US3633365A

US3633365A - Hydraulic jack

Info

Publication number: US3633365A
Application number: US76178A
Authority: US
Inventors: John C Belknap
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-09-28
Filing date: 1970-09-28
Publication date: 1972-01-11
Anticipated expiration: 1989-01-11

Abstract

A hydraulic jack comprises a first and second piston mounted on the opposite ends of a hollow piston rod which extends through a partition in a cylinder, said rod having an intermediate floating piston mounted thereon for axial movement relative to the first and second pistons. A first chamber is defined between the first and intermediate pistons, and second and third chambers are provided are on opposite sides of the second piston. These three chambers are filled with hydraulic fluid. An actuating piston, preferably of the same diameter as the other three pistons, is disposed in spaced relation to the second piston and is subjected to pressure transmitted through the fluid present in the third chamber to extend the rod of the actuating piston and thus engage the work or load. A sequence valve is located within the hollow piston rod to control the flow of fluid between the chambers and is normally positioned to establish communication between the first and second chambers. The sequence valve is responsive to an external load encountered by the actuating piston rod to interrupt such communication and establish communication between the second and third chambers whereby the pressure in the second and third chambers is intensified to a high-pressure sufficient to overcome the resistant force of the load encountered by the rod of the actuating piston. Air under pressure is employed to move the first piston and the sequence valve is operative to permit transfer of hydraulic fluid in a self contained supply from a low-pressure state to a highpressure stage through the hollow piston rod. Retraction of the actuating piston is also accomplished by compressed air and the hydraulic fluid is returned by means of the sequence valve to its original position.

Description

United States Patent [72] Inventor John C. Belknap 229 South Shore Drive, Buffalo, N.Y. 14219 [2]] Appl. No. 76,178 [22] Filed Sept. 28, 1970 Patented Jan. 11, 1972 [54] HYDRAULIC JACK 12 Claims, 7 Drawing Figs.

[52] US. Cl 60/545 A, 60/545 HA, 60/546 [51] Int. Cl Fl 5b 7/00 Field of Search. /54.5 R,

54.596 H, 54.596 HA, 54.596 A [56] References Cited UNITED STATES PATENTS 3,059,433 10/1962 Hirsch 60/54.6 A 1,970,999 8/1934 Ferris et al 60/54.5 HA

Primary Examiner-Martin P. Schwadron Assistant Examiner-A. M. Zupcic Attorney-Ashlan F. Harlan, Jr.

ABSTRACT: A hydraulic jack comprises a first and second piston mounted on the opposite ends of a hollow piston rod which extends through a partition in a cylinder, said rod havllll 3,633,365

ing an intermediate floating piston mounted thereon for axial movement relative to the first and second pistons. A first chamber is defined between the first and intermediate pistons, and second and third chambers are provided are on opposite sides of the second piston. These three chambers are filled with hydraulic fluid. An actuating piston, preferably of the same diameter as the other three pistons, is disposed in spaced relation to the second piston and is subjected to pressure transmitted through the fluid present in the third chamber to extend the rod of the actuating piston and thus engage the work or load. A sequence valve is located within the hollow piston rod to control the flow of fluid between the chambers and is normally positioned to establish communication between the first and second chambers. The sequence valve is responsive to an external load encountered by the actuating piston rod to interrupt such communication and establish communication between the second and third chambers whereby the pressure in the second and third chambers is intensified to a high-pressure sufficient to overcome the resistant force of the load encountered by the rod of the actuating piston.

Air under pressure is employed to move the first piston and the sequence valve is operative to permit transfer of hydraulic fluid in a self contained supply from a low-pressure state to a high-pressure stage through the hollow piston rod. Retraction of the actuating piston is also accomplished by compressed air and the hydraulic fluid is returned by means of the sequence valve to its original position.

