US3695473A

US3695473A - Tag line control mechanism

Info

Publication number: US3695473A
Application number: US84717A
Authority: US
Inventors: Robert W Martin
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-10-28
Filing date: 1970-10-28
Publication date: 1972-10-03
Anticipated expiration: 1989-10-03

Abstract

A control mechanism for a tag line extending from a drum on the crane chassis to a clam shell bucket or similar lifting instrumentality suspended in the normal manner by the crane. The tag line drum is powered by stored hydraulic pressure for tensioning of the tag line to prevent undesired bucket movement. Drum rotation occurs as the clam shell bucket is lowered with such rotation being translated into piston movement to charge a fluid pressure accumulator. Oppositely, raising of the clam shell bucket, resulting in lessening of tag line tension, permits the stored hydraulic pressure to rewind the drum to maintain desired tension on the tag line. A sprocket and chain assembly in combination with reduction gearing serves to translate rotary drum movement into rectilinear piston movement and vice versa.

Description

United States Patent Martin [54] TAG LINE CONTROL MECHANISM [72] lnventor: Robert W. Martin, 7102 N. E. 63rd Ave., Vancouver, Wash. 98661 221 Filed: 0a. 28, 1970 211 App]. No.: 84,717

[52] US. Cl ..2l4/657, 74/8929, 242/54 R,

254/186 [51] Int. Cl ..B66c 23/94 [58] Field of Search ..2l4/656, 59 A, 657, 59 R; 74/25, 89.2, 89.21; 254/186; 242/54 R;

[56] References Cited UNITED sTATEs PATENTS 2,185,101 12/1939 Brell ..74/25 x FOREIGN PATENTS OR APPLICATIONS 1,007,040 4/1957 Germany ..2l4/657 14 1 Oct. 3, 1972 Primary Examiner -Gerald M. Forlenza Assistant Examiner-George F. Abraham Att0rneyJames D. Givnan, Jr.

[57] ABSTRACT A control mechanism for a tag line extending from a I drum on the crane chassis to a clam shell bucket or similar lifting instrumentality suspended in the normal manner by the crane. The tag line drum is powered by stored hydraulic pressure for tensioning of the tag line to prevent undesired bucket movement. Drum rotation occurs as the clam shell bucket is lowered with such rotation being translated into piston movement to charge a fluid pressure accumulator. Oppositely, raising of the clam shell bucket, resulting in lessening of tag line tension, permits the stored hydraulic pressure to rewind the drum to maintain desired tension on the tag line. A sprocket and chain assembly in combination with reduction gearing serves to translate rotary drum movement into rectilinear piston movement and vice versa.

7 Claims, 5 Drawing Figures PATENTEDnma m2 3,695,473

sum 1 or 2 I INVENTOR. ROBERT W. MARTIN AGENT PATENTEnnma 1912 3,695,473

SHEET 2 OF 2 I NVENTOR.

ROBERT W. MARTIN AGENT TAG LINE CONTROL MECHANISM BACKGROUND OF THE INVENTION The present invention relates generally to a mechanism for powering a tag line carrying drum of a crane with the outer end of the tag line beingin attachment with a lifting instrumentality carried by a crane.

The prior art discloses various mechanical arrangements for the tensioning of tag lines, which arrangelo SUMMARY OF THE INVENTION The present invention is embodied within a mechanism carried by a crane wherein a tag line drum and tag line are utilized for retaining the load carrying instrumentality against undesired oscillation or twisting. The weight of the bucket is advantageously used to unreel the tag line drum for resultant transfer of hydraulic fluid into an accumulator. The subsequent reverse flow of the fluid into the hydraulic cylinder imparts a winding force to the drum for tensioning of the tag line during raising of the clam shell bucket. Otherwise stated, drum rotation during unreeling is translated into piston movement exhausting fluid from a cylinder and into an accumulator while oppositely the stored fluid pressure is later used to tension the tag line and hence retain the clam shell bucket against undesired movement. Accordingly, by so using the weight of the lifting instrumentality several components necessary in prior art tensioning mechanisms may be dispensed with resulting in obvious advantages.

A second form of the invention includes an operator controlled valve and a secondary source of fluid pressure for directing fluid through a blank hydraulic cylinder for regulating the quantity of fluid entering the accumulator and first mentioned hydraulic cylinder. In this form of the invention means are provided for insuring the proper relationship of piston rod extension (and hence tag line extension) to accumulator pressure. The blank hydraulic cylinder includes a free floating piston which expels a specific quantity of oil during one stroke of the piston. The accumulator feature is common to both forms of the invention as is the hydraulic cylinder with its mechanical power transmission means connecting same to the tag line drum.

