US3298447A - Control of variable-stroke power hammers - Google Patents

Description

Jan. 17, 1967 G. J. GENDRON CONTROL OF VARIABLE-STROKE POWER HAMMERS Filed April 15, 1964 4 Sheets-Sheet 1 wm wm /IIIIIIIIIIIIIIIIIII ul/l Jan. I7,' 1967 G. J. GENDRON CONTROL OF VARIABLE-STROKE POWER HAMMERS Filed April 15. 1964 4 Sheets-Sheet 2 7 G. J. GENDRON ,2 3,

CONTROL OF VARIABLE-STROKE POWER HAMMERS I Filed April 15, 1964 4 Sheets-Sheet s Jan. 17, 1967 G. J. GENDRON CONTROL OF VARIABLE'STROKE POWER HAMMERS Filed April 15, 1964 4 Sheets$heet 4 will lillIILlF.

United States Patent 3,298,447 CONTROL OF VARlABLE-STROKE POWER HAMMERS George J. Gendron, Oradell, N.J., assignor to Raymond International Inc., New York, N.Y., a corporation of New Jersey Filed Apr. 15, 1964, Ser. No. 359,911

9 Claims. (Q1. 173---8) This invention relates to hydraulic powerv hammers, and more particularly to the control of the length of the stroke thereof under varying conditions of use.

The invention is particularly well adapted for use in connection with differential types of hydraulic hammers, that is, those in which, during the working stroke, the spaces both above and beneath the piston are filled with liquid under pressure, but the space beneath is partially occupied by the piston rod, so that the total pressure applied above the piston is greater than that on the underside, by reason of the fact that the area of the underside of the piston is less than the area on the upper side by an amount equal to thecross-sectional area of the piston rod. The invention under some circumstances may also be desirable for use .in connection with the so-called doubleacting types of hydraulic power hammers.

Such power hammers are frequently used for purposes such as pile driving and the conditions are generally such that the length of the working stroke may be adjusted to a predetermined value. In driving piles, pile cores or mandrels therefor, a so-called cap block or cushioning means is placed on the upper end thereof and the hammer is suspended in such manner that it will be lowered successively as the pile or the like is driven, so that very effective working strokes can be obtained without the necessity of successively adjusting the lengths of the stroke.

However, if a power-driven hydraulic hammer is to be used to rapidly force a mass of cementmix or the like down into or through a pile shell for forming, for example, a pile with a bulbous lower end in accordance with one of the uses of such hammers as contemplated by this invention, then it is necessary to vary the length of each working stroke, because the point at which the hammer ram meets heavy resistance at the bottom of each stroke may vary considerably. Hydraulic power hammers controlled in accordance with the present invention are well adapted to meet these and similar conditions and same are also adapted to be utilized for purposes such as forging heavy metal members, the thickness or height of which diminishes with each successive stroke so that the hammer, if suspended in fixed position, should have a working stroke of varying length, depending on the extent to which the workpiece or pieces become compressed as the forging operation proceeds. In the usual power hammer constructions, mechanical valves are provided to be actuated automatically to cause reversal of the piston movement at the end of each stroke, but such automatically operated valves are not well adaptedfor any form of automatic variation of the length of the working stroke, and so far as is known, there has heretofore been no satisfactory available method for variably controlling the stroke to meet conditions such as above referred to.

Furthermore, with such mechanically operated valve arrangements, there will necessarily be some premature valve action and consequent throttling and reduction of the energy of the blow. Althoughsuch arrangements are designed to restrict this difliculty to a minimum, with the present invention, the nature of its operation is such as to eliminate any such premature valve action. 7

The present invention provides a solution to this problem preferably by way of utilizing the so-called water hammer effect which occurs in the hydraulic fluid above the piston just following the moment the hammer strikes "ice its blow. That is, at thev moment of impact, the violent deceleration of the fast-moving column of hydraulic fluid accompanying the piston on its downward stroke, has the effect of momentarily causing sharply increased pressure, due to the kinetic energy of the moving liquid. express-ion water hammer as used herein is intended to be applicable whether the hydraulic fluid used is actually water, oil or some other appropriate liquid.) According to the present invention, the kinetic energy of such water hammer is utilized to actuate control valve means so as to release the hydraulic pressure above the piston promptly following the moment of impact, even though each succeeding stroke of the piston may dilfer in length from the preceding one.