T l 22 i 50 48 54 36 47 g 26' 6O 1- 78 )65 35 1 I 42 41s 62 72 m 52 5 20 $6 75 82 65 PATENIEB Jun 1 m2 SHEET 1 [IF 2 om on @m W 30 mm mm m Q Q R N Om AW Om up. M wn 3 mm \o\\ m O I :1 X w I VJ 1 mm om A wm n} HQ 32:) W$- wmw i mm VN Na wk 3 3 M? NR fim w ON m mm mm v mm Q N@ R 3 mm H 8 mm NR & Q Q w HEN mm mm R 8 Nu NR 8 N 8 8 mm 8 Q QQ JOHN C BEL/(NAP ATTORNEY HYDRAULIC JACK BACKGROUND OF THE INVENTION This invention relates to hydraulic jacks and, more particularly, to hydraulic jacks operative successfully in two stages, under low and high pressures, respectively.

In certain hydraulic jack or cylinder applications, such as those employed in various presses for die-stamping, riveting, crimping and the like, it is not necessary for the power piston and its red or ram to transmit a high working force throughout its entire stroke, but only for a desired proportion of the stroke, usually near the conclusion thereof. Accordingly, many hydraulic cylinders and jacks have been designed for applying a low pressure to the piston to initially extend the rod or ram in an approach stroke toward the work or load and then applying a high pressure to the piston to carry out the remaining portion of the stroke to perform the work. While many such jacks are admirably suited for the intended purposes, they possess certain disadvantages. For example, these jacks are generally complex and expensive and often include a multiplicity of movable parts susceptible to wear and failure. Sometimes also, electrical control systems incorporating limit switches, pressure-responsive switches, timing mechanisms and like components, are used in conjunction with these jacks, thereby increasing the cost thereof and the possibility of failure.

SUMMARY OF THE INVENTION The hydraulic jack of the present invention, as hereinafter described, obviates the above deficiencies by providing a new and improved dual-stage hydraulic cylinder, which is simple and strong in construction, relatively low in cost, rugged and durable in use, and which employs a combination of pneumatic and hydraulic pressures to effect the two-stage operation.

Generally speaking, the hydraulic jack of the present invention comprises a first and second piston mounted on the pposite ends of a hollow piston rod which extends through a partition in the cylinder, said rod having an intermediate floating piston mounted thereon for axial movement relative to the first and second pistons. A first chamber is defined between the first and intermediate pistons, and a second and third chamber are provided on opposite sides of the second piston. These three chambers are filled with hydraulic fluid. An actuating piston, preferably of the same diameter as the other three pistons, is disposed in spaced relation to the second piston and is subjected to pressure transmitted through the fluid present in the third chamber to extend the rod of the actuating piston and thus engage the work or load. A sequence valve is located within the hollow piston rod to control the flow of fluid between the chambers and is normally positioned to establish communication between the first and second chambers. The sequence valve is responsive to an external load encountered by the actuating piston rod to interrrupt such communication and establish communication between the second and third chambers whereby the pressure in the second and third chambers is intensified to a high pressure sufficient to overcome the resistant force of the load encountered by the rod ofthe actuating piston.

Air under pressure is employed to move the first piston and the sequence valve is operative to permit transfer of hydraulic fluid in a self-contained supply from a low-pressure stage to a high-pressure stage through the hollow piston rod. Retraction of the actuating piston in also accomplished by compressed air and the hydraulic fluid is returned with the aid of the sequence valve to its original position.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of one form of hydraulic jack constructed in accordance with this invention;

FIG. 2 is a view similar to FIG. 1, showing an operative position ofthe pistons within the jack shown in FIG. 1;

FIG. 3 is a view similar to FIGS. 1 and 2 showing still another operative position of the pistons;

FIG. 4 is a fragmentary, sectional view, on an enlarged scale, showing details of the sequence valve incorporated in the hollow piston rod of the jack shown in FIGS. 1-3;

FIG. 5 is a view similar to FIG. 4, but showing the sequence valve in an alternate position;

FIG. 6 is a diagrammatic view of a pneumatic circuit usable with the jack of the present invention; and

FIG. 7 is a longitudinal sectional view of another form of hydraulic jack according to this invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT The terms top, bottom right," left," and similar terms of position or direction as used hereinafter refer to the illustration in FIGS. l-3, but are used only for convenience of description. They should not be construed as limiting the scope of this invention or implying a necessary positioning of the structure of positions thereof.

