US3399603A - Air and oil cylinder - Google Patents

Description

nited States ABSTRACT OF THE DISCLOSURE There is herein disclosed a combination oil-air cylinder in which air exhausted from the air cylinder in a manner causing cooling of the air is used to cool the oil cylinder and in which valve means in the oil cylinder control the rate of fiow of oil in a new and improved manner.

This invention relates to control devices of the type utilized to impart movement to and control movement of power operable machinery. More particularly, this invention relates to a combination oil-air cylinder by which a press unloading device or the like may be moved between operative positions and whereby the movement between the positions may be controlled.

This invention is adapted for use with a swinging arm type press unloader as shown in prior Patents US. 3,206,- 040 and US. 3,204,783. In prior art apparatus of this type, an air cylinder has been provided to move the swinging arm between a down position adjacent a die cavity in a press and an up position spaced outwardly therefrom. A separate oil cylinder has been provided to control the rate of return of the swinging arm from the up position to the down position. The primary object of the present invention is to provide new and improved means for controlling a swinging arm type unloader. In general the inventive features reside in the provision of a combination oil-air cylinder by which several prior art problems have been eliminated or substantially overcome and by which ease of manufacture, ease of assembly, and reliability in use have been increased.

Referring now to the drawing, an illustrative embodiment of the oil-air cylinder is shown in side elevation, partly in section, with an associated fluid control system shown diagrammatically.

Referring now to the drawing, an air cylinder and an oil cylinder 12 are mounted in telescoped relationship concentrically about a common central longitudinal axis 14. The air cylinder 10 comprises a cylindrical tubular member 16 and spaced end caps formed by wall members 18, 20 which define a cylindrical chamber 22. The end wall portions 18, 20 include annular disc portions 22, 24 which, in the preferred embodiment, fit within the end portions of the tubular member 16. The outer ends of the end wall members 18, 20 may be enlarged and of polygonal shape as indicated at 26 to receive fastening devices 30 such as tie rods for securing the end Walls and mounting bolts or the like by which the air-oil cylinder may be fixedly mounted relative to the swinging arm.

An air inlet port 32 is provided at one end of the air cylinder and an air outlet port 34 is provided at the other end. A supply of high pressure air 36 is connected to the inlet port 32 through a conventional control valve 38 which is adapted to selectively connect a supply line 40 to an inlet line 42 at predetermined times in a cycle of operation of the press unloading machine with which the air-oil cylinder is to be associated. An exhaust line 44 is provided to connect the exhaust port 34 to the inlet line 42 or to atmosphere via line 45 through the valve 38 at preselected times.

A piston means in the form of an assembly 44 is reciprocably mounted in the air cylinder chamber 22 and atent O 3,399,603 Patented Sept. 3, 1968 divides the air cylinder chamber into variable volume upper and lower chamber portions. The piston assembly is slidably mounted on a central longitudinally extending support rod means 46 which is fixedly mounted in the plate 20. The piston assembly comprises a bronze bushing or the like 48 mounted in and supporting a cap element 50. A spacer disc 52 is mounted about the cap element 50 and slidably engages the inner surface of the air cylinder chamber as indicated at 54. A conventional cup-shaped packing 56 is secured on the piston assembly by a piston follower plate 58. A backing plate 60 abuts the spacer plate 52 and threadably receives suitably fastening elements 62 by which the elements of the piston assembly are securely fastened to one another.

The piston assembly 44 is formed integrally with and is part of the oil cylinder 12 which extends through and defines part of the upper chamber portion of air chamber 22. The oil cylinder is formed by an elongated cylindrical tubular member 64 which is closed at one end by an annular disc portion 65 of the cap element 50 of the piston assembly and at the other end by an annular end plate 66 to define a cylindrical chamber 68. The tubular element 64 is slidably movable longitudinally within the air cylinder 16 relative to the support rod 46 and in effect acts as a piston rod for the piston assembly 44 to which it is fixedly attached as by suitable welds or the like. The cylinder 64 is slidably supported in a bushing means in the form of a bearing sleeve 71 mounted within the end plate element 18 and the support plate 26. The bearing sleeve 71 is provided with a plurality of longitudinally extending circumferentially spaced slots 76 for a purpose to be hereafter described in detail.

