fixed-displacement pumps P1 and P2 which draw their oil through a strainer S from a tank T. They are driven at a substantially constant speed lby a motor 103. Pump P2 is the larger of the two pumps and provides the majority of the oil when the device is in operation, while the smaller pump P1 serves primarily to pressurise the circuit when the pump P2 is oft-loaded.

Oil from pump P1 passes iirst through a check valve 104 then through a pressure filter F into a line 105 which delivers oil to the underside of the pistons of the jacks 96, to the cylinders 97, to the line 67 and hence through the 13 restrictor 12 to the chamber 11 (FIGURE 3) of the device, and to a piston 240 which acts on the spool 109` of the valve 106 tending to move the spood to the right (FIGURE 17).

A cock 108y is closed when the device is to be used. When open it dumps all pressure in the circuit and allows the motor 103 to start oti-load.

Consider the circuit with the lever 101 in the position B, that is as drawn. The delivery from pump P1 will flow back to tank T through a pressure relief valve 107 which maintains the required circuit pressure in the line 105. Pump P2 is oE-loaded through

ports

241 and 242 of the Valve 102 back to the tank T. 'Ihe jacks 96 are locked and the relative areas of the face and underside of the piston of each of these jacks is such that the pressure in line 110 is approximately half the pressure in the line 105. Line 110 is connected to la piston 243 at the end of the spool 109 opposite to the piston 240. The sizes of the two

pistons

240 and 243 are such that in these circumstances the net hydraulic thrust on the spool 109 is to the right (FIGURE 17) and the spool 109 is in the position shown, connecting the line 66 to the tank T through a restrictor 2'44 and a port 245 of the valve 106.

When the level 101 is moved to position C, the pump P2. remains ott-loaded to tank T and the line 110 is connected to the tank through a restrictor 111. The jacks 96 contract drawing the device back into the cradle, and the pressures in

lines

105 and 110 remain substantially unchanged until the jacks 96 complete their strokes when pressure in the line 110 falls to that of the tank T. The spool 109 remains in the position shown in FIGURE 17.

When the lever 101 is moved to position A, the pump P2 is isolated from the tank T by closure of the port 242 and its delivery is divided; some oil flows into the line 110 through the restrictor 111, while the remainder ows through a check valve 112 and the lilter F into the line 105. Owing to te restrictor 111 and to the proportions of the jacks 96, the pressure in the line 110 remains at approximately half that in the line 105 while the device slides forward unrestricted, but when the tool 3 cornes into contact with the body to be struck the pressure in the line 110 rises as the ilow through the restrictor falls, and, when this ow ceases the pressures in the

lines

105 and 110 are the same. As the pressure in the line 110 approches that in the line 105, the net hydraulic thrust on the spool 109 moves to the left (FIGURE 17). The line 66 is thus connected to the pressure circuit and the device begins to operate.

As the tool 3 cuts or Ibreaks the body against which it bears, the jacks 96 advance the device to keep the tool 3 in contact with the body, and this continues until the cam 100 (FIGURES 15 and 16) trips the valve 98 and the line 110 is connected to the tank T. The pressure in the line 110 drops and the spool 109' moves to the right (FIGURE 17) cutting otf the line 66 from the pressure pressure line 105 and connecting it to the tank T.

A light spring 113 holds the spool 109 in this righthand position when the pumps are not working or when the cock 108 is open.

The proportions of the jacks 96 with respect to the designed circuit pressure should Ibe such that they can resist Without movement the recoil of the device as the hammer is accelerated lforward, and can also resist the forces tending to move the device forward which are applied to it during the iirst stage of restraint of the shaft 2 when the pistons 7 are moving into their respective cylinders 8.

Should the second stage of restraint develop when the shaft 2 moves far enough forward to require both pistons 7 and cylinders -8 to move together, then the restraint of the ,jacks 96 may be overcome so that the whole device will move forward. Normally the jacks 96 will have enough stroke remaining to bring the device to rest, but should the condition described occur near the end of the stroke of the jacks 96, the cylinders 97 provide a much greater resistance to movement and bring the device to rest Without damage either to the device or to the cradle.

