hydraulic jack safety valve free sample

The present invention relates to an improved safety valve structure for a hydraulic jack, particularly to an improved structure of the safety valve inside a pump base of the jack so that high pressure hydraulic fluid can smoothly and accurately flow through the valve and return to a reservoir.

A one-way valve is usually provided between the reservoir and the pump base of a hydraulic jack. The one-way valve is used to control hydraulic fluid flowing from the reservoir into a pump. The valve also cooperates with the up-and-down movement of a lever on the jack so that the hydraulic fluid can be forced into a pressure tank for pushing a piston upward. When the jack is overloaded and the hydraulic pressure inside the jack has reached a predetermined limit, a safety device is needed to discharge the hydraulic fluid back into the reservoir. A conventional safety device uses a steel ball and a safety spring secured by an adjustment screw. The adjustment screw is used to adjust the pressure of the safety spring which presses against the steel ball. When the pressure inside the pressure tank is higher than the pressure of the safety spring set by the adjustment screw, the steel ball will automatically be pushed rearwardly against the force of the safety spring so that the safety spring is compressed, thus enabling the steel ball to disengage from a valve seat. Thus, the path previously closed by the steel ball is opened and the hydraulic fluid can return to the reservoir, thereby lowering the pressure within the pressure tank and preventing the pressure tank from cracking or exploding. However, the operation of the above arrangement is not reliable, since it is easy for the steel ball to deviate from an opening path of movement. Therefore, discharge of the hydraulic fluid is unstable and results in rough operation.

The main object according to the present invention is to provide an improved safety valve structure for hydraulic jacks. The structure is provided with a push pin, a safety spring and an adjustment screw. The end of the push pin is placed inside the axial hole of the adjustment screw. The adjustment screw is used to adjust the compression of the safety spring so as to control the pushing force of the push pin. By such configuration, the push pin can be used to seal the opening as well as to guide the hydraulic flow when the push pin is retracted. Thus, it provides for smooth operation when the hydraulic oil is discharging.

As shown in FIGS. 2 and 3, a safety valve according to the present invention is provided inside a valve body of a one-way valve 1 of a hydraulic jack. The one-way valve 1 is provided inside a pump base 6 of the hydraulic jack and a pump 7 is provided on the pump base 6. The one-way valve 1 includes a cylindrical valve body. The cylindrical valve body has an annular recess or slot 11 formed in an exterior wall thereof.

An L-shaped oil inlet channel 12 defines an oil inlet port 121 at slot 11 and a port opening at the top surface of the one-way valve 1. A filtering screen is provided in the inlet channel 12 at oil inlet port 121. The L-shaped oil inlet channel 12 is a two-step channel having a larger diameter portion at the top and a smaller diameter portion at the bottom. A steel ball 123 and a compressed spring 124 are provided in the larger portion of the channel. The compressed spring 124 engages a projection defining the upper opening so as to be secured without disengaging. Also, the steel ball 123 seals the upper neck opening of the smaller diameter portion of the channel. In addition, the top surface of the one-way valve 1 is provided with an oil discharge port or hole 13, which is a two-step passage or hole having a larger diameter bottom portion and a smaller diameter top portion. The larger diameter portion of the channel is provided with a steel ball 131 and a compressed spring 132. The compressed spring 132 is secured in place by engaging an inwardly extending projection defining a bottom opening. Also, steel ball 131 seals the bottom opening of the smaller diameter portion. In addition, the wall of the annular slot 11 of the one-way valve 1 is provided with a safety oil discharge port or hole 14, which communicates with the smaller channel portion of the oil discharge port or hole 13.

As shown in FIGS. 2 and 3, the safety oil discharge hole 14 is a two-step passage or hole having a smaller diameter portion 141 which communicates with the smaller portion of the oil discharge hole 13. A rearward section of a larger diameter portion 142 is provided with inner screw threads. A push pin 2, as well as a safety spring 3, are placed in the larger portion 142 and an adjustment screw 4 is used to secure the pin 2 and spring 3 in place. A forward portion of push pin 2 is a cone-shaped body 21 and a rearward portion is a two-step rod or post 22, in which a large-diameter portion is inserted into the safety spring 3 in the axial direction, the small-diameter portion is inserted into an axial hole 41 of the adjustment screw 4. In this configuration, the resilient force of the safety spring 3 is applied so that the cone-shaped body 21 of the push pin 2 seals an end of the smaller portion 141 of the safety oil discharge passage 14. An end of safety spring 3 is engaged by adjustment screw 4, which is screwed and secured inside the larger portion 142 of the safety oil discharge hole 14. Also, the force of the safety spring 3 and thus the sealing force of push pin 2, can be adjusted by adjusting the adjustment screw 4 in the larger portion 142 of the safety oil discharge hole 14. In addition, the axial hole 41, provided on top of the adjustment screw 4, is used for discharge of the hydraulic fluid.