Support rod 46 is securely fastened in the plate 20 and includes a shoulder portion 78, which abuts the end plate 20, and a reduced diameter shaft portion 80 which extends into a correspondingly dimensioned hole 82 in the end plate. The end 83 0f the shaft portion 80 extends beyond the end plate 20 and is threadably secured by means of a threaded nut arrangement 84. The other end 85 of the support shaft 46 is provided with a reduced diameter portion 86 providing a shoulder 88 on which a valve body means in the form of valve disc body element 90 is secured by means of a valve supporting sleeve 92 and a threaded fastener arrangement 94 to divide the oil cylinder into variable volume upper and lower chamber portions. A further reduced portion 96 of the support rod extends beyond the threaded fastening means 94 and terminates in a chamfered end portion 98 which is adapted to be matingly slidably received within a correspondingly dimensioned chamber 100 in a cap sleeve element 102. The entrance 104 to the chamber 100 is similarly chamfered to facilitate sliding engagement. A sealing groove and O-ring 108 are provided to effect a seal between the shaft portion 96 and the sleeve 102 in the engaged position shown. Chamber 100 terminates in a passage 110 in a rod like extension 112 by which the movable cylinder 64 may be connected to the machine to be operated. A removable fill cap 114 is provided in the end of the passage 110 to enable the oil cylinder 64 to be filled.

A flow controlling valve assembly is provided in the oil cylinder and includes a plurality of oil passages 122 extending longitudinally through the valve body 90. Valve means in the form of a valve plate 124 is slidably mounted on the valve sleeve 92 on support rod 46 and is movable between an open position, as shown in the drawing, permitting flow of oil through the passages 122 and a closed position in abutting engagement with the adjacent side surface of the valve body 90 and closing the passages 122. A bypass 126 of reduced diameter may be provided to enable flow in either direction at certain times. Oil flow between opposite sides of the valve plate 90 is also provided by a central longitudinally extending passage 128 in the support rod 46 which terminates at one end at 130 and at the other end in transverse passage means 132. The rate of flow of oil through the passage is controllable by means of a conically tipped control rod 134 which extends within an extension 136 of the passage 128 to the other end of the air-oil cylinder. Control rod 134 is connected, as at 138 to an adjustment rod 140 which is provided with tool receiving means 142 for making adjustments and fastening means 144 for securing the rod in any of a plurality of adjusted positions.

An O-ring seal 150 is provided to prevent leakage of oil from passage 136. The piston assembly 44 is sealed on the support rod 46 by means of spaced sealing assemblies 152, 154 which are identical but reversely positioned. Each sealing assembly comprises a plurality of packing elements 156, a spacer 158, and wafer type spring means 160. Suitable O-ring seals are provided as necessary between the bushing 48 and the cap 50, between the end cap 50 and the cylinder 64, about the support shaft 46, and between the end plate 20 and the wall of cylinder Wall 10. Thus, the air cylinder chamber 22 is substantially airtight between the piston assembly 44 and the end plate 20. However, at the other end of the air chamber 22, passages 76 are provided for the escape of air to the atmosphere during movement of the piston assembly from the retracted position adjacent end wall 20 to an extended position adjacent end wall 18.

