US3740782A

US3740782A - Method and apparatus for servicing counterbalanced lifting device

Info

Publication number: US3740782A
Application number: US00211241A
Authority: US
Inventors: O Newman
Original assignee: SVERDRUP AND PARCEL ASS Inc
Current assignee: SVERDRUP AND PARCEL ASS Inc
Priority date: 1971-12-23
Filing date: 1971-12-23
Publication date: 1973-06-26
Anticipated expiration: 1990-06-26

Abstract

A counterbalanced lifting apparatus includes two weighted members suspended from cables which are trained over sheaves supported in an elevated position on a framework. One of the weighted members may be a bridge span and the other a counterweight. The first weighted member (bridge span) normally seats against a terminal surface while the second weighted member (counterweight) is normally suspended. During operational cycles, the relative positions of the weighted members reverse, and the counterweight may seat on cylinder-type buffers affixed to its underside. Some servicing operations require slack in the cables and this is achieved by seating the first weighted member against its terminal surface and then supporting jacking beams on a temporary support system installed directly beneath the cylindertype buffers of the second weighted member. Thereafter, a hydraulic pump is connected with the barrels of the cylinder-type buffers and hydraulic fluid is pumped into these barrels to cause the piston rods therein to extend against the jacking beams. This raises the second weighted member and thereby loosens the cables.

Description

[ June 26, 1973 United States Patent [191 Newman ABSTRACT METHOD AND APPARATUS FOR G m m m an m Mm m WA C md n NA La L m A m n E & N N .n. U m 0 Rd C en v MOS V nmD Rve EEV SDhA UH WU Inc., Saint Louis, Mo.

Dec. 23, 1971 weighted member (bridge span) normally seats against a terminal surface while the second weighted member (counterweight) is normally suspended. Durin [22] Filed:

g opera- [211 Appl' 211241 tional cycles, the relative positions of the weighted members reverse, and the counterweight may seat on cylinder-type buffers affixed to its und 14/42, 187/94 erside. Some ser- E01d 15/02 vicing operations require slack in the cables and this is 14/ 1, 42, 52, 66, achieved by seating the first weighted member against 14/77, 36; 248/325, 364; 187/94, 71, 67; 254/178 its terminal surface and then supporting jacking beams on a temporary support system installed directly beneath the cylinder-type buffers of the second weighted [52] 11.8. [51] lnt. [58] Field of Search [56] References Cited UNITED STATES PATENTS 2,198,810 4/1940 member. Thereafter, a hydraulic pump is connected with the barrels of the cylinder-type buffers and hydraulic fluid is pumped into these barrels to cause the piston rods therein to extend against the jacking beams. This raises the second weighted member and thereby loosens the cables.

3,466,686 /1969 Allen 3,707,011 12/1972 Launay 392,753 11/1888 FOREIGN PATENTS OR APPLICATIONS 996,179 6/1965 Great 14/1 Primary ExaminerRoy D. Frazier Assistant Examiner-Thomas .l. Holko 14 Claims 9 Drawing Figures Atlorney- Frederick M. Woodruffand Edward A.

Boeschenstein METHOD AND APPARATUS FOR SERVICING COUNTERBALANCED LIFTING DEVICE BACKGROUND OF THE INVENTION This invention relates in general to counterbalanced lifting devices and more particularly to a method and apparatus for servicing the same.

A conventional lift bridge has a pair of towers set on piers and a lift span which extends between the piers. The span is usually counterbalanced against a massive counterweight in each tower so relatively little power is required to lift the span. These counterweights are connected to the span by cables which are trained over sheaves at the top of the towers. The cables must be replaced at periodic intervals and the sheave bearings may need to be pulled for servicing or repair. To replace the cables or to pull the sheave bearings, the cables must be unloaded and relaxed so that slack exists in them.