Referring now in detail to the drawings, there is shown in FIGS. 1, 2 and 3 a preferred embodiment of a hydraulic jack constructed in accordance with this invention and comprehensively designated 10. It comprises a pair of coaxial cylindrical tubes, 12 and 14. The tube 12 is suitably sealed at its opposite ends to an end headplate 16 and an intermediate plate 18. Likewise, the tube 14 is suitably sealed at its opposite ends to an intermediate plate 20 and an end headplate 21. The

plates

16, 18, 20, and 21 and the

tubes

12 and 14 are held in alignment by suitable means such as the conventional rods 22 passing through holes (not shown) in the plates and drawn tightly together by nuts 23 threadedly engaged on the ends of the rods, a suitable seal being interposed between

plates

18 and 20 if desired. Thus, there is formed a generally continuous cylindrical housing having a partition comprised of the

plates

18 and 20 fixed therein between the opposite ends thereof the dividing said housing into an input section and an output section.

The end headplate 16 is provided with a radial port or bore 24 adapted to be connected to a suitable source of air under pressure and an axial passage 26 communicating with the port 24 and leading to the interior of tube 12. The other end headplate 21 also is provided with a radial port 28 adapted to be connected to a suitable source of air under pressure and communicating with an axial passage 30 extending through said headplate into the interior of tube 14.

The

intermediate plates

18 and 20, respectively, are provided with radial ports or

bores

32 and 34 communicating with

passages

36 and 38, respectively, that extend axially through the respective plates. In the embodiment of the invention herein illustrated, the port 34 is closed off by a plug 40 and the port 32 is adapted to be connected to a suitable source of air under pressure. If desired, the plug 40 can be omitted and the bore or port 34 can be used as a pressure sensing port, e.g. by connection thereto of a pressure gauge or a pressureoperated switch.

A first piston 42 is mounted within the tube 12 for reciprocating movement therein and is provided with suitable annular sealing members 44 to form a fluidtight seal between the piston 42 and the interior of the tube 12. The piston 42 is threadedly secured on or otherwise suitably connected to one end of a hollow piston rod 46 that extends axially through the casing 12 and through the

passages

36 and 38 of

intermediate plates

18 and 20. The piston rod 46 is provided with a plug 47 that closes the end of the longitudinal passage 50 through the rod adjacent piston 42. Suitable annular sealing members 48 are disposed around the piston rod 46 intermediate its length and held in place by annular retainers 52 provided in the stationary

intermediate plates

18 and 20. The other end of the piston rod 46 is provided with an end portion of reduced diameter having a second piston 56 threadedly secured thereon or otherwise'suitably connected thereto and disposed in tube 14. Suitable annular sealing members 58 are disposed about the piston 56 to provide pressure sealing between the same and the interior of tube 14. A sequence valve, generally designated 60, is positioned within the bore 50 of the piston rod 46 adjacent piston 56 for a purpose that will hereinafter be described. A third, intermediate, floating piston 62 is provided within the tube 12 between the piston 42 and the intermediate plate 18. It is slidable longitudinally with respect to both the tube 12 and the piston rod 46 and has a pair of annular sealing members 64 disposed about the periphery thereof in sealing engagement with the interior of the tube 12. Also, a pair ofannular sealing members 68 provide pressure sealing between the piston 62 and the piston rod 46.