In operation, high pressure air from the source 36 is delivered through a first passage means comprising line 40, valve 38, line 42, and inlet 32 to drive the piston assembly 44 from the position shown toward the other end of the cylinder. The connecting rod portion 112 is connected to the device to be operated and its movement results in the desired movement of the device being operated. In association with a swinging arm press unloader, the swinging arm is moved upwardly from a down position adjacent the press to an up position spaced outwardly from the press as the piston assembly 44 moves from its lowermost position adjacent end wall 20 to its uppermost position adjacent end wall 18. As the piston assembly 44 is extended upwardly, the oil cylinder 64 is also moved by sliding action in the bearing 74. During the upward movement of the piston, the outlet port 34 may be connected by line 44 through valve 38 to exhaust line 45. When the piston assembly is to be returned to the starting position, it is a feature of the present invention to connect the inlet port 32 and line 42 to the outlet port 34 and line 44 through the valve 38 a first passage means comprising. Thus, as the piston is returned to its starting position, air in the air cylinder is driven through the lines 42, 44 from one side of the piston assembly to the other side. The air undergoes a substantial temperature drop and provides a low temperature cooling medium which is then utilized in the air cylinder to cool the oil cylinder casing.

When the oil cylinder is initially filled with oil with the oil cylinder in a vertical attitude in a retracted position, the oil enters through the passage 110, passage 128, and outlet 132. The oil level is maintained approximately at 170 so as to provide a pocket of air above the oil which is subsequently mixed with the oil to provide compressibility in operation.

The oil cylinder also includes valve means in the form of a valve element 174 which is slidably mounted on the support shaft 46 and biased outwardly in spaced relationship to the piston assembly 44 by a spring element 176 fixedly mounted on the piston assembly at one end and on the valve element at the other end. The valve 174 is provided with a flat side wall 178 adapted to abut the side wall 180 of the valve body 90 and to close the ports 122 when the piston assembly 44 is moved upwardly to the extended position. A centrally located annular groove 182 in valve 174 is connected through the face 178 by a plurality of circumferentially spaced transversely extending passage means 184. The axial spacing of the groove 182 relative to the face 178 is such as to communicate with the outlet port 132 in the closed position of the valve against the face 180. Consequently, during return movement, high pressure oil coming through passage 132 will fill the groove 182 and travel through passages 184 to react against the face 180 and positively separate the valve 174 from the valve body 90. The valve 174 is mounted in an enlarged portion 186 of the oil cylinder chamber so that substantial clearance is provided at 188 between the periphery of the valve and the inner wall of the oil cylinder. In this manner, oil in the cylinder is able to flow around the valve as the oil cylinder moves relative thereto in the latter stages of extension of the device. When the valve 174 abuts the valve body 90, the piston assembly 44 will move against the spring 176 toward the valve element 178 and a throttling action will occur as the oil flows through the restricted passage 188 between the valve element and the enlarged portion 186 of the cylinder wall around the valve element 174 and the valve body which has a corresponding diameter. In this manner, the terminal portions of the upward movement are cushioned by the aerated oil in the oil cylinder and the movement is decelerated at a controlled rate until the piston assembly 44 bottoms against the valve 174.

Thus, the up operation of the device comprises delivery of high pressure air through the inlet 42 to the air cylinder 22 which causes the piston assembly 44 to be moved from its normal retracted position, shown in the drawing, adjacent the end wall 20 to an extended position adjacent the end wall 18. With the connecting rod 112 connected to a swinging arm of a press unloader, the swinging arm is moved from a lowered position adjacent a press bed to a raised position relative thereto. In order to return the swinging arm from the raised position to the lowered position, the high pressure air is exhausted from the air cylinder and the swinging arm is allowed to return to its lowered position by gravity. The oil cylinder is effectively divided into an upper and lower chamber by the valve body 90 with the aerated oil being driven into the upper chamber during upward movement and into the lower chamber during downward movement. The rate of return of the swinging arm is controlled by the rate of flow of oil in the oil cylinder 12 from the upper chamber to the lower chamber.

