US3541928A - Lift truck upright - Google Patents

Description

United States Patent [72] Inventors Charles W. Conwell Portland, Oregon; Donald A. Harris, Vancouv er, Washington; Robert C. Shoemaker, Portland, Oregon [21] App1.No. 716,746 [22] Filed March 28, 1968 [45] Patented Nov 24, 1970 [73] Assignee Hyster Company, Portland, Oregon a corporation of Nevada [54] LIFT TRUCK UPRIGl-lT 31 Claims, 5 Drawing Figs.

[52] U.S. Cl 92/146, 92/165;187/9,187/17 [51] Int. Cl F01bl/00, B66b 9/20, B66b 11/09 [50] Field of Search 92/61,146, 51,52, 53, 150, 8,-151;91/178,422,468; 137/216.01,216.2;187/9,17

[56] References Cited UNITED STATES PATENTS Re. 25.432 8/1963 Barnes 92/51X Primary Examiner-Martin P. Schwadron Assista'm Examiner- Leslie J. Payne Attarney- Buckhorn, Blore, Klarquist and Sparkman ABSTRACT: A lift truck with a four stage upright having a load carriage on the upper stage movable by a hydraulic cylinder on such stage. Another hydraulic cylinder on the lower stage extends and retracts the upright. A passage in the piston and piston rod of the upright cylinder conducts fluid from a source on the lift truck to the carriage cylinder without such fluid first passing through the cylinder cavity of the upright cylinder. An additional passage in such piston directs fluid into the cavity of the upright cylinder below the piston. The carriage cylinder operates under a lower pressure than the upright cylinder to elevate the carriage before the upright extends.

Pafiented Nov. 24, 1970 3,541,928

m 5/ \q 21 L as DONALD A. HARRIS ROBERT C. SHOEMAKER CHARLES W. CONWELL INVENTO/PS BUG/(HORN, BLORE, KLA/POU/ST 8 SPAR/(MAN ATTORNEYS Patenied Nov. 24, 1970 Sheet BUG/(HORN, BLORE, KLAROU/ST 8 SPAR/(MAN ATTORNEYS LIFT-TRUCK UPRIGHT BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to industrial lift trucks and more particularly to a lift truck having a multiple-stage upright with hydraulic means for raising a load carriage on the upper stage without extension of the upright stages.

2. Description of the Prior Art In the past, some lift trucks with multiple stage uprights have incorporated a so-called free-lift cylinder on the upright for raising the load carriage on the upper stage of the upright while the upright remains fully retracted, thereby enabling use of the lift truck in places requiring low height clearances as well as in circumstances requiring the elevation of loads to great heights attainable with the uprights fully extended. However, multiple-stage free-lift uprights in the past have required the use of excessive lengths of exposed flexible hydraulic hose for supplying the free-lift cylinder with hydraulic fluid. This has presented a problem in reeving the hose to avoid development of slack as the length of the upright is varied and to protect the hose against rupture through external damage.

In attacking the foregoing hose problems and in attempting to simplify the hydraulic circuitry required .to operate the cylinders in phase, attempts have been made to route hydraulic fluid through the hoist cylinder to the free-lift cylinder. However, these attempts have led to premature extension of the hoist cylinder and upright, thus defeating the purpose of the free-lift cylinder, without solving the hose problem satisfactorily.

The foregoing problems'are most acute with respect to fourstage uprights because of the great variation in distance between the source of hydraulic fluid and the free-lift cylinder. As a result, the free-lift concept has not been used extensively heretofore in conjunction with four-stage uprights.

SUMMARY OF THE INVENTION The foregoing problems of the prior art are overcome by the resent invention through the provision of a multiple stage upright wherein pressure fluid is conducted from a source on the lift truck directly into the piston and piston rod of a hoist cylinder on the lower stage without first passing through the cavity of such cylinder and then through a flexible hose extending from an upper end of such piston rod to a free-lift cylinder on the upper stage. A passage within the piston of the hoist cylinder also directs a portion of the flow from the source into the hoist cylinder cavity below the piston. A preloaded check valve in the piston passage leading to the hoist cylinder cavity helps prevent premature extension of the hoist cylinder and raising of the upright. Such check valve also prevents a sudden drop ofthe extended upright in the event of rupture of the hose leading to the free-lift cylinder, and serves to slow the descent of the piston within the hoist cylinder as it approaches the bottom of the cylinder upon retraction of the uprights.