The apparatus of the invention is also inherently capable of thus actuating the control valve, even in cases where the impact or blow of the hammer is not so severe as to cause the water hammer effect, such as in cases described below in connection with FIG. 3, or at times when the hammer is being started and when on its first upstroke it is necessary to release obstructing pressure which would otherwise occur above the piston. In such cases the system of the present invention using positive displacement pumps in a hydraulic system of a closed nature, results in the power source continuing to supply fluid against the immobile piston, thereby raising the general level of the system pressure to actuate the above-mentioned control valve means so as to release the hydraulic pressure above the piston promptly following the impact, or the desired termination of the downstroke. Thus while the invention makes possible automatic variation of the length of the working stroke responsive to the water hammer effect, it still permits normal starting of the hammer and normal full stroke operation when the impacts are not such as to cause a water hammer.

Various further and more specific objects, features and advantages of the invention will appear from the description given below, taken in connection with the accompanying drawings, illustrating by way of example preferred forms of the invention.

FIG. 1 is an elevational view of the upper portions of a differential hydraulic hammer assembly, this view showing the disposition of certainof the mechanical parts as arranged to provide for the features of the present invention;

FIG. 2 is a horizontal sectional view taken approximately through the mid-portion of FIG. 1 and further showing somewhat schematically an appropriate disposition of various of the mechanical parts and devices as arranged to provide for the present invention;

FIG. 3 is a schematic diagram of a hydraulic circuit arrangement in accordance with one embodiment of the present invention and showing, more particularly the relationship of the parts during the downstroke of the piston in a differential hydraulic hammer and showing the relationship of a cycling valve therefor operable hydraulically in one direction and by cam means in the other direction;

(In this diagram, as well as in the other diagrams referred to below, American Standards Association symbols are used for showing various of the hydraulic valve and other parts of the hydraulic circuit.)

FIG. 4 is a schematic diagram similar to that of FIG. 3, but showing the hydraulic circuit in accordance with another embodiment of the invention, wherein a main cycling valve is provided for hydraulic operation in both directions, a supplemental or pilot valve being provided, operable hydraulically in one direction and by cam means in the other direction, this diagram illustrating the condition of the circuit during the downstroke of a differential hydraulic hammer;

(The

FIG. 5 is a'view like FIG. 4, but illustrating the relationship of the parts of the hydraulic circuit during the upstroke of the hammer;

FIG. 6 is a view corresponding to FIG. 3, but illustrating another embodiment of the invention as applied to a so-called double-acting type of hydraulic hammer, as contrasted with the differential hammer of the previous diagrams; and

FIG. 7 is a vertical sectional view somewhat diagrammatically showing a possible disposition of the mechanical parts of a hydraulic hammer assembly embodying the invention and in a form adapted for use internally of a casing and pile shell as driven into the ground, FIG. 7A illustrating the lower portions of the assembly, of which FIG. 7 shows the upper portions.

It will be understood that, while in the drawings and the following description, the cylinders and pistons are shown and described in positions so that the active or working stroke will be downward and the return stroke upward, yet these hammers may, of course, be mounted or used in any desired position or orientation and thus terms such as downstroke and upstroke and upper and lower are herein used only for convenience and not as limitations.

Referring now to the drawings in further detail, in FIG. 1 the cylinder of a differential hydraulic hammer is indicated at 12, suitably connected, by known means as at 13 at its upper end, to an upper supporting plate structure 14, which in turn is carried by a suitable known form of sheave housing 15, containing for example a pair of sheaves 16, for cables 17, used in suspending the hammer in operating position.

The assembly may also include a lower or base plate 13, through an aperture 19 at the center of which the cylinder 12 extends downwardly, the piston rod for the hammer being indicated at 20, the lower end thereof be- FIG. 2. As further shown in FIG. 2, an accumulator tank 37 may be suitably mounted between the supporting plates 14 and 18, this accumulator being connected in communication with the incoming source of hydraulic pressure fluid. Also, if desired, another accumulator tank may be provided, as indicated at 38, connected in communication with the outlet side of the hydraulic circuit, these accumulators serving functions similar to those described in the above-mentioned co-pending application.