It will be seen that the third piston 62 divides the portion of the input section, comprised in tube 12 between the piston 42 and the intermediate plate 18, into a first chamber 70 and a second chamber 72 and that the second piston 56 secured to the rod 46 in the tube 14 divides the output section into a primary chamber 74 and a secondary chamber 76. A plurality of radial ports 78 are provided in the piston rod 46 to establish communication between the first chamber 70 and the passage 50 through the piston rod. Also, a plurality of radial ports 80 are provided adjacent the other end of piston rod 46 which normally provide communication between the passage 50 and the chamber 74.

An actuating or driving piston 82 is mounted within the tube 14 for reciprocable movement therewithin. The piston 82 on its left side forms a boundary for the secondary chamber 76 and between its other side and the end plate 22 establishes an air chamber 83. A pair of annular sealing rings 84 are disposed about the periphery of the piston 82 in sealing engagement with the inner wall of the tube. The piston 82 is rigidly secured to one end of a piston rod 86 which extends through the axial passage 30 in end plate 22 and has a distal end 88 adapted to engage a load which is identified by the reference numeral 90. An annular rod bushing 92 provided in the outer end face of the end plate 22 carries an annular seal 94 for providing pressure sealing between the piston rod 86 and end plate 22 and a rod wiper 96 for cleaning dirt, grit and other foreign matter from the outer surface of rod 86. The rod bushing 92 is held in place by a retainer 98 secured on the outer end face of the end plate 22. A stop collar 100 is suitably secured on the rod 86 adjacent its outer end to restrain inward movement of the rod and the attached piston 82.

As shown in FIG. 4, the sequence valve 60 comprises a cup 102 slidably mounted in an enlarged portion 104 of the bore 50 through the piston rod 46. Cup 102 comprises an end wall 106 and a cylindrical wall 108 defining a chamber 110 which communicates through the open end of the cup 102 with secondary chamber 76. A plurality of radial ports 112 extend through the cylindrical wall 108 of valve 60 and are held in alignment with the ports 80 by suitable means (not shown). A central cylindrical opening 114 is provided in the end wall 106 of cup 102, the periphery of the inner end of the opening 114 constituting a seat for a ball check valve 116 in the chamber 110. The valve 1 16 normally closes the opening 1 14 under the urging of a coil spring 118 suitably anchored in the interior wall of the chamber 110 and bearing on the ball.

The cup 102 of sequence valve 60 is fixed against movement to the right by a retainer ring 120 disposed in an annular groove in the enlarged portion 104 of piston rod passageway 50 and is normally held in the position shown in FIG. 4 by means of a coiled compression spring 122 disposed between an annular shoulder 124, provided at the inner end of a portion 126 of intermediate diameter in the passageway 50 adjoining the enlarged diameter portion 104, and the outer face of end wall 106. An O-ring seal 128 is disposed in a suitable annular groove provided in the wall of enlarged portion 104 of passageway 50 to provide pressure sealing between the latter and the cylindrical wall 108 of cup 102 when the latter is moved to its alternate position which is shown in FIG. 5.

FIG. 6 is an illustration of a pneumatic system including the hydraulic jack l and a distributor valve 130 (shown schematically and which may be of any desired type) which is continuously supplied through a conduit 132 with air under pres sure from a suitable source (not shown). Leading from the valve 130 is a conduit 134 connected to the port 24 of end plate 16. A conduit 136 connects the distributor valve to the

ports

32 and 28 of intermediate plate 18 and end plate 22, respectively, by means of branch lines 138 and 140. The conduits may be of any suitable construction and may be connected to the jack and the distributor valve by any suitable type of coupling (not shown). A reducing valve 142 is provided in the branch line 138 to permit use of air under lower pressure in the port 32.

