US3258921A

US3258921A - Hydraulic jack

Info

Publication number: US3258921A
Application number: US342615A
Authority: US
Inventors: David B Prescott
Original assignee: Walker Manufacturing Co
Current assignee: McNeil Corp; Walker Manufacturing Co
Priority date: 1964-02-05
Filing date: 1964-02-05
Publication date: 1966-07-05
Anticipated expiration: 1983-07-05

Description

July 5, 1966 D. B. PREscoTT 3,258,921

HYDRAULIC JACK Sheets-Sheet l Filed Feb. 5, 1964 3 j; V 24x E a. g//// July 5, 1966 D. B. PREsco'r-r HYDRAULI C JACK 3 Sheets-Sheet 2 Filed Feb. 5, 1964 July 5, 1966 D. B. PREsco'rT HYDRAULI C JACK 3 Sheets-Sheet 3 Filed Feb. 5, 1964 INVENTOR. E. Jan/415. cns'caiz? United States Patent Office 3,253,921 Patented `Iuly 5, 1966 3,258,921 HYDRAULC JACK David B. Prescott, Racine, Wis., assigner to Walker Manufacturing Company, Racine, Wis., a corporation of Delaware Filed Feb. 5, 1964, Ser. No. 342,615 1 Claim. (Cl. 611-52) This invention relates generally to hydraulic jacks, and more particularly, to valve means for operatively controlling the flow of pressurized fluid to the hydraulic ram assembly of a multi-speed hydraulic jack.

It has heretofore been the practice in the construction of hydraulic jacks of the type used in automotive vehicle repair shops and which include a wheeled frame or carriage and a hydraulic pressure-operated load-lifting lever, to provide means to raise or elevate the lifting lever at a relatively fast rate while it approaches the load, and thereafter to supply sufcient power to elevate the load to the desired height. Generally, such means consists of a pair of hydraulic piston assemblies or pumps, one of which is larger than the other and is adapted to supply a large quantity of low pressure hydraulic uid to a ram or lifting cylinder under no-load conditions to obtain rapid ram movement. The smaller pump is, of course, the low speed or power pump and is adapted to supply high pressure uid to the lifting cylinder to slowly elevate the load thereon. The larger or speed pump and the power pump are usually arranged in parallel and operate simultaneously until such time as the lifting lever engages the load, whereby the speed pump is automatically rendered inoperative, and the power pump operates alone to ctfect the lifting of the load.

It is an object of the present invention to provide a multispeed hydraulic jack of the above character which is adapted to minimize to the extreme, the effort required to elevate the lifting lever once the high speed pump becomes ineffective.

It is another object of the present invention to provide a multispeed hydraulic jack of the above character having an improved hydraulic circuitry and valve means therein Which operate to automatically render the speed pump inoperable when the hydraulic ram pressure reaches a preselected level.

It is still another object of the present invention to provide a multispeed hydraulic jack of the above character wherein actuation of the above valve means is controlled by the fluid pressure in the ram displacement chamber.

Other `objects and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is an elevated perspective view of a conventional hydraulic jack assembly having a preferred embodiment of the present invention in operative association;

FIGURE 2 is a top elevational view of the pump `and ram assembly of the jack illustrated in FIGURE 1, and which is taken substantially along the line 2-2 of FIG- URE 1;

FIGURE 3 is a fragmentary longitudinal cross-sectional view of the structure illustrated in FIGURE 2, taken along the line 3-3 thereof;

FIGURE 4 is a longitudinal cross-sectional view of the structure illustrated in FIGURE 2, taken along the line 4--4 thereof;

FIGURE 5 is a transverse cross-sectional view taken along the line 5 5 of FIGURE 2;

FIGURE 6 is a fragmentary cross-sectional view taken along the line 6-6 of FIGURE 5;

FIGURE 7 is an enlarged fragmentary View of the valve structure illustrated in FIGURE 6;

FIGURE 8 is a view similar to FIGURE 7 and illustrates the valve structure shown in FIGURE 6 in its closed position;

FIGURE 9 is a fragmentary cross-sectional view taken along the line 99 of FIGURE 5; and

FIGURE l0 is a schematic representation of the hydraulic circuitry of the pump and ram assembly illustrated in FIGURE 2.