More specifically, as the piston assembly 44 is moved to the extended position, the oil cylinder 64 is slidably displaced relative to the bearing 74 and relative to the sup port rod 46 and the valve body 90 attached thereto. As the oil cylinder is extended, the shaft portion 96 becomes disassociated from the sleeve 102 which, forming part of the oil cylinder casing, is also moved outwardly. As the piston assembly 44 is extended, the volume of the lower oil chamber diminishes while the volume of the upper oil chamber increases. As the valve element 174 and the wall portion 50 approach the fixed valve body 90, oil in the lower oil cylinder chamber is driven through the passages 122 and into the expanding upper chamber on the other side of the valve body 90. Valve 124 is main tained in the open position shown by the oil under pressure as it flows through the passages 122. After the shaft portion 96 separates from the sleeve 102, the quantity of oil in the upper chamber is such as to provide a substantial depth of oil above the end of the passage 128 in rod portion 96. When the piston assembly 44 approaches the end of its outward movement, the valve element 174 comes into abutting engagement with the valve body 90 and passages 122 are closed. The inside diameter of the oil cylinder is constant except at the central enlarged portion 186 which tapers gradually from the shoulder 187 toward the piston assembly 44 for a substantial distance so as to provide a gradually restricted opening around the valve 90. The enlarged portion of the enlarged portion of the oil cylinder at 186 moves by the valve body 90 permitting the restricted flow of oil after the passages 122 are closed and the piston assembly 44 continues movement toward the valve body 90 aganist the bias of the compression spring 176 and the terminating movement of the swinging arm is cushioned by oil trapped between the piston assembly and the valve body 90 as outward movement is terminated. Air in the air compression cylinder is exhausted through the slots 76 in the bushing 74 and the line 44 may be connected to exhaust line 45 in the valve 38.

Return movement of the swinging arm is efiected by opening line 42 so that the high pressure air can exhaust from the air cylinder through the port 32. The line 42 may be connected to exhaust or, preferably, connected to the line 44 to deliver the exhausting and cooled air through the port 34 into the air cylinder chamber to cool the oil cylinder. The swinging arm will move downwardly under gravity as the high pressure air is exhausted and the oil cylinder 12 and piston assembly 44 will'be forced toward the end wall 20. As the downward movement of the swinging arm is started, the aerated oil in the upper chamber of the cylinder is immediately forced through opening 130 into passage 128 and through passage means 132 to the groove 182 in the valve element 174. The oil is delivered from the groove 182 by passage means 184 into the face 180 of the valve body 90 to positively separate the valve 174 from the valve body 90 and permit flow outwardly along the face 180 of the valve body to open passage 132 and bypass passage means 126. In addition, the aerated oil initially flows around the valve body 90 and the valve 174 until the enlarged portion 186 of the oil cylinder slides past the valve body. When the valve element 174 clears the passage 132 and valve body 90 enters the narrow diameter portion of the cylinder, the rate of flow of oil from the upper portion of the oil chamber to the lower portions of the oil cylinder is controlled by the position of the adjustable control rod 134. The valve element 124 is forced against the adjacent face of the valve body 90 at the beginning of the return movement to close the passages 122. Oil flows out of the passage 132 into the expanding lower chamber at a rate suflicient to lower the swinging arm at the rate desired. Toward the end of downward movement of the piston assembly 44 and oil cylinder 64 toward the retracted position, the rod end 96 enters the chamber 110 which causes the remaining aerated oil to be trapped between the valve body 90 and the wall 66 so as to cushion and stop the downward movement of the swinging arm.

Among the many advantages of the present invention are:

(1) increased compactness reducing the space required for mounting of the parts on the machine with which it is to be utilized.

(2) Reduction in the number of assembly steps and assembly procedures required to install the air-oil cylinder device on a machine with which it is to be used.

(3) Reduction in stress on the air-oil cylinder and associated parts in use by transmitting forces developed during raising and lowering movements through a common central axis.

(4) Reduction in the overall length of the apparatus.

(5) Utilization of aerated oil to cushion both terminal portions of the movement.