Primary objects of the invention are to provide:

1. A lift truck having an improved four-stage upright with a free-lift load carriage onits upper stage;

2. A multiple stage free-lift upright for a lift truck having an improved hoist cylinder with novel hydraulic circuitry for operating the load carriage independently of upright movement and without premature extension of the upright;

3. An improved hydraulic phasing circuit for sequential operation of a pair of hydraulic motors wherein one of the motors is a hydraulic cylinder;

4. An improved hoist cylinder for a multiple stage free-lift I upright with a novel hydraulic phasing circuitry built into the piston and piston rod thereof for transmitting fluid pressure to the free-lift cylinder without appreciable pressure loss in the hoist cylinder to insure raising of the freelift lift cylinder without premature extension of the hoist cylinder;

5. An improved hoist cylinder for a multiple stage free-lift upright of a lift truck which will not retract abruptly in the event of rupture of the hydraulic line from the hoist cylinder to the free-lift cylinder when the upright is extended;

6. An improved hoist cylinder for a multiple-stage upright with means for slowing the descent of the piston of such cylinder as it approaches the bottom of the hoist cylinder cavity during retraction of the upright;

7. An improved hose reeving for a four-stage free lift upright of a lift truck, such reeving requiring a minimum use of exposed hydraulic hose and preventing the development of slack in the hose upon varying the length of the upright; and

8. An improved four-stage free-lift upright for a lift truck having simplicity of design.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects and advantages of the present invention will become more apparent fromthe following detailed description which proceeds with reference to the accompanying drawings wherein:

FIG. 1 is a side elevational view of a lift truck incorporating a four-stage free-lift upright in accordance with the present invention, with the upright being shown in a fully retracted position;

FIG. 2 is a fragmentary side elevational view similar to that of FIG. 1 showing the upright in a partially extended position;

FIG. 3 is a view similar to FIG. 2 showing the upright in a fully extended position;

FIG. 4 is a schematic elevational view of the upright of FIG. 3 in its fully extended position with portions broken away to reveal the free-liftand hoist cylinders; and

FIG. 5 is a partial sectional view through the hoist cylinder on an enlarged scale and with the cylinder in its retracted position.

DETAILED DESCRIPTION General Assembly With reference to the drawings, FIGS. 1, 2 and 3 disclose an industrial lift truck 10 having a four-stage upright 12 mounted at its forward end for forwardly and rearwardly tilting movement through a hydraulically controlled linkage 14. The fourstage upright includes a first, stationary lower stage 16, movable second and third stages 17, 18 and a movable upper stage 19. Upper stage 19 mounts a load carriage 21 including a load lifting fork 22 for vertical movement thereon. The several stages, or sections, of the uprightare mounted for telescoping extension and retraction relative to one another in any one of several manners well known in the art. For example, the uprights may be mounted in the manner shown in Shaffer U.S. Pat. No. 3,208,556 wherein each upright section includes a pair of laterally spaced channel members within which the channel members of a telescopingly related upright section slide. Alternatively, the upright sections may be mounted on rollers for movement relative to one another to reduce friction. I

Referring to FIG. 4, the four-stage upright includes a hydraulic powered hoist cylinder 24 mounted on lower stage 16 and having an extensible ram means including piston rod 26 connected at its upper end at 28 to second stage 17 so that extension of the piston rod raises the second stage with respect to the lower stage in a 1:1 ratio. A second hydraulic cylinder 30, the free-lift cylinder, is mounted on upper stage 19 and includes an extensible piston rod 32 which supports at its upper end sheave means 34 about which a chain means 36 is trained. Chain 36 is connected at one end to carriage 21 at 37 and at the otherend to the free-lift cylinder casing at 38 so as to raise and lower the load carriage 21 on the upper stage in a 2:1 ratio with respect to movement of the free-lift cylinder. Because the free-lift cylinder is supported on the upper stage and because its chain reeving 36 is not operatively connected to any other stage, the free-lift cylinder elevates and lowers the load carriage without effecting any movement of the stages relative to one another. This free-lift feature is most valuable in multiplestage uprights so that load fork 22 can raise and lower a load at low levels with the uprights in a fully retracted position. This feature enables passage of the lift truck through low doorways and its use in low ceilinged enclosures such as boxcars, while also enabling the handling of loads at great heights when necessary.