In both forms of the invention the tag line drum is operatively associated, through gear elements and a roller chain, with the piston rod of a hydraulic cylinder for extraction of said piston rod upon paying out of the tag line under the influence of a bucket weight. Upon subsequent lifting of a loaded bucket stored fluid pressure acts to bias the piston in an opposite direction to assure proper tensioning of the tag line. One of the desired features of the present invention is thereby provided i.e., the provision for tensioning the tag line to prevent bucket rotation or oscillation. i

A further object is to provide a tag line tensioning mechanism automatic in its operation yet not susceptible to periodic failure as occurs with spring biased tag lines. The latter type of tag line arrangements, in addi' tion to an inherent spring fatigue problem, has a limited capability to exert tension on the tag line when substantial distances exist between the load pick-up site and the discharge site. Considerable winding of the spring or springs occurs during each bucket loading cycle resulting in early spring failure.

A further object of the prevent invention is to permit the crane operator to position the bucket (or other load handling instrumentality) horizontally without booming up or booming down to move the bucket in or away from the crane. As in some bucket loading situations the discharge site has a different horizontal component from the crane machine than the loading or pick-up site. Bucket position between the two positions is commonly accomplished by inclining movement of the crane boom as conventional spring biased tag lines are of no assistance in such bucket placement.

A modified form of the invention provides an operator control valve by which the operator may, if desired, control the movement of the piston rod for rewinding of the tag line or oppositely for slackening of the tag line. In this form of the invention a blank (no rod) hydraulic cylinder is added to the basic components to assure a proper relationship between accumulator pressure and rod extension or stated in another way accumulator pressure and the length of'unreeled tag line. In operations where the vertical component of bucket travel is not adequate to cause full pressurization of the accumulator during each cycle of operation a pump in the second form of the invention may be relied upon.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a side elevational view of the tag line control mechanism in place on a structural member of a crane the latter fitted with a boom and clam shell bucket,

FIG. 2 is a plan view of the tag line control mechanism taken downwardly along line 2 2 of FIG.

FIG. 3 is an enlarged detail view of the tag line mechanism of FIG. 1 with the piston rod retracted into a tag line retrieved position,

FIG. 4 is an enlarged detail view taken along line 4- 4 of FIG. 3 showing details of the piston rod and roller chain attachment, and

FIG. 5 is a view similar to FIG. 1 showing a modified form of the invention with associated components disclosed in schematic form.

DESCRIPTION OF PREFERRED EMBODIMENTS With continuing reference to the drawings wherein applied reference numerals indicate parts similarly identified in the following specification, the reference numeral 1 of FIG. 1 indicates a structural member of a crane machine which may be the cranes turntable which characteristically mounts the usual crane components such as the engine, transmission, cable drums and controls therefor. The last mentioned components do not require alteration to permit use of the present invention and hence their further discussion is believed unnecessary.

Secured in place upon the structural member 1 is a box-like housing structure 2, as best seen in FIGS. 1 and 2, which serves conveniently to mount the'following described tag line control mechanism components. A tag line drum is indicated at 3 having a length of tag line cable 4 coiled thereabout of sufficient length to permit the normal travel of a clam shell bucket indicated at 5. The bucket, not being part of the present invention, may be of any suitable design for suspension from the cranes boom 6 typically by a hoist line 7 and a closing line 8.

Returning to the tag line control mechanism components a shaft 10, rotatably with drum 3, is suitably journalled in upright walls 2A of the housing. Shaft 10 additionally carries a first rotatable guide such as spur gear at 1 1. Enmeshed with the spur gear 1 l is a second rotatable guide such as spur gear 12 of greater diameter which may for example be a forty tooth gear while spur gear 1 1 may be a 12 tooth gear.

A shaft 13 is also journalled in the housing walls 2A and carries the spur gear 12 and further, mounts a flexible member or roller chain sprocket 14, the latter keyed to shaft 13 for rotation therewith and with spur gear 12. From the foregoing it will be understood that upon rotation of tag line drum 3, the spur gears 11 and 12 as well as sprocket 14 will all rotate with spur gear 12 and sprocket 14, on shaft 13, rotating oppositely to the direction of the drum and spur gear 1 l.

