GB1594452A

GB1594452A - Impact apparatus

Info

Publication number: GB1594452A
Application number: GB4468576A
Authority: GB
Original assignee: BSP International Foundations Ltd
Current assignee: BSP International Foundations Ltd
Priority date: 1976-10-27
Filing date: 1976-10-27
Publication date: 1981-07-30
Also published as: AU513866B2; AU3003877A; FR2369386A1; IT1088608B; JPS5355603A; NL7711699A; FR2369386B3; JPS622003A; DE2748020A1

Description

(54) IMPROVEMENTS IN OR RELATING TO IMPACT APPARATUS (71) We, BSP INTERNATIONAL FOUNDATIONS LIMITED, a British Company of Claydon, Ipswich, Suffolk, IP6 OJD do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to hydraulically operated apparatus for reciprocating hammer mechanisms to produce a series of impacts such as may be employed for piling operations.

Hydraulically operated pile drivers are known in which a hydraulic ram is mounted in a hammer frame with its piston rod attached to a hammer weight that is guided in the frame and is reciprocated by operation of the ram. This arrangement suffers the disadvantage that, even though shockabsorbing mountings may be provided for the ram and its control equipment on the mounting frame, there are considerable shock loads experienced that inevitably have an adverse effect on the operational life of the mechanism.

According to one aspect of the invention, there is provided impact apparatus comprising a leader, a hammer weight being guided on said leader for generating an impact force to act on a displacement member, a hydraulic ram mounted at a fixed position relative to the leader, and a rope or cable from which the weight is suspended being operable by said ram to raise the weight, said rope or cable being connected to means that are adapted to allow the weight to follow the displacements of the member independently of the stroke of said ram as reciprocating operation of the ram causes the weight to generate a series of impacts.

In one form of the invention, the rope or cable has one end connected to an element that is secured or is adapted to be secured to the elongate member. The invention may accordingly, in another aspect, provide an impact apparatus for displacing an elongate member, comprising a leader, a hammer weight guided on said leader for generating an impact force to act on the elongate member, a hydraulic ram mounted at a fixed position relative to the leader and being reciprocable by hydraulic pressure supply and control means to act on a rope or cable having one end connected to the hammer weight for reciprocating the weight, the rope or cable having its other end connected to an anchorage on said elongate member whereby the position of the rope or cable is adjusted with displacement of the elongate member during the operation of the apparatus to allow the hammer weight to follow displacements of the elongate member independently of the reciprocation of the ram as said reciprocation causes successive impulses to be applied to the elongate member, said hydraulic supply and control means being arranged to co-operate with the ram to apply a force through the ram to the rope or cable element during the fall of the weight to maintain tension in said rope or cable without significantly retarding the fall of the hammer weight.

In an alternative form of the invention, the rope or cable has one end connected to a winch drum from which it can be paid out or reeled in with changes in the mean position of the reciprocable hammer weight. In this further aspect, the invention can provide an impact apparatus for displacing an elongate member, comprising a leader, a hammer weight guided on said leader for generating an impact force to act on the elongate member, a hydraulic ram mounted at a fixed position relative to said leader and being reciprocable by hydraulic pressure supply and control means to act on a rope or cable having one end connected to the weight so that reciprocation of the ram causes said reciprocation of the hammer weight, the opposite end of the rope or cable being connected to a winch drum that is rotatable for adjustment of the length of the rope or cable in use, there being friction brake means for said drum arranged to be adjustable by said hydraulic pressure supply and control means in order to hold the winch drum locked against rotation during the ram stroke raising the hammer weight in each cycle of reciprocation and to reduce the braking force during the return stroke in each said cycle when the hammer weight is allowed to fall, whereby the weight is able to draw out a further length of rope or cable from the winch- drum without substantial resistance when it falls below a previous bottom position while said supply and control means are arranged to co-operate with the ram to apply a force through the ram to the rope or cable during said fall of the weight to maintain tension in said rope or cable without significantly retarding the fall on the weight.