Referring now t-o the drawings, FIGURE 1 illustrates a portable hydraulic service jack, generally designated 10, of the general type with which the valve assembly of the present invention is ladapted to be operatively associated. The jack 10 comprises in general, an elongated main frame or carriage 12 having transporting wheels 14 at one end and a manipulating handle 16 pivotably connected at its opposite end. A longitudinally extending load-lifting lever 18 is pivotably mounted to a medial portion of the carriage 12 and is provided with a load-engaging saddle 19 on the swinging or unattached end thereof. A hydraulic pump and ram assembly 20 (illustrated in FIGURE 2) is mounted within the carriage 12 and includes a reciprocal plunger or ram 22 that is pivotably connected to the lifting lever 18 and which is movable in one direction by the action of pressurized hydraulic uid to elevate the lever 18 and saddle 19, and is movable in the opposite direction to lower the lever 18 and saddle 19. The uid pumping section of the assembly 20 is connected through a pair of links 24 and 26 to the handle 16 and is operable upon the oscillation of the handle 16 to deliver hydraulic fluid under pressure from a reservoir chamber 28 (illustrated in FIG- URES 3, 4 and 6) past suitable valve means and into the rams displacement chamber or cylinder 30, thereby forcing the ram 22 outwardly and elevating the lever 18. A release valve assembly 32 is provided in the assembly 20 and is connected to a rotatable knob 34 on the swinging end of the handle 16 through a shaft 36 which is rotatable within the handle 16. Upon proper rotation of the knob 34, the hydraulic pressure within the ram displacement chamber 30 may be released thereby retracting the ram 22 to lower the lifting lever 18 and saddle 19.

The aforegoing jack structure is well known in the art, and the present invention is particularly directed toward the hydraulic valve means and associated hydraulic circuitry incorporated in the assembly 20 which controls the flow of hydraulic fluid between the pumping and ram sections thereof under different operating conditions.

Referring now in detail to the pump and ram assembly 20, as illustrated in FIGURES 2, 3 and 4, the pumping section of the assembly 20 is contained wi-thin a housing o-r casing 38 which preferably consists of la single casting having a speed pump displacement chamber 40 and a power pump displacement chamber 42 formed in the outer end thereof. As seen in FIGURE 4, a piston 44 is reciprocally mounted within the speed pump displacement chamber 40. The outer end of the piston 44 is pivotably connected by a transversely extending pin 46 to the links 24 and 26. Similarly, a piston 48 is reciprocally mounted within the power pump displacement chamber 42, and the outer end of the piston 48 is pivotably connected to the links 24 and 26 by the pin 46. Conventional cotter pins 50 and 52 extend through the ends of the pin 46 to prevent it from sliding axially from its operative position.

The inner end of the piston 48 is provided with a plurality of V packing rings, generally designated 54. The rings 54 are secured to the -stud end of the piston 48 by a nut 56 and male adapter washer 58, .and are adapted to provide a fluid-tight seal between the piston 48 and the interior of the displacement chamber 42. The piston 44 is provided with a packing or O-ring 6i) which extends around an annular groove 62 on the inner end of the piston 44 and functions to provide a iluid-tight seal between the interior of the displacement chamber 40 and the piston 44.

To prevent leakage of hydraulic fluid from the

displacement chambers

40 and 42, ya plurality of packing washers, generally designated 64 and 66, are respectively located at the outer ends of the

displacement chambers

40 and 42 and are operatively maintained therein by gland nuts 68 and 70.

By virtue of the fact that both of the links 24 and 26 are connected to the handle 16, it will be apparent that upon oscillation of the handle 16, the

pistons

44 and 48 willsimultaneously reciprocate within their

respective displacement chambers

40 and 42.

The end of the casing 38 opposite the

chambers

40 and 42 is formed with an annular threaded recessed portion 72 into which is threaded one end of the ram displacement cylinder 30. Spaced radially outward from the cylinder 30, and being substantially coextensive therewith, is an elongated reservoir housing 74. The housing 74 is rigidly connected to the casing 38 by being axially compressed between 4an annular shoulder 76 formed on the end of the casing 38 and an annular boss portion 78 formed on the outer periphery of a hollow end plug 80 which is threaded on the outer end of the displacement cylinder 30. The annular chamber deiined by the housing 74 and the exterior surface of the ram cylinder 30 forms the reservoir chamber 28.