Spaced from sprocket 14 is a companion of idler sprocket 15. of like size and number of teeth with the sprocket 15 being rotatably mounted upon a shaft at 16 also journalled within the housing walls 2A. A flexible member in the form of a length of roller chain 17 extends about the sprockets with its ends being in attachment to a rod end clevis 20 of a piston rod 21 of a single-acting hydraulic cylinder 22. Accordingly, upon rectilinear movement of piston rod 21 the roller chain 17 will rotate sprockets l5 and 14 in a like direction. Details of the chain attachment to the clevis 20 are shown in FIG. 4 wherein a pin 23 extends through clevis 20 and through aligned link and roller openings in opposite ends of the roller chain 17.

Hydraulic cylinder 22, at its rod end 19, has a port in communication with a fluid conduit 24 through which hydraulic fluid passes between the cylinder 22 and a pre-charged fluid pressure accumulator at 25. The hydraulic cylinder may be of a two inch bore with its blank end vented and a stroke of twenty four inches while the accumulator is preferably of a V2 gallon capacity precharged to 1,500 PSI in a typical embodiment of the invention. The foregoing components are subject to variation to suit the particular requirements of the crane, the clam shell bucket and the job at hand.

In operation of the first described form of the invention with the clam shell bucket empty and in a raised or load discharge position the piston rod 21 of cylinder 22 is in a retracted position by reason of the fluid pressure of the accumulator. For subsequent loading of the bucket 5, the crane boom 6 is positioned to spot the suspended clam shell bucket over the loading site. During this spotting of the bucket, the bucket is restrained against undesired rotation or oscillation by the tag line exerting a pull thereon. If the boom 6 requires lowering to spot the bucket over the load, the buckets weight is such as to cause partial extension of piston rod 21. If

raising of the boom 6 is required for bucket placement, a consequent reduction in tag line tension permits piston rod 21 to be partially retracted with rewinding of the tag line occurring. Accordingly, the desired precharge of the accumulator and the bucket weight (empty) are closely related in each embodiment of the invention.

Upon the crane operator paying out the cranes hoisting line 7 the descending bucket acts to further extend piston rod 21. The counter-clockwise rotation of drum 3 and spur gear 11 will impart clockwise rotation to spur gear 12 and sprocket 14 to accomplish further extension of piston rod 21 via the roller chain segment intermediate sprocket 14 and the rod end. Oil ahead of the piston in cylinder 22 is forced out of the piston via conduit 24 into the accumulator. Full extension of rod 21 will result in a maximum accumulator and system pressure of approximately 3,000 PSI. With the spur gears above described the tag line drum 3 and its spur gear 11 rotate on a 3% to 1 ratio to spur gear 12 and sprocket 14 on shaft 13. The length of the tag line 4 will be such as to be fully payed out upon full extension of piston rod 21. Obviously abnormal vertical distance travelled by the bucket from a loading to discharge site may require variations in the components.

With the bucket in place and closed about a load of material to be lifted, raising of the bucket by the hoist line 7 past sheaves 26 will reduce the tension on the tag line to the extent that the fluid pressure inthe accumulator (approx. 3,000 PSI) may act to rearwardly' move the piston in cylinder 22 thus retracting rod 21 as the bucket is raised. Throughout lifting of the bucket the tag line 4 is tensioned to prevent undesired bucket movement. The crane operator may continue lifting of the bucket as same is moved (by simultaneous boom positioning) to a discharge site which is standard practice.

In this form of the invention the tag line mechanism operates automatically with no operator controls provided or necessary. It is to be noted that although automatically operating spring operator tag lines have been used in the past they are unsuitable for use with certain crane operations as earlier noted. Further, the foregoing embodiment is not limited to use with a clam shell bucket but rather has equally useful applications with other load lifting instrumentalities.

In the second described form of the invention as shown in FIG. 5 previously described components are again utilized and are indicated by prime reference numerals.

The modified form of the invention primarily differs from that first described in that an operator control is provided along with the addition of other hydraulic components.

The tag line drum 3' carries a quantity of tag line 4 which is attached at its outer end to a clam shell bucket or other load lifting instrumentality. The housing 2 is in place on the crane structure 1 and serves to mount spur gears 11', 12' on shafts 10' and 13' with the latter also carrying a sprocket 14. A chain 17' extends about sprockets 14 and its companion or idler sprocket 15 suitably journalled with housing 2. A cylinder 22 includes piston rod 21 in attachment at its outer end with the ends of chain 17' all as previously described. An accumulator 25' is in hydraulic communication with the cylinder 22.