The invention will be more particularly described by way of example with reference to the accompanying drawings, wherein: Figure 1 is a side elevation of a pile driving and extracting rig incorporating a hydraulically driven impact apparatus according to the invention, Figures 2 and 3 are rear and side elevations respectively of the hydraulic ram drive unit of the apparatus in Figure 1, Figure 4 is a sectional view of the hydraulic ram of Figures 2 and 3, Figure 5 is a hydraulic circuit diagram for the ram of Figures 2 to 4 Figure 6 is an electrical circuit diagram of the control means for the hydraulic circuit of Figure 5, Figures 7 to 11 are diagrammatic side elevations of respective further embodiments of the invention, and Figure 12 is a hydraulic circuit diagram for the embodiments of Figures 9 to 11.

The rig illustrated in Figure 1 comprises a leader 2 mounted from the jib 4 of a crane on a crawler chassis 6 by an extendable stay 7 that allow the angle of the leader to the vertical to be adjusted, in known manner.

The foot 8 of the leader is arranged to rest on the ground immediately behind a pile (or a tubular steel casing for a cast in situ pile) P being driven and a pile cap (or other bearing device) 10 fixed to the top of-the pile has guide elements 12 engaging a slide 14 extending along the leader to maintain the pile parallel to the leader. Above the bearing device and located on the same slide of the leader is a hammer weight 16: Figure 1 shows the weight incorporated in a pile extraction device which will be described in more detail below, but for pile driving the weight can be an entirely conventional member of a mechanism already well known in winch-driven hammers used in pile driving, suspended through a sheave block 17, from a rope or cable 18.

In such known mechanisms, the cable is reeled on a winch drum of the crane or an auxiliary winch mounted thereon, and the weight is alternatively lifted by the winch and allowed to drop to impact the pile cap.

An advantage of this arrangement is its simplicity, and therefore its operational reliability, but there are considerable disadvantages in terms of the maximum striking rate that can be obtained, in the difficulty of controlling the hammer blows especially when the movement of the pile with each blow is relatively large, and in the inability to achieve the potential striking force of the hammer weight since the cable should be kept taut at all times and this requires the fall of the weight to be retarded to a significant degree to allow for the considerable inertia of the winch reel.

In the embodiment of the invention illustrated in Figure 1, the cable 18 suspending the hammer weight is engaged by a hydraulic ram 20 (shown, e.g. in Figures 2 to 4) of a drive unit 21 located at a fixed position, which may be at any convenient location and is here shown mounted in a unit frame 22 that is secured to the lower part of the leader. The cable extends from the weight, over a sheave 24 at the top of the leader 2, round a further sheave 26 mounted on a crosshead 28 at the lower end of a piston rod 30 of the ram, and from there upwards to an attachment point 32 on the pile bearing device 10 which provides an anchorage for one end of the cable.The ram crosshead 28 is slidably guided by the unit frame and cylinder 34 of the ram is pinned by an eye 36 at its upper end to the unit frame so that as the ram is extended the sheave 26 is lowered, as shown in broken lines in Figure 1, and the weight is raised through twice the stroke of the ram from the position shown in Figure 1. It will be understood that the mechanical advantage can be varied as desired by the use of multiple sheave blocks.

The raising of the weight occurs in the pressure or working stroke of the ram and the ram hydraulic connections are then switched to allow the ram to contract and the weight to fall, retarded only by a residual pressure maintained in the ram. On impact of the pile being driven, the pile.will move downwards to a greater or lesser extent, depending on the resistance of the ground to its penetration. It will be noted that the end of the cable fixed to the bearing device 10 shares this movement, the attachment point 32 forming for the cable a datum that moves with the pile and the ram moving the weight relative to that datum. In other words, whatever the stroke of the ram, the weight is able to fall a distance matching the movement of the pile.