(6) Reduction of leakage of oil by reducing the number of fittings required for the oil system.

(7) Reduction of leakage of oil in the oil cylinder by reducing the number of scaled joints.

(8) Reduction of leakage of oil by cooling of the oil and the oil cylinder parts to reduce expansion. and contraction.

(9) Reduction of frost problems in the air cylinder by heating from the oil cylinder.

(10) Reduction in the number of total parts by combining the functions of various parts.

' (l1) Eliminating the requirement for separate tie rods for the oil cylinder.

(12) Eliminating the requirement for a separate piston rod for the air cylinder.

It will be apparent to those skilled in the art to which this invention relates that the many advantages of the present invention may be otherwise obtained by various modification and change in the details of construction of the illustrative embodiment. Accordingly, it is intended that the claims appended hereto be construed to include other apparatus and arrangements which utilize the inventive principles except insofar as limited by the prior art.

The invention claimed is:

1. Apparatus for moving a swinging arm of a press unloader or the like between a lowered position adjacent a press and a raised position located outwardly away from the press comprising:

an air cylinder operable by high pressure air between a retracted position and an extended position to move the swinging arm from the lowered position to the raised position and operable between the extended position and the retracted position to move the swinging 'arm from the raised position to the lowered position,

an oil cylinder mounted within said air cylinder to cushion the terminal portions of the movement and to control the rate of movement between the extended position and the retracted position,

valve body means mounted in said oil cylinder and dividing said oil cylinder into upper and lower chamber portions and having flow passage means connecting said chamber portions, support rod means mounted within said oil cylinder, valve means mounted on said support rod means and being cooperable with said valve body means to control flow of oil through said passage means between said upper chamber portion and said lower chamber portion so as to cushion the terminal portions of the movements and control the rate of movement between the extended position and the retracted position, said valve means comprising:

a first valve element slidably mounted on said support rod means on one side of said valve body means and being movable into engagement with said valve body means to close said flow passage means during the terminal portion of the movement from the retracted position to the extended position, spring means spacing and holding said first valve element in spaced relationship to said valve body means during the other portion of the movement from the retracted position to the extended position and being compressible to hold said first 'valve element on said valve body means during the terminal portion of the movement, a second valve element slidably mounted on said support rod means on the other side of said valve body means and being movable to an open position relative to said flow passage means permitting free flow during movement from the retracted position to the extended position and to a closed position relative to said passage means restricting free flow during movement from the extended position to the retracted position. 2. Apparatus for moving a swinging arm of a press unloader or the like between 'a lowered position adjacent a press and a raised position located outwardly away from the press comprising:

an air cylinder operable by high pressure air to move the swinging arm from the lowered position to the raised position,

an oil cylinder mounted within said air cylinder to cushion the terminal portions of the movement and to control the rate of movement,

valve body means mounted in said oil cylinder and dividing said oil cylinder into upper and lower chamher portions and having flow passage means connecting said chamber portions, support rod means mounted within said oil cylinder, valve means mounted on said support rod means and being cooperable with said valve body means to control flow of oil through said flow passage means, 1

said support rod means having a central longitudinally extending oil passage providing for flow past said valve body means,

one opening for said oil passage being located on one side of said valve body means,

and another opening for said oil passage being located on the other side of said valve body means,

and a control rod mounted in said oil passage and being associated with one of said openings to control the rate of flow of oil through said oil passage.

3. The invention as defined in claim 2 and wherein portions of said oil cylinder being of varying inside diameter and providing restricted flow passages between said upper chamber portion and said lower chamber portion.