By use of the push pin 2, provided in the safety oil discharge hole 14 to cooperate with the safety spring 3 and the adjustment screw 4, the pump 7 can be removed and the one-way valve 1 can be taken out. By turning the adjustment screw 4, the compression ratio of the safety spring 3 can be set and the force of the push pin 2 acting against the smaller portion 141 of the safety oil discharge hole 14 can also be adjusted. Thus, the force from the safety spring 3 pushing against the push pin 2 can be set as the critical value of the hydraulic safety load coefficient. In other words, safety spring 3 and push pin 2 limit the pressure of the hydraulic jack. During operation, when the safety load value of the hydraulic fluid within the jack reaches the limit (i.e., when the load exceeds the setting of the push pin 2), the push pin 2 inside the safety oil discharge hole 14 is displaced backwardly by the hydraulic pressure and compresses the safety spring 3. At this time, the push pin 2 disengages from the smaller portion 141 of the safety oil discharge hole 14 and therefore, the hydraulic circuit is a closed circuit. This means that the hydraulic oil can circulate through the safety oil discharge hole 14, the axial hole 41 of the adjustment screw 4, the annular slot 11 of one-way valve 1 and return into the oil storage tank, allowing the pressure inside the jack to be depressurized. When the pressure inside the hydraulic jack decreases to within the safety load limit, the force from the safety spring becomes higher than the internal hydraulic pressure of the hydraulic jack, and therefore, the safety spring 3 automatically biases the push pin 2 forward so as to seal off the small portion 141 of the safety oil discharge hole 14. By this setup, the safety of the hydraulic jack can be assured and an explosion can be prevented. In addition, the push pin 2 is a linear fluid guide inside the safety oil discharge hole 14. When the latter is discharging, turbulence is prevented and a smooth operation can be assured. It is indeed a compact, practical and modern design.

By use of the above configuration, the flow of the hydraulic oil is described as follows: when the lever 5 is pulled up, the hydraulic oil inside the reservoir is sucked through an inlet 61 inside of the pump base 6. The oil follows the L-shaped oil inlet channel 12 and flows into pump 7. When lever 5 is pressed downwardly, hydraulic oil inside pump 7 is forced out through oil discharge hole 13 of the one-way valve. The oil follows an outlet path 62 of pump base 6 back into the pressure tank of the hydraulic jack so as to drive a piston up for lifting (now shown in Figure). However, if the lifting load of the jack exceeds the maximum design load and a user continues to operate lever 5 to force hydraulic oil into the pressure tank; the pressure could cause the pressure tank to crack or explode. Therefore, when the hydraulic pressure exceeds the safety limit, the improved safety valve structure, according to the present invention, allows the hydraulic pressure to push the push pin 2 inside the safety oil discharge hole 14 backwardly so that the hydraulic oil can follow the path through the annular slot 11 and through the inlet path 61 of the pump base and then return into the oil reservoir. Thus, the pressure inside the pressure tank can be controlled. In addition, the structure of push pin 2 provides a linear fluid guide so that the oil flow is smooth and accurate.

The invention relates to a hydraulic bottle jack; particularly to a control valve of the hydraulic bottle jack having a hand operable knob, and an automatic return to close the valve.

Hydraulic bottle jacks are well known, and function in accordance with Pascal"s principle wherein an incompressible fluid exerts equal pressure within a closed container; and in this case, the closed container includes a small cylinder (plunger chamber) interconnected to a large cylinder (piston lift chamber). The jack utilizes a small area pump plunger under a force to exert a high pressure on fluid within the plunger chamber and equally into a lift chamber and against the inner end of a large area piston. A one-way valve between the chambers enables the piston to be progressively raised. The differential in the area of the plunger and the area of piston, along with the leverage of a long pivotal handle, result in the hydraulic jack having tons of lifting capability, by only a few pounds of downward force on the end of the handle.

Referring to FIG. 1 (PRIOR ART), a typical hydraulic bottle jack 10 is shown having an internal hydraulic fluid control valve with an external rotatable shaft 12 of the prior art. The proximal end of the rotatable shaft has a diameter of about 38 inch and has a pair of opposed lateral pins 14 having a diameter of about 0.12 inch and a combined width of about 0.88 inch forming a “double-key head” 16.

The double-key head is engagable by a tubular handle 18 having a “slotted tubular wrench” 20 located in one end of the handle. A typical slotted wrench has an internal diameter of about 0.62 inch, an external diameter of about 0.88 inch, and opposed slotted openings about 0.20 inch wide and about 0.20 inch deep. The handle is also utilized in an actuator 22 having a tubular opening 24 therein to pump the jack. The rotatable shaft 12 is typically rotated in a clockwise direction to close the control valve for raising the jack, and rotated in a counter-clockwise direction to open the control valve for lowering the jack.

In operating the jack, the slotted tubular wrench 20 of the pump handle 18 is first fitted over the end of the rotatable shaft 12 and is rotated until the slotted openings of the wrench mate with and over the pins 14 of the double-key head 16 to engage the rotatable shaft. The handle is then rotated clockwise to close the control valve. The handle is then withdrawn from the rotatable shaft, and is inserted into the actuator opening 24, and is pumped up and down to raise the jack. To lower the elevation of the jack, the handle is withdrawn from the actuator opening, and is again fitted onto the end of the rotatable shaft, and is rotated counter-clockwise to release the control valve. The fluid flows from the lift chamber back into the reservoir, and the piston drops back within the housing of the jack.