Presently, the cables are loosened or relieved of load by hoisting the counterweights with hydraulic lift jacks which are positioned adjacent to the sheaves during the jacking operation. Each jack actually rests on ajacking girder and lifts a jacking beam which is connected to the counterweight through a tie rod. The jacking girders are all temporary installations and must be emplaced at the top of the tower for the lifting operation to proceed. Moreover, since cables have a relatively long life, the jacks are used infrequently and this leads to a deterioration of the seals and packing in them. Consequently, the jacks sometimes become inoperable or fail in use. Also, when emplaced, the jacks are positioned closely opposite the inner sheave bearings which makes it extremely difficult to pull these bearings or to otherwise service them. In the same vein, most lift bridges have the hoist machinery located at the tops of their towers adjacent to the sheaves for driving the sheaves. Thus, in most lift bridges the tops of the tower are congested areas and the emplacement of the jacking equipment to temporarily elevate the counterweight merely creates more congestion and compounds the servicing problem.

SUMMARY OF THE INVENTION One of the principal objects of the present invention is to simplify the lifting of counterweights on lift bridges and the like to facilitate servicing of the cables and related equipment. Another object is to eliminate the need for emplacing jacking equipment at the top of the towers on such bridges when it is necessary to loosen the cables or service bearings. A further object is to provide a method and apparatus for simplifying the servicing of counterbalanced lifting devices having cylinder-type pneumatic buffers through dual utilization of existing components. These and other objects and advantages will becomeapparent hereinafter.

The present invention is embodied in a method of loosening a flexible connector which is trained over a sheave and is connected to first'and second weighted members of a counterbalanced lifting apparatus. The second weighted member carries cylinder-type pneumatic buffers. The method includes bringing the first weighted member against a terminal surface, and thereafter placing an adequate load carrying jacking surface under the cylinder-type buffer. Hydraulic pump means is then connected to the cylinder-type buffer to cause the piston and rod to extend and lift the second memher, thereby loosening the flexible connector. In addition, the invention resides in the apparatus to practicing the method. The invention also consists in the parts and in the arrangements and combinations of parts hereinafter described and claimed.

DESCRIPTION OF THE DRAWINGS In the accompanying drawings which form part of the specification and wherein like numerals refer to like parts wherever they occur:

FIG. 1 is a lift bridge on which the jacking system of the present invention is utilized;

FIG. 2 is an enlarged side elevational view of one of the towers on the bridge;

FIG. 3 is an enlarged front elevational view of the tower;

FIG. 4 is a plan view of the hoist machinery sheaves located in the top of the tower;

FIG. 5 is a sectional view of one of the cylinder-type buffers on the underside of the counterweight;

FIG. 6 is a schematic view showing the pneumatic circuit connected with the buffers;

FIG. 7 is a schematic view of the hydraulic circuit forming part of the present invention; and

FIGS. 8 and 9 are side elevational views of optional towers in which variations for providing the jacking surface are utilized.

DETAILED DESCRIPTION Referring now in detail to the drawings, 2 designates a counterbalanced lift bridge (FIG. 1) including a pair of concrete piers 4, a lift span 6 bridging the piers 4, and towers 8 positioned over the piers 4 and located at the ends of the lift span 6. Both towers 8 are the same, and consequently only the construction of and the equipment housed in the right tower 8 will be discussed in detail.

The right tower 8 (FIGS. 2 and 3) has a framework 10 anchored on the pier 4 and extending upwardly therefrom. This framework 10 includes a pair of front corner legs or columns 12 and a pair of rear corner legs or columns 14, and each of these

corner columns

12 and 14 is formed from a series of upright girders positioned end to end. The two front columns 12 are connected at the top thereof by a horizontal front girder l6 and below the front girder 16 they are further connected by a horizontal intermediate girder l8. Similarly, the rear columns 14 are connected at their tops by a horizontal rear girder 20, and downwardly therefrom by another intermediate girder 22 which is at the same elevation as the intermediate girder 18. The four

columns

12 and 14 are further connected by other horizontal and diagonal girders which act as bracing for the tower 8.