The chamber 28 is adapted to be filled with a suitable hydraulic iiuid through a bore 82 formed in the top of the casing 38 and which is normally closed by 4a plug 84. As seen in FIGURE 4, the plug 84 is .provided with a sealing gasket 86 land is formed with a central passage 88 in which is disposed a filter element 90. The passage 88 is closed by a shipping screw 32 which is adapted to be removed upon oper-ation of the jack so that the passage S8 may conduct filtered vent air to the reservoir charnber 28.

It will be seen in FIGURE 4 that the ram 22 is reciprocably mounted in the ram cylinder 30 and has its outer end portion 94 extending axially through a central passageway 96 formed in the end plug 80. An annular sealing gasket 98 is retained in an annular recess 100 formed around the passageway 96 and is adapted to provide a duid-tight seal to prevent hydraulic fluid from passing between the end plug 80 and the ram 22.

Referring now in detail to the hydrau-licY circuitry Vcommunicating the

displacement chambers

40 and 42 with the ram cylinder 30 and reservoir chamber 28, it will be seen in FIGURE 3 that a vertically extending bore, generally designated 102, is formed in the casing 38 interjacent the threaded recess portion 72 and the inner end of the displacement chamber 42. The bore 102 is formed with an enlarged upper section 10251 in which is threadably mounted :a plug 104 having a sealing gasket 106 and a screwdriver-receiving slot 108. The bore 102 is also formed with an intermediate section 102b which is of a slightly smaller diameter than the upper lsection 102er, and the bore 102 is further formed with a lower section 102e which is of a smaller diameter than either of the upper section 102g or the intermediate section 102b. A longitudinal passageway 110, having inner :and outer sections 11051 .and 110b, extends between the innermost portion of the reservoir chamber 28 and the bore section 102C. Another longitudinal passageway 112 communicates the upper bore section 102:1 with the interior of the ram cylinder 30. Still another passageway 114 communicates the y inner end of the displacement chamber 42 with the bore 102. A pair of

ball valves

116 and 118 are supported within the bore 102 by annular shoulders 120 and 122 formed at the lower ends of the -bore sections 102e and 102k, respectively. Also provided in the bore 102 is a pair of limit pins 124 and 126, the former of which is slidably disposed in the bore section 102b between the

ball valves

116 and 118. The other limit pin 126 is rigidly connected or integrally formed on the bottom of the plug 104 and extends -axially downward within the bore section 10241. It will be apparent that the limit pins 124 and 126 are operable to prevent the

ball valves

116 and 118 from moving axially upward within the bore 102 beyond a preselected position.

Referring again to FIGURE 4, a bore 128, similar to the bore 102, is formed in the casing 38 interjacent the threaded recess 72 and the inner end of the displacement chamber 40. The bore 128 is formed with an enlarged -upper sec-tion 128:1, a smaller diameter Vintermediate section 128:5 and an even smaller diameter lower section 128C. Ball valves 130 and 132'are supported within the bore 128 on Iannular shoulders 134 and 136 formed at the lower ends of the bore sections 128a and 128b. A limit pin 138 is slidably disposed in the bore section 128b to restrict the movement of the ball valve 132 to a preselected amount. The upper end of the bore 128 is closed by a plug 140 having la sealing gasket 142 and a screwdriver receiving slot 144, and which is threadably mounted in the bore section 128:1. It will be seen that a cupshaped recess 145 is formed in the lower end of the plug 140 within which the upper end of a coil spring 146 is seated. The opposite or lower end of the spring 146 rests directly on the ball valve 130 and thereby acts to resiliently resist upward movement of the ball valve 130.

A longitudinal passageway 148 extends between the innermost end of the reservoir chamber 28 and the lower bore section 128C. Another passage 150 extends between the inner end of the ram cylinder 30 and the upper bore section 128a. The bore 128 is also communicated with the speed pump displacement chamber 40 and with the rel-ease valve bore 152 by

passageways

154 and 156, respectively. It may be noted that a wire mesh inlet screen or filter 157 projects into the reservoir chamber 28 from the

passageways

148 and 110 and is .adapted to filter contaminents from the hydraulic fluid being pumped from the chamber 28 by the

pistons

44 and 48.