In using ajack as illustrated in FIGS. l-3,

chambers

70, 74, and 76 are filled with a substantially incompressible hydraulic fluid. The fluid may be introduced through the port 34 in the intermediate plate 20 before the plug 40 is inserted therein. Then, with the distributor valve 130 actuated to the position shown in FIG. 6, air under pressure is supplied from the conduit 132 through valve 130 and the conduit 134 and introduced into the port 24. As will be evident, in this position of the distributor valve 130 air in the second chamber 72 and in the chamber 83 will be exhausted through branches 138 and 140, respectively, the conduit 136, and the valve 130. Air pressure acting against the piston 42 forces the same to the right, carrying along with it piston rod 46 and piston 56 as shown in FIG. 2. Hydraulic fluid from the chamber 70 is drawn into chamber 74, because of the reduced pressure in the latter caused by movement ofthe piston 56 to the right, via the ports 78 in the piston rod 46, passage 50 and ports 80. As the piston 56 advances to the right it displaces the volume of hydraulic fluid present in chamber 76 to the right as shown in FIG. 2, thereby forcing the actuating or driving piston 82 in the same direction, carrying along with it the piston rod 86.

If prior to the piston 82 reaching the end plate 24, the distal end 88 of rod 86 encounters resistance such as a load 90 (see FIG. 2), which resistance is greater than the force exerted on the piston 42 by the air pressure introduced through port 24, the resistance is transmitted to the piston 82 and to the hydraulic fluid in chamber 76, thus increasing the pressure in said chamber to that of the air acting against the piston 42 and causing the sequence valve 60 to operate. In such operation the fluid under pressure in chamber 76 shifts the cup 102 to the left against the bias of spring 122 and past the O-ring seal 128 into engagement with the shoulder formed at the juncture of the portions 104 and 126 of the passage 50. Communication between the

chambers

70 and 74 through piston rod passage 50 is thereby interrupted. Consequently, the piston 42, the fluid in chamber 70, piston 62, piston rod 46 and the piston 56 now constitute a staticassembly, the recited elements having a fixed relation therein, which is movable, as shown in FIG. 3, as a whole by air pressure acting on the piston 42. Since communication between

chambers

74 and 76 is established when the sequence valve 60 shifts to the position shown in FIG. 5, the ports 112 in the wall 108 of the cup 102 being placed in registry with the ports in piston rod 46, so that fluid from chamber 76 may transfer to chamber 74 when the static

assembly including pistons

42 and 56 continues to advance to the right, the piston 56 is in effect eliminated as a partition between

chambers

74 and 76.

Since the piston rod 46 occupies a portion of the space in chamber 74, a volume differential exists between

chambers

74 and 76. Because the fluid capacity of chamber 74 is less than the fluid capacity of chamber 76 there is a certain volume of hydraulic fluid in the latter that cannot transfer into the former. As the applied air pressure continues to force piston 42 to the right, it carries with it the piston 56 which, as explained above, is in effect eliminated by operation of the sequence valve 60. Consequently the piston rod 46 serves as a ram acting on the fluid in

chambers

74 and 76 and increasing the pressure therein as piston 42 continues to advance. This increased pressure is applied to piston 82 which exerts force on the load through the smaller rod 86. There are thus two stages of pressure.

In order to retract the piston rod 86 and return the other movable elements to their original positions, the distributor valve 130 is shifted to a position to connect conduit 136 to air pressure line 132 and conduit 134 to atmosphere or exhaust. In such position the air under pressure introduced through the port 28 into chamber 83 acts against the piston 82 to return it to its original position as shown in FIG. 1. To prevent blocking of the piston 82 by the hydraulic fluid in the system, the air introduced into the port 32 is reduced in pressure by the reduction valve 142 while air under full line pressure is introduced into the port 28. When piston 82 reaches the end of its retraction stroke, which is determined by the stop collar 100 on the rod 86 engaging the face of retainer 98, the pressure in chamber 72 continues to force the rest of the assembly to its original position. The sequence valve will return to its normal position under the influence of coil spring 122, thereby interrupting communication between the

chambers

74 and 76 and reestablishing communication between the

chambers

70 and 74. The ball check valve 116 of sequence valve 60 may be unseated to permit passage of hydraulic fluid into the chamber 76 from either

chamber

70 or 74 as required to allow proper positioning of the

pistons

42, 62, and 72. Of course, retraction of the actuating piston 82 removes the piston rod 86 from load 90.