' Extending from the rod end of the cylinder is a fluid conduit 30 terminating in a pilot operated two way valve 31. Pressurized fluid for operation of pilot valve 31 enters the valve via a line 32 as more fully described later. Valve 31 in the absence of pressure in line 32 is open for transfer of fluid between the cylinder 22' and accumulator 25' while oppositely (with pressure in line 32) closes off fluid transfer therebetween.

Indicated at R is a fluid reservoir from which a positive displacement pump 33 draws for delivery via conduit 35 of fluid to a manually operated three position,

four way valve 34. Pilot operated relief valves at 36, 37

are upstream and downstream from valve 34 and function respectively to unload fluid pressure at desired set points. A flow control valve at 38 is in communication with the operator actuated valve 34 via a line 40 with the flow control valve 38 embodying both a return check and flow control means the latter to enable control of the rate of return flow to the reservoir R.

A blank cylinder at 41 receives fluid at one of its ends via a line 42 for admitting fluid against a floating piston 43. The opposite end of blank cylinder 41 is in communication, via a line 44, with the conduit 30 serving hydraulic cylinder 22'. Further, fluid from blank cylinder 41 may enter accumulator upon pilot valve 31 being in an open position.

In operation the pump 33, which is preferably in continuous operation to importantly avoid constant startings, delivers pressure to the operator controlled valve 34. With the latter valve in C position pumped fluid flows through flow control valve 38 past the check therein to one side of blank cylinder 41 to pressurize same. Simultaneously fluid pump pressure via pilot line 32 repositions pilot valve 31 to a closed position to isolate accumulator 25'. Fluid pressure in the left hand end of blank cylinder 41 and line 44 results in fluid being directed into the rod end of cylinder 22' for pressurizing the rod side of piston rod 21. Accordingly, as the loaded bucket is raised the tag line 4' will be reeled in to the extent necessary to spot the bucket in place over the discharge site.

With the bucket inward of the end of the boom and raised to the height necessary, for unloading purposes, the operator will position his control valve 34 to B position whereat pump fluid is returned to the reservoir with the system pressure, upstream from valve 34, being held. B position of valve 34 results in a static pressure in hydraulic cylinder 22 assuming the bucket and boom are stationary. Assuming it has been necessary to pull the bucket at the end of tag line 4' inwardly for spotting of same, a portion of the fluid in blank cylinder 41 will have been transferred into the rod end of cylinder 22'. Maximum inward positioning of the bucket would be affected by the entire displacement of fluid from cylinder 41 into the rod end of cylinder 22'.

After discharge of the inwardly located loaded bucket it is necessary to relieve the fluid pressure in the rod end of cylinder 22' to permit extension of its rod 21' and ultimately pay out of tag line 4'. This is accomplished by positioning valve 34 to A position whereby the pump output is again directed to the tank while pressure upstream of valve 34 is also vented to the tank. Accordingly, fluid in the rod end of cylinder 22 may now exhaust via conduit and line 44 into cylinder 41 with consequent return of piston 43 to the right as seen in FIG. 5. In each cycle of operation all fluid initially forced out of cylinder 41 and into cylinder 22 is oppositely returned to cylinder 41 upon piston rod extraction by the unloaded bucket as it swings outwardly to its loading position below the boom end.

An additional result of unloading the system above valve 34 and particularly pilot line 32 is the repositioning of valve 31 to an open position. Continued extraction of piston rod 21' by the weight of the outwardly moving bucket will cause the additional fluid (to that already returned to cylinder 41) exhausted from cylinder 22' to pass pilot valve 31 and enter accumulator 25'.

A desired relationship is thereby retained between accumulator pressure and rod extension as the volume of extra fluid delivered into cylinder 22' from cylinder 41 is returned to cylinder 41.

Initial setting up of the mechanism of FIG. 5 would entail the locationing of the bucket in close proximity to the tag line drum in which case the accumulator precharge pressure of 1,500 PSI would be exerting a minimum tension on tag line 4'. Booming down of the cranes boom will cause gravitational swinging movement of the bucket to a location below the boom tip during which movement the tag line 4 is pulled off reel 3. Consequent extraction of rod 21', the extent of which is determined by the travel of the bucket, .will determine the accumulator pressure.

