US2730228A - Automatic tripper for belt conveyors - Google Patents

Description

Jan. 10, 1956' M. s. GREELEY ETAL 2,730,228

A TOMATIC TRIPPER FOR BELT CONVEYORS Filed March 19, 1952 4 Sheets-Sheet l HTTGRNE Y5 AUTOMATIC TRIPPER FOR BELT CONVEYORS Filed March 19, 1952 4 Sheets-Sheet 2 INVENTORS. MAWK 5. GREELE) T2} 2 wkw HTT'OANEYS 1956 M. s. GREELEY ETAL A TOMATIC TRIPPER FOR BELT CONVEYORS 4 Sheets-Sheet 5 Filed March 19, 1952 m w? m mrv v w 5 r mv 9 Z 0 M 1911- 1956 M. s. GREELEY ETAL A TOMATIC TRIPPER F OR BELT CONVEYORS 4 Sheets-Sheet 4 Filed March 19, 1952 INVENTORS. MAWA 5. GKEELE) BY Ruff/TON a. K/MBKO firm/mars United States Patent Mark S. Greeley and Rushton 0.

Ala, assignors to Continentai Gin Company, a corporation of Delaware Application March 19, 1952, Serial No. 277,468 12 Claims. (Cl. 198186) This invention relates to an automatic tripper for belt conveyors and has for an object the provision of .fluid pressure means for propelling, movement of the tripper.

Another object of our invention is to provide an automatic fluid pressure actuated belt conveyor tripper embodying improved means for actuating a rail gripping brake member in event there is a pressure failure or a break in the hydraulic or pneumatic lines.

Another object of our invention is to provide an automatic tripper of the character designated having reversing means incorporated therewith which shall be operated by adjustable limit means positioned along the track upon which the tripper moves.

A further object of our invention is to provide a fluid pressure actuated tripper having associated therewith braking means adapted to be energized upon contact with a stationary member positioned along the track upon which the tripper moves, thus limiting the distance the tripper will move along the track and preventing the tripper from getting out of control when there is a pressure failure, or in any part of the tripper.

A more specific object of our invention is to provide an automatic tripper of the character designated including means for regulating the pressure in the hydraulic or penumatic lines, thus keeping a constant pressure in the lines at all times, and including means for automatically stopping the tripper in event the pressure falls below a predetermined amount.

Heretofore in the art to which our invention relates, trippers have been propelled either mechanically or electrically. The mechanical type is usually propelled by coupling power from the conveyor belt through the trip per head and bend shafts and a clutching system to the tripper axle, or by an arrangement of friction wheels on the head and bend shafts coupled to the tripper axle. In order to operate such systems automatically a series of levers, cams, links and weights, are used to engage one clutch and at the same time disengage another. Accordingly, there are several adjustments that must be made and maintained in order to obtain satisfactory operation since the wearing of the clutch facing constantly changes these adjustments. Furthermore, since the operation is usually of a trigger action type, close maintenance is necessary in order to keep all the mechanism in operating condition. When the clutches are both in a neutral position the tripper is a free rolling body, and the belt has a tendency to roll the tripper toward the conveyor head pulley. The tripper thus gains velocity in the direction of belt travel, approaching the belt speed as a limit. The same action results when a belt hangs in any part of the tripper, such as results from a broken pulley shaft. Run-away trippers have in the past caused considerable damage to installations.

While electrically operated trippers have been satisfactory in operation, the electric power must be fed to them either by trolleys orby an automatic cable reel. Aninthe event the conveyor belt hangs in stopping and reversing the i stallation of this type is much more expensive than the mechanically operated type. Also sparking of trolleys and reel brushes are a hazard in some installations, thus preventing this type of tripper from being accepted for all types of installations. Furthermore, the electric type trippers, so far as we are aware, are provided with no means for preventing the tripper from being dragged along its track by thebelt in the event a shaft is broken, or if for any reason the belt should become fastened to the tripper.

We overcome the above mentioned difliculties by providing automatic hydraulic or pneumatic means for propelling, stopping and reversing the tripper as it moves along its tracks.

Briefly our invention comprises means for taking the propelling power directly from the conveyor belt. The power taken from the conveyor belt is utilized to drive a fluid pressure pump which may be either a hydraulic or pneumatic pump and which in turn provides fluid under pressure for propelling a fluid pressure motor. The motor is operatively connected to an axle of the tripper, thereby driving the tripper along its track. The reversal of the tripper is obtained by mounting a four-way pilot valve on the tripper in position to engage a stationary projecting member positioned along the side of the track upon which the tripper moves. The pilot valve reverses the direction of movement of the tripper by reversing the direction of flow of the fluid through the motor. Our tripper also includes a braking member which is operable upon release of pressure in the pressure system or when the tripper passes beyond a predetermined point along the track.