The double-key head of the rotatable shaft and the slotted tubular wrench of the pump handle have been utilized for many decades to operate a hydraulic bottle jack. However, as described above, the operation of the jack involves multiple transfers of the tubular handle from the rotatable shaft to the actuator opening and back; and the control valve can not be rotated while simultaneously pumping the actuator, if needed, for seeking a precise elevation of the jack.

The limitation of the single handle to either maneuver the control valve for raising or lowering the jack, or to maneuver the actuator to raise the jack, can also present a safety issue. If the control valve is needed to be immediately closed or opened in an emergency situation, the wrench handle may not be immediately available or not quickly utilized to perform this task. It is very desirable to be able to maneuver the control valve immediately, independently and simultaneously with pumping the actuator, without the need of the tubular handle.

In the operation and function of a hydraulic bottle jack, the jack is predominately used with the control valve in the closed position. Once the control valve is closed, the tubular handle can be readily used in the actuator opening 24 to raise the jack. It is desirable to have the jack with a control valve having an automatic return that is always biased into the closed position. The jack is always ready to be raised, and if the control value were to be accidentally hit and rotated open, it would immediately self correct, and not fall completely down.

The above features are desirable in a new hydraulic bottle jack, and it would also be desirable if the millions of existing prior art jacks could be readily retrofit and converted to include these features.

In view of the foregoing, it is an object of the present invention to provide a hydraulic bottle jack with a control valve having a hand operable knob and does not require the use of a tubular handle.

It is another object to provide a kit of components for adapting the valve of a conventional hydraulic bottle jack to one having a control knob, and a control knob having an automatic return. SUMMARY OF THE INVENTION

The foregoing objects are accomplished with a hydraulic bottle jack having a housing with an internal control valve having an external shaft that is rotatable in the counter-clockwise direction to open the valve for lowering the jack, and rotatable in the clockwise direction to close the valve for raising the jack. An improvement includes a control knob mounted on the rotatable shaft for manually rotating the valve. Another improvement includes a means for biasing the control valve into the closed position. These improvements can be incorporated separately or combined.

Another improvement is to provide a control knob type wrench for operating the valve. Another improvement is to provide a tubular handle with a control knob on the proximal end thereof for operating the valve. Another improvement is to provide a kit of components and method for retrofitting a standard jack to a jack having one or more of the various improved features.

An example of the improvements includes the hydraulic bottle jack having a control knob on the rotatable shaft, and further having a biasing means in the form of a torsion spring having one end fixed to the housing and the other end fixed to the rotatable shaft. The knob can be rotated in the counter-clockwise direction for opening the control valve; and when the knob is released, the torsion spring automatically forces the shaft to rotate back in the clockwise direction for closing the valve.

The standard hydraulic bottle jack has the internal control valve with an external rotatable shaft having a standard double-key head thereon. The jack can also be improved by a means for biasing the rotatable shaft into the closed position. In this example, the valve is opened with the conventional slotted wrench tubular handle, and the jack does not utilize the aforementioned control knob.

A kit of one or more components including a control knob can be provided for use with a hydraulic bottle jack having a housing with an internal control valve having an external shaft with a double-key head thereon for engagement by a slotted wrench tubular handle. The shaft is rotatable in the counter-clockwise direction to open the valve for lowering the jack, and is rotatable in the clockwise direction to close the valve for raising the jack. The control knob is a generally circular disc having an outer front face with an extended double-key head thereon for engagement by a slotted wrench tubular handle. The control knob has an inner central hub with a recessed cavity including a central cylindrical opening with a first pair of slotted openings therein for manually rotating the valve. The control knob is attachable to the rotatable shaft.

The kit further includes a torsion spring having one end attachable to the housing and having the other end attachable to the rotatable shaft for biasing the valve in the closed position. The recessed cavity in the inner central hub of the control knob preferably further includes a second pair of slotted openings therein arranged perpendicularly to the first pair of slotted openings.

A method of installing the kit on a stand hydraulic bottle jack comprises the following steps: preparing the housing to receive a fastener for securing one end of the torsion spring to the housing; securing one end of the torsion spring to the housing; securing the other end of the torsion spring to the control knob; pulling the control knob outward so that the recessed cavity of the inner hub is free of engagement with the double-key head of the rotatable shaft; rotating the control knob counter-clockwise at least 90°, and further until the next pair of slotted openings are aligned with the double-key head, for pre-loading and sufficiently biasing the control knob into the closed position; pressing the control knob inward with the recessed cavity of the inner hub engaged with the double-key head on the rotatable shaft; and securing the control knob to the rotatable shaft.