What I claim as my invention and desire to secure by Letters Patent of the United States is:

1. A device for applying impact forces to a body, including a hammer, spring means, means for transmitting energy to said spring means to be stored in said spring means, a hydraulic transmission system for transmitting stored energy from said spring means to said hammer, and means for initiating said transmission of energy to the hammer in response to the retraction of the hammer to a predetermined position.

2. A device as claimed in claim 1, further including a hydraulic transmission system for transmitting the energy to be stored in the spring means to the spring means.

3. A device as claimed in claim 1, including an accumulator piston slidable in an accumulator cylinder and a quantity of gas under pressure in an enclosed space and acting on said accumulator piston, said accumulator piston and said quantity of gas constituting said spring means.

4. A device as claimed in claim 3, including a driving piston slidable in a driving cylinder, a connecting rod connecting said driving piston to said hammer, means for causing hydraulic fluid under pressure to act on the side of the accumulator piston remote from the quantity of gas to compress said gas, means for causing hydraulic fluid under pressure act on the side of the driving piston at which the connecting rod is attached to retract the hammer, and means for causing hydraulic fluid under pressure to act on the opposite side of the piston to move the hammer in a direction to apply said impact forces.

5. A device as claimed in claim 4, including valve means controlled in dependence on the position of said hammer in such a Way that they are changed over from a iirst state to a second state when the hammer has been retracted to its predetermined position, said valve means controlling said hydraulic transmission system in such a Way that, when the valve means are in their iirst state, hydraulic fluid operates to retract the hammer land store energy in the spring means whereas, when the valve means are in their second state, hydraulic fluid serves to transmit the stored energy to the hammer.

r6. A device as claimed in claim 5, wherein said valve means include a iirst valve and a series of other valves interconnected in such a way that the setting of the iirst valve determines the settings of the remaining valves.

7. A device as claimed in claim 6, including a spring arranged to transfer the first valve from a position of unstable equilibrium to either of two end positions.

8. A device as claimed in claim 6, including means for delaying the change in the settings of said other valves when said lirst valve is changed from its second end position to its iirst end position.

9. A device as claimed in claim 5, including a rst hydraulic connection between said valve means and exhaust, a second hydraulic connection -between said valve means and the end of the driving cylinder remote from the connecting rod, a third hydraulic connection between a source of fluid under pressure and said valve means, a fourth hydraulic connection between said valve means and the end of the accumulator cylinder remote from the quantity of gas and also the end of the driving cylinder containmg the connecting rod, said rst and second and said third and fourth hydraulic connections lbeing respectively placed in communication through said valve means when said valve means are in their first state, and said second and fourth hydraulic connections being in communication when the valve means are in their second state.

10. A device as claimed in claim 9, including a small by-pass port by means of which the end of the accumulator cylinder remote from the quantity of gas under pressure 1s in communication with the source of uid under pressure when the valve means are in their second state.

11. A device as claimed in claim 9, including a push rod forming part of a mechanical linkage serving to initiate change of the valve means from their iirst state to their 1 5 second state and contacted by said hammer during its retraction before it reaches its predetermined position.

12. A device as claimed in claim 11, including a piston rod extending from said accumulator piston towards said driving piston and arranged to make contact with the driving piston before the hammer cornes into contact with the push rod.

13. A device as claimed in claim 12, including a buffer piston slidable in a cylinder in said piston rod of said accumulator piston and la buffer piston rod extending from said butter piston towards said driving piston.

14. A device as claimed in claim 13, including a hydraulic connection between the end of the cylinder containing the buffer piston rod and the end of the driving cylinder remote from the connecting rod and a further hydraulic connection between the opposite end of the cylinder in the accumulator piston rod and the end of the accumlator cylinder remote from the quantity of gas under pressure.

15. A device as claimed in claim 4, including a sleeve sealed in the end of the driving cylinder and adapted to provide a close tit around the piston rod and the driving piston which is itself a close fit in the driving cylinder.

16. A device as claimed in claim 1S, including a spherical joint at each end of said connecting rod.

17. A device as claimed in claim 16, including a sleeve of resilient material contained within the driving piston rod, said connecting rod passing through said sleeve with clearance, and means for axially compressing said resilient sleeve so that it is radially expanded to exert pressure on the bore of the piston rod when the driving piston is applying force to the hammer.