While with one embodiment of the hydraulic circuit arrangements in accordance with the invention, a main cycling valve may be used, as indicated at 34, 34a in FIGS. 1 and 2, yet with other embodiments, for reasons hereinafter explained, it is desirable to provide a main cycling valve, located for example as shown at 40 in FIG. 2, in which case other valves will operate as pilot valves.

Referring now to the schematic diagram of the hydraulic circuit arrangement of FIG. 3, certain of the parts as above referred to are here identified by the same numerals, the piston in the hydraulic cylinder being shown at 41 on its downstroke, and the cam follower 29 being shown in its position as swung to the right, where it remains after the cam 28 has started down and until the time of termination of the downstroke, whereupon the cycling valve is hydraulically operated in a direction to swing the cam follower 29 to the left in a position ready to be engaged by the cam 28 when the latter approaches the termination of the upstroke again.

It will be understood that a suitable known form of power pack may be used to provide a source of hydra-ulic fluid under pressure to the intake conduit 42 of ing suitably connected (by means not shown) to a hamv mer ram 21. The upper and lower supporting plates 14 and 18 may be suitably connected by four tubes as at 22, 23, 24 and 25, welded at their upper and lower ends respectively to the plates 14 and 18.

The construction as thus far described may be in accordance with prior known practices, as disclosed in the U.S. patent of Ernst W. Spannhake et al. No. 3,237,406, granted March 1, 1966, for example, from which it will be noted that these hammers operate at speeds of about 100 blows per minute or substantially in excess thereof, and have rams weighing 5000 to 15,000 pounds or more. In hammers such as there disclosed, the limits of the downward and upward strokes are controlled by mechanically operating cycling valve means, actuated for example by a vertically-extending actuating bar, like that here shown in FIGS. 1 and 2 at 26, attached at its lower end to the ram and slidable in suitable guide means as at 27. In accordance with prior practices, such slide bar means has been arranged to carry two cams, one for reversing the hammer cycling valve near the end of the downstroke, and the other for reversing the valve near the end of the upstroke. But with the present invention, only one such cam is provided, viz. as shown at 28, for controlling the valve at or near the end of the upstroke, the cycling valve being hydraulically controlled at the end of the downstroke as hereinafter explained. As here shown, the cam 28 on the upstroke is adapted to engage a cam follower 29 pivoted about an axis at 30 and operatively connected to the lever 31 and thence by a link 32 to the end of a valve-operating stem 33 of a cycling valve (or alternatively a pilot valve) shown generally at 34, 34a (or a cycling valve as at 72 in FIG. 6), and the constructions and operation of which are further explained below.

In case the hammer is to be mounted or carried as a part of a pile driving rig, the hammer assembly may be slidably mounted in vertical guide means, or verticallyextending so-called leads," as indicated at 35 and 36 in the hydraulic circuit of FIG. 3, the release or drain conduit for which is indicated at 43. As illustrated in this diagram, it will be noted that the fluid pressure is in communication with the accumulator 37 and also (by way of a conduit 44) in communication through a valve passage 45 and conduits 46 and 47 with the space above the piston 41, thus forcing the piston down. Although the pressure supply conduit 42 is also in communication (by way of a conduit 48) with the space beneath the piston, this does not prevent the piston from being forced down, because the effective pressure-receiving area on the underside of the piston as compared with that on the upper side, is diminished by reason of the cross-sectional area of the piston rod 20 (as is common with such differential pistons).

Assuming now that before the piston reaches the lower end of the cylinder 12, the ram strikes a blow by engaging with whatever object is to receive an impact, then the above-referred-to water hammer effect will take place, momentarily causing a sharp increase in the liquid pressure in the cylinder above the piston. Thus a substantial impulse of increased pressure will be conveyed through the conduit 47, to a pressure release valve, as schematically indicated at 50, through a connection 51, whereby, through a connection 52, pressure will be applied to the hydraulically operated end 53 of the cycling valve 34, causing the valve spool therein to be thrust to the right. Thereupon a valve passage 54 will be brought into position to connect conduit 46 to an outlet conduit 55 connected to the drain conduit 43. Thus fluid will be re leased from above the piston 41, allowing the pressure which is still being maintained beneath the piston, to move the piston on its upward stroke. At the same time, the shifting of the cycling valve 34 toward the right will have moved the cam follower 29 to the position shown in dotted lines, ready to be engaged by the cam 28 when the upstroke is about to be terminated. At termination of the upstroke, cam 28 will operate the follower 29 to shift the cycling valve 34 back to its position for controlling the downstroke. The pressure which actuated device 53 will then be released through a check valve 50a.