4. Apparatus for moving a swinging arm of a press unloader or the like between a lowered position adjacent a press and a raised position located outwardly away from the press comprising:

an air cylinder operable by high pressure air to move the swinging arm from the lowered position to the raised position,

an oil cylinder mounted within said air cylinder to cushion the terminal portions of the movement and to control the rate of movement,

valve body means mounted in said oil cylinder and dividing said oil cylinder into upper and lower chamber portions and having flow passage means connecting said chamber portions,

support rod means mounted within said oil cylinder,

valve means mounted on said support rod means and being cooperable with said valve body means to control flow of oil through said passage means between said upper chamber portion and said lower chamber portion so as to cushion and control the rate of movement of said air cylinder,

said support rod means terminating in a shaft portion extending into said upper chamber portion,

said support rod means having a central longitudinally extended oil passage providing for flow of oil past said valve means,

one opening for said oil passage being located on one side of said valve body means in the end of said shaft portion,

another opening for said oil passage being located on the other side of said valve body means,

and sleeve means mounted on said oil cylinder and being cooperable with said shaft portion to close said one of said openings to the upper chamber portion in the retracted position.

5. The invention as defined in claim 4 and having an oil filling passage provided in said sleeve means.

6. The invention as defined in claim 4 and said sleeve means forming connecting rod means for connecting said air cylinder to the swinging arm through said oil cylinder.

7. Apparatus for moving a swinging arm of a press unloader or the like between a lowered position adjacent a press and a raised position located outwardly away from the press comprising:

an air cylinder operable by high pressure air to move the swinging arm from the lowered position to the raised position,

an oil cylinder mounted within said air cylinder to cushion the terminal portions of the movement and to control the rate of movement,

support rod means mounted within said oil cylinder,

valve body means mounted in said oil cylinder and dividing said oil cylinder into upper and lower chamber portions and having flow passage means connected said chamber portions,

valve means mounted on said support rod means and being cooperable with said valve body means to control flow of oil between the upper chamber portion and the lower chamber portion so as to cushion and control the rate of movement of said air cylinder,

said valve means comprising a valve element slidable on said support rod means,

a surface of said valve body means abuttingly engageable with said valve element in one of said positions to close said flow passage means,

oil passage means in said support rod means extending through said valve body means and connecting said lower chamber portion of said oil chamber to said upper chamber portion of said oil chamber,

an oil outlet passage in said support rod means located in alignment with said valve element in the abutting position against said valve body means,

an oil passage means provided in said valve element and connected to said oil outlet passage to positively separate said valve element and said valve body means as movement begins from the one of said positions to the other of said positions.

8. The invention as defined in claim 7 and wherein said oil passage means comprises an annular oil groove and transverse passage means extending toward said valve body means. I

9. Apparatus for controlling the rate of movement of an associated movable mechanism. between an extended position and a retracted position and for cushioning the terminal portions of the movement comprising:

a movable oil cylinder having axially spaced end wall portions and being filled with compressible aerated oil and connected to the movable mechanism and movable therewith,

fixedly mounted support rod means extending into said oil cylinder and supporting said oil cylinder for sliding movement relative thereto between an extended position and a retracted position,

valve body means fixedly mounted on said support rod means and dividing said oil cylinder into upper and lower chamber portions and having flow passage means connecting said chamber portions,

valve means mounted on said support rod means and being cooperable with said valve body means to control flow of oil through said flow passage means between said chamber portions,

said valve means comprising:

a first valve element slidably mounted on said support rod means on one side of said valve body means, i I

a spring means holding said first valve element in spaced relationship to the adjacent end wall portion of said oil cylinder,

said first valve element being in an open position spaced from said valve body means in the retracted position and movable along said support rod means with said oil cylinder during movement from the retracted position .to the 7 extended position to a closed position in engagement with said valve body means and restricting flow through said How passage means during the terminal portion of the movement from the retracted position to the extended position, 1

said spring means permitting movement of said oil cylinder relative to said first valve element after engagement of said first valve element and said valve body means and compressibly holding said first valve means on said valve body means, first restricted passage means providing for flow past said valve body means after engagement of said first valve element with said valve body means to permit restricted flow around said first valve element and said valve body means during the terminal portion of the movement from the retracted position to the extended position,

means for separating said first valve element from said valve body means during movement from the extended position to the retracted position and for returning said first valve element to the open position,

a second valve element on the opposite side of said valve body means movable to an open position relative to said flow passage means during movement from the retracted position to the extended position and to a closed position relative to said flow passage means during movement from the extended position to the retracted position.

a second restricted passage means providing flow past said valve body means when said second valve element is in the closed position and controlling the rate of movement between the extended position and the retracted position,

and cushioning means etfective during the terminal portion of the movement from the extended position to the retracted position.