Apparatus embodying features of our invention is illustrated in the accompanying drawings forming a part of this application in which:

Fig. l is a side elevational view of the tripper partly broken away and in section;

Fig. 2 is a plan view thereof partly broken away and in section and showing the belt removed;

Fig. 3 is a front elevational view thereof;

Fig 4 is a diagrammatic view showing the hydraulic or pneumatic pressure lines employed and the means for braking the tripper;

Fig. 5 is a detailed view taken generally along the lines VV of Fig. 4; and,

Figs. 6 and 7 are detail sectional views of the four-way pilot valve.

Referring now to the drawings for a better understanding of our invention, we show a tripper frame indicated generally by the numeral 10. The frame is mounted on wheels 11 which travel along tracks 12. Mounted for rotation adjacent the upper forward end of the frame 10 and extending transversely thereacross is an upper shaft 13 having secured thereto a pulley 14. Mounted for rotation on, and extending transversely across, the frame 10 at a point inwardly of and below the shaft 13, is a bend shaft 16, having secured thereto a pulley 17. Passing around the pulleys 14 and 17 and having a reverse lapportion therein is a conveyor belt 18, which is employed to convey any suitable material, such as coal, sand, gravel, limestone, and the like. The material to be conveyed is indicated generally at 19 and is transported to the conveyor belt 18 by a second belt 20. Secured to the forward end of the tripper frame 10 is a suitable hopper 21 arranged to receive the material conveyed by the belt 18 and adapted to discharge the same into a suitable" bin or bins at the sides of the track 12 or back onto the belt for discharge over the head end. The shaft 13 is rotably mounted in suitable bearings 22 and the shaft 16 is rotatably mounted in suitable bearings 23.

Secured to the bend shaft 16 and spaced laterally of the pulley 17 is a sprocket 24. Mounted for rotation on the frame above the bend shaft 16 in bearings is a counter-shaft 26 having secured thereto a sprocket 27. The sprockets 24 and 27 the connected by means of a drive chain 28. Sprocket 24 is larger in diameter than sprocket 27, thus causing the counter-shaft 26 to rotate at a higher speed than the bend shaft 16. Also secured to the counter-shaft 26 is a sprocket 29. Mounted on the frame 10 rearwardly of the counter-shaft26 is a fluid pressure pump 31 havinga drive shaft 32. For the purpose of this description the pump 31 is shown as a hydraulic pump. Secured to the shaft 32 is a sprocket 33 driven from the sprocket 29 through a drive chain 34. As shown in Fig. 1, the sprocket 33 is smaller in 7 diameter than the sprocket 29, thus causing the pump drive shaft 32 to be driven at a higher speed than the counter-shaft 26. A By providing these speed increases between the shaft 16 and the shaft 26 and between shaft 26 and shaft 32, we are enabled to employ conventional types of hydraulic pumps which must run at a relatively higher speed than the tripper bend shaft 16.

The iii-take side of the hydraulic pump 31 communicates with a reservoir or tank 36 by means of a pipe 37. The

out-put side of the hydraulic pump 31 communicates with a pressure relief valve 38 of any well known design. by means of a pipe 39. The pressure relief valve 38 is set at a predetermined operating pressure so that the hydraulic pump maintains a pressure equal substantially to the pressure built up when the tripper is moving along the track with the belt 18, which is the lowest speed of the pump 31. When the tripper is moving along the track 12 opposite the direction of belt travel, the pump 31 operates at a higher speed, but the pressure relief valve 38 by-passes the excess fluid to the reservoir 36 through pipe 35, thereby holding the hydraulic operating circuit at a constant pressure in both directions of tripper travel.

The pump 31 delivers fluid under pressure through the valve 38 and a pipe 41 to a four-way pilot operated valve 42, of any well knowndesign. Mounted on the tripper frame 10 in position to receive fluid under pressure from the four-way pilot operated valve 42 selectively through conduits 43 and 44 is a conventional hydraulic motor 4-6. To move the tripper in one direction, the fluid is delivered to the hydraulic motor 46 through pipe 43, and the fluid is delivered from the motor through pipe 44 back to the four-way valve 42, thence through a pipe 47 and pipe to the tank 36 at atmospheric pressure.- The pipe 47 thus serves as an exhaust line for the valve 42. To reverse the tripper, the pilot operated valve 42 is actuated to reverse the flow of fluid through the pipes 43 and 44 and hydraulic motor 46.

