US2935049A - Safety mechanism for lifting devices - Google Patents

Description

y 1960 w. F. KRENNING 2,935,049

SAFETY MECHANISM FOR LIFTING DEVICES Filed Jan. 15, 1958 '4 Sheets-Sheet 1 llllull lll Ills! llill ll |l ||||l||. lllll. .llll

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SAFETY MECHANISM FOR LIFTING DEVICES Filed Jan. 13, 1958 4 Sheets-Sheet 2 Mum Ir? KEEN/V/NG 6250afly Ari-K May 3, 1960 w. F. KRENNING 2,935,049

SAFETY MECHANISM FOR LIFTING DEVICES Bf W ' tion so they cannot fall.

United States.

i SAFETY MECHANISM FOR LIFTING DEVICES William F. Krenning, St. Louis, Mo., assignor to Curtis Manufacturing Company, St. Louis, Mo., a corporation of Missouri This invention relates to improvements in lifting devices. provements in safety mechanisms for lifting devices.

It is therefore an object of the present invention to provide an improved safety mechanism for lifting devices.

In the operation of lifting devices, and in particular in the operation of plunger-type lifts for automobiles, it is desirable to lock the lifting devices in elevated posi- In recognition of this fact, a number of different safety mechanisms have been proposed for lifting devices, and some of those safety mechanisms have been used. Some of those safety mechanisms have not been as positive in action as they could, or should, be; and other of those safety mechanisms have been unduly complicated. The present invention obviates these disadvantages by providing a safety mechanism for lifting devices which is both positive in action and-simple in construction.

The safety mechanism provided by the present invention has retractible and extendable pins that are retracted whenever the lifting device is in its lowered position and that are extended into locking position whenever the lifting device is in its raised positions. The pins are biased to. extended position by springs, and they move promptly into extended position as the lifting device moves to its elevated positions; and those locking pins thereupon prevent accidental lowering, or falling, of the lifting device. As a result, if the hydraulic or pneumatic pressure of the lifting device were to fail and the lifting device were to start downward, the locking pins would promptly check that downward movement and thereby prevent injury to persons adjacent the lifting device and also prevent injury to the objects raised by the lifting device. It is therefore an object of the present invention to provide a lifting device with locking pins that are springbiased to extended position to prevent accidental lowering of the lifting device.

A manually-operable cam is carried by the plunger of the lifting device, and that cam can 'rnove the locking pins to retracted position and thereby permit lowering of the plunger of the lifting device. That cam will maintain the locking pins in retracted position until the plunger is almost fully telescoped within its cylinder, and thereafter that cam will free the locking pins for extending movement. The cylinder will prevent any extending movement of those locking pins until the plunger is elevated; and thereafter those pins can, and will, move to locking position.

Other and further objects and advantages of the present invention should become apparent from an examination I of the drawing and accompanying description.

A atent Q More particularly, this invention relates to imree In the drawing:

Fig. 1 is a plan view of a lifting device that is made in accordance with the principles and teachings of the present invention,

Fig. 2 is a front elevational view of the lifting device' of Fig. 1, and it shows the safety mechanism and cylinder of that lifting device embedded within the ground,

Fig. 3 is a sectional view, in elevation, through the safety mechanism of the lifting device of Figs. 1 and 2, and it shows that safety mechanism in lowered position,

Fig. 4 is a sectional view through the safety mechanism of Fig. 3, and it is taken along the plane indicated by the line 4-4 of Fig. 3, Fig 5 is another sectional view, in elevation, through the safety mechanism of the lifting device of Figs. 1 and 2, and it shows that safety mechanism in partially elevated position, Fig. 6 is another sectional view, in elevation, through the safety mechanism of the lifting device of Figs. 1 and 2, and it shows that safety mechanism in fully elevated position,

Fig. 7 is another sectional view, in elevation, through the safety mechanism of the lifting'device of Figs. 1 and s 2, and it shows that safety mechanism after the retracting lever has been operated,

Fig. 8 is another sectional view, in elevation, through the safety mechanism of the lifting device of Figs. 1 and 2, and it shows that safety mechanism after it has moved part of the way to lowered position,

Fig. 9 is a sectional view, on an enlarged scale, through a portion of the safety mechanism shown in Figs. 3 and 5-8, and it is taken along the plane indicated by the line 9-9 in Fig. 7, and

Fig. 10 is a sectional view, on a still larger scale, through another portion of the safety mechanism shown in Figs. 3 and 5-9, and it is taken along the plane indicated by the line 10-10 in Fig. 7.