Extension of hoist cylinder 24 effects an extension of the three movable stages 17, 18 and 19 simultaneously through a system of chain reeving between the stages. This reeving includes a first chain means 40 trained about sheave means 42 carried by the upper end of piston rod 26 of the hoist cylinder. Chain means 40 is fixed at one end at 44 to the casing of hoist cylinder 24 and at its opposite end at 46 to a lower portion of third stage 18, whereby the third stage 18 is moved at a ratio of 2:1 with respect to the second stage 17 upon extension of the hoist cylinder. A second chain means 48 is trained about a sheave means 50 near an upper end of third stage 18 and is connected at 51 to an upper end of second stage 17 and at 52 to a lower end portion ofupper stage 19. Thus, upon extension of hoist cylinder 24, chain means 48 raises upper stage 19 at a 2:1 ratio with respect to third stage 18, and at a 3:1 ratio with respect to second stage 17.

Hydraulics Hoist cylinder 24 and free-lift cylinder 30 are hydraulically connected so that the cylinders operate in sequence, with freelift cylinder 30 extending first to raise load carriage 21 to the top of the upper stage, followed by extension of hoist cylinder 24 to extend the various upright stages simultaneously while the load carriage remains in its elevated position on the upper stage. The hydraulic circuitry is unique in that pressure fluid is conducted first through the piston and piston rod of the hoist cylinder and then to the free-lift cylinder and cavity of the hoist cylinder with minimal pressure loss, with a minimal use of hydraulic hose, and with a minimal differential in operating pressures between the two cylinders.

Referring to FIGS. 4 and 5, a length of flexible hydraulic hose 54 extends from a pump 56 on the lift truck to a fitting 58 at a lower side wall of hoist cylinder casing 60. These elements define a fluid passage means referred to herein as the third fluid passage means. Fitting 58 defines an inlet port 62 through the side wall of the casing through which pressure fluid is led into a piston 64 when the piston is within the lower end of the cylinder casing. The piston is provided with internal fluid passage means including a first inlet passage means including a horizontal passage; portion 66 leading from an enlarged inlet cavity 68 at a cylindrical surface portion of the piston in register-with inlet port 62 to a second, axial fluid passage means or portion 70 extending axially upwardly from passage 66 through piston 64. Axial piston passage 70 communicates at its upper end with an axial passage 72 within piston rod 26 which terminates at an exit port oroutlet 74 at the upper end of the piston rod. A length of flexible hose 76 extends from a fitting 78 connected to outlet 74 to the free-lift cylinder 30. In doing so, hose 76 extends about a sheave'80 on third stage 18 of the upright and thence upwardly to a fitting 32 connected to an inlet ofthe free-lift cylinder 30. Sheave 80 is adjustable'vertically on the third stage to take up slaclt in hose 76 when needed.

The first passage means also includes an axial lower passage portion 84 which opens at 86 into the interior cavity 88 of cylinder casing 60 on the pressure side of piston 64. A ball check valve 90 within piston passage 84 prevents the reverse flow of fluid from cylinder cavity 88 through the passage into rod passage 72 leading to the free-lift cylinder and into inlet passage 66, for reasons which will'become apparent shortly. Check valve 90 also includes a preload spring 92 which closes the valve to fluid flow toward the lower pressure side of piston 64 until a small predetermined fluid pressure of, say, about five to 10 p.s.i. builds up in the piston passages. This feature helps prevent a surge of fluid pressure within cavity $8 and against piston 64 upon the initial flow of fluid into the piston and rod passages to prevent any premature extension of the upright.

Piston 64 includes a bypass orifice 9A which extends between cylinder pressure cavity 88 and inlet cavity 68 to bypass the check valve. This orifice allows a controlled bleeding of fluid from the pressure side of piston 6d and thus a slow, controlled descent of the piston and upright from their extended positions in the event of a rupture of hydraulic hose 76 leading to the free-lift cylinder. The orifice also operates in conjunction with the piston itself in slowing the descent of piston 64 as it approaches the bottom of the cylinder casing during normal retraction of the extended cylinder to prevent damage to the cylinder casing and piston.