Extending between the front and

rear girders

16 and 20 are four sheave girders 26 which are arranged two pairs at each side of the tower 8. The sheave girders 26 in turn support trunnion bearings 28, which are preferably the cylindrical roller variety, and the pair of bearings 28 for each pair of sheave girders 26 receive a single trunnion shaft 30. Each trunnion shaft 30 has a sheave 32 mounted on it between its bearings 28 so that the sheaves 32 rotate between the sheave girders 26 of each pair. The bearings 28 are positioned such that the sheaves 32 project forwardly beyond the front columns 12. Each sheave 32 has a plurality of circumferential cable grooves 36 (FIG. 4) extending around it and may carry a large spur gear on sheave-drive type installations.

The sheave girders 26 also may support a machinery floor 40 on which the hoist machinery for the span 6 rests. That'mahinery is conventional and will not be described in detail, other than to note that it includes (FIG. 4) drive motors 42 which are connected by means of drive shafts 44 to a speed reducer 46. The speed reducer 46 delivers the power to a common drive shaft 48 which extends along the back sides of the sheaves 32 and has pinion gears 50 which mesh with the spur gears 34 on the sheaves 32. Brakes 52 are provided for retarding rotation of the drive shaft 44. The hoist machinery may also be located at the base of the tower 8 or on the lift span 6.

Trained over the sheaves 32 are cables 54 (FIGS. 2 and 3) which are arranged in two setsone at each sheave 32--and these cables 54 extend downwardly in front of the front corner columns 12 and are attached to the span 6 by means of cable connectors 56. Each cable set includes a plurality of cables 54 with each cable 54 being maintained in the proper axial position by a single circumferential cable groove 36 on the sheave 32. On the opposite sides of the sheaves 32, the cables 54 depend through generally the center of the tower 8 and their ends are connected by means of cable connectors 58 to a counterweight 60 located within the tower 8. The counterweight 60 weighs approximately half the weight of the span 6 and preferably is a large steel tank filled with concrete. At its sides, the counterweight is provided with guide shoes 62 which engage vertical guide rails 64 on the framework so that the counterweight 60 is free to move vertically but not horizontally.

The span 6 is also provided with guide shoes 66 (FIG. 2) and these shoes are located at its ends and engage guide rails 68 on the two front corner columns 12. The span 6, when in its lowermost position, rests on bearing shoes 70 (FIG. 1) which are supported on the pier 4 in front of the tower 8. The bearing shoes 70 thus form a terminal surface for the span 6.

Since the span 6 is counterbalanced by the counterweights 60 relatively little energy is required to raise the span 6 off of its bearing seat 70. This'energy is supplied through the drive motors 42 which rotate the sheaves 32 at the tops of the towers 8. As the span 6 rises, the counterweights 60 descend, the former following the guide rails 68, and the latter the guide rails While the span 6 rests on the bearing seat 70 when in its lowermost position, the counterweights 60 when they come to their lowermost position, rest against pads 72 (FIG. 1) which are elevated above the seats to approximately the level of the bridge deck by posts 74 extending upwardly from the piers 4.

The counterweight 60 does not directly engage its pads 72, but on the contrary, is provided with a pair of cylinder-type pneumatic buffers 80 which cushion the impact with the pads 72. Likewise, the span 6 on its underside is also provided with cylinder-type pneumatic buffers 80 which retard the downward movement of the span 6 prior to its engagement with the bearing seats 70 so that the span is eased onto the bearing seats 70. The buffers 80 therefore avoid inducing bounce or shock in the structure.

The buffers 80 for each counterweight 60 are disposed at the sides of the counterweight 60 directly beneath the cable connections 58, and are accordingly centered with respect to its front and rear faces. Each buffer includes (FIG. 5) a barrel 82 having a cylindrical sidewall which is closed at its upper end by a head or cap 84 and at its lower end by a head 86. The cylindrical side wall is clamped between the

heads

84 and 86 to bolts 88, while the upper head 84 is further bolted or otherwise fastened against the underside of the counterweight 60. The head 84 has a port 90 and a passageway 92 which provides communication between the port 90 and the interior of the barrel 82. The lower head 86, on the other hand, has a vent port 94 which communicates with the interior of the barrel 82. The lower head 86 also receives a piston rod 96 and carries a guide sleeve 98 which wipes the outer surface of the rod 96. Within the barrel 82 the piston rod 96 is fastened to a piston 100 having piston rings 102 which wipe and seal against the inwardly presented surface of the barrel 82. The lower ends of the piston rods 94 are fitted with striking heads 104 which align with the pads 72 on the pier 4.