As a result, the working stroke of the ram is automatically related to the pile position without any action being needed on the part of the operator, regardless of the movement of the pile in the preceding stroke, and the input force is correspondingly regulated.

This can be contrasted with the operation of a conventional winch-driven hammer weight where the operator is required to judge by eye the lift of the weight at each working stroke in order to control the impact force.

Since it is no longer necessary to keep the pile position under close observation, the pile and/or the weight can be shrouded to reduce noise. The noise level is also reduced because of the connection of pile bearing device 10 to the hammer weight through the cable 18, which will tend to inhibit separation of the impacting parts, and in particular will damp the rebound of the hammer weight when the resistance to penetration of the pile is high.

The sheave block 17 has a lifting cable 37 passing round it and running to a main winch of the crane which tensions the cable 37 for an extraction operation as will be described below. A similar cable connection can be provided for driving operations to lift and reposition the hammer weight after each pile is driven. A further cable 38 to another winch drum on the crane is provided for a concrete skip (not shown) when cast in situ concrete piles are to be formed in a removable tubular steel casing.

The ram comprises a piston 42 sliding in an inner main cylinder 44, the piston rod 30 extending downwards from the piston through a lower seal 46 of the cylinder so that the piston divides the cylinder interior into sealed upper and lower spaces 48 and 50 respectively. Pressure fluid is admitted through inlet conduit 52 (Figure 2) to annular space 53 and reaches the upper cylinder space 48 through a piston valve 54 that slides in the upper part of the cylinder.

With the valve in its lowermost position as shown in Figure 4 pressure fluid to the port 52 flows to the upper space 48 by way of aligned ports 56, 58 in the cylinder 44 and the valve 54 respectively. The valve is upwardly displaceable to shut off this connection and then opens a series of ports 60 between the upper space 48 and an annular space 62 between the main cylinder 44 and an outer cylinder jacket 64 that communicates through a further series of ports 66 with the lower cylinder space 50.

The movement of the valve is controlled by a servo cylinder 72 formed in a cylinder block 74 fixed to the top of the ram cylinder, a piston 76 fixed to the valve sliding in the cylinder which has upper and lower ports 78, 80 above and below the piston seal respectively. The space below the servo cylinder block 74 is connected by a vent 82 to the upper cylinder space 48 and is so maintained at the same pressure as that space.

With servo pressure applied to the top of the servo piston, the valve 54 assumes the lower position shown in Figure 4 and pressure fluid is admitted to the upper cylinder space 48 driving the ram piston 42 downwards and raising the hammer weight. The lower cylinder space 50 is isolated from the space 48 at this stage and exhausts fluid through the ports 66 to an exhaust outlet 88 (Figure 2) to which a low-pressure accumulator 90 is connected When the servo connections 78, 80 are switched, by means that will be described below, the piston valve 54 rises to shut off the pressure supply to the upper cylinder space 48 and at the same time it connects the upper and lower cylinder spaces by way of the ports 60, the annular space 62, and the ports 66.Both spaces 48, 50 are then also in communication with the exhaust outlet and the hammer weight is able to fall while lifting the ram piston 42 against a residual pressure force arising from the different areas of the top and bottom faces of the piston 42. This residual pressure force maintains tension in the cable 18 and thereby avoids the danger of a slack loop of the cable becoming tangled or trapped.

As the weight falls and the ram piston rises, the free internal volume of the ram reduces so that there is a net outflow of hydraulic fluid but the immediately adjacent low-pressure accumulator 90 prevents an excessive pressure rise. During this phase of the cycle the pressure fluid input to the ram goes to charge a high-pressure accumulator 92 in direct communication with the inlet conduit 52, which so provides an adjacent reservoir of pressure fluid to assist the next expansion stroke of the ram. In this way, throttling of the inlet flow during the expansion stroke can be minimised and a faster cycle is achived without increasing the rating of the hydraulic pump supplying the ram.