Referring to the drawing in detail, the numeral 20 denotes the customary and usual cylinder for a lifting device that is useful in lifting automobiles. That cylin der receives a vertically movable plunger, not shown; and that plunger has a securing plate 21 secured to the top thereof. A cylinder 22 is provided for the safety mechanism of the lifting device of the present invention; and that cylinder is both shorter and smaller in diameter than cylinder 20. Struts 24 are secured to, and extend between, the cylinders 20 and 22; and those struts hold those cylinders in a predetermined and fixed spaced relation. A concrete mass 26 is set in the ground to support and embeded the lower part of the cylinder 20; and a concrete mass 28 is provided at ground level to surround the upper ends of cylinders 20 and 22. The concrete mass 28 helps keep the cylinders 20 and 22 plumb and also helps the struts 24 maintain the desired spacing between the cylinders 20 and 22.

The plunger, not shown, for the cylinder 20 supports a superstructure 30 which can engage and raise an automobile. The superstructure shown in the drawing is of the frame contact type, but the roll on type of superstructure will usually be preferred. The construe tion and design of the cylinder 20, the construction and design of the superstructure 30, and the construction and design of the concretemasses 26 and 28 are not, per se, part of the present invention.

The numeral 32 denotes the plunger which telescopes into, and is guided and confined by, the cylinder 22. That plunger is hollow, as shown by the drawing; and a securing block 34 of cylindrical form telescopes downwardly into the open upper end of the plunger 32. A cross pin'36 extends through aligned openings in that plunger and in the securing block 34 to fixedly secure that block in position within the upper end of plunger 32. An axially threaded opening 38 is provided in the upper end of block 34, and that opening receives a heavy bolt 40. That bolt extends downwardly through an to the distance between the cylinders 22 and 20.

The plunger 32 has a narrow, vertically-directed slot 42 in the wall thereof; and that slot begins at a point a short distance below the lower end of securing block 34 and extends downwardly therefrom. A pair of circular openings 44 is formed in the wall of the plunger 32, and those openings are at opposite ends of a diameter of that plunger. A second set of circular openings 46 is formed in the wall of the plunger 32, and that second set of openings is formed at the opposite ends of another diameter of that plunger.

Smaller openings 47, with axes transverse of the axes of openings 44 and 46, are formed at opposite ends of another diameter of the plunger 32; and those openings fixedly support a pivot 48. Before that pivot is set in position within the openings 47, the elongated hub 52 of a hand-operated lever 50 is set in register with the small diameter openings 47 in the wall of plunger 32; and thereupon the pivot 48 is telescoped through one of those openings, through that elongated hub, and then through the other of those openings. That pivot permits readyv rotation of the lever 50 relative to the plunger 32. That pivot holds the free end of lever 50 in register with the slot 42; and that slot is wide enough to permit a man to insert his finger through that slot to engage and pull on the free end of that lever.

A second pair of small diameter openings is provided in the wall of plunger 32, and the axes of those openings are parallel to the axes of openings 47. The openings of the second pair of openings accommodate a stop pin 54, as shown particularly in Fig. 4. That stop pin is set adjacent the lever 50, and it is set so itholds the free end of that lever immediately adjacent the slot 42 whenever that lever is in retracted position.