Operation Free-lift cylinder 30 is extensible under slightly lower fluid pressure than hoist cylinder 24 when the loading on both cylinders is taken into consideration. Thus, when pump 56 is activated with both cylinders retracted to build up fluid pressure within the various fluid passages, free-lift cylinder rod 32 extends first to its fully raised position to raise load carriage 23 before there is a sufficient buildup of fluid pressure within the pressure side ofthe hoist cylinder to raise piston 64 and piston rod 26 to extend the upright. The capacity of pump 56 is such that after free-lift cylinder is fully extended, fluid pressure continues to rise within the system to a level where the hoist cylinder can be fully extended. The differential between the operating pressures of the two cylinders need only be slight, since the bypassing of hoist cylinder cavity 88 in directing fluid to the free-lift cylinder through the piston and piston rod of the hoist cylinder, prevents pressure surges in the cavity 33 and thus premature extension of the upright and minimizes pressure losses in the hoist cylinder. By maintaining the operating pressure differential between the cylinders small, the upright can be extended immediately after the carriage has been raised, without significantly changing the vertical speed of the load.

Referring to FIGS. 1, 2 and 3, FIG. 1 illustrates the initial fully retracted position of the upright stages and load carriage when both the hoist cylinder and free-lift cylinder are fully retracted. The dashed line position of the carriage and fork 22 of FIG. 1 illustrates the relative positions of the upright stages and carriage with the free-lift cylinder fully extended and the hoist cylinder still fully retracted. FIG. 2 illustrates the partially extended upright stages upon partial extension of the hoist cylinder. The free-lift cylinder remains fully extended to maintain the carriage in its elevated position on the upper stage. In FIG. 3, hoist cylinder rod 26 has become fully extended, and thus the upright too is extended fully, with the load carriage remaining in its fully raised position on the upper stage. The FIG. 3 position of the carriage and upright represents the greatest height to which a load can be raised by the lift truck.

From FIG. 5 it will be apparent that after the free-lift cylinder has been extended and piston 64 rises an initial distance from the bottom of cylinder casing 60, pressure fluid will ceaseentering the cylinder through inlet cavity 68 and piston passage 66 and instead will flow directly into the pressure side of the cylinder cavity 86 below the piston to continue raising the piston. The enlarged shape of piston inlet cavity 623 and the short distance between its lower extremity and the bottom of piston 64 insures that there will be no interruption in the buildup of fluid pressure against the bottom of the piston as the piston rises past the inlet port 62.

When lowering a load on fork 22 from a fully extended position of the upright, the direction of fluid flow through inlet port 62 is reversed so that it becomes the fluid outlet. Because of the higher pressure necessary to extend the hoist cylinder than the free-lift cylinder, a reduction in fluid pressure retracts the hoist cylinder and thus the upright before the free-lift cylinder retracts to lower the load carriage on the fourth stage.

During the descent of piston 64 within cylinder casing 60, check valve 90 closes, and the piston forces fluid out of the lower end of the casing through outlet port 62. However as piston 64 nears the bottom of the casing, the piston itself slides over port 62, cutting off fluid flow directly from the cylinder cavity to the port. Check valve 90 also prevents flow from the cylinder cavity through the internal piston passages 84 and 66 to port 62. Thus, the descent of the piston slows as it approaches the bottom of the casing and finally bottoms only as fast as fluid can bleed from the cylinder cavity below the piston through orifice 94. This self-cushioning effect of the piston prevents cylinder and piston damage which might otherwise result from a rapid, unchecked piston descent.

The check valve and orifice also prevent the same sort of damage in the event of rupture of hose 76 to the free-lift cylinder should it break while the upright and carriage are extended and under heavy load. in such circumstances, the resulting pressure drop would not cause a rapid descent of piston 64 since fluid below such piston could only bleed slowly to the hose break through orifice 94, and thus the piston and rod, and the upright, would descend slowly.

Having illustrated and described a preferred embodiment of my invention it should be apparent to those skilled in the art that the same permits of modification in arrangement and detail.

lclaim:

1. Pressure fluid-actuated means for use with an extensible multistage mast or boom apparatus including:

a first fluid motor for mounting on one stage of said apparatus;

a second fluid motor separated from said first fluid motor for mounting on another stage of said apparatus;

at least one of said motors comprising a fluid cylinder means including a casing, and an extensible ram means within said casing and capable of extension outside said casing, said ram means having a fluid exit port in an outer portion thereof outside said casing;

a source of pressure fluid;

first fluid passage means within said ram means communicating with the interior of said cylinder means on a pres sure side of said ram means;

second fluid passage means within said extensible ram means interconnecting said first fluid passage means and said exit port; flexible hose means interconnecting said exit port and said second fluid motor means; and

third fluid passage means extending through said casing for connecting said source to said first fluid passage means in a predetermined position of said ram means wherein pressure fluid enters said first fluid passage means from said source before passing to the pressure side of said ram means.