An improved handle is provided for an otherwise standard hydraulic bottle jack. The jack has a housing with an internal control valve having an external shaft with a-double-key head thereon that is rotatable in the counter-clockwise direction to open the valve for lowering the jack, and rotatable in the clockwise direction for closing the valve for raising the jack. The handle includes a tubular shaft having a slotted tubular wrench at the distal end thereof for engaging the double-key head of the jack, and has a proximal end with a control knob having a diameter of about twice the diameter of the tubular shaft for facilitating control of the valve. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 4 is left side elevational sectional view of another embodiment of a jack with a control shaft having an automatic return, of the present invention;

FIG. 7 is left side elevational sectional view of another embodiment of a jack with a control knob and having an automatic return of the present invention;

FIG. 11 is left side elevational sectional view of another embodiment for adapting a conventional jack with the control knob and automatic return features of the present invention;

Referring now to FIG. 2, a first embodiment is illustrated for an improved hydraulic bottle jack 30 with a fluid control valve having a control knob of the present invention. The present invention relates only to external features and structure of the jack and the internal features are therefore not illustrated, but the internal features and functions are reviewed below in terms of the external structure.

The jack 30 includes a housing base 32 with a housing vertical portion 34 extending therefrom, with the vertical portion enclosing a hydraulic fluid reservoir and a lift chamber. The housing base includes a pump chamber (within housing vertical portion 36, and adjacent to housing vertical portion 34) with a pump plunger therein having an upper end 38 extending from the pump chamber. The lift chamber has a hydraulic piston therein having an upper end 40 extendable from the housing. An internal fluid passage interconnects the reservoir and the pump chamber and through a one-way valve to the lift chamber; and further includes a fluid passage interconnecting the lift chamber through a fluid control valve, back to the fluid reservoir. The control valve has an external rotatable shaft 42. The jack has the actuator 22 that is pivotally mounted (at 44) to the housing base and is further pivotally connecter (at 46) to the upper end of the plunger for sliding the plunger up and down, and pumping the fluid from the reservoir to the lift chamber.

The control valve has the rotatable shaft 42 extending from the housing base and is rotatable in the clockwise direction to close the valve for pumping the cylinder, and is rotatable in the counter-clockwise direction to open the valve to lower the cylinder. The rotatable shaft further includes a control knob 50 mounted on the proximal end thereof for manually rotating the control valve. The housing can further be designed to provide suitable recesses or peripheral flanges for protecting the control knob from unwanted lateral contact.

A typical control value requires only about one-quarter revolution (about 90°) from fully closed to fully open position, and the critical transition occurs within a few degrees of rotation. The large 2.00 inch diameter of the knob (relative to the 0.88 inch diameter of the tubular handle) allows the operator to provide a larger but more gradual, precise torsional force on the rotatable shaft to finely control the valve, the rate of decent of the piston, and the elevation of the piston. This is particularly useful when trying to align and match the elevation of adjacent components, for leveling adjacent surfaces, or for aligning apertures for inserting an interconnecting fastener into adjacent components, etc.

The outer front surface of the control knob 50 preferably includes an outward extended double-key head 56 (similar to conventional head 16) for engagement in the conventional manner by the slotted wrench 20 of the tubular handle 18. This double-key head is preferably recessed within a cylindrical opening 58 for receiving the tubular handle. In certain situations, i.e. when the jack may be positioned far into the interior of a lifting project, the control knob may be more accessible with the tubular handle than by the hand of the operator. In such situations, the jack and control knob can function like the double-key head of a conventional jack and the tubular handle.

Referring now to FIG. 3, another significant improvement to a hydraulic bottle jack 60 is shown with the control valve having an automatic return to the closed position. The basic concept is to provide an otherwise conventional control valve with a biasing means (typically a torsion spring) to automatically and continuously urge the rotatable shaft into the closed position. The rotatable shaft can be rotated in the conventional manner with the tubular handle 18 in the counter-clockwise direction to open the valve to lower the jack. When the handle is removed, the torsion spring automatically forces the rotatable shaft to rotate back to the original position to close the control valve.

The rotatable shaft 42 includes the double-key head (similar to the conventional head 16) and is used in conjunction with the slotted wrench 20 of the jack handle 18 to open the control valve. In this example of a first embodiment, the double-key head is provided in the form of a cylindrical cap 62; and the biasing means is provided in the form of a cylindrical wire torsion spring 64. The wire torsion spring is positioned longitudinally around the rotatable shaft and the cylindrical cap is attached to the proximal end of the rotatable shaft. The wire torsion spring has an inward coil with the end 66 attached to the housing with a suitable fastener 67; and has an outward coil with the end 68 attached to the rotatable shaft, as shown, by attachment to the cap 62 with a suitable fastener 69.

The inward end and the outward end of the cylindrical torsion spring 64 are designed and fastened so that the cylindrical cap 62 is pre-loaded with sufficient torsional force to ensure that the control valve is normally securely biased into the closed position.