The numeral 56 denotes a length of cylindrical rod which is machined to have a recess 58 therein. That recess extends to, and communicates with, one end of the rod 56; and it reciprocally receives a locking pin 60. That pin is short enough to telescope within the recess 58 and still have its inner end spaced from the inner end of that recess. A slot 62 is provided at each side of the recess 58 in the rod 56, and those slots accommodate a stop pin 64 carried by the locking pin 60'. A helical compression spring 66 is disposed within the recess 58, and it is positioned between the closed end of that recess and the innermost end of locking pin 60. The spring 66 strongly biases the locking pin 68 for movement out of the recess 58, but the engagement of stop pin '64 with the right-hand ends of the slots 62 limits the outward movement of the pin 60. While the spring 66 is strong, it will yield to permit the locking pin 60 to be retracted into the recess 58 in rod 56; and thereupon the outermost end of the locking pin 60 will not interfere with vertical reciprocation of plunger 32 relative to cylinder 22.

The numeral 68 denotes a second rod which is comparable to the rod 56. The rod 68 has a recess 70 therein which is comparable to the recess 58; and that recess reciprocally accommodates a pin 71 which is identical to the pin 60. A slot 72 is formed in the side walls of the recess 70 in rod 68, and those slots accommodate a stop pin 74 carried by the locking pin 71. A helical compression spring 76 is disposed between the closed end of the recess 70 and the innermost end of the locking pin 71.

The numeral 78 denotes a vertically-directed camming bar, and the numeral 80 denotes a second vertically-directed camming bar. Each of these camming bars has an-upper cam 82 and a lower cam 84; and each of the cams has an inclined rise and a low dwell. Each of those cams also has an inclined surface which extends upwardly from its low dwell, and that surface smoothly interconnects the low dwell with the left-hand edge of the camming bar. The cams 82 and 84 are spaced apart a distance equal to the spacing between the stop pins 64 and 74 on looking pins 60 and 71, and those cams can urge those stop pins and those locking pins to retracted position. v

The camming bars 78 and are spaced apart by three sleeve-like spacers 86, and they are held in assembled relation by three pins 88. The pins 88 coact with the sleeve-like spacers 86 and with the camming bars 78 and $0 to form a rigid camming frame. One edge of each of the camming bars 78 and 80 is chamfered, and those edges closely approximate chords of the arc defined by the interior of the plunger 32.

The numeral 90 denotes a short, vertically-directed, connecting bar which is rotatably secured to the upper end of camming bar'78 by a pivot 92. That pivot is shown in the form of an elongated rivet, but any other suitable pivot could be used. A short connecting bar 94, similar to the connecting bar 90, is rotatably secured to the upper end of camming bar 80 by pivot 92. The upper ends of the connecting bars 90 and 94 are fixedly secured, as by welding or otherwise, to the downwardly depending arm of a J-shaped connector 98. The upper end of that connector extends through an opening in the lower end of the lever 50, and is held in that opening by a cotter pin.

In assembling the safety mechanism of the present invention, the upper end of connector 98 is passed through the opening in lever 50 and is held by the cotter pin. Thereafter the depending end of that connector is secured to the upper ends of connector bars 90 and 94; and the lower ends of those bars 90 and 94 are then suitably pivoted to the camming frame which includes the two camming bars 78 and 80, the spacers 86 and the pins 88. The subassembly of lever 50, connector 98, connector bars 90 and 94, and the camming assembly is then telescoped downwardly into the plunger 32. That subassembly will be suitably moved to a position where the pivot 48 can be telescoped through the openings 47 in the wall of plunger 32 and through the sleeve 52 carried by the lever 50. That sleeve is long enough to closely engage the inner surfaces of plunger 32 and thereby confine the lever 55} to a position squarely in register with the slot 42 in the wall of plunger 32.