In case the ram, during the lower part of the downstroke, does not meet with any object to apply an impact thereto, such as would stop the downstroke of the piston, then cushioning means for terminating the downstroke may come into play, as will now be described. That is, the hydraulic pressure is applied to the space beneath the piston, as above mentioned, by way of a conduit 48 which is connected into the cylinder at an orifice 56 spaced somewhat above the bottomof the cylinder. Thus when the piston 41 moves down far enough to shut off orifice 56, there will still remain a cushioning volume of liquid beneath the piston, and the pressure in this volume will rapidly increase, thereby checking and stopping the movement of the piston before it can forcefully strike the bottom of the cylinder, or in any way cause destructive effects. However, the increase of pressure in this volume of liquid is kept from becoming excessive by the provision of a throttling type of check valve at 57, having, if desired, an adjustable spring to permit adjustment of the rate of release of the excess pressure beneath the piston. It will be noted that the throttling check valve 57 is connected by a conduit 58 through an orifice 59 at the lower end. of the cylinder, so that such excess pressure within the bottom of the cylinder is released back through the check valve 57, and back into the pressure supply line 42. When the piston starts to rise again, and before it opens the orifice 56, liquid is admitted thereunder through a check valve 60, positioned to admit pressure liquid from the supply lines 42, 48, through conduit 58 into orifice 59. And, of course, after the piston passes up beyond orifice 56, liquid will continue to be admitted thereunder through connection 48.

It will be noted that a like cushioning arrangement is provided at the lower end of the cylinder in each of the other embodiments of the invention, as illustrated in the diagrams of FIGS. 4, 5 and 6.

In some cases the downstroke of the piston may be terminated with insufiicient abruptness to cause any substantial water hammer effect, for example the downstroke may be terminated by the above-described cushioning arrangement, or by reason of the ram engaging some relatively soft mass and becoming stopped, without being abruptly stopped. In such cases, nevertheless, the cycling valve 34 will be caused to operate by reason of actuation of the pressure-release valve 59, for the reason that the power pack for supplying the hydraulic pressure to the system will ordinarily comprise positive displacement pumps connected into the closed hydraulic system, whereby the power source continuing to supply fluid will thereby raise the general level of the system pressure and actuate the cycling valve arrangement, so as to release the hydraulic pressure above the piston promptly following termination of its downstroke.

The basic principles of operation of the alternative embodiment of the invention schematically illustrated in FIG. 4, are similar to those involved in FIG. 3. However, in FIG. 4 the valve 34a acts in effect as a pilot valve, Where-as the valve shown at 40 constitutes the main cycling valve. It may be desirable to use the arrangement of FIG. 4 in case the quantity of fluid released through the release valve 50 is not sufl'ifiicient to cause actuation of the cycling valve 34 of FIG, 3. In such cases, the main cycling valve 40 may be used, accompanied by the pilot valve 34a, which is utilized to control fluid from the main supply line, for hydraulically actuating the cycling valve 40. Also it may be desirable to use an arrangement with the pilot valve of FIG. 4 to reduce the mechanical load and thereby to minimize wear of the cam mechanism and associated parts 2832.

In FIG. 4, the cycling valve 40 has a hydraulic actuator 6-1 for moving the valve toward the left, and a hydraulic actuator 62 for moving the valve toward the right. This valve has passages 63 and 64. Pilot valve 34a has a hydraulic actuator 65 for moving this valve toward the right, its actuation toward the left being caused by the cam means 28, 29. This pilot valve has passages 6 66, 67, 68 and 69. This valve, being in its left hand position during the downstroke of the hammer, the passage 68 connects the source of pressure 42 to the actuator 62 of valve 40, holding the latter valve in its right hand position. Also, passage 69 of valve 34a connects hydraulic actuator 61 to the drain passage 43, thus releasing the pressure in actuator 61 during the downstroke of the hammer.