The pressure port 90 of each buffer 80 is connected (FIG. 6) to an air discharge line 108 and the two discharge lines 108 empty into a common choke line 110 containing a choke valve 112 and a pressure relief valve 114, the former of which limits,the rate at which air may be expelled from the barrels 82. The choke valve 112 should be adjustable and preferably takes the form of a needle valve. Each discharge line 108 intermediate its ends communicates with a check valve 116 which is oriented such that it allows air to flow into the discharge line 108, that is toward the buffer barrels 82, but not in the opposite direction. The vent port 94 of each buffer 80 is connected to a vent line 118 containing a check valve 120 which is oriented to allow air to flow toward the buffer barrel 82, but not in the opposite direction. Intermediate the vent port 94 and the check valve 120, a choke valve 122 communicates with the vent line 118. The choke valve 122 likewise is adjustable and is preferably a needle valve.

When the counterweight 60 is in its elevated position, as it normally is, the pistons 100 of the buffer 80 are in their lowermost positions, that is against the apertured head 86, and the piston rods 96 are extended. Once the drive motors 42 are energized, the span 6 rises, while the counterweight 60 descends. As the span 6 nears its uppermost position the speed of the drive motors 42 is reduced and in the last increment of movement the striking heads 104 at the ends of the piston rods 96 engage the fixed pads 72. Continued movement of the counterweight 60 causes the pistons 100 to move through their respective barrels 82 and compress the air trapped in the barrels 82. The compressed air is expelled through the discharge lines 108 and choke line 110, but since the choke valve 112- permits only a restricted flow of air, air compresses within the barrels 82, causing the pistons 100 to move progressively more slowly through their barrels 82, and this prevents the counterweight 60 from coming to an abrupt halt on the pads 72. The check valves 120 allow air to enter the portions of the barrels 82 below the pistons 100 so vacuums do not develop in those portions of the barrels 82.

When the span 6 is lowered by reversing the drive motor 42, the counterweight 60 rises. As the counterweight 60 lifts away from the pads 72, the weight of the pistons 100 and piston rods 96 in the barrels 82 of buffers 80 causes these pistons 100 to pass downwardly in their barrels 82 and force air out of the barrels 82 through the vent ports 94. Again the movement is impeded by the choking effect the choke valves 120 have on the airstream. A vacuum is not drawn above the pistons 100 since the check valves 116 allow air to flow into the upper portions of the barrels 82 through the discharge lines 108.

The buffers 80 on the span 6 operate in the same manner.

To replace the cables 54 or to pull the trunnion bearings 28 it is necessary to relax the tension in the cables 54 to the point that some slack exists in them, and this is achieved by converting the pneumatic buffers 80 into hydraulic jacks. In particular, with the span 6 in its lowermost position, that is resting on the pads 70, the buffers 80 on the counterweight 60 are disconnected from the discharge lines 108 and the vent lines 118, and are instead connected into a hydraulic jacking circuit 130 (FIG. 7). That circuit 130 includes a reservoir 132 containing hydraulic fluid and a pump 134 having its suction port connected with the reservoir 132. The discharge port of the pump 134 is connected to a 3 position bidirectional valve 136, through a supply line 138, and this valve is further connected to the reservoir 132 through a return line 140. In one position, the valve 136 directs pressurized fluid from the supply line 138 to a feed line 142 which is connected to the pressure ports 90 at the upper ends of the buffer barrel 82. In another position the valve 136 directs fluid from the high pressure supply line 138 to a feed line 144 which is connected to the vent ports 94 at the lowerv ends of the buffer barrels 82. Of course, when the

lines

138 and 142 are in communication, the feed lines 144 and return line 140 communicate through the valve 136, and likewise when the

lines

138 and 144 are in communication, the feed line 142 and return line 140 communicate through the valve 136. In its third position, the valve 136 places the supply line 138 and return line 140 in communication so that fluid is merely circulated back to the reservoir 132 without pressurizing either of the

feed lines

142 or 144.