. After the said subassembly has been set in position and suitably held in that position by the insertion of the pivot 48, the stop pin 54 can be set in position, the securing block 34 can be set in position and the cross pin 36 can be telescoped through the openings in the wall of the plunger 32 and through the aligned opening in the securing block 34. ,Thereupon, the rod 56 which has been suitably machined and equipped with its locking pin 60, its stop pin 64 and itsspring 66 is set in position within the opening 44. A weld can then be formed to fill the gap between the periphery of the rod 56 and the openings 44 and thereby fixedly secure the rod' 56 to the plunger 32. Similarly, the rod 68 which has been suitably machined and suitably equipped with its locking pin 71, its stop pin 74, and its springv 76 is suitably set in openings 46 and welded to the plunger 32.

Whenever the lifting device is in the lowered position shown in Fig. 2, the component parts of the safety mechanism will assume the positions shown in Fig. 3. At such time, the springs 66 and 76 within the rods 56 and 68 will be urging the pins 60 and 71 into engagement with the inner surface of the cylinder 22. The low dwells" of the cams 82 and 84 will be in register with the stop pins 64 and 74 on the locking pins 60 and 71, and hence the cams 82 and will permit full extending movement of those stop pins'and of the locking pins 60 and 71 when the lifting device moves upwardly. The cams 82 and 84 will be held with their low "dwells in register with the stop pins 64 and 74 by reason of the engagement of lever 50 with the stop pin 54.

During the upward movement of the lifting device, the locking pin 60 will rise above the top of cylinder 22, and thereupon the spring 66 will force that pin out into extended position where it will overlie the top edge of cylinder 22. In overlying the top edge of cylinder'22, the pin 60 prevents accidental lowering of the plunger 32 and thereby prevents accidental lowering of the lifting device. The pin 60 is made large enough in cross section, and is made oftough enough metal, to support the dynamic load of the lifting device and its load as that lifting de vice and load move downwardly during an accidental lowering movement.

The lifting device can be held in raised position with only the pin 60 overlying the top edge of cylinder 22; and in that event the pin 60 willfully protect the operator of the lifting device from injury due to an accidental lowering of the lifting device. Such an arrangement is shown in Fig. 5. However, if desired, the lifting device can be raised upwardly until the locking pin 71 is above the level of the top edge of cylinder 22; and thereupon the spring 76 will force that pin outwardly into extended position to overlie that upper end of cylinder 22. Such an arrangement is shown in Fig. 6.

Whenever it is desired to lower the lifting device, it is only necessary for the operator to reach through the slot 42 in the wall of plunger 32, grasp the free end of lever 50, and pull downward. That lever will then assume the position shown in Fig. 7; and at that time, it will have caused the camming bars 78 and 80 to move upwardly and shift the low dwe1ls" of the earns 82 and 84 out of register with the stop pins 64 and 74shifting the rises of those cams 82 and 8 4 into engagement with and past those pins. This shifting of earns 82 and 84 forces the stop pins 64 and 74 to retract the locking pins 60 and 71 back within the recesses 58 and 70 of the rods 56 and 68. In retracting within the recesses of the rods 56 and 68, the locking pins 60 and 71 will be moved out of register with the upper edge of the cylinder 22, and will thereby make it possible for plunger 32 to move downwardly into cylinder 22.

As the plunger 32 moves downwardly into cylinder 22, the projecting end of lever 50 will strike the upper edge of that cylinder. Thereupon, further downward movement of the plunger 32 into cylinder 22 will cause the lever 50 to rotate to the position shown in Fig. 8. In that position, the lever 50 will again hold the low dwells of cams 82 and 84 in register with stop pins 64 and 74;

and it will thereby permit the locking pins to move to extended position as soon as the lifting device raises those pins above the upper edge of cylinder 22.

The locking pins 60 and 71 are shown spaced apart an appreciable distance, but in actual practice they will preferably be from four to seven inches apart. Those pins provide full protection for the operators of the lifting device while also permitting that device to be set in different vertically spaced positions.

Whereas a preferred embodiment of the present invention has been shown and described in the drawing and accompanying description, it should be apparent to those skilled in the art that various changes may be made in the form of the invention without affecting the scope thereof.