It is a feature of the illustrated ram that the working or expansion stroke is made with pressure applied to the larger area side of the piston. This has advantages in giving a greater driving force for the same cylinder bore and simpler sealing arrangements, but it is clearly possible to provide a construction in which pressure is applied to the piston rod side of the piston for the working stroke of the ram.

The hydraulic circuit for the ram is shown in Figure 5. Pump 102 draws hydraulic fluid from a reservoir 104 and the pressure line 106 from the pump is directed to a threeposition manual master valve 108 that controls the admission of pressure fluid to the main ram circuit, while from a tapping in the line 106 upstream of the valve 108 a further pressure line 110 directs pressure fluid to a solenoid valve 112 that controls the flow to the servo cylinder 72. The rig operator has manual operating means (not shown) for controlling the switching of the solenoid valve 112 and is alternatively able to put the solenoid valve under automatic control of limit switches on the ram frame, as will be described below.

The manual valve 108 has three positions of adjustment and is biased to its uppermost position M1 in which the pump output is connected directly through return line 116 to the reservoir and the high pressure accumulator 92 is also connected to the reservoir, via line 118 and the valve 108, but the return flow rate from the accumulator is limited by a restrictor 120. The solenoid valve 112 is biased to its illustrated position S1 but there is insufficient pressure inthe line 110 to operate the piston valve 54.

This is the condition of the circuit on start-up of the pump, the manual valve preventing pressurisation of the main and servo hydraulic circuits. To bring the circuit to an operative state the manual valve is switched to position M3, and in so doing it passes through position M2. Because the direct return flow from the pump through line 116 is then momentarily blocked, pressure is applied through line 122 to the lower connection port 80 of the servo cylinder 72.

The piston valve 54 is thereby switched to its upper position if it is not already in that position, so that the main cylinder spaces are interconnected, which corresponds to the hammer weight being in its lowered position.

That is the position of the hammer weight, therefore, when the manual valve has been switched to position M3, in which the pump delivery line 106 is connected to the supply line 118 to the high pressure accumulator and the ram, and the return line 89 from the low pressure accumulator is connected to the reservoir 104. The ram is then ready to be operated by switching the solenoid valve so that pressure fluid is applied alternately through line 124 to the servo cylinder upper connection port 78, to cause the weight to be raised, and through the line 122 to the lower port 80 to allow it to fall again. The intermediate position M2 of the valve 108 is also a holding position in which pressure fluid is not admitted to the ram circuit and the pump flow is returned through relief valve 130, but any pressure in the high pressure accumulator is retained.

A non-return valve 132 prevents reverse flow in the pressure line. A pre-set valve 134 in the return line to the reservoir 104 is arranged to open when there is a positive, although small, pressure in the line from the ram, e.g. 20 p.s.i., to ensure that a moderate back pressure always exists in exhaust line 89 during operation. As already mentioned, the back pressure helps to maintain the hammer weight cable taut but the pressure force is kept relatively low to avoid undue retardation of the falling weight.

Intended mainly as protection when the ram is under manual control, upper and lower overstroke buffer stops 144, 146 are provided between the ram piston crosshead 28 and the unit frame 22.

The manual hydraulic control valve can be mounted in any convenient fixed position. For controlling the operation of the hammer weight, a hand-held control pendant 125 is provided, illustrated only in relation to the solenoid valve circit in Figure 6. On the pendant is a press-button switch 126 for operating the solenoid valve under manual control and Figure 6 shows an auto/manual changeover switch 138 on the pendant set to the manual operation mode (contacts 138a closed) to bring the switch 126 into use. In this state, the solenoid of the valve 112 is energised and de-energised between positions S1 and S2 solely by use of the manual switch 126.If the automatic mode is used (contacts 138b closed) the operator is also able to use a selector 140 to bring into circuit any one of a series of four spaced lower limit switches, 142a to 142d to vary the rise of the hammer weight). In each case the contracted ram position is controlled by the same upper limit switch 144. The limit switches are preferably proximity switches to avoid mechanical wear, and are operated by the movement past them of proximity detector 136 on the ram pulley crosshead.