FIG. 7 illustrates a modified form of the present invention. The construction of this form is substantially identical with the form illustrated in FIGS. 1-3 except that the actuating piston is moved from the tube 14 to an auxiliary casing 145. Consequently, the interior of the tube 14 is divided into only a primary chamber 74 and a secondary chamber 76 and the end plate 146 of the tube 14 is provided with an outlet port 147 for the hydraulic fluid in the chamber 76'. A pipe or conduit 148 connects the chamber 76' through the port 147 with the inlet port 149 of an end plate 150 suitably secured, as by rods 22 and nuts 23 on one end of the tubular auxiliary casing 145. Mounted for reciprocation in the casing 145 is a piston 82 rovided withannular sealing rings 84 and attached to a piston rod 86 that extends through the other end plate 24 of the casing. The piston 82 divides the interior of the casing 145 into a chamber 151 on the right side of the piston and an air chamber 83. The construction of the parts of and accessories for the casing 145 identified by reference characters is the same as that of the corresponding parts and accessories in the embodiment of FIGS. l-3.

The operation of the embodiment of the invention illustrated in FIG. 7 will be clear from the foregoing description when it is recognized that the chamber 76the interior of the pipe or conduit 148, and the chamber 151 in the casing 145 are filled with hydraulic fluid at all times during use and thus are functionally merely an enlargement of the secondary chamber 76 ofthe other embodiment. The mode of operation is thus also the same as that the other embodiment except that the portion of the jack comprising the

tubes

12 and 14 may be moved as convenient with respect to the load and only the smaller casing 145 must be aligned to engage the load, thus permitting the main portion of the jack to be at a distance from the point of work. It will also be appreciated that by suitable connections (not shown) a plurality of casings 145, each with an actuating piston and attached rod may be attached to a single main jack portion for use at a plurality of load-engaging points.

The present invention thus provides a new and improved multiple stage hydraulic cylinder employing a combination of pneumatic and hydraulic pressures to provide both a low-pressure and high-pressure condition. By the provision ofa novel sequence valve mounted within a hollow piston rod and responsive to pressure generated by the load encountered, the fluid pressure present in the working chamber is intensified, when needed, to overcome the resistance of the load.

Preferred embodiments of this invention having been described and illustrated in detail, it is to be understood that numerous modifications thereof may be made without departing from the broad spirit and scope of this invention, as

defined in the appended claims. For example, instead of employing a single distributor valve for controlling the novel jack of the present invention, a plurality of separate valves with appropriate connections may be employed. Such substitution of fluid control elements is well-known in the art. Also, of course, instead of compressed air, any other convenient pressure fluid may be used to actuate the jack and/or return the parts to normal position after use.

Iclaim:

l. A hydraulic jack having a housing comprising an input section and an output section and containing hydraulic fluid means providing a flow path connecting said input section and said output section; a first piston in said input section; a second piston in said output section; said first piston being movable to move hydraulic fluid from said input section into said output section on one side of said second piston; means operable by pressure on the other side of said second piston to interrupt flow of hydraulic fluid from said input section to said output section and permit flow of hydraulic fluid from said other side of said second piston to said one side; and means for transmitting fluid power from said output section of a load.

2. A hydraulic jack according to claim 1 wherein said means providing said flow path comprises a hollow piston rod the interior of which provides communication between said input section and said output section, said rod also carrying said piston.