As in the first fonn of the invention the tag line 4' is at all times tensioned to exert a controlling force on the bucket to prevent undesired random movement of same. The second fonn of the invention particularly is directed toward avoiding constant boom positioning between a bucket pick up site and a discharge site. The additional fluid transferable into cylinder 22 from blank cylinder 41 permits reeling in of the tag line 4' to move the bucket inward of its normal position below the boom tip. This is accomplished by the supplemental fluid from cylinder 41 without upsetting the relationship of rod extension to accumulator pressure. Stated another way the purpose of the floating piston in hydraulic cylinder 41 is to control the amount of fluid in the system, cylinder 22 and accumulator 25', so that regardless of the point at which the operator applies ad ditional line pull through the pump system or releases that pressure, the proper relationship of cylinder rod extension and accumulator pressure is maintained.

While I have shown but two embodiments of the invention, it will be apparent to those skilled in the art that the invention may be embodied still otherwise without departing from the spirit and scope of the invention.

Having thus described the invention what is desired to be secured under a Letters Patent is:

1. A tag line control mechanism for use in conjunction with a crane suspended lifting instrumentality, said control mechanism comprising,

a tag line drum and shaft assembly rotatably carried by the crane with a length of tag line wound upon the drum and extending outwardly terminating in attachment to the instrumentality,

a hydraulic cylinder with a displaceable piston and piston rod,

a pre-charged accumulator in fluid communication with one end of said cylinder,

power transmission means acting intermediate the tag line drum shaft and the outer end of the piston rod for converting rotational movement of said shaft during paying out of the tag line during lowering of the instrumentality to a linear force for extracting the piston rod whereby the accumulator is additionally charged,

said accumulator with the pressure so stored being utilized oppositely to retract the piston rod in the presence of reduced tag line tension during lifting of the loaded instrumentality,

a two position pilot operated valve controlling fluid flow into and out of said accumulator,

a blank hydraulic cylinder having a pressure responsive piston therein with the cylinder in communication at one of its ends with said hydraulic cylinder and in communication with said accumulator via said two position valve whereby fluid pressure from said accumulator and said blank hydraulic cylinder may actuate the piston rod of said hydraulic cylinder,

a fluid pump supplied with a source of fluid, and

an operator controlled valve for directing the output of said pump into the other end of said blank cylinder causing the piston therein to pressurize the first mentioned hydraulic cylinder supplementary to accumulator pressure to further retract its piston rod for additional retrieval of the tag line causing off vertical inward movement of the lifting instrumentality during raising of same, said pilot operated valve simultaneously positioned during such pressurization to block off the accumulator from receiving fluid pressure originating in said blank cylinder, said operator controlled valve additionally positionable to relieve upstream pressure to permit the discharge of fluid from the first mentioned hydraulic cylinder during extraction of the piston rod directing the fluid into said blank cylinder with additionally exhausted fluid entering the accumulator whereby the relationship between accumulator pressure and tag line extension is retained regardless of supplementary fluid being temporarily added to the first mentioned hydraulic cylinder from the blank cylinder, such supplementary fluid being for the purpose of retrieving the tag line and instrumentality inward of a normal vertical position below the crane boom end.

2. The tag line control mechanism as claimed in claim 1 wherein said power transmission means includes a length of roller chain and a pair of sprockets carrying said chain, said length of chain connected at its ends to the piston rod.

3. The tag line control mechanism as claimed in claim 2 wherein said sprockets locate at least a segment of said chain for rectilinear movement along a course in axial alignment with said hydraulic cylinder and its piston rod.

4. The tag line control mechanism as claimed in claim 3 additionally including a pair of meshing gear elements one of which is carried by the tag line drum shaft, the other of said gear elements being mounted coaxially for rotation with one of the sprockets for driving the tag line drum shaft and said one of the sprockets in gne g lirectior rof rotation.

. e tag me control mechanism as claimed in claim 2 wherein said sprockets are journalled for rotation about fixed axes, one of said axes being located adjacent the outermost point of travel of the piston rod and the remaining sprocket axis being located adjacent the retracted position of the piston rod.

6. In combination with the tag line drum of a crane having a tag line terminating outwardly in attachment with a lifting instrumentality for tensioning of the line during lowering of the instrumentality and automatic retrieving of the line during raising of the instrumentality, the improvement comprising,

a hydraulic cylinder having a piston and piston rod,

a pre-charged accumulator in fluid communication with the rod end of said cylinder for reception of fluid exhausted from the cylinder during piston rod extraction with the fluid exhausted from the cylinder further charging the accumulator,

power transmission means intermediate the tag line drum and the piston rod for translating rotational movement of the drum during paying out of the tag line into a linearly directed force exerted axially of the piston rod to extract same, said power transmission means including elongate flexible means comprising a segment coupled to the piston rod for exerting said linearly directed force thereon, said power transmission means further including rotatable guide members for entrainment of said segment with said rotatable guide members located adjacent the inner and outer limits of piston rod travel to locate a run of the segment in alignment with the piston rod, and

said flexible means also operable -in an opposite direction during retraction of the piston rod by accumulator pressure in the presence of a reduced tension on the tag line during raising of the lifting instrumentality to impart retrieving rotation to the tag line drum.