Referring now to FIG. 4 and 5, an example of another embodiment of an improved hydraulic bottle jack 70 is shown with the control valve having an automatic return to the closed position. In this example, the double-key head is provided in the form of a cylindrical cap 72; and the biasing means is provided by a spiral-clock torsion spring 74. The spiral-clock torsion spring is positioned laterally around the rotatable shaft 42, and the cylindrical cap 72 is attached to the rotatable shaft. The spiral-clock torsion spring has an inner portion with an end 76 attached to the housing with a suitable fastener 77; and has an outer portion with an end 78 attached to the rotatable shaft, as shown, by attachment to the cap 72 with a suitable fastener 79.

Referring now to FIG. 6, an example of a preferred embodiment of an improved hydraulic bottle jack 80 is shown featuring the control valve having a control knob combined with an automatic return to the closed position. The jack 80 has the rotatable shaft 42 extending from the housing as previously discussed. In this example, the automatic return is provided by a cylindrical wire torsion spring 82 positioned longitudinally around the rotatable shaft. The torsion spring 82 has an inward coil with an end 84 secured to the housing with a suitable fastener 85, and has an outward coil with an end 86 secured to the rotatable shaft by a suitable fastener 87.

The jack 80 is always ready to be deployed by positioning the jack and then pumping to the desired elevation. When the lifting project is completed, or the height of the piston needs an adjustment, the operator grasps the control knob and rotates it counter-clockwise as precisely as needed to gradually lower the jack. The jack handle can remain within the actuator opening in the event that pumping is needed. When completed and fully lowered, the control knob is released and it automatically rotates clockwise to close the valve, and is always ready for the next lifting project.

Referring now to FIGS. 7 and 8, an example of another embodiment of an improved hydraulic bottle jack 100 is shown featuring the control valve having a control knob combined with an automatic return to the closed position. The jack 100 has the rotatable shaft 42 extending from the housing as previously discussed. In this example, the automatic return is provided by a spiral-clock torsion spring 102 positioned laterally around the rotatable shaft. The torsion spring 102 has an inner portion with an end 104 secured to the housing with a suitable fastener 105, and has an outer portion with an end 106 secured to the rotatable shaft by a suitable fastener 107. (As a matter of design choice, the inner portion may alternatively be designed to be secured to the rotatable shaft, and the outer portion secured to the housing.)

The control knob 108 preferably includes a peripheral shirt 116 for enclosing the torsion spring and providing a protective, clean appearance for the jack. In the present example, the knob further includes a suitable longitudinal access aperture 118 through the front face for installing and servicing the fastener 105, and a suitable lateral access aperture 120 through the shirt for installing and service the fastener 107.

Referring now to FIGS. 1, and 9-13, the existing conventional bottle jack 10 of FIG. 1 can also be retrofit and adapted to a hydraulic bottle jack having a valve control knob (as shown and discussed in reference to new jack 30 in FIG. 2). The retrofit components include a control knob 130 having a generally circular disc structure (about 0.50 inches in depth) with an optimized diameter of about twice the size of the double-key head 16, and that is rotatable without interference with the housing or the supporting surface for the jack (about 1.50 to 2.00 inches in diameter).

The control knob 130 has a unique inner back surface including a central hub 132 having a recessed cavity 134 adapted to fit over the double-key head 16 of the control valve of the conventional jack. This recessed cavity has a cylindrical central opening with a pair of opposed slots 136 for nesting over the opposed pins 14 of the double-key head. The cavity preferably includes another pair of opposed slots 138, arranged perpendicularly to slots 136 also for nesting over the double-key head, and for orienting the knob (90° when desired) on the double-key head.

The control knob 130 is attachable to the rotatable shaft 12 with a suitable fastener, or clipping, or bonding the knob to the rotatable shaft. The control knob preferably has a central aperture 140 for inserting a fastener. The proximal end of the rotatable shaft can be suitably drilled and tapped to receive a threaded screw fastener 142 for securing the knob to the shaft. Alternatively, the hub 132 can have a lateral threaded aperture for receiving a set screw (not shown) for securing the control knob to the rotatable shaft. The knob can further alternatively be secured with a suitable adhesive (i.e. J-B Weld® or other two-part epoxy, etc) to bond the control knob to the rotatable shaft. After the control knob 130 is securely fastened to the rotatable shaft 12, the jack functions as Jack 30 as described in reference to FIG. 2.

Referring particularly to FIGS. 9 and 10, the control knob 130 is illustrated in more detail. The control knob 130 may also the utilized as a separate “control knob wrench” without permanent attachment to the rotatable shaft 12, to finely adjust the control valve. The control knob wrench can be temporarily positioned onto the rotatable shaft, with the recessed cavity 134 engaged with the double-key head 16, and manually operated to make fine adjustments or otherwise open and close the control valve without the use of the tubular handle 18. The pairs of slotted openings 136 and 138 of the recessed cavity preferably further included flexible detent nipples 139 that tend to grip the lateral pins 14 of the double-key head, to temporarily retain the control knob wrench onto the rotatable shaft.

Referring further to FIGS. 1 and 9-13, a hydraulic bottle jack can be adapted to retrofit the existing conventional bottle jack 10 of FIG. 1, with a control knob and automatic return (as shown and discussed in reference to jack 100 in FIGS. 7 and 8). An example of the retrofit components includes the control knob 130 as previously discussed, and a torsion spring 144.