With the automatic mode selected, the solenoid valve is controlled through relays 146, 148. At start up the operator must first energise the solenoid valve 112 using the push-button 126 to raise the hammer weight until the ram has extended sufficiently to close the normally-open upper limit switch 144. He can then release the button and the solenoid valve remains energised through selector switch contacts 138b, relay 148, upper limit switch 144, the chosen normallyclosed bottom limit switch 142 and its selector switch 140, and relay coil 146a.

The coil 146a being energised, this also closes contact 145 and thereby energises relay coil 148a to close both contacts 140, 152. With the continuing extension of the ram, the upper switch soon re-opens, but the solenoid continues to be energised via the closed contact 150. Relay coil 146a remains in circuit also, switch contacts 138a, relay contact 152, and the chosen bottom limit switch and its selector switch 140. The extending ram eventually opens the operative bottom limit switch, whereupon relay coil 146a is de-energised and its contact 145 is opened to de-energise the relay coil 148a also. The contacts 150, 152 are opened and the solenoid valve 112 is de-energised to allow the weight to fall. As the detector 136 on the rising cross-head passes the upper limit switch 144, this is re-closed to start the cycle again.

By choice of the operative lower limit switch it is possible to vary the height to which the hammer rises and so reciprocate the hammer weight with different reducedlength strokes to suit particular operating conditions. Another way of obtaining a controlled reduction of stroke length dispenses with bottom limit switches and employs instead an adjustable timer triggered by the operation of the top limit switch and causing the solenoid valve to changeover and allow the hammer weight to fall after a delay determined by the timer adjustment: the delay period then sets the hammer weight stroke. As another way of providing stroke adjustment, a variable position bottom limit switch can be employed, e.g. using a remotely controlled mechanism to displace such a switch upwards and downwardly in the unit 21.

As already mentioned, the rig shown in Figure 1 is arranged for extraction of a pile or a removable tubular steel casing of a cast in situ concrete pile, a function that it is able also to perform because of the adjustability of the ram stroke. The main lifting winch of the crane has suspended from its cable 37 a saddle 160 from which cable loops 162 extent round grooved semi-circular cheek plates 164 on the pile bearing device 10, fixed to the pile. The saddle comprises a cage round which the cable loops pass and the winch rope is resiliently connected to the saddle by a coupling that comprises compression springs 166 against which the lifting force acts.

In the extraction operation, while a steady upwards force is applied to the pile by the crane lifting winch, the weight performs a relatively short reciprocating movement impacting against the saddle cage to agitate the pile and help to free it. The springs 166 acting between the plates allow some movement relative to the cage to occur and so reduce the transmission of shock loads to the winch cable.

Figure 7 illustrates a rig analogous to that already described, arranged for driving a pile, and similar parts are indicated by the same reference numbers. The crane with its jib 4 supports the leader 2 from a lifting eye 2a but is not connected to the hammer weight 16 while the pile P is being driven.

The hydraulic drive unit 21 and its control means are of the form already described.

The cable 18 has one end attached to the hammer weight and runs over pulleys 24, 26 with its other end attached at 168 to a tubular hammer carriage 170 connected in a virtually fixed manner to cap 172 of the pile by very short sling loops 174. The carriage 170 therefore provides a datum point for the cable 18 that moves with the descent of the pile as in the first-described example. The carriage 170 is guided slidably on the leader and the weight is now guided by the carriage. The figure also illustrates hydraulic hoses 176 from the unit 21 to a pump and reservoir on the crane.