Communicating with pipe 41 is a pipe 48 which sup plies fluid under pressure to a conventional four-way pilot valve 4-9 which operates the valve 42. Dogs 51 and 52, see Fig. l, are placed at desired limits along the tripper track 12 for engaging the valve 49 and thus reversing the direction of tripper travel. The four-way pilot valve 49 communicates with opposite sides of the pilot-operated valve 42 by means of pipes 53 and 54, and communicates with the tank 36 by means of a pipe 56 and pipes 47 and'35; In the position shown in Fig. 7, valve 49 conducts fluid from pipe 48 to pipe 53 thence to one side of the pilot-operated valve 42 to operatethe same. Fluid from the opposite side of the valve 42 and the fluid in the pipe 54, is conveyed through valve 49 to the pipe 56 and thence through pipes 47 and 35 to tank 36 at atmospheric pressure. The pipe 56 is in effect an exhaust line for the valve 49. When the pilot valve 49 is tripped to the opposite position, as shown in Fig. 6, pressure is reversed through pipes 53 and 54, thus operating the valve 42, and causing a reversal of the fluid flow through the motor 46 and a reversal of the direction of tripper travel along the track 12. The pilot valve 49 has a blocked center portion 60 and does riot release pressure atone side of the valve 42 until it is in position to apply pressure at the opposite side thereof. Also, when the valve 42 is in the center position all of its ports are closed. In other words, there is no reversal of fluid until the operation of the valves is complete. Accordingly, there is no lag in the operation of the reversing mechanism as there is when mechanical means are employed to reverse the tripper. The blocked center portion 60 is provided with a cross connection 60a which conveys the fluid from pipe 48 to pipe 53, and a cross connection 60b which conveys the fluid to the pipe 56 from either of the pipes 53 or 54 that is not connected to the supply pipe 48.

The hydraulic motor 46 drives an input shaft 58 of a worm gear speed reducer 59 through a flexible coupling 61. The speed reducer 59 has a low speed shaft 62 which is secured to a sprocket 63. The Wheels 11 of the tripper are mounted on axles 64 and 65 and secured to the axle 64 is a sprocket 66. The sprocket 63 drives the sprocket 66 through a chain 67. While we show the sprocket 66 asbeing mounted on the axle 64 it will be apparent that the sprocket could be mounted on axle 65, thereby driving the tripper through axle 65. The speed reducer arrangement between the hydraulic motor 46 and the tripper axle 64 or 65, as the case may be, is employed so as to make it possible to use conventional types of hydraulic or pneumatic motors.

Communicating with the pressure relief valve 38 is a pipe 68 which connects with a port 70 in the lower end of a valve chamber 69. A pipe 71 communicates with the upper end of the valve chamber 69 through a port 71a. In normal operation, the valve chamber 69prevents the flow of fluid from the pipe 68 to the pipe 71 which latter communicates with pipe 35. When for any reason it becomes necessary or desirable to stop movement of the tripper along the track, a valve memher in the valve chamber 69 is moved downwardly by means of a handle 101 which is connected to the valve member by a rod 105, thus connecting pipe 68 to pipe 71 and permitting the fluid to flow back to the tank 36 at atmospheric pressure. With the valve memher 100 in the position just described there is no driving force for propelling the tripper.

A pipe '72 connects pipe 68 to a fluid pressure cylinder 73 which is mounted on the tripper frame 10 by means of a suitable brackt75. Operating within the cylinder 73 is a piston 74 having a downwardly extending pis ton rod 76. Mounted at the lower endof piston rod 76 are a pair of gripping arms 77 and 77a which are adapted to engage the rail 12 upon downward movement of thepiston rod 76. Mounted on the frame 10 below the cylinder 73 is a bracket 78 having an opening 79 therein for receiving the piston rod 76. A shoulder 81 is provided on the piston rod 76 below thebracket 78. Surrounding the piston rod between thebracket 78 and the shoulder 31 is a compression spring 82. An exhaust port 83 is provided at the upper end of the cylinder 73 for releasing back pressure therefrom as the piston 74 is moved upwardly by the fluid pressure received from line 72. i

As long as there is fluid of sufficient pressure within the cylinder 73 acting on the piston 74, the shoulder 81 on the rod 76 is forced upwardly against the compression spring 82 and the rail gripping arms 77 and 7 711 are in the inoperative position. If for any reason there is a release of pressure, such as would result when the handle 101 moves the valve member 100 from between the ports 70 and 71a or when there is a break in the hydraulic or pneumatic lines, or when a pump driving chain is broken, the compression spring 82 forces the piston rod 76 downwardly and moves the rail gripping arms into engagement with the rail 12.