An alternative to drilling and taping the housing, as described above, includes an intervening disc 143 about 1 inch in diameter and about 0.25 inches in thickness positioned over and clear of the rotatable shaft 12, and bonded to the-housing with a suitable adhesive. The disc includes a pre-drilled and taped aperture (145) for receiving the fastener 147. It is preferable to provide directions or a template for properly orienting the disc for a respective model of jack. The use of such a bonded disc precludes drilling into the housing, and precludes any possible damage to any internal fluid passages or leakage of hydraulic fluid.

The spiral-clock torsion spring 144 is sufficiently flexible so that when the respective ends are attached to the housing and to the control knob 130, the control knob can be pulled outward and clear of engagement with the double-key head 16, to find a neutral torsion position of the knob. Once the neutral position is determined, the knob in rotated at least 90° counter-clockwise, and further until the next pair of recessed slots, 136 or 138, in the underside of the hub, are aligned with the double-key head. The knob is then pressed inward to nest and engage the double-key head, now having sufficient pre-loaded torsion force to ensure that the control valve is always biased into the fully closed position.

The knob can further alternatively be secured with a suitable adhesive (i.e. J-B Weld® or other two-part epoxy, etc.) to bond the control knob to the rotatable shaft. After the control knob 130 is securely fastened to the control shaft 12, the jack functions as Jack 100 as previously described in reference to FIGS. 7 and 8.

Referring particularly to FIG. 13, the method of performing the retrofit is reviewed in more detail. The control knob, torsion spring, fastener, etc., components may be purchased by the owner of a conventional jack, separately or in “kit” form, with the jack upgraded as a do-it-yourself project by the owner. The upgrade may also be performed by a professional service center, with components provided by the owner or supplied by the service center. A service center can also provide complete jacks that have been retrofit with the features of the present invention, and then sold to the customer.

rotating the control knob counter-clockwise at least 90°, and further until the next pair of slotted opening 136 or 138 are aligned with the pins 14 of the double-key head, to pre-load and sufficiently bias the control knob (and rotatable shaft of the control valve) into the closed position; and

Referring now to FIG. 14, the conventional hydraulic bottle jack 10 is typically provided with a two-piece handle, including the tubular handle 18 and a handle extension 154. As previously discussed the tubular handle has a slotted wrench 20 at the distal end, and has a proximal end for receiving the extension and including a single “bayonet slot” 156. The tubular handle has an inner diameter of about 0.62 inches, an outer diameter of about 0.88 inches, with opposed slotted openings about 0.20 inch wide and about 0.20 inch deep for engaging the double-key head of the jack, and has a length of about 12 inches.

The handle extension 154 is typically a solid rod having a diameter of about 0.60 and a length of about 12 inches, and is insertable into the proximal end of the tubular handle for providing additional leverage to pump the jack. The extension has a radial bayonet stud 158 (about 0.16 inch in diameter and extending about 0.12 inch) about 1 inch from the distal end for mating and engaging with the bayonet slot 156 in the tubular handle to temporarily extend the operating length of the handle.

The tubular handle 18 is improved with the addition of a control knob 160 of the present invention, for providing the desired gradual torque and precise adjustment and control of the control valve of the jack. The control knob has a suitable circular disc configuration having the size and shape as the previously discussed control knobs. The inner surface of the control knob 160 includes a unique hub for temporarily or permanently attaching the knob to the respective tubular handle 18 or the handle extension 154.

The control knob 160 can alternatively be provided with an inner central hub for attachment to the proximal end of the handle extension 154. The inner hub is preferably a tubular configuration for enclosing the proximal end of the extension, and having a suitable fastener for securing the knob to the extension. The control knob can alternatively be permanently bonded to the extension with a suitable adhesive. The attachment of the knob to the extension provide for the knob to be available and attachable whenever needed, but otherwise does not encumber routine use requiring only the tubular handle 18 and no precision adjustment of the control valve.

Referring now to FIG. 15, an improved prefabricated handle 164 for a hydraulic bottle jack is provided with a control knob 166 attached to the proximal end of the handle. The handle includes the slotted tubular wrench 20 at the distal end, and the generally circular disc knob at the proximal end having a diameter of about 2.00 inches. The length of the handle suitably ranges for about 12 inches to about 24 inches and preferably is about 18 inches in length. The improved prefabricated handle can be marketed as an after market jack handle, or marketed along with a new conventional jack.

The present invention provides a hydraulic bottle jack with a control valve having a hand operable knob and does not require the use of a tubular handle. The present invention provides a hydraulic bottle jack with a control valve having an automatic return to the closed position. The present invention provides a kit of components and a method for adapting the valve of a conventional hydraulic bottle jack to one having a control knob, and a control knob having an automatic return. The present invention further provides an improved handle with a control knob for use with a hydraulic bottle jack.

The present application relates generally to jacks. More particularly, the present invention relates to hydraulic power units for jacks with safety relief valves. BACKGROUND OF THE INVENTION

Floor jacks are used in repair shops to lift a vehicle from the ground. An operator positions the floor jack underneath a lift point and raises the vehicle at that point. Floor jacks can be powered by manual or automated means, and have become important to the automotive repair industry.