From. the structure thus far described, it will he `apparent that upward movement of the handle 16 will, rthnough the links 24 and 26, bias the

pistons

44 and 48 outwardly, thereby eiecting the ow of hydraulic iiuid from the reservoir chamber 28 through the passages and 148, and the passages 114 and 154, into the

displacement chambers

40 and 42. Subsequent downward movement of the handle 16 will force the

pistons

44 and 48 inwardly within their

respective chambers

40 and 42, thereby forcing the liuid in the

chambers

40 and 42 through the pass-ages 114 and 154, past the

ball valves

116 and 130, and finally .through the longitudinal passages 112 and 150 into the interior of the ram cylinder 30. It will be noted that the uid is forced out of the

chambers

40 and 42, the ball valves 132 and 11S will be searted lagainst the 'annular shoulders 136 and 122, thereby preventing the tiuid from flowing back through the

passages

148 and 110 into the reservoir chamber 28. Subsequent upward movement of the handle 16 will again retract the

pistons

44 and 48 in their respective chambers, whereby the ball valves and 116 will become seated against the shoulder portions 134 and 120, and Vwhereby the

ball valves

118 and 132 will become unseated to permit tiuid to be pumped from the reservoir chamber 28 'into the

displacement chambers

40 and 42, as previously described.

It will thus be seen that as the

pistons

44 and 48 recipnocate within the

displacement chambers

40 and 42, hydraulic fluid will be pumped :from the reservoir chamber 28 into the ram 4cylinder 30, thereby moving the rain 22 outwardly to elevate the lifting lever 18. It will be apparent that since the

pistons

44 and 48 are actuated simultaneously, hydraulic uid will be supplied to the ram cylinde-r 30 at a relatively fast rate, thereby moving the ram 22 and elevating the lifting lever 18 at a correspondingly fast rate. It will further be apparent that when the lift arm 1S encounters a load, the back pressure within the ram cylinder 30 will increase substantially and effect a corresponding increase in the force required to pump the hydraulic uid into the ram cylinder 30. In

accordance with the principles of the present invention, the hereinafter described valve assembly and associated hydraulic circuitry is adapted to minimize tothe extreme, 'the additional effort required to pump hydraulic lluid into the ram cylinder 30 as the lifting lever 18 engages and elevates a load.

Referring now to FIGURES 5 through 9, it will be seen that there is :an upwardly extending bore 156 formed in the lower side of the casing 38 in which is disposed a valve assembly hereinafter generally referred to as the spool valve assembly 158. The bore 156 is formed in four coaxial sections 156a, 156b, 156e and 156:1, which progressively vary in diametric size yfrom lthe larges/t section 156a which is `adjacent the .outer surface of the casing 38 to the smallest section 156d which is formed in the innermost end ro-f the bore 156i. The Valvle assembly 158 comprises a valve plug 168 that is provided with a screwdriver receiving slot 162 and an annular gasket 164, and which is threadably mounted within theouter bore section 156a. The plug 160 has a central axially extending cavity 166 formed in the threaded portion thereof in which is disposed one end of a helical coil spring 168. A valve spool 170, which consists of a sleeve section 17861 and a stem section 17tlb, is slidably disposed in the lbore Isection 156b with its stem section 17817 extending coaxially within the coil spring 168. A cylindrical valve member 172 is disposed Within the bore section 156e and is yformed with a central stem section 172a which is seated within a central recess 174 formed in the valve spool sleeve section 170m A flexible cupshaped packing element 176 is provided on the inner end of the valve member 172 which element by virtue of being slightly larger than the bore section 156C, is adapted to provide a relatively slidable, fluid-tight seal therein.

As best seen in FIGURE 6, a longitudinal passage 178 extends between the inner end of the ram cylinder 38 and the bore section 156d. Also, as seen in FIGURE 6, a longitudinal passage 180 extends between the speed pump displacement chamber 40 and the bore section 156b. Still another passage 182 extends longitudinally from the lbore section 156b to a bore 184 which extends vertically Within the casing 38 and which communicates the passage 182 with the passage 148 that extends between the displacement chamber 40 and the reservoir chamber 28. The juncture of the