The feed line 142 possesses a common branch containing a manual auxiliary shut-off valve 146 and a pair of individual branches leading to the ports 90 of each individual buffer barrel 82, and these individual branches contain manual regulator valves 148 for controlling the distribution of hydraulic fluid to the two barrels 82. At the juncture of its common and individual branches, the feed line 142 has a bleed valve 150 through which air is purged from the hydraulic circuit 130. Connected between the supply line 138 and the return line 140 is a pressure relief valve 152.

After the counterweight 60 is in its uppermost position and the hydraulic jacking circuit 130 is connected to the buffers 80 at the pressure and vent

ports

90 and 94 thereof (FIG. 7); the pump 134 is energized and the valve 136 is set to direct the pressurized fluid into the line 144. This fluid enters the lower end of the buffer barrels 82 through the vent ports 94 and causes the piston rods 96 to retract into the barrels 82. Next, jacking beams 160 (FIGS. 2 and 3) are placed across and supported on the horizontal

intermediate girders

18 and 22 of the tower framework 10, and these beams are positioned such that they are directly beneath the retracted piston rods 96 of the buffers 80. These jacking beams 160 provide a reaction surface against which the buffers 80 act when they are converted to jacks, and this reaction surface may be elevated slightly by placing blocking 162 between the beams 1 60 and the striking heads 104 of the piston rods 96.

Once the jacking beams 160 and blocking 162 are in place, the valve 136 is moved to direct the high pressure fluid from the pump 134 and supply line 138 to the feed line 142 from which it is introduced into the upper ends of the barrels 82 through the pressure ports 90. This fluid acts against the pistons and lifts the barrels 82 along with the entire counterweight 60. As the counterweight 60 moves upwardly support columns 164 and shims 166 are placed between it and the jacking beam to prevent the counterweight 60 from falling in the event ofa hydraulic blowout. If it is necessary to reblock the jacking arrangement, the support columns 164 and shims 166 are used to support the counterweight 60 while the piston rods 96 are again retracted and additional blocking 162 is placed between them and the beams 160. Of course, as the counterweight 60 is elevated by the buffers 80, the tension in the cables 54 lessens and they become slack.

In lieu of supporting the jacking beams 160 on both the horizontal

intermediate girders

18 and 22, the front ends of the beams 160 may be supported on the front intermediate girders 18 while the rear ends are suspended from the sheave girders 26 by hanger rods 170 (FIG. 8). Indeed, both the front and rear ends of the jacking beams 160 may be suspended by hanger rods 170 from the sheave girders 26 (FIG. 9). In either case, stabilizing struts 172 extend between the framework 10 and the beams 160. The hanger rods 170 are more suitable for towers in which the rear corner columns 14 are not vertical or for towers which do not have horizontal

intermediate girders

18 and 22 or else have such girders in a position not suitable for jacking.

Since the jacking equipment is all positioned beneath the counterweight 60, sufficient room exists at the top of the tower 8 for servicing the sheaves 32 and its bearings 28. Also, no additional jacks are necessary. Since the buffers 80 are used and serviced frequently, the chances of the deterioration of the equipment is greatly reduced, and this lessens the chances of the buffers 80 being inoperative or failing when they are employed as jacks.

This invention is intended to cover all changes and modifications of the example of the invention herein chosen for purposes of the disclosure which do not constitute departures from the spirit and scope of the invention.

What is claimed is:

1. A method of servicing a counterbalanced lifting apparatus including first and second weighted members suspended from a flexible connector which is trained over a sheave supported on a frame and wherein the first weighted member normally rests on a fixed terminal surface and the second weighted member carries a cylinder-type pneumatic buffer having a barrel and a piston and piston rod shiftable in the barrel; said method comprising: seating the first member on the terminal surface; placing a reaction surface under the cylinder-type buffer of the second member; and pumping hydraulic fluid into the barrel of the cylinder-type buffer to cause the piston rod therein to extend against the reaction surface and lift the second weighted member, whereby slack is imparted to the flexible connector.