. What I claim is:

1. In a lifting device, a cylinder that is stationary throughout the operation of said device, a plunger that is vertically movable during the operation of said device, a hollow guide that is carried by said plunger and is transverse of the longitudinal axis of said plunger, a locking pin that is carried by said guide and reciprocates relative to said guide, said locking pin being selectively movable to a first position wherein it is within said plunger or to a second position wherein on? {ind thereof is disposed outwardly of said plunger, said locking pin having its axis parallel to the axis of said guide and transverse of the longitudinal axis of said plunger, a spring biasing said locking pin for movement to said second position, a stop in the form of a pin that is carried by said locking pin and that extends into a slot in the wall of said guide, said stop being adapted to limit outward movement of said pin and to releasably hold said pin in said second position, a second hollow guide that is carried by said plunger and is transverse of the longitudinal axis of said plunger, a second locking pin carried by and reciprocable relative to said second guide, said second locking pin being selectively movable to a first position wherein it is within said plunger or to a second position wherein one end thereof is disposed outwardly of said plunger, said second locking pin having its axis parallel to the axis of said second guide and transverse of the longitudinal axis of said plunger, a second spring biasing said second pin to its second position, a second stop in the form of a pin that is carried by said second locking pin and that extends into a slot in the wall of said second guide, said second stop being adapted to limit outward movement of said second pin and to releasably hold said second pin in its second position, a cam that has spaced apart rises that act upon said stops for said pins to move said pins to their first positions and that has spaced apart low dwells that free said locking pins for movement to their second positions whenever said low dwells are in register with said stops, and a lever that can be moved to move the cam and thereby move said pins to their first positions, said lever being movable by hand to move said pins to their first positions and being moved to pin-freeing position by engagement with an obstruction during the downward movement of said plunger, said obstruction being the upper edge of said cylinder, the frictional engagement between said cam and said stops enabling said lever to resist accidental movement out of its hand-moved position.

2. In a lifting device, a cylinder that is stationary throughout the operation of said device, a plunger that is vertically movable during the operation of said device, a hollow guide that is carried by said plunger and is transverse of the longitudinal axis of said plunger, a locking pin that is carried by said guide and reciprocates relative to said guide, said locking pin being selectively movable to a first position wherein it is within said plunger or to a second position wherein one end thereof is disposed outwardly of said plunger, a spring biasing said locking pin for movement to said second position, a stop in the form of a pin that is carried by said guide, said stop being adapted to limit outward movement of said pin and to releasably hold said pin in said second position, a second hollow guide that is carried by said plunger and is transverse of the longitudinal axis of said plunger, a second locking pin carried by and reciprocable relative to said second guide, said second locking pin being seiec tively movable to a first position wherein it is within said plunger or to a second position wherein one end thereof is disposed outwardly of said plunger, a second spring biasing said second pin to its second position, a second stop in the form of a pin that is carried by said second guide, said second stop being adapted to limit outward movement of said second pin and to releasably hold said second pin in its second position, a cam that has spaced apart rises that act upon said stops for said pins to move said pins to their first positions and that has spaced apart low dwells that free said locking pins for movement to their second postions whenever said low dwells are in register with said stops, and a lever that can be moved to move the cam and thereby move said pins to their first positions, said lever being movable by hand to move said pins to their 7 first positions and being moved to pin-freeing position by engagement with an obstruction during the downward movement of said plunger, the frictional engagement p -7 tween said cam and said stops enabling said lever-to resist accidental movement out of its and-moved position. [3. In. a lifting device, a cylinder that is stationary throughout the operation of said device, a plunger that is vertically movable during the operation of said device, a hollow guide that is carried by said plunger and is transverseof the longitudinal axis of said plunger, a locking pin that is carried by said guide and reciprocates relative to said guide, said locking pin being selectively movable to a first position wherein it is within said plunger or to a second position wherein one end thereof is disposed outwardly of said plunger, a spring biasing said locking pin for movement to said second position,a stop to limit outward movement of said pin and to releasably hold said pin in said second position, a second hollow guide that is carried by said plunger and is transverseof the longitudinal axis of said plunger, a second locking pin carried by and reciprocable relative to said second guide, said second locking pin being selectively movable to a first. position wherein it is within said plunger or to a second position wherein one end thereof is disposed outwardly of said plunger, 21 second spring biasing said second pin to its second position, a second stop to limit outward movement of said second pin and to releasably hold said second pin in its second position, a cam that acts upon said stops for said pins to move said pins to their first positions, and a lever that can be moved to move the cam and thereby move said pins to their first positions, said lever movable by hand to move said pins to their first positions and being moved to pin-freeing position by engagement with an obstruction duringthedownward movement of said plunger.