passages

182, 184 and 148 together with a spherical .plug 185 which closes the outer end of the passage 184, may best be seen in FIGURE 9. It will thus be apparent that the bore section 156b is communicated with both the speed pump displacement chamber 40 (through passage 180), and with the reservoir chamber 28 (through passages 182, 184 and 148). Accordingly, it will be seen in FIGURES 7 and 8 that when the spool valve assembly 158 is in its expanded or closed condition (as seen in FIGURE 8), the valve spool 170 is disposed at the inner end of the bore section 156b, thereby preventing fluid :from passing from the passage 180 through the valve bore 156 to the passage 182. However, as seen in FIGURE 7, when the valve assembly 158 is in its contracted or open condition, which will occur when there is suflicient fluid pressure in the passage 178 to 'force the packing cup 176, valve member 172 and valve spool 170 axially downward in the bore 156, the valve member 172 is at least partially positioned in the bore section 15617 and, by vintue of the fact that valve member 172 is of `a smaller diameter than the bore section 156b, hydraulic fluid is allowed to freely flow from the passage 188, around the valve member 172 and into the passage 182.

Referring now to FIGURES 5 and 9, it will be seen that a vent passage 186 is formed in the side of the housing 38 and communicates the passage 148 with the back (spring) side of the valve bore 156. This passage 186 is provided to assure that the ram pressure acts on the face (packing) of the valve assembly 158, and that the reservoir pressure (atmospheric) actsion the back or 6 spring side of the assembly 158. As seen in FIGURE 5 a spherical plug 187 is press tted within and closes the outer end of the passage 186.

It may be noted that since the packing element 176 is Iformed in a generally cup-like configuration, lluid pressure being communicated through -the passage 178 to the bore section 156C will tend to expand the walls of the packing cup 176, thereby assuring a fluid-tight seal between the packing cup 176 and the bore 156.

Since the bore section 156e is communicable with the interior of the ram cylinder 30 through the passage 176, it will be seen that the condition of the valve assembly 158 (open or closed is entirely determined by the interaction of the coil spring 168 and the fluid pressure in the ram cylinder 30. Therefore, when the pressure Within the cylinder 30 is below a preselected level, the coil spring 168 maintains the valve spool 170 in the position illustrated in FIGURE 8, thereby preventing hydraulic uid from flowing from the speed pump displacement chamber 40 back to the reservoir chamber 28, At such time as the lifting lever 18 engages a load and the back pressure within the ram cylinder 38 exceeds a preselected Value, the packing cup 176, valve member 172 and valve spool 170 move against the resistance of the coil spring 168, thereby opening a flow path through which hydraulic fluid may pass from the displacement chamber 40 to the reservoir chamber 28. It will therefore be seen that while the fluid pressure in the ram cylinder 30 exceeds a preselected value, the valve assembly 158 will be maintained in its open position as illustrated in FIGURE 7. Moreover, it will be seen that the valve assembly 158 is held in this position entirely by the fluid pressure in the ram cylinder 38, and not by the oil which is being pumped to the ram cylinder 30 from the displacement chamber 40. Thus, the uid which is passing from the speed pump back to the reservoir chamber 30 is not required to impinge upon and maintain the valve in its open position in order to ow thereby. This feature is critical in view of the fact that in the analogous valve assemblies yin conventional multispeed jack constructions, there is a substantial loss of pumping energy as hydraulicuid being returned to the supply reservoir continually resists the force of the valve assemblys closure spring. In the spool valve assembly 158 described herein, the valve components are biased to, and are maintained in their open position, entirely by the hydraulic pressure in the ram cylinder 30, thereby permitting the hydraulic fluid to flow freely through the open valve without having to resist the force of the valve spring 168.

To more clearly illustrate the importance of the above features, together with correlating the hereinbefore described structure, the operation of the entire jack assembly 10 will now be described with particular reference being made to the schematic diagram of the jack assemblys hydraulic circuitry illustrated in FIGURE l0.

In operation, on the suction stroke (upward movement Iof the handle 16), the pistons 44 yand 48 simultaneously draw hydraulic fluid from the reservoir chamber 28 through the