2. A method according to claim 1 wherein the second member is elevated when the first member is seated against the terminal surface and the reaction surface is carried by a jacking member; and wherein the step of placing a reaction surface under the buffer includes supporting the jacking member on the frame.

3. A method according to claim 1 wherein the reaction surface is carried by a jacking beam; and wherein the step of placing the reaction surface under the buffer includes resting both ends of the beam on the frame.

4. A method according to claim 1 wherein the reaction surface is carried by a jacking beam; and wherein the step of placing the reaction surface under the buffer includes resting one end of the beam on the frame and suspending the other end of the beam from the frame.

5. A method according to claim 1 wherein the reaction surface is carried by a jacking beam; and wherein the step of placing the reaction surface under the buffer includes suspending both ends of the beam from the frame.

6. A method according to claim 2 and further characterized by pumping hydraulic fluid into the barrel of the cylinder-type buffer to cause the piston rod therein to retract prior to supporting the jacking member on the frame.

7. A method according to claim 6 and further characterized by placing shims between the jacking member and the first weighted member as the cylinder-type buffer expands.

8. In a counterbalanced lifting apparatus including first and second weighted members suspended from a flexible elongated connector which is trained over a sheave supported on a frame, and wherein the second weighted member carries a cylinder-type pneumatic buffer having a barrel and a piston and piston rod shiftable in the barrel and the first weighted member normally rests on a fixed terminal surface; the improvement comprising a jacking member supported on the frame beneath the pneumatic buffer when the first weighted member is seated againstthe terminal surface, the jacking member being removable from the path of the buffer so as not to interfere with the normal operation of the lifting apparatus, and hydraulic pump means connected to the cylinder-type buffer to pump pressurized fluid into the end of the barrel which causes the piston rod to extend, whereby the cylinder-type buffer expands between the jacking member and second weighted member and lifts the second weighted member, whereby slack is imparted to the cable.

9. The structure according to claim 8 wherein the hydraulic pump means is also connected to the cylindertype buffer to pump pressurized fluid into the opposite end of the barrel to cause the piston rod to retract, whereby the cylinder type buffer will contract so that the jacking member may be placed under the buffer.

10. The structure according to claim 9 wherein the hydraulic pump means includes a valve for directing hydraulic fluid to either end of the barrel on the cylinder type buffer.

11. The structure according to claim 8 wherein the jacking member is a beam, both ends of which rest on the frame.

12. The structure according to claim 8 wherein the jacking member is a beam, one end of which rests on the frame; and wherein a hanger rod is connected between the frame and the opposite end of the beam for suspending that opposite end of the beam from the frame.

13. The structure according to claim 8 wherein the jacking member is a beam; and wherein hanger rods are connected between the frame and both ends of the beam for suspending the beam from the frame.

14. The structure according to claim 9 wherein the first weighted member is a bridge span and the second weighted member is a counterweight.

Claims

8. In a counterbalanced lifting apparatus including first and second weighted members suspended from a flexible elongated connector which is trained over a sheave supported on a frame, and wherein the second weighted member carries a cylinder-type pneumatic buffer having a barrel and a piston and piston rod shiftable in the barrel and the first weighted member normally rests on a fixed terminal surface; the improvement comprising a jacking member supported on the frame beneath the pneumatic bufFer when the first weighted member is seated against the terminal surface, the jacking member being removable from the path of the buffer so as not to interfere with the normal operation of the lifting apparatus, and hydraulic pump means connected to the cylinder-type buffer to pump pressurized fluid into the end of the barrel which causes the piston rod to extend, whereby the cylinder-type buffer expands between the jacking member and second weighted member and lifts the second weighted member, whereby slack is imparted to the cable.

9. The structure according to claim 8 wherein the hydraulic pump means is also connected to the cylinder-type buffer to pump pressurized fluid into the opposite end of the barrel to cause the piston rod to retract, whereby the cylinder type buffer will contract so that the jacking member may be placed under the buffer.