, 4. In a lifting device, a cylinder that is stationary throughout the operation of said device, a plunger that is vertically movable during the operation of said device, a locking pin that is carried by said plunger and selectively movable to a first position wherein it is within said plunger or to a second position wherein one end thereof is disposed outwardly of said plunger, said locking pin being transverse of the longitudinal axis of said plunger, a spring biasing said locking pin for movement to said second position, a stop to limit outward movement of said pin and to releasably hold said pin in said second positiorua second locking pin carried by saidplunger, said second locking pin being selectively movable to a first position wherein it is within said plunger or to a second position wherein one end thereof is disposed outwardly of said plunger, said second locking pin being transverse of the longitudinal axis of said plunger, a second spring biasing said second pin to its second position, a second stop to limit outward movement of said second pin and to releasably hold said second pin in its second position, a cam that acts upon said stops for said pins to move said pins to their first positions, and a lever that can be moved to move the cam and therebymove said pins to their first positions, said lever being movable by hand to move said pins to their first positions and being moved to pin-freeing position by engagement with an obstruction during the downward movement of said plunger, said lever normally remaining in hand-moved position until it engages said obstruction.

5. In a lifting device, a cylinder that is stationary throughout the operation of said device, a plunger that is vertically movable during the operation of said device, a locking pin that is carried by said plunger and is selectively movable to a first position wherein it is within said plunger or to a second positionwherein one end thereof is disposed outwardly of said plunger, a spring biasing said locking pin for movement to said second'position, a stop tolimit outward movement of said pin and to releasably hold said pin in said second position, a second locking pin carried by said plunger, said second locking pin being selectively movable to a first position wherein it is within said plunger or to a second position wherein one end thereof is disposed outwardly of said plunger, a

second spring biasing-said second pinto its second position, a second stop to limit outward movement of said second pin and to releasably holdsaid second pin in its second position, a cam that acts upon said stops for said pins to move said pins to their first positions, and a lever that can be moved to move the cam and thereby move said pins to their first positions, said lever being movable by hand to move said pins to their first positions and being moved to pin-freeing position by engagement with an obstruction during the downward movement of said plunger.

6. in a lifting device, a cylinder that is stationary throughout the operation of said device, a plunger that is vertically movable during the operation of said device, a locking pin that is carried by said plunger and is selec?- tively movable to a first position wherein it is within said plunger or to a second position wherein one end thereof disposed outwardly of said plunger, a spring biasing said locking pin for movement to said second position, a stop to limit outward movement of said pin and to releasablyhold said pin in said second position, a second locking pin carried by said plunger at a point spaced vertically from the first said locking pin, said second locking pin being movable independently or" the first said locking pin and being selectively movable to a first position wherein it is within said plunger or to a second position wherein one end thereof is disposed outwardly of said plunger, a second spring biasing said second pin to its second position, a second stop to limit outward movement of said second pin and to releasably hold said second pin in its second position, a cam thatnormally frees said pins for independent movement to said second positions and that selectively moves said pins to their first positions, and a lever that can be moved to move the cam and thereby move said pins to their first positions, said lever being movable by hand to move said pins to their first positions,