7. The improvement as claimed in claim 6 wherein said segment terminates at its end in attachment with the piston rod.

Claims

1. A tag line control mechanism for use in conjunction with a crane suspended lifting instrumentality, said control mechanism comprising, a tag line drum and shaft assembly rotatably carried by the crane with a length of tag line wound upon the drum and extending outwardly terminating in attachment to the instrumentality, a hydraulic cylinder with a displaceable piston and piston rod, a pre-charged accumulator in fluid communication with one end of said cylinder, power transmission means acting intermediate the tag line drum shaft and the outer end of the piston rod for converting rotational movement of said shaft during paying out of the tag line during lowering of the instrumentality to a linear force for extracting the piston rod whereby the accumulator is additionally charged, said accumulator with the pressure so stored being utilized oppositely to retract the piston rod in the presence of reduced tag line tension during lifting of the loaded instrumentality, a two position pilot operated valve controlling fluid flow into and out of said accumulator, a blank hydraulic cylinder having a pressure responsive piston therein with the cylinder in communication at one of its ends with said hydraulic cylinder and in communication with said accumulator via said two position valve whereby fluid pressure from said accumulator and said blank hydraulic cylinder may actuate the piston rod of said hydraulic cylinder, a fluid pump supplied with a source of fluid, and an operator controlled valve for directing the output of said pump into the other end of said blank cylinder causing the piston therein to pressurize the first mentioned hydraulic cylinder supplementary to accumulator pressure to further retract its piston rod for additional retrieval of the tag line causing off vertical inward movement of the lifting instrumentality during raising of same, said pilot operated valve simultaneously positioned during such pressurization to block off the accumulator from receiving fluid pressure originating in said blank cylinder, said operator controlled valve additionally positionable to relieve upstream pressure to permit the discharge of fluid from the first mentioned hydraulic cylinder during extraction of the piston rod directing the fluid into said blank cylinder with additionally exhausted fluid entering the accumulator whereby the relationship between accumulator pressure and tag line extension is retained regardless of supplementary fluid being temporarily added to the first mentioned hydraulic cylinder from the blank cylinder, such supplementary fluid being for the purpose of retrieving the tag line and instrumentality inward of a normal vertical position below the crane boom end.

4. The tag line control mechanism as claimed in claim 3 additionally including a pair of meshing gear elements one of which is carried by the tag line drum shaft, the other of said gear elements being mounted coaxially for rotation with one of the sprockets for driving the tag line drum shaft and said one of the sprockets in one direction of rotation.

5. The tag line control mechanism as claimed in claim 2 wherein said sprockets are journalled for rotation about fixed axes, one of said axes being located adjacent the outermost point of travel of the piston rod and the remaining sprocket axis being located adjacent the retracted position of the piston rod.

6. In combination with the tag line drum of a crane having a tag line terminating outwardly in attachment with a lifting instrumentality for tensioning of the line during lowering of the instrumentality and automatic retrieving of the line during raising of the instrumentality, the improvement comprising, a hydraulic cylinder having a piston and piston rod, a pre-charged accumulator in fluid communication with the rod end of said cylinder for reception of fluid exhausted from the cylinder during piston rod extraction with the fluid exhausted from the cylinder further charging the accumulator, power transmission means intermediate the tag line drum and the piston rod for translating rotational movement of the drum during paying out of the tag line into a linearly directed force exerted axially of the piston rod to extract same, said power transmission means including elongate flexible means comprising a segment coupled to the piston rod for exerting said linearly directed force thereon, said power transmission means further including rotatable guide members for entrainment of said segment with said rotatable guide members located adjacent the inner and outer limits of piston rod travel to locate a run of the segment in alignment with the piston rod, and said flexible means also operable in an opposite direction during retraction of the piston rod by accumulator pressure in the presence of a reduced tension on the tag line during raising of the lifting instrumentality to impart retrieving rotation to the tag line drum.