Shop floor jacks are sometimes manufactured with internally-relieved hydraulic systems to limit lifting load output. This is a feature for floor jacks that may be used to meet the American Society of Mechanical Engineers Portable Automotive Service Equipment (PASE) standards. These valves are normally adjustable via a relief screw exposed to the outside of the valve block via a port. The relief valve adjustment port is commonly located in close proximity to other bolt heads and fill-port caps, which can lead to confusion for the operator, who may mistakenly access the port and adjust the relief valve by mistake. Such uncalibrated adjustments can result in failure of the jack to lift its rated load, or worse, may allow the jack to lift more than it"s rated capacity, resulting in failure, property damage, and personal injury. SUMMARY OF THE INVENTION

The present invention relates broadly to a floor jack and a hydraulic power unit for the floor jack with an internally-adjustable relief valve that is inaccessible to an operator without removing the power unit from the jack assembly and disassembling the power unit. By placing the relief valve inside of the hydraulic assembly, hidden from operators, the operator cannot inadvertently adjust the relief valve when looking to add fluid or perform other service to the jack"s power unit. Nonetheless, the relief valve is adjustable, so the power unit can be properly calibrated and set during product assembly, refurbishment, and repair. Access to the relief valve requires accessing the inside of the pump, requiring the removal of the power unit from the jack assembly, and disassembly of the power unit to access the interior of the valve block itself. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 7 is a surface view of a tamper-resistant cap disposed over the integrated relief valve from FIGS. 5 and 6, looking down the long axis of the valve.

FIG. 10 is a surface view of a tamper-resistant cap disposed over the adjustable relief valve cartridge relief valve from FIGS. 8 and 9, looking down the long axis of the valve.

FIG. 11 is a cut-away view of the tamper-resistant cap from FIG. 10 disposed over the adjustable relief valve cartridge relief valve from FIGS. 8 and 9. DETAILED DESCRIPTION

The present invention broadly relates to a floor jack and a hydraulic power unit for the floor jack with an internally-adjustable relief valve that is inaccessible to an operator without removing the power unit from the jack assembly and disassembling the power unit. By placing the relief valve inside of the hydraulic assembly, hidden from operators, an operator cannot inadvertently adjust the relief valve when looking to add fluid or perform other service to the jack"s power unit. Nonetheless, the relief valve is adjustable, so the power unit can be properly calibrated and set during product assembly, refurbishment, and repair. Access to the relief valve requires accessing the inside of the pump, requiring the removal of the power unit from the jack assembly, and disassembly of the power unit to access the interior of the valve block itself.

Referring to FIGS. 1 and 2, a jacking mechanism includes a handle 104 operably coupled to a lifting arm 206 that is coupled to and movable relative to the frame 102 in response to motion of the handle 104. A saddle base 208 is coupled to the lifting arm 206 and moves with the lifting arm 206 in response to motion of the handle 104, allowing the saddle base 208 to raise a vehicle. The saddle base 208 may include an opening 210 that receives a stalk or other connector extending from an underside of a saddle 212. A pad 214 may be included on a vehicle-facing surface of the saddle 212 to help avoid marring or damaging the vehicle. The saddle 212 and pad 214 may be changeable to accommodate different types of lift points, depending upon the vehicle.

The hydraulics of the jack 100 are part of a power unit 220 or a power unit 221, depending upon the internal configuration of the power unit. The power unit 220/221 includes a drive piston 222 slidably mounted in a fluid cylinder 224 to compress/pump fluid within the fluid cylinder 224, and a release valve mechanism 226. Externally, the power unit 220 and the power unit 221 are similar. A valve block 228 of the power unit 220/221 is coupled to the frame 102, and a lift piston 248 that is slidable within a lift-piston assembly 230 of the power unit 220/221 is coupled to a trunnion block 232, which is coupled to the lift piston 248 (such as by a cotter pin 234).

The trunnion block 232 is coupled to the lifting arm 206. Pressure on the hydraulic fluid generated in the fluid cylinder 224 is transferred by the valve block 228 into the lift-piston assembly 230, to push against the lift piston 248 in the piston assembly 230. This generates a unidirectional force as the lift piston 248 pushes against the trunnion block 232. The trunnion block 232 transfers the force from the lift piston 248 to the lifting arm 206, causing the saddle base 208 to rise.

A handle yoke 238 is pivotably coupled to the frame 102 by pivot bolts 240. The handle 104 is inserted into and coupled to the handle yoke 238 via a retaining pin 242. A yolk pump roller assembly 244 is coupled to the handle yolk 238, and disposed or positioned so that when the handle 104 is pushed or pumped, a roller of the roller assembly 244 compresses the drive piston 222, creating hydraulic pressure within the fluid cylinder 224. A spring (not illustrated) may be compressively mounted around the periphery of the drive piston 222, or enclosed within the fluid cylinder 224, to cause the drive piston 222 to rebound from the fluid cylinder 224 for the upstroke during pumping.