' During the downstroke, passage 64 in valve 40, it will be noted, serves to connect the supply pressure from pressure inlet 42 and accumulator 37 to the connection 47 running to the upper end of the hammer cylinder, connection 47 also having a branch'going to the pressure relief valve 50. At the time of termination of the downstroke, either the above-mentioned water hammer effect, or increased pressure conditions in the system, will serve to actuate pressure relief valve 54 thereby admitting pressure to the hydraulic actuator 65 for valve 34a. This will cause the hydraulic circuit conditions to shift into accord with the diag ram of FIG. 5. Here, it will be noted, passage 66 of valve 3401 will serve to connect the source of pressure 42 to actuator 61 for valve 40, thus moving that valve to the left, as shown in FIG. 5. In that position passage 63 of valve 40 serves to connect the outlet drain conduit 43 and outletaccumulator 38 to the conduit 47, thereby releasing pressure from the upper part of the hammer cylinder. At the same time, in valve 34a, passage 67 will serve to connect actuator 62 of valve 40 to the outlet drain 43, thus releasing the pressure from actuator 62, permitting the valve 40 to move to the left as aforesaid. With the circuit in this condition, the hammer piston will continue on its upstroke until, at the proper time near the top of its stroke, cam 28 will actuate follower 29, thereby shifting valve 34a to the left, thus restoring conditions for the downstroke, as above described in connection with FIG. 4. Other details as to the operation of the hydraulic circiuts of FIGS. 4 and 5 will be apparent from the above description of FIG. 3.

Reference will now be made to FIG. 6, schematically showing the hydraulic circuit of the invention as applied in one of its forms to a double-acting type of hydraulic hammer, wherein a cylinder 70 is schematically shown, having a piston 71 connected to the piston rod 20', this piston being adapted to be actuated on itsdownstroke by pressure above the piston and during a time when pressure is released from below the piston, and the piston being adapted to operate on its upstroke when pressure is applied under the piston and released from above the piston. P-arts'of FIG. 6 comparable to those of FIG. 3 are identified by the same reference numerals, but here the passages of a cycling valve, shown at 72, are necessarily different. Valve 72 is moved to the right by hydraulic actuator 73, and the valve has passages 74, 75, 76 and 77. During the downstroke of the hammer, as shown in FIG. 6, valve 72 is in its lefthand position, having been moved to that position by the cam follower 29 just prior to the termination of the upstroke. With valve 72 in this position, passage 76 therein connects the pressure source by way of conduit 47 to the upper end of the cylinder 70. Meanwhile, the space within the cylinder beneath piston 71 is in communication with the outlet drain 43 by way of connection 78, passage 77 and conduit 79. Then, when the piston reaches the end of its downstroke with the resulting increased pressure conditions or water hammer effect above the piston, this will actuate pressure release valve 50, which in turn applies pressure to hydraulic actuator 73 for moving the cycling valve towards the right. Thereupon passage 74 will connect the space above the piston 71 to the outlet drain 43 and passage 75 will connect the space under the piston 71 to the pressure source 42, thereby starting the hammer upstroke.

In a typical case for hydraulic hammer situations such as used in pile driving for example, the power pack constituting the source of pressure may be such as normally to maintain an operating pressure in the neighborhood of 5000 lbs. per square inch and may have a relief valve set to release pressure at 6500 to 7000 lbs. per square inch, for example, although normally the system will be so designed that during the downstroke of the hammer and prior to termination of the downstroke, the pressure supplied to the hydraulic system will be less than 6000 lbs. per square inch. The pressure at which relief valve 50 may then be set to open Will be of the range of 6000 to 6200 lbs. per square inch. However, of course, these pressures are given merely by way of examples, since widely different pressures or pressure ranges may be desirable, depending upon the size and purposes of the hydraulic hammer.