passages

110 and 148,

past ball valves

118 and 132, and into .the displacement chambers 42 and On the discharge stroke (downward movement of the handle 16), hydraulic lluid within the power pump displacement chamber 42 is directed past the ball valve 116, through the passage 112, and into the ram cylinder 30, thereby moving the ram 22 to the lef-t to elevate the lifting lever 18. If the system pressure is low, as is the case when the jack is unloaded, the speed pump will discharge the hydraulic fluid within the displacement chamber 40 past the ball valve 130 and into the ram cylinder 30, also moving the ram 22 to the left. At this low pressure, the spool valve spring 168 holds the spool 170 in a position that prevents hydraulic fluid from passing through the spool valve assembly 158 from the speed pump back to the reservoir chamber 28. When the lifting lever 18 engages a load and the back pressure within the ram cylinder 30 reaches a predetermined value, the spool 170 moves against the resistance of the spring 168 to permit oil to pass from the speed pump back to the reservoir thereby automatically rendering the speed pump ineffective in elevating the lifting lever 18, and the power pump operates alone to elevate the load. It will thus be seen that once the system pressure reaches this predetermined level, each stroke of the speed pump merely draws hydraulic fluid from the reservoir into the displacement chamber 40 and then returns :this fluid back to the reservoir through the valve assembly 158. As previously described, since the valve assembly 158 is'maintained in its open position entirely by the system pressure within the ram cylinder 30, the lluid being forced back to the reservoir from the speed pump is not resisted by the force of the valve spring 168. Accordingly, all of the pumping energy exerted by the jack operator will be directed towards elevating the load and none will be required to maintain the spool valve -in the open position.

As briefly hereinbefore mentioned, there is provided a release valve assembly 32 which is mounted in the valve bore 152, and is operable upon suitable rotation of the shaft 36 by the knob 34, to relieve the hydraulic pressure within the ram cylinder 30, thereby permitting the ram to be retracted to lower the lifting lever 18. As seen in FIGURE 4, the release valve assembly 32 consists of a piston 188 which has a conically shaped forward end 189 and an outer cylindrical portion 190 which is threadably mounted in the outer end of the vallve bore 152. The shaft 36 is provided with a sleeve coupling 102 which is disposed circumjacent the outer end of the valve piston 188. The opposite ends of a diametrically extending pin 194 protrude radially outward through a pair of axially extending slots 196 on the opposite sides of the coupling 192 and, as seen in FIGURE 4, when the coupling 192 is rotated by the shaft 36, the piston 188 will move axially within the bore 152 with the outer end thereof sliding axially outward within the coupling 192. The valve pistons inner end 189 is provided with an annular packing ring 198 which is adapted to be normally seated within a reduced diameter inner section of the bore 152, thereby providing a fluid-tight seal between the interior of the bore 152 and a fluid passage 200 (illustrated in FIGURES 4 and 5) which communicates the valve bore 152 with the reservoir chamber 28.

With the structure thus described, it will be seen that when it is desired to relieve the fluid pressure within the ram cylinder 30, it is merely necessary to rotate the knob 34 on the handle 16, thereby unscrewing or unseating the valve piston 188 and permitting hydraulic fluid within the ram cylinder 30 to flow through the passage 156 into the valve bore 152, and through the passage 200 into the reservoir chamber 28. It will be apparent, of course, that prior to again operating the jack mechanism 10, it is necessary to reseat the valve Vpiston 188 in order to elect the desired hydraulic pressure within the -ram Icylinder 30.

Referring again to FIGURE 4, it will be seen that an axially extending bore 202, having inner and outer sections 202a and 20211, is formed in the inner end of the ram 22. The section 2026: terminates on the outer end thereof in a diametrically extending bore 204 in which is disposed a cylindrical pin 206 that extends radially outward on the opposite sides of the ram 22. A ball valve 208 is resiliently seated against the outer end of the bore section 202:1 by a Coil spring 210 which is disposed in the bore section 202er. A filter screen 212 is provided across the inner end of the ram 22 and is operatively maintained thereon by a snap-ring 214 which is disposed around an annular groove 216. It may be noted that the snap-ring 214 also supports an annular collar 218 on the end of the ram 22, which collar in turn retains a resilient packing ring 220 and packing backing ring 222 against a shoulder portion 224 on Ithe ram 22. A cylindrical pin 226 is coextensive within the bore section 202b and is oper-able upon axial inward movement of the pin 206 to unseat the ball valve 208.