If the drive chain 67 should break, the tripper becomes a free rollingbody on the track so long as the pressure in the cylinder 73 is suflicient to hold the gripping arms 77 and 77a in the released position. However, as the tripper gains velocity as it moves along its track in the direction of belt travel, the relative velocity of the conveyor belt around the pulley 17 decreases, thereby driving the pump 31 at a slower speed. As a result, the hydraulic pressure from the pump 31 decreases and the hydraulic motor then speeds up under a noload condition, thus further reducing the hydraulic pressure. By having a proper balance of pressure exerted by the spring 82 and piston 74 for normal operating conditions, the gripping arms are automatically set upon release of pressure before the tripper would have gained sufficient speed to cause any damage to the tripper and conveyor apparatus.

The valve member 100 is connected to a downwardly extending rod 86 and connected to the lower end of rod 86 is a releasable connecting member 87 having downwardly extending legs 85 and 85a. Each of the downwardly extending legs is provided with a recess 88 adjacent the lower end thereof. Mounted on frame beneath the connecting member 87 are a pair of vertically spaced brackets 89 and 91 having openings 92 and 93 therein respectively, for receiving a vertical rod 94. Extending laterally from the rod 94, adjacent to the upper end thereof, is a pin 96 which is adapted to fit in the recess 88 thereby releasably connecting the rod 86 to the rod 94.

Secured to the lower end of the rod 94 by means of a set screw 97 is a bracket 98. An opening 99 is provided in the outer end of the bracket 98 for slidably receiving the lower end of the piston rod 76. When there is a release of pressure in the line 72 the rod 76 moves downwardly to operate the gripping arms 77 and 77a, and the shoulder 81 engages the bracket 98 thereby moving the rods 94 and 86 downwardly and permitting fluid to flow through the valve chamber 69. With the valve member 100 in position to connect pipe 68 to pipe 71, thefluid is recirculated to the tank 36 as hereinbefore described through pipe 35. It will be apparent that if air pressure is employed instead of hydraulic pressure, the pipes 47, 71 and 35 would not be necessary and exhaust ports could be substituted therefor.

Mounted on the frame 10 and spaced laterally from the lower portion of rod 94 are a pair of vertically spaced brackets 102 and 103. Slidably mounted in the brackets 102 and 103 for vertical movementis a rod 104 having .mounted adjacent the bottom thereof a U-shaped bracket 106. Mounted for rotation in the U-shaped bracket 106 is a roller 107. Extending outwardly from the frame 10. between the upper end of rod 104 and rod 94 is a pin 108. Pivotally mounted on the pin 108 is a bar 109 having one end thereof engaging the top of the rod 104 and the other end thereof engaging a collar 111 which is secured to the rod 94 by means of set screw 112. Surrounding the rod. 94, between bracket 91 and the collar 111 is, a compression spring 113 which biases the rod 94 upwardly and positions the valve member 100 between the ports 70 and 71a thus blocking the flow of fluid through valve chamber 69. Positioned outwardly of each of the dogs 51 and 52 is a bracket 114 having inclined surfaces 116 and 117 in positionto be engaged by the roller 107. As the roller 107 engages the inclined surface of the bracket 114, the rod 104 is moved upwardly, pivoting the arm 109 and causing the collar 111 and the rod 94 to be moved downwardly. Upon downward movement of the rod 94 the valve member 100 is positioned below the ports 70 and 71a causing the fluid to recirculate to the tank 36 thus releasing pressure within the cylinder 73. Upon release of pressure in the cylinder 73, the spring 82 moves the rod 76 downwardly thereby causing the gripping arms 77 and 77a to engage the rail 12 as shown in Fig. 4. It will thus be seen that by providing the brackets 114 outwardly of the dogs 51 and 52 and the pressure release means associated therewith there is no possibility of the tripper running away. In other words the brackets 114, roller 107, rod 104, and the linkage to valve chamber 69 provides an extra safety device which prevents the tripper from running away. After the rod 104 has been moved upwardly by the bracket 114, it is necessary to disengage the rod 94 from the rod 36 before the tripper can be placed into operation again. The rods 86 and 94 are disengaged by moving the connecting member 87 out of engagement with the pin 96. The rod 86 is then moved upwardly by the handle 101, thus positioning the valve member 100 between the ports and 71a and blocking the flow of fluid from pipe 68. The pressure is then built up in the system and the tripper is moved away from the bracket 114. As the pressure builds up in the cylinder 73 the rod 76 and shoulder 81 are raised thus releasing pressure on the bracket 98 and permitting the spring 113 to force the rod 94 upwardly. When the rod 94 is thus moved upwardly the pin 96 falls into the recess 88 thereby connecting the rods 94 and 86.