Figure 8 shows an arrangement similar in many respects to that in Figure 7, but one in which the hydraulic ram unit 21 is mounted on a short leader 2' to provide a selfcontained arrangement mounted on and supported by the pile P or the like. Parts already described in Figure 7 are indicated by the same reference numbers. The leader has a pile guide 178 fixed to its lower end in which the pile is slidably located. A buffer 179 on the leader 2' rests on the hammer carriage 170 and the weight of the leader and the drive unit 21 is transmitted through the buffer 179, the carriage 170 and the pile cap 172 to the pile itself. As in the example of Figure 7, the carriage 170 is effectively fixed relative to the pile and allows the apparatus to follow the progressive displacement of the pile.

In the further examples of the invention illustrated in Figures 9 to 11, the rope or cable from the drive unit to the hamer weight has its dither end connected to a winch drum instead of to a member fixed directly to the pile. Parts already described are again indicated by the same reference numbers. The reciprocation of the hammer weight is still effected by the drive unit and many of the advantages already referred to still are obtained if the winch is suitably controlled.

The arrangement in Figure 9 shows the drive unit again fixed in position adjacent the bottom of the leader. The rope or cable 18 from the weight 16 passes over the pulleys 24, 26 and is then led by way of a further pulley 180, attached to the drive unit, to a winch 182. The winch is so controlled that during expansion of the hydraulic ram it holds its end of the cable fixed, but when the hammer weight impacts the pile it allows cable to be paid out sufficient to match the increased length required between the weight 16 and the pulleys 24 to match the descent of the pile.

In other. words, the pattern of movement of the cable through the drive unit is the same as in the embodiments already described, and the distance through which the weight falls in each cycle is dictated by the movement of the pile independently of the stroke of the ram. When the hammer weight is to be raised for driving a further pile, the winch is already connected to reposition it.

One way of obtaining this effect is shown in Figure 12 which illustrates a hydraulic control circuit similar in many respects to the circuit of Figure 5 and having parts already described indicated by the same reference numbers. The winch 182 is provided with a friction brake 184 operated by a hydraulic cylinder 185 having a supply line 186 branched from the supply line from the solenoid valve 112 to the upper ram servo connection 78. When the connection 78 is energised to begin the extension of the ram, the line 186 is simultaneously pressurised to brake the winch and the end of the cable on the winch is thus held fixed as the hammer weight is raised.When pressure is taken off the connection 78 to allow the hammer weight to fall, the brake cylinder pressure is also released and the cable can run off the winch drum to follow the movement of the pile as it is impacted, only a residual braking force then being felt at the winch drum, sufficient to maintain the cable taut.

It is also possible to apply a continuous braking force to the winch drum, greater than the force required to lift the hammer weight, but allowing the momentum of the weight after it has impacted the pile to draw cable off the drum so that the weight is able to move downwards with the pile.

Figures 10 and 11 show arrangements similar to that in Figure 9, with the same control means but with the drive unit 21 and the winch 182 mounted at the top of the leader for use in underwater pile driving and extraction. It will be clear from the drawings that in this way all the driving and control mechanism can be kept above the water line W. The cable 18 is shown connected to the hammer weight through multiple sheaves 190, 192 to permit very large hammer weights to be operated.

In Figure 11 the drive unit is mounted in an inverted position to that which it has in the previous embodiments, but its construction and operation are as already described.

In Figure 10, the cable 18 has one end wound on the winch drum and the other end attached to the upper sheave 190, which is itself suspended from a further short rope or cable 194 fixed to the leader. In Figure 11, the upper end of the cable 194 is attached to the ram piston rod instead of the leader, which gives a similar result to the arrangement in Figure 10 but alters the mechanical advantage between the ram and hammer weight movements.

It will be noted that in all the configurations described, with the mounting of the ram 20 in its frame 22 the hydraulic drive can be produced as a unit that is readily added to existing rigs, or that can be employed in other apparatus. The unit may be applicable to a wide range of equipment in which a reciprocating actuator is required for delivery impacts to a displaceable elongate member, for example, rock hammers, forging hammers, punches and presses, and can be constructed in a wide range of sizes.