In FIGS. 7 and 7A, a form of differential hydraulic hammer is shown of a relatively narrow and vertically elongated shape, adapted for use internally, for example, of a metal pile shell or core, such as a corrugated pi-le shell indicated at 80, which has been driven into the earth, and which may contain a hollow mandrel, such as indicated at 81. Here the upper body portion of the hammer may include upper and lower supporting plate structures, as at 14', 18, interconnected by suitable frame means 82, upon which may be carired (at the places indicated) a pilot valve 34' or 34a and a cycling valve 40', these valves being for purposes corresponding to the valves hereinabove referred to in connection with the other embodiments. Here the cylinder 83, connected to the underside of plate 18', contains a piston 84, connected to an elongated piston rod 85, extending and connected at its lower end to a large ram as at 86, the ram at its upper position being adapted to be contained within a shielding chamber 87.

While there are various situations in which it is desirable to provide such a hydraulic hammer for use internally of a shell or caisson or the like, the particular example here shown in FIGS. 7 and 7A is well adapted for use in forming so-called bulb piles. For that purpose, the assembled shell 80 and mandrel 81 may be first driven down into the earth (as by a suitable mandrel), while the lower ends thereof are closed (for example by a sheet metal disc), then a quantity of concrete mix, preferably of a relatively dry consistency, is deposited in the bottom of the assembly. Then the hydraulic hammer assembly may be lowered into place, as shown in FIGS. 7 and 7A, and so operated that the ram 86 will pound the dry-mix concrete charge down into the earth beneath the shell, and from time to time, as the driving proceeds, additional charges may be discharged into the shell assembly to pass down around the hammer and down beneath the ram, so that a bulbous formation of concrete as at 88 is finally developed beneath the pile shell. Thereupon the hollow mandrel 81 and the hammer may be removed from the shell 80 and the shell filled with concrete.

This provides a very efiicient, relatively inexpensive and rapid way of forming a concrete bulb-type pile, in that the successive charges of the concrete dry pack mix may be pounded into place without the necessity of removing and replacing the ram and hammer assembly each time an additional charge is to be supplied.

Although certain particular embodiments of the invention are herein disclosed for purposes of explanation, further modifications thereof, after study of this specification, will be apparent to those skilled in the art to which the invention pertains. Reference should accordingly be had to the appended claims in determining the scope of the invention.

What is claimed and desired to be secured by Letters Patent is:

1. In combination with a high speed reciprocating hydraulic power hammer having a cylinder and operating piston: a source for supplying liquid under pressure; valve means for controlling the admission of liquid from such source into the cylinder space for subjecting the piston to a pressure within a normal predetermined range for actuating the piston on its working stroke, said valve r 0 means being actuatable for thereafter controlling release of the liquid from said space upon the return stroke of the piston, such pressure in said space being subject to an abrupt increase causing a water hammer impulse upon stopping of the piston movement as the result of the striking of a heavy blow by the hammer; and means acting responsive to the kinetic energy of such impulse for causing such valve actuation and consequent release of the liquid from said space.

2. The combination as set forth in the foregoing claim 1 and in which hydraulic cushioning means is associated with the cylinder at a position at the region of the termination of the normal full working stroke of the piston for cushioning the stopping of the working stroke in the absence of a prior heavy blow being made by the hammer.

3. The combination as set forth in the foregoing claim 1 and in which said hammer and its operating parts, including said valve means, cylinder and piston, and a ram connected to the lower end of the piston rod, all being arranged within the confines of a vertically elongated cylindrical space, whereby the assembly is adapted to be lowered for operation into a pile shell or the like.

4. In combination with a differential type hydraulic power hammer having a cylinder and operating piston: a source for supplying liquid under pressure; valve means for controlling the admission of liquid from such source into the cylinder space above the piston for subjecting the piston to a pressure within a normal predetermined range for actuating the piston on its working stroke; means for maintaining a differential pressure beneath the piston for moving same on its return stroke, said valve means being actuatable for controlling release of the liquid from said space upon such return stroke, such pressure in said space being subject to an abrupt increase causing a Water hammer impulse upon stopping of the piston movement as the result of the striking of a heavy blow by the hammer; and means acting responsive to the kinetic energy of such impulse for causing such valve actuation and consequent release of the liquid from said space.