When the valve member is moved manually to connect the ports 70 and 71a the spring 113 cannot force the valve member 100 into position between the ports 70 and 71a due to the fact that the fluid is recirculated to the reservoir 36 thus releasing pressure in the cylinder 73 and causing the spring 82 to hold the bracket 98 and rod 94 in the down position. It will thus be seen that the handle 101 would have to be actuated to place the apparatus back into operation.

From the foregoing it will be seen that we have devised an improved automatic tripper which has all the advantages of the trippers heretofore employed and one which requires very little maintenance and adjustments to keep the same in operation. By providing pneumatic or hydraulic means for propelling the tripper along the track and automatic means for stopping the tripper in the event there is a pressure failure, we have eliminated the chances of a tripper running away. Also, by providing automatic means for reversing the fiow of fluids through the propelling motor upon a predetermined distance of tripper travel, there is a reversal of the tripper along the track without the necessity of having to employ electrical or mechanical clutch means for reversing the same.

While we have shown our invention in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing from the spirit thereof, and we desire, therefore, that only such limitations shall be placed thereupon as are specifically set forth in the appended claims.

What we claim is:

l. The combination with a conveyor belt tripper frame mounted on wheels and having pulleys journaled thereon around which a conveying belt passes and which are driven by said belt, of a fluid pressure pump mounted on said frame in driven relation with one of said pulleys, means supplying fluid to said pump, a fluid pressure motor mounted on said frame and connected in driving relation with said wheels, conduits communicating with opposite sides of said motor, a four-way valve having an exhaust port and communicating with said conduits and said pump, said valve being operable to introduce fluid selectively under pressure to the motor through one of said conduits and discharge fluid through the other of said conduits and said exhaust port, and a four-way pressure operated pilot valve communicating with said pump and with the four-way valve to be operated for actuating the same upon a predetermined distance of tripper travel, said pilot valve having an exhaust port and being constructed and arranged'for the operation thereof to be completed before there is a change of flow in the valve to be controlled.

2. The combination set forth in claim 1 in which the pilot valve is provided with a blocked center portion having awe -22s cross connections which convey fluid under pressure selectively from a source of supply to opposite sides of the four-way valve to be operated and exhaust thefluid from the four-way valve to be operated opposite the side thereof that'pressure is applied.

3". The combination with a conveyor belt tripper frame mounted on wheels for rotation along rails and having pulleys journaledthereon around which a conveying belt passes andwhich are. driven by said belt; of a fluidpressure pump mounted on said'frame in driven relation with one of said pulleys, means supplying fluid to said pump, a fluid pressure motor mounted on said frame in driving relationwith said wheels, conduits conveyingfluid under pressure from said pump selectivelyto opposite sidesof the motor, a pressure relief valve in one of said; conduits maintaining a constant pressure therein, a rail gripping member attached to saidfrarne and extendingdowriwardly t refr m n. pos t on to. e seqne f id d means actuating said rail gripping member upon a predetermined decrease of pressure in said conduits andconcomitantly actuating other means which, release the pressure in saidconduits.

4. The combination, with a conveyor belt tripper frame mounted on wheels for rotation along rails and having pulleys journaled thereon around which a conveying belt passes and which are driven by said belt, of a fluid pres sure pump mounted on said frame in driven relation with one of said pulleys, means supplying fluid to said pump, a fluid pressure motor mounted on said frame in driving relation with said wheels, conduits conveying fluid under pressure from said pump selectivelyto opposite sides of the motor, a pressure relief valve in one of said conduits. maintaining a constant pressure therein, a rail gripping member attached to said frame and extending downwardly therefrom in position to engage one of said rails, a cylinder mounted on the frame, said cylinder communicating ad-. jacent the bottom. thereof with the conduits supplying fluid under pressure and being provided with an exhaust port adjacent the top thereof, a piston in said cylinder, a piston rod connecting said piston tov the, rail gripping member, and means associated with said rod, adapted upon a predetermined decrease of pressure in said; cylinder to bias said rod downwardly and actuate said rail gripping member. 7 A

5. The combination set; forth. in claim 4 in which the means for biasing the rod downwardly upon a predeter mined decrease of pressure in the cylinder wmPrises a bracket secured to the frame below the cylinder and having an opening therein slidably receiving said rod, a shoulder on said rod beneath said bracket andacoxnpression spring surrounding said rod between said bracket and said shoulder.