2. Apparatus according to claim 1 wherein said first fluid passage means includes a pressure fluid inlet on a side of said ram means in sliding engagement with a wall of said-cylinder means, and said third fluid passage means includes a fluid inlet port means in said wall and in registration with said pressure fluid inlet of said ram means in said predetermined position of said ram means.

3. Apparatus according to claim 2 wherein said first passage means includes a first fluid outlet opening to the pressure side of said ram and a second fluid pressure outlet connected to said second passage means.

4. Apparatus according to claim 1 including one-way valve means in said first passage means permitting fluid flow from said source to said other fluid motor means and to the pressure side ofsaid ram means but preventing fluid flow from the pressure side of said ram means through said valve means to said second and third passage means. Y

5. Apparatus according to claim 4 wherein said one-way valve means includes means preloading said valve means in a direction to permit fluid flow to the pressure side of said ram means only when said fluid exceeds a predetermined pressure.

6. Apparatus according to claim 4 including restricted fluid passage means bypassing said one-way valve means and connecting the-pressure side of said ram means with said first passage means at a position between said third passage means and said valve means.

7. Apparatus according to claim 1 wherein said first passage means includes a first passage portion within said ram means connected to said second passage means and a second passage portion in parallel with said first passage portion communicating with the pressure side of said ram means, and orifice means within said ram means connecting said first passage means to the pressure side of said ram means in parallel with said second passage portion.

8. Apparatus according to claim 2 wherein said cylinder means comprises a one-way hoist cylinder with said inlet port serving as a fluid outlet from said cylinder upon retraction of said ram means from an extended position, and one-way valve means in said first passage means permitting fluid flow through said first passage means to the pressure side of said ram means but preventing fluid discharge from said pressure side through said first passage means to said inlet port, so that upon retraction of said ram means said ram means blocks the discharge of fluid from said pressure side to said inlet port when said ram means approaches its fully retracted position.

9. Apparatus according to claim 8 including orifice means bypassing said valve means and interconnecting said pressure side of said ram means and said inlet port when said ram is in blocking relation to said inlet port, so as to permit a slowed movement of said ram means to a fully retracted position when said ram means approachessaid retracted position.

10. Apparatus according to claim 1 wherein said cylinder means and said other fluid motor means are sized so that one of said fluid motor means is operable under a lower fluid pressure than the other said fluid motor means whereby said two motor means will operate in sequence.

11. Apparatus according to claim 1 wherein said other fluid motor means comprises a second fluid cylinder means having a second ram means and is operable under a lower fluid pressure than the ram means of said first-mentioned cylinder means so that said second ram means will extend before the extension of the ram means of said first cylinder means.

12. Apparatus according to claim 11 wherein said first and second fluid cylinder means comprise hoist cylinders in a lift truck having a telescoping multiple stage upright means with a load carriage movable on an upper stage of said upright means, said first cylinder means being operable to extend and retract the stages of said upright means and said second cylinder means being operable to move said load carriage vertically on said upper stage.

13. Apparatus according to claim 12 wherein said first cylinder means is connected to a lowermost stage of said upright means and said second cylinder means is carries by said upper stage. 7

14. Apparatus according to claim 13 wherein said upright means includes four stages including a fixed lower stage and three movable stages, with said stages being interconnected so that upon pressure fluid from said source entering said first cylinder means, first said load carriage is elevated to the upper end of said upper stage through extension of said second generally axially extending fluid passage means within said piston portion and said rod means and having a first fluid outlet in an outer end portion of said rod means outside said casing and a second fluid outlet opening into said cylinder casing on a pressure side of said piston portion;

lateral fluid passage means within said piston portion extending from a fluid-inlet at a surface portion of said piston into communication with said axial passage means at a position between said fluid outlets; and

fluid inlet port means in said casing in registration with said fluid inlet in said piston at a predetermined position of said piston within said casing.