5. In combination with a high-speed reciprocating hydraulic pile driving hammer having a cylinder and operating piston: a source for supplying liquid under pressure; valve means including connections operable mechanicaliy responsive to piston movement for actuating the valve to control the admission of liquid from such source into the cylinder space for subjecting the piston to a pressure within a normal predetermined range for actuating the piston on its Working stroke, said valve means being reversely actuatable for thereafter controlling release of the liquid from said space upon the return stroke of the piston, such pressure in said space being subject to an abrupt increase causing a water hammer impulse upon stopping of the Working stroke of the hammer as a result of an abruptly resisted blow; and means acting directly responsive to the kinetic energy of such impulse for causing such reverse actuation of the valve and the consequent release of the liquid from said space.

6. The combination as set forth in the foregoing claim 5 and in which the hydraulic hammer is of the differential type, means being provided for maintaining a differential pressure beneath the piston.

7. The combination as set forth in the foregoing claim 5 and in which the hydraulic power hammer is of the double-acting type.

8. In combination with a hydraulic power hammer having a cylinder and operating piston: a source for supplying liquid normally maintained under a pressure within a predetermined range; a first valve means hydraulically actuatable to either of two positions and which in one position is connected to admit liquid from such source into the cylinder under such pressure for moving the piston on its Working stroke, said valve means when in a reverse position acting to release such liquid; a pilot valve means hydraulically actuatable in one direction; means connected thereto for operating same in the opposite direction responsive to movement of the piston to the region of termination of its return stroke; and a pressure release valve actuatable responsive to a substantial increase above said normal pressure range of the operating pressure in said cylinder upon the stopping of the working stroke of the piston, said pressure release valve being connected then to actuate hydraulically said pilot valve, whereupon the latter becomes connected to move said first valve means to its reversed position, thereby to terminate the Working stroke.

9. In combination with a hydraulic power hammer of the differential type having a cylinder and operating piston: a source for supplying liquid normally maintained under a pressure within a predetermined range, the lower end of the cylinder being connected to such source; a first valve means hydraulically actuatable to either of two positions and which in one position is connected to admit liquid from such source into the upper end of the cylinder under such pressure for moving the piston on its Working stroke, said valve means when in a reverse position acting to release such liquid from the upper end of the cylinder; a pilot valve means hydraulically actuatable in one direction; means connected thereto for operating same in the opposite direction (responsive to movement of the piston to the region, of termination of its return stroke; and a pressure release valve actuatable responsive to a substantial increase above said normal pressure range of the operating pressure in the upper end of the cylinder upon the stopping of the working stroke of the piston, said pressure release valve being connected then to actuate hydraulically said pilot valve, whereupon the latter becomes connected to move said first valve means to its reversed position, thereby to terminate the working stroke.

References Cited by the Examiner FRED C. MATTERN, JR., Primary Examiner.

MILTON KAUFMAN, Examiner.

L. P. KESSLER, Assistant Examiner.

Claims (1)

1. IN COMBINATION WITH A HIGH SPEED RECIPROCATING HYDRAULIC POWER HAMMER HAVING A CYLINDER AND OPERATING PISTON: A SOURCE FOR SUPPLYING LIQUID UNDER PRESSURE; VALVE MEANS FOR CONTROLLING THE ADMISSION OF LIQUID FORM SUCH SOURCE INTO THE CYLINDER SPACE FOR SUBJECTING THE PISTON TO A PRESSURE WITHIN A NORMAL PREDETERMINED RANGE FOR ACTUATING THE PISTON ON ITS WORKING STROKE, SAID VALVE MEANS BEING ACTUATABLE FOR THEREAFTER CONTROLLING RELEASE OF THE LIQUID FROM SAID SPACE UPON THE RETURN STROKE OF THE PISTON, SUCH PRESSURE IN SAID SPACE BEING SUBJECT TO AN ABRUPT INCREASE CAUSING A WATER HAMMER IMPULSE UPON STOPPING OF THE PISTON MOVEMENT AS THE RESULT OF THE STRIKING OF A HEAVY BLOW BY THE HAMMER; AND MEANS ACTING RESPONSIVE TO THE KINETIC ENERGY OF SUCH IMPULSE FOR CAUSING SUCH VALVE ACTUATION AND CONSEQUENT RELEASE OF THE LIQUID FROM SAID SPACE.

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