7. in a lifting device, a cylinder that is stationary throughout the operation of said device, a plunger that is vertically movable during the operation of said device, a locking pin that is carried by said plunger and is selectively movable to a. first position wherein it is within said plunger orto a second position wherein one end thereof is disposed outwardly of said plunger, a spring biasing said locking pin for movement to said second position, a second locking pin carried by said plunger at a point spaced vertically from the first said locking pin, said sec-. ond locking pin being movable independently of the first said locking pin and being selectively movable to a first position wherein it is within said plunger or to a second position wherein one end thereof is disposed outwardly of said plunger, :1 second spring biasing said second pin to its second position, a cam that normally frees said pins for independent movement to said second positions and that selectively moves said pins to their first positions, and a lever that can be moved to move the cam and thereby move said pins to their first positions.

8. In a lifting device, a cylinder that is stationary throughout the operation of said device, a plunger that is vertically movable during the operation of said device, a locking pin that is carried by said plunger and is selectively movable to a first position wherein it is within said plunger or to a second position wherein one end thereof is disposed outwardly of said plunger, said locking pin being biased for movement to said second position, a stop to limit outward movement of said pin and to releasably hold said pin in said second position,-a second locking pin carried by said plunger at a point spaced vertically from the first said loc ting pin, said second locking pin being movable independently of the first said locking pin and being selectively movable toa first'position wherein it is withinsaid plunger or'to a second position wherein ne end thereof is disposed outwardly of said plunger, said second locking pin being biased for movement to its second position, and a second stop to limit outward movement of said second pin and to releasably hold said second pin in its second position, the first said locking pin preventing accidental lowering of said device whenever said device is at a predetermined elevation, said second locking pin preventing accidental lowering of said device whenever said device is at an elevation above the level of said predetermined elevation.

9. In a lifting device, a cylinder that is stationary throughout the operation of said device, a plunger that is vertically movable during the operation of said device, a locking pin that is carried by said plunger and is selectively movable to a first position wherein it is within said plunger or to a second position wherein one end thereof is disposed outwardly of said plunger, said locking pin being biased for movement to said second position, and a second locking pin carried by said plunger at a point spaced vertically from the first said locking pin, said second locking pin being movable independently of the first said locking pin and being selectively movable to a first position wherein it is within said plunger or to a second position wherein one end thereof is disposed outwardly of said plunger, said second locking pin being biased for movement to its second position, the first said locking pin preventing accidental lowering of said device whenever said device is at a predetermined elevation, said second locking pin preventing accidental lowering of said device whenever said device is at an elevation above the level of said predetermined elevation.

axis parallel to the axis of said guide and transverse of the longitudinal axis of said plunger, a spring biasing said locking pin for movement to said second position, a stop in the form of a pin that is carried by said locking pin and that extends into a slot in the wall of said guide, said stop being adapted to limit outward movement of said'pin and to releasably hold said pin in said second position, a cam that normally frees said pin for movement to said second position and that selectively acts upon said stop for said pin to move said pin to its first position, and a lever that can be moved to move the cam and thereby move said pin to its first position.

11. In a lifting device, a cylinder that is stationary throughout the operation of said device, a plunger that is vertically movable during the operation of said device, a locking pin that is carried by said plunger and is selectively movable to a first position wherein it is within said plunger or to a second position wherein one end thereof is disposed outwardly of said plunger, said locking pin being biased for movement to said second position, a stop to limit outward movement of said pin and to releasably hold said pin in said second position, a cam that normally frees said pin for movement to said second position and that selectively acts upon said stop for said pin to move said pin to its first position, and a lever that can be moved to move the cam and thereby move said pin to its first position.

References Cited in the file of this patent UNITED STATES PATENTS 1,824,866 Bristol Sept. 29, 1931 1,827,966 Bristol Oct. 20, 1931 2,326,972 Rosin Aug. 17, 1943 2,771,060 Allbright Nov. 20, 1956 FOREIGN PATENTS 466,824 France Mar. 14, 1914 287,658 Switzerland Apr. 1, 1953

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