6 The combination with a conveyor belt tripper frame mounted on wheels for rotation along rails and having pulleys journaled thereon around which a conveying belt passes and which are driven by said belt, of a fluid pressure pump mounted on said frame in driven relation with one of said pulleys, means supplying fluid to said pump, a fluid pressure motor mounted on said frame in driving relation with said wheels, conduits conveying fluid under pressure from said pump selectively to opposite sides of the motor, a pressure relief valve in one. of said conduits maintaining a constant pressure therein, a rail gripping member attached to said frame and extending down ardly therefrom and operable to engage one of said rails upon a predetermined decrease of pressure in said conduits, a valve chamber mounted on the frame and having a pair of vertically spaced ports therein, one of said ports being communication with the conduit conveying fluid under pressure and the other being an exhaust port, a valve member in said chamberdisposed to block the flow of fluid therethrough when positioned be tween said ports and; to exhaust; saidfluidwhen moved to connect salidports, andnieans moving said valve membet to connect said-port s, upp'n'a predetermined distance of tripper travel;

' The combination set forth in claim 6 in which the means for moving the valve member to connect, said'ports comprises a rod attached to said valve member and an operating handle attached to said rod for moving the same. i v

8, The combination set forth in claim 6 in which the means for moving the valve member to connectsaidports comprises a rod attached to the valve member andextending downwardly therefrom a second rod mounted on said frame for vertical movement positioned laterally of the first, mentioned rod, a collar on the first mentioned rod, a linlcpivotally rncunted on the. frame betweensaid e and. ha n Que endfia a n e t aid ce la andthe other endthereof engaging the top of said second od. an m a he we. d. o aid' ewns rod adapted to be actuated uponapredetermined distance of tripper travel, and move the said secondrod upwardly.

9 The combination setforth in, claim 8 in which a con lpression. spring. surrounds the first mentioned rod beneath the collar, and a spring abutment is mounted on said frame in position to engage'the bottom of said spring, said spring biasing the valve member, upwardly to block the flow of fluid through thevalye chamber.

10. The combination set. forth in claim 8 in which the first mentioned rod is diyidedintodetachable sections,

11. lfor. use in actuating a rail gripping. member of a conveyor belt tripper. mounted for rotation along rails and propelled by a fluid pressure nnit which is driven by a moving conveyor belt, a cylinder mounted on said tripper above one of said rails, a conduit connecting the fluid pressure unit to. the cyli der adjacent the bottom thereof, there being an exhaust, opening adjacent the top of said cylinder, a piston in said cylinder, a 'pistonrod connecting said piston to. said rail gripping member, and means; adapted upon a predetermined decrease of pressure. in said. cylinder to biassaid. rod downwardly and actuate said rail gripping member.

12. For. use in actuating a rail gripping member of a conveyor belt tripper mounted for-rotation along rails, a a sr o ed. on a e a o e ne f, s r s; a conduit supplying. fluid. under pressure, to the cylinder adjacent the bottom thereof, there being an exhaust opening adjacent the top of said cylinder, a piston in said cylinder, a piston rod connectingsaid pistonv to said rail gripping member, means adapted to. bias said rod down: e r an ac ua aid ra gripping emb upon release of pressure infsaid cylinder, a valve chamber mounted on. the tripper and having a pair of vertically spaced, ports therein, one of said pcrt s being in communi; cation with" said conduit supplyihg'fluid under pressure. and the otherbeing an exhaust port, a valve member in said valve chamber disposed to block the, flow of fluid therethrough whenpositioned between said ports and to, exhaust said fluid when moved to. connect said ports and means moving said valve member. to connect said ports] upon a predetermined distance of; tripper travel.

Re erenc s. Cited. th fil thi P n UNITED STATES PATENTS 758,810 Baldwin May 3, 1904 1,575,655. Stinson Mar. 9 1 926 1,651,656. Yerkes Dec. 6, 1927 1,937,077 West Nov. 28, 19.33 2,906,280 Schlueter June 25, 1935 2,081,465 Stewart et a1. May 25., 193.7 2,228,411 Sheridan Jan. 14, 1941

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