WHAT WE CLAIM IS: 1. .Impact apparatus comprising a leader, a hammer weight being guided on said leader for generating an impact force to act on a displaceable member, a hydraulic ram mounted at a fixed position relative to the leader, and a rope or cable from which the weight is suspended being operable by said ram to raise the weight, said rope or cable being connected to means that are adapted to allow the weight to follow the displacements of the member independently of the stroke of said ram as reciprocating operation of the ram causes the weight to generate a series of impacts.

2. Impact apparatus according to claim 1 wherein the ram is in a hydraulic circuit that comprises means for maintaining a minimum positive pressure in the ram during the fall of the weight so as to keep the rope or cable in tension without substantially retarding the fall of the weight.

3. Impact apparatus according to claim 2 wherein said means in the hydraulic circuit comprise means for applying a biasing force to the ram tending to keep it in engagement with the rope or cable and means for restricting fluid flow from the ram during the fall of the hammer weight.

4. Impact apparatus according to any one of claims 1 to 3 wherein the rope or cable has one end connected to an element that is in use secured or is adapted to be secured to the member.

5. Impact apparatus according to claim 4 wherein the ram is secured on the leader and the leader is arranged to be mounted on and supported by the displaceable member whereby the apparatus can be removably positioned as a unit on the displaceable member.

6. Impact apparatus according to any one of claims 1 to 3 wherein the rope or cable has one end connected to a winch drum from which it can be paid out or reeled in to allow changes in the mean position of the reciprocable hammer weight.

7. Impact apparatus according to claim 6 wherein the winch drum has a friction brake for maintaining a minimum tension in the rope or cable and providing a resistance to movement of the rope or cable by the ram greater than the tension from the hammer weight whereby extension of the ram raises the hammer weight.

8. Impact apparatus according to claim 6 wherein the winch drum has brake control means operated by means responsive to the movement of the ram, whereby said control means holds the drum fixed during the rise of the weight and allows the rope or cable to

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. One way of obtaining this effect is shown in Figure 12 which illustrates a hydraulic control circuit similar in many respects to the circuit of Figure 5 and having parts already described indicated by the same reference numbers. The winch 182 is provided with a friction brake 184 operated by a hydraulic cylinder 185 having a supply line 186 branched from the supply line from the solenoid valve 112 to the upper ram servo connection 78. When the connection 78 is energised to begin the extension of the ram, the line 186 is simultaneously pressurised to brake the winch and the end of the cable on the winch is thus held fixed as the hammer weight is raised.When pressure is taken off the connection 78 to allow the hammer weight to fall, the brake cylinder pressure is also released and the cable can run off the winch drum to follow the movement of the pile as it is impacted, only a residual braking force then being felt at the winch drum, sufficient to maintain the cable taut. It is also possible to apply a continuous braking force to the winch drum, greater than the force required to lift the hammer weight, but allowing the momentum of the weight after it has impacted the pile to draw cable off the drum so that the weight is able to move downwards with the pile. Figures 10 and 11 show arrangements similar to that in Figure 9, with the same control means but with the drive unit 21 and the winch 182 mounted at the top of the leader for use in underwater pile driving and extraction. It will be clear from the drawings that in this way all the driving and control mechanism can be kept above the water line W. The cable 18 is shown connected to the hammer weight through multiple sheaves 190, 192 to permit very large hammer weights to be operated. In Figure 11 the drive unit is mounted in an inverted position to that which it has in the previous embodiments, but its construction and operation are as already described. In Figure 10, the cable 18 has one end wound on the winch drum and the other end attached to the upper sheave 190, which is itself suspended from a further short rope or cable 194 fixed to the leader. In Figure 11, the upper end of the cable 194 is attached to the ram piston rod instead of the leader, which gives a similar result to the arrangement in Figure 10 but alters the mechanical advantage between the ram and hammer weight movements. It will be noted that in all the configurations described, with the mounting of the ram 20 in its frame 22 the hydraulic drive can be produced as a unit that is readily added to existing rigs, or that can be employed in other apparatus. The unit may be applicable to a wide range of equipment in which a reciprocating actuator is required for delivery impacts to a displaceable elongate member, for example, rock hammers, forging hammers, punches and presses, and can be constructed in a wide range of sizes. WHAT WE CLAIM IS:

1. .Impact apparatus comprising a leader, a hammer weight being guided on said leader for generating an impact force to act on a displaceable member, a hydraulic ram mounted at a fixed position relative to the leader, and a rope or cable from which the weight is suspended being operable by said ram to raise the weight, said rope or cable being connected to means that are adapted to allow the weight to follow the displacements of the member independently of the stroke of said ram as reciprocating operation of the ram causes the weight to generate a series of impacts.

be paid out with descent of the mean position of the reciprocable hammer weight.

9. Impact apparatus according to any one of claims 6 to 8 arranged for underwater piling operations and wherein the ram and the winch are located at the top of the leader in a region arranged to be disposed above water level.

10. Impact apparatus according to any one of the preceding claims wherein the ram has a bypass connection between the end spaces of its cylinder on opposite sides of the ram piston, and valve means are provided for said connection whereby fluid is allowed to flow from the contracting end space to the expanding end space during the fall of the hammer weight.

11. Impact apparatus according to claim 10 wherein the ram has a piston rod extending from its lower end and said bypass valve means are disposed at the upper end of the cylinder above the piston.

12. Impact apparatus according to any one of the preceding claims wherein the ram carries a pulley sheave around which the rope or cable passes and which is displaced with the reciprocation of the ram to move the weight with a mechanical advantage.

13. Impact apparatus for displacing an elongate member, comprising a leader, a hammer weight guided on said leader for generating an impact force to act on the elongate member, a hydraulic ram mounted at a fixed position relative to the leader and being reciprocable by hydraulic pressure supply and control means to act on a rope or cable having one end connected to the hammer weight for reciprocating the weight, the rope or cable having its other end connected to an anchorage on said elongate member whereby the position of the rope or cable is adjusted with displacement of the elongate member during the operation of the apparatus to allow the hammer weight to follow displacements of the elongate member independently of the reciprocation of the ram as said reciprocation causes successive impulses to be applied to the elongate member said hydraulic supply and control means being arranged to co-operate with the ram to apply a force through the ram to the rope or cable element during the fall of the weight to maintain tension in said rope or cable without significantly retarding the fall of the hammer weight.

14. Impact apparatus for displacing an elongate member, comprising a leader, a hammer weight.guided on said leader for generating an impact force to act on the elongate member, a hydraulic ram mounted at a fixed position relative to said leader and being reciprocable by hydraulic pressure supply and control means to act on a rope or cable having one end connected to the weight so that reciprocation of the ram causes said reciprocation of the hammer weight, the opposite end of the rope or cable being connected to a winch drum that is rotatable for adjustment of the length of the rope or cable in use, there being friction brake means for said drum arranged to be adjustable by said hydraulic pressure supply and control means in order to hold the winch drum locked against rotation during the ram stroke raising the hammer weight in each cycle of reciprocation and to reduce the braking force during the return stroke in each said cycle when the hammer weight is allowed to fall, whereby the weight is able to draw out a further length of rope or cable from the winch drum without substantial resistance when it falls below a previous bottom position while said supply and control means are arranged to co-operate with the ram to apply a force through the ram to the rope or cable during said fall of the weight to maintain tension in said rope or cable without significantly retarding the fall on the weight.

15. Impact apparatus according to claim 9 wherein the hammer weight is suspended from further pulley sheaves whereby to increase the mechanical advantage of the ram.

16. Impact apparatus for driving and/or extracting an elongate member constructed and arranged for use and operation substantially as described herein with reference to any of the embodiments illustrated in the accompanying drawings.