10. The invention as defined in claim 9 and wherein said second restricted passage means comprising an oil passage through said valve body means connecting said chamber portions, an inlet opening spaced axially beyond said valve body means and located in said upper chamber portion, and an outlet opening spaced axially beyond said valve body means and located in said lower chamber portion.

11. The invention as defined in claim 10 and having adjustable fiow control means associated with said oil passage to vary the rate of flow of oil therethrough to obtain a predetermined rate of movement of the associated device.

12. The invention as defined in claim 11 and said second restricted passage means, oil passage and said flow control means being mounted in said support rod means.

13. The invention as defined in claim 10 and wherein said second restricted passage means further comprises a bypass passage through said valve body means permitting restricted fiow from the upper chamber portion to the lower chamber portion when the second valve element is in the closed position and the first valve element is in the open position.

14. The invention as defined in claim 10 and wherein said second restricted passage means further comprises a passage between the oil cylinder and the valve body means open during initial movement and closed during the rest of the movement of the oil cylinder from the extended position to the retracted position.

15. The invention as defined in claim 14 and wherein the passage is formed by varying the inside direction of said oil cylinder.

16. The invention as defined in claim 15 and the upper portion of said oil cylinder having a diameter substantially equal to the diameter of said valve body means so as to prevent flow therebetween, and the lower portion of said oil cylinder having a diameter greater than the diameter of said valve body means so as to permit flow therebetween.

17. The invention as defined in claim 16 and the lower portion of said oil cylinder being tapered so as to provide a varying diameter defining a variable flow passage with said first valve means providing cushioning means as said oil cylinder is moved from the retracted position to the extended position.

18. The invention as defined in claim 9 and said cushioning means for cushioning the return movement from the extended position to the retracted position comprismg:

a plug member formed on the end of said support rod in the upper chamber portion, and

a sleeve member in said upper chamber portion and arranged to receive said plug member and trap and compress a portion of the aerated oil therebetween during the terminal portion of the movement from the extended position to the retracted position.

19. The invention as defined in claim 18 and wherein said second restricted passage means comprising:

an oil passage in said support rod extending through said valve body means and connecting said chamber portions,

an inlet opening in said upper chamber portion at the upper end of said plug member, and

an outlet opening spaced axially beyond said valve body means and located in said lower chamber portion.

20. The invention as defined in claim 19 and wherein said first valve element having passage means connectable to said outlet opening in the closed position in engagement with said valve body means to provide for flow of high pressure oil from the upper chamber portion to the lower chamber portion between the first valve element and the valve body means to cause separation of the second valve element and the valve body means as the return movement from the extended position to the retracted position is started.

References Cited UNITED STATES PATENTS 2,746,557 5/1956 Augustin 928 3,149,541 9/ 1964 Hunter et al 928 3,302,533 2/1967 Hutter et al. 928

FOREIGN PATENTS 149,708 1/ 3 Australia. 819,353 9/ 1959 Great Britain.

PAUL E. MASLOUSKY, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,399,603 September 3, 1968 Harlan R. Cagle It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 48, "a first passage means comprising" should read to provide a second air passage means Column 4, line 72, cancel "enlarged portion of the". Column 8, line 2, "connected" should read connecting Column 10, line 49, Hunter et al." should read Hutter et a1.

Signed and sealed this 10th day of February 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

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