During the operation of the jack assembly 10, the structure thus described operates as a means for preventing further outward movement of the ram 22 when the lifting lever 18 has reached a preselected elevated position. As the ram 22 is biased outwardly upon increasing lthe hydraulic pressure within ram cylinder 30, the diametrically extending pin 206 engages an -annular shoulder 228 formed on the outer end of the cylinder 30. As the pressure within the cylinder increases `and the ram 22 moves further outward, the pin 206 is biased axially inward within the bore 204 -thereby causing the pin 226 to unseat the ball valve 208. With the valve 208 thus unseated, it will be seen that the hydaulic fluid in the inner end of the cylinder 30 will flow through the bore sections 202e, 202b, and lthrough the bore 204 into the cylinder 30 0n -the outer side of the packing rings 220 and 222, thereby equalizing the hydraulic pressure in the cylinder 30 on each `side of the rings 220 and 222. Subsequent uid that is pumped into the cylinder 30 will flow back to the reservoir chamber 28 through a plurality of radially extending passages in the plug 80, two of which are illustrated in FIGURE 4 and designa-ted by the number 230. It will .be apparent, of course, that when the pressure differential across the packing rings Y 220 and 222 is eliminated, the ram will no longer lbe biased-outward within the cylinder 30, even though the overall system pressure in the cylinder 30 is increased by subsequent operation of the speed and/or power pumps. Thus, when the pin 206 engages the ram cylinders shoulder portion 228, outward movement of the ram 30 and the corresponding upward movement of the lifting lever 18 will automatically be terminated.

It may be noted that the structure indicated in FIG- URES 2 and l0 by the numeral 232 consists of a relief or overload valve. This valve is ram pressure sensitive and is adapted to be adjusted at :assembly of the jack 10 to prevent it from elevating a load appreciably in excess of its capacity.

While it will be apparent that the preferred embodi- "ment herein illustrated is well calculated to fullill the objects stated, it will be appreciated that the present invention is susceptible to modification, variation and change without departing from the proper scope or `fair meaning of the subjoined claim.

What is claimed is:

In a multispeed hydraulic jack assembly, an elongated jack carriage, a longitudinally extending load-lifting lever pivotably mounted in said carriage, a manipulating handle pivotably connected to one end of said carriage, a hydraulic pump and ram assembly operatively mounted in said carriage and including a pump and ram housing, a fluid reservoir in said housing for storing an actuating fluid, a ram displacement chamber in said housing having a reciprocal ram therewithin, said ram being pivotably connected to said lifting lever, speed pump and power pump displacement chambers in said housing, pist0n means in each of said displacement chambers and being pivotably connected to said manipulating handle, a first valve bore in said housing, a first fluid passage means extending between said speed pump displacement chamber and said reservoir and including a portion of said first valve bore, a second fluid passage means extending between said first valve bore and said ram displace- Vment chamber, check valve means in said first valve bore operable to selectively permit fluid to pass between said reservoir and said speed pump chamber and between said speed pump chamber and said ram displacement chamber, a second valve bore in said housing, a third uid passage means extending between said power pump displacement chamber and said reservoir and including a portion of said second valve bore, a fourth fluid passage means extending between said second valve .bore and said ram displacement chamber, check valve means in said second valve bore operable to selectively permit luid to tlow between said reservoir and said power pump displacement chamber and between said power pump displacement chamber and said ram displacement chamber, a spool valve bore formed in said housing and being communicable with said ram displacement chamber, said rst fluid passage means including a straight section and said spool valve bore intersecting said straight section at an angle, and having a valve spool reciprocably mounted therewithin -to extend across said straight section and control ilow through it, one end of said valve spool being exposed to fluid pressure in the ram displacement chamber, spring means acting on Ithe v-alve spool in opposition to fluid pressure in said ram displacement chamber, said spool valve bore having -a rst diameter section and a second and larger diameter section, said spool valve having rst and second diameter sections slidably fitting said rst and second lspool bore diameter sections, said second diameter section intersecting said straight section of said rst uid passage means, said 1t) pist-on means in said speed pump and power pump displacement chambers being operable to simultaneously pump fluid from said reservoir to said displacement chamber to elfect the movement of said ram, and said valve spool being movable -against said spring means when a preselected uid pressure is reached in said ram displacement chamber to move its first diameter section across the straight section of said first passage means to open said straight section norm-ally being closed by the second diameter section of the spool so that the uid pumped by said speed pump is returned to said reservoir.

References Cited bythe Examiner UNITED STATES PATENTS 2,138,263 ll/1938 V-an CleaVe et al. 60-52 X 2,250,551 7/ 1941 Pfauser 60-52 X 2,439,796 4/ 1948 Dearsley 60-52 X JULIUS E. WEST, Primary Examiner.