16. Apparatus according to claim including check valve means within said axial passage means between said second outlet and said lateral passage means restricting fluid flow from the interior of said casing tosaid lateral passage means and said first outlet.

17. Apparatus according to claim 16 including orifice means within said piston bypassing said check valve means and connecting said interior portion of said casing with said fluid inlet port means.

18. Apparatus according to claim 16 wherein said check valve means includes means closing said valve means to flow in a direction toward the interior of said casing and operable under a predetermined fluid pressure to open said valve means to fluid flow in said direction.

19. In a lift truck having an upright with multiple-telescoping stages including:

a lower stage, an upper stage and at least one intermediate stage, with a load carriage movable vertically along said upper stage;

a first extensible power cylinder means on said upper stage for moving said load carriage;

a second extensible power cylinder means on one of said stages other than said upper stage for extending and retracting said stages;

said second power cylinder means including a cylinder cavity and an extensible ram means slidable within said cavity; and

fluid passage means including passage means extending through said ram means and from an outlet port of said ram means to said first power cylinder means for directing fluid from a source of pressure fluid on said'lift truck through said ram means and to said first power cylinder means without said fluid first passing into said cylinder cavity on a pressure side of said ram means when said ram means is retracted.

20. Apparatus according to claim 19 wherein said second cylinder means is on said lower stage.

21. Apparatus according to claim 19 wherein there are four of said stages and said second cylinder means is on said lower stage.

22. Apparatus according to claim 19 wherein said fluid passage means includes an inlet passage portion extending from said source into the interior of said ram means, a first branch passage portion extending from said inlet passage portion within said ram means to said outlet port, a flexible passage portion extending from said outlet port to said first cylinder means, and a second branch passage portion extending from said inlet passage portion within said ram means to said cylinder cavity ofsaid second cylinder means.

23. Apparatus according to claim 22 including check valve means restricting fluid flow from said cylinder cavity through the fluid passage portions within said ram means.

24-. Apparatus according to claim 22 wherein said first cylinder means is extensible under a lower fluid pressure than said second cylinder means.

25.1n a lift truck, an upright comprising:

four telescoping sections, including a first lower section,

second and third intermediate sections and a fourth upper section;

a load carriage movable vertically on said upper section, a

first hydraulic cylinder means interconnecting said first and second section; a second hydraulic cylinder means on said upper section for raising and lowering said load carriage on said upper section;

fluid passage means within a piston rod portion of said first cylinder means for conducting pressure fluid from a source on said truck to said second cylinder means; and flexible hose means interconnecting said fluid passage means and said second cylinder means.

26. Apparatus according to claim 25 wherein said hose means extends from an upper portion of said piston rod, about a sheave means on said third section and thence to a fluid inlet port on said second cylinder means.

27. Apparatus according to claim 26 wherein said sheave means is vertically adjustable on said third section to take up slack in said hose means.

28. In a multiple-stage extensible mast or boom apparatus;

a first fluid motor on one stage of said apparatus;

a second fluid motor separated from said first fluid motor on another stage of said apparatus;

said second fluid motor comprising an extensible fluid cylinder means for extending and retracting said multiple stage apparatus;

said cylinder means including a cylinder casing defining a cylinder cavity and an extensible ram means movable within said cavity and outwardly of an open end of said casing; fluid passage means extending from a source of pressure fluid outside said casing to an inlet port in said casing;

ram fluid passage means extending within said ram means and including an inlet opening in communication with said inlet port in a retracted position of said ram means, a first outlet port at an outer end of said ram means, and a second outlet port at an inner end of said ram means opening into said cylinder cavity; and

flexible fluid passage means operably interconnecting said first outlet port of said ram means and said first fluid motor so that the pressure side of said ram means and said first fluid motor are connected in parallel to said source through said ram means.

29. Apparatus according to claim 28 wherein said first fluid motor is operable under a lower fluid pressure than said second fluid motor whereby the arrangement of said passage means inhibits premature extension of said cylinder means.

30. Apparatus according to claim 28 including one-way valve means within said ram passage means restricting fluid flow from said cavity to said inlet and outlet ports.

31. Apparatus according to claim 30 wherein said valve means includes fluid pressure sensitive means preventing fluid flow through said valve means to said cylinder cavity until there is a predetermined fluid pressure buildup within said ram passage means.

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