3. A hydraulic jack according to claim 1 in which said first piston is moved by air under pressure.

4. A hydraulic jack comprising: a cylindrical housing, a partition fixed in said housing, said partition dividing said housing into an input section and an output section; a first piston in said input section; a second piston in said output section and dividing said section into a primary chamber and a secondary chamber, said first and second pistons being mounted on and carried together by a piston rod which extends through said partition, said piston rod being hollow and opening into said secondary chamber; a third piston slidably mounted on said piston rod within said input section whereby to divide the portion of said section between said first piston and said partition into a first chamber and a second chamber, said chambers being variable in size; means for admitting fluid under pressure to said input section whereby to move said first piston toward said output section; first port means in said piston rod providing communication between said first chamber and the interior of said rod; second port means in said piston rod providing communication between said primary chamber and the interior of said piston rod; and valve means in said piston rod adjacent said second piston, said valve means being operative in one position to permit flow from the interior of said piston rod to said primary chamber and operative in another position to permit flow to said primary chamber from said secondary chamber; and means for transmitting fluid power from the output section of said housing, said first chamber, said primary chamber, and said secondary chamber being filled with hydraulic fluid.

5. A hydraulic jack according to claim 4 wherein said means for transmitting fluid power comprises an actuating piston responsive to pressure in said secondary chamber.

6. A hydraulic jack according to claim 5 wherein said actuating piston carries a piston rod adapted to engage an external load.

7. A hydraulic jack according to claim 6 wherein said actuating piston is movably mounted within said secondary chamber.

8. A hydraulic jack according to claim 6 wherein said actuating piston is movably mounted in a separate casing removed from said housing and means are provided for passage of fluid under pressure from said secondary chamber to the interior of said separate casing.

9. A hydraulic jack according to claim 4 wherein means is provided for admitting fluid under pressure to return said pistons to normal position after operation of said jack.

contain hydraulic fluid; wherein said valve means includes a passage, a check valve adapted to close said passage. and a spring biasing said check valve to closed position, whereby when said check valve is closed communication is cut off between said secondary chamber and said first chamber; wherein means is provided for admitting fluid under pressure to return said pistons to normal position after operation of said jack; and wherein there is no communication between opposite sides of said first piston.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatentNo- 365 Dated January 11, 1972 Inventor(s) John C. Belknap It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the abstract: Line 7, "are", second occurrence, has been cancelled.

In the specification:

Column 2; line 19, "of positions. has been changed to or portions I line 35, "the" has been changed to and--.

Column 5; line 53, v-of-- has been inserted after "that", first occurrence.

In the claims:

Claim 1; line 3, "sand" has been changed to and--.

(SEAL) Attest:

ROBERT GOT'I'SCHALK Commissioner of Patents EDEIZKBB M.FLETCHER,JR. Attesting Officer FORM PO-105O (10-69) USCOMM-DC 60376-P69 t u.s. GOVERNMENT PRINTING OFFICE: I969 0-366-334

Claims

1. A hydraulic jack having a housing comprising an input section and an output section and containing hydraulic fluid means providing a flow path connecting said input section and said output section; a first piston in said input section; a second piston in said output sectioN; said first piston being movable to move hydraulic fluid from said input section into said output section on one side of said second piston; means operable by pressure on the other side of said second piston to interrupt flow of hydraulic fluid from said input section to said output section and permit flow of hydraulic fluid from said other side of said second piston to said one side; and means for transmitting fluid power from said output section of a load.

10. A hydraulic jack according to claim 4 in which the hydraulic fluid is isolated in said first chamber, said primary chamber and said secondary chamber.

11. A hydraulic jack according to claim 4 wherein said valve means includes a passage, a check valve adapted to close said passage, sand a spring biasing said check valve to closed position, whereby when said check valve is closed communication is cut off between said secondary chamber and said first chamber.

12. A hydraulic jack according to claim 6 wherein said first chamber, said primary chamber, and said secondary chamber contain hydraulic fluid; wherein said valve means includes a passage, a check valve adapted to close said passage, and a spring biasing said check valve to closed posiTion, whereby when said check valve is closed communication is cut off between said secondary chamber and said first chamber; wherein means is provided for admitting fluid under pressure to return said pistons to normal position after operation of said jack; and wherein there is no communication between opposite sides of said first piston.