18. A device as claimed in claim 1, including means for a-bsorbing energy which is transmitted to the hammer but is not absorbed by the body.

19. A device as claimed in claim 18, including a shaft to which the impact forces are applied by the hammer and a thrust member adapted to engage with `a shoulder provided on said shaft.

20. A device as claimed in claim 19, including a plurality of thrust-absorbing cylinders to which said thrust member transmits thrust exerted `'by said shoulder on said shaft when said shaft has travelled a predetermined distance.

21. A device as claimed in claim 20, including a hydraulic accumulator :and a hydraulic connection adapted to transmit fluid from said thrust-absorbing cylinders to said hydraulic accumulator.

22. A device as claimed in claim 20, including means for increasing the restraining force exerted by said thrustabsorbing cylinders on said thrust member when said thrust member has been moved a predetermined distance by the thrust transmitted thereto by said shoulder on said shaft.

23. A device as claimed in claim 20, including a storage cylinder, a storage piston slidable in said storage cylinder, said spring means acting on one side of said storage piston, and a hydraulic connection adapted to transmit fluid from said thrust-absorbing cylinders to the end of said storage cylinder remote from said spring means.

24. A device as claimed in claim 21, including restricting means connecting said thrust-absorbing cylinders to` a source of uid under pressure.

25. A device as claimed in claim 24, including a valve coupling the thrust-absorbing cylinders to the hydraulic accumulator in such a way that it allows free ow of uid out of the cylinders but restricts any 110W in the reverse direction.

26. A device for applying impact forces to a body including a hammer, a shaft to which impact forces are apstorage cylinder, a storage piston slidable in said storage cylinder, means for containing a quantity of gas under pressure acting on one side of said accumulator piston and on one side of said storage piston to urge said pistons in opposite directions, means for urging said accumulator piston towards said quantity of gas to store energy therein, a rst hydraulic transmission system for transmitting stored energy from said accumulator piston to said hammer, means for restraining movement of said shaft under the iniiuence of said impact forces after it has moved a predetermined distance, and a second hydraulic transmission system for transmitting energy from said restraining means to said storage piston.

27. A device as claimed in claim 26', including means responsive to movement of said accumulator piston towards said quantity of gas for initiating said transmission of energy to said hammer and a piston rod extending from said storage piston towards said accumulator piston and adapted to prevent the initiation of said transmission of energy to said hammer when said storage piston has been displaced a predetermined distance towards said quantity of gas.

28. A device as claimed in claim 1, including means for preventing operation of the device until a predetermined load has been applied to the body.

29. A device as claimed in claim 1, mounted for axial motion along a carriage and provided with at least one hydraulic jack adapted to move the device towards the body.

30. A device as claimed in claim 1, mounted in bearings at one end of a boom of a movable vehicle.

31. A method of applying impact forces to a body, wherein energy stored in spring means is applied to a hammer through a hydraulic transmission system.

32. A device for applying impact forces to a body, including an outer casing, a shaft mounted for axial movement in said casing, a hammer mounted for axial movement in said casing and adapted to impact on the inner end of said shaft, a rst cylinder co-axial with said outer casing, a rst piston slidable in said first cylinder, a rst piston rod extending from said rst piston and connected to said hammer, a second cylinder, a second piston slidable in said second cylinder, means for containing a quantity of gas under pressure acting on one end of the second piston, a first chamber in communication with the end of the first cylinder remote from the first piston rod, a second chamber in communication with the end of the second cylinder remote from the quantity of gas under pressure, and -valve means changed from a rst state to a second state when said hammer is retracted to a predetermined position, said walve means serving when in their rst state to connect the first chamber to exhaust, to connect the second chamber to a source of fluid under pressure and to isolate the first lchamber from the second chamber, whereas when said valve means are in their second state, the rst chamber is isolated from exhaust, the second chamber is substantially isolated from the source of pressure and the yfirst and second chambers are placed in communication.

References Cited UNITED STATES PATENTS 2,132,962 10/1938 Mueller 173-119 3,216,510 11/1965 Briden 173-119 JAMES A. LEPPINK, lrmary Examiner.