Depending on how the release valve mechanism 226 and the handle yoke 238 are configured, moving the handle 104 forwardly or twisting the handle 104 pulls on the release valve mechanism 226, causing the release valve mechanism 226 to release the hydraulic pressure within the power unit 220/221. Springs 236 may be disposed between the trunnion block 232 and the frame 102 to compress the lift piston 248 back into the piston assembly 230, creating reverse pressure on the hydraulic fluid in the piston assembly 230 so that the saddle base 208 descends when the release valve mechanism 226 is opened, even if there is no load on the jack 100.

Various components of the jack may be coupled in place, among other ways, using retaining rings 246. Once the jack 100 is assembled, a cover plate 250 may be coupled to the frame 102 to shield the internal components. An end of the handle 104 may be knurled or textured to provide a grip surface. As an additional grip surface, a handle pad 252 (e.g., foam) may be disposed over the handle 104. The jack 100 may have wheels for ease-of mobility. FIG. 2 illustrates one-of-two front wheel assemblies 254, and one-of-two rear wheel assemblies 256, mounted to the frame 102. However, it should be appreciated that the wheels may be replaced by a singular roller.

The power unit 220/221 includes a fluid reservoir/tank, formed in part by a first reservoir cap 362aand a second reservoir cap 362bon opposite sides of the valve block 228. As shown in FIG. 5, the valve block 228 includes a first recess 560aand a second recess 560bon opposite sides of a long axis of the piston assembly 230. As shown in FIGS. 3 and 5, an open face of the first recess 560ais enclosed by the first reservoir cap 362a, and an open face of the second recess 560bis enclosed by the second reservoir cap 362b. Through-bores 464 and 468 (FIG. 4) through the valve block 228 fluidly couples the first recess 560aand the second recess 560b, providing a passage for the free-flow of fluid within the reservoir/tank formed by the combined recesses 560a/b, caps 362a/b, and through-bores 464 and 468.

A threaded through-bore 366 in the upper surface of the valve block 228 provides a port opening into the first recess 560a, via which hydraulic fluid may be added to the reservoir/tank. The threaded through-bore 366 is sealed by a threaded fill plug 367.

Another port in the upper surface of the valve block 228 is a vertical bore hole 368 containing a vertically-oriented lift cylinder check valve 471 and a vertically-oriented vacuum-to-tank check valve 472. A threaded plug 374 over the lift cylinder check valve 471 seals the external port at the top of the vertical bore hole 368. The sealed vertical bore hole 368 provides an internal vertical passage 475 for the flow of hydraulic fluid within the valve block 228.

The lift cylinder check valve 471 includes a bias member (such as a spring) and ball, with the ball located in the vertical passage 475 between a first horizontal passage 476 and a second horizontal passage 478. The first horizontal passage 476 connects the fluid cylinder 224 to the vertical passage 475. The first horizontal passage 476 may be formed as a bore hole in the valve block 228 that extends inward from the second recess 560b, to intersect the vertical passage 475 and a base of the fluid cylinder 224. The port of the bore hole forming the first horizontal passage 476 opens into the second recess 560band is sealed, such as by a threaded plug 577. The first horizontal passage 476 provides a fluid pathway between the fluid cylinder 224 and the lift cylinder check valve 471, and vacuum-to-tank check valve 472 disposed in the vertical passage 475. The second horizontal passage 478 is a bore hole in the valve block 228 that extends from the back of the piston assembly 230 to an upper-end of the vertical passage 475.

To lift a vehicle, movement of the handle 104 actuates the drive piston 222, compressing the fluid in the fluid cylinder 224. Pressure generated in the fluid cylinder 224 reaches the lift cylinder check valve 471 via the first horizontal passage 476, causing the lift cylinder check valve 471 to open so that hydraulic fluid flows through the second horizontal passage 478 into the lift cylinder 480 of the piston assembly 230. The pressure at the back of the lift cylinder 480 pushes against the lift piston 248, with the resulting force mechanically transferred to the lift arm 206 by the trunnion block 232.

When the pressure from the drive piston 222 and fluid cylinder 224 decreases, such as during an uptake of the handle 104 during pumping, the lift cylinder check valve 471 closes, to prevent the hydraulic fluid from flowing out of the lift cylinder 480 via the second horizontal passage 478. Also, if the reverse pressure on the hydraulic fluid in the piston assembly 230 exceeds the pressure generated by the fluid cylinder 224, the lift cylinder check valve 471 may not open in response to actuation of the drive piston 222.

The bottom of the vertical passage 475 connects to a fluid intake passage 482. The fluid intake passage 482 includes a bore hole in the valve block 228 extending from the bottom of the second recess 560bto the bottom of the vertical passage 475. The vacuum-to-tank check valve 472 includes a bias member (such as a spring) and ball, located in the vertical passage 475 beneath the lift cylinder check valve 471. The ball of the vacuum-to-tank check valve 472 is disposed or positioned between the junction of the first horizontal passage 476 with the vertical passage 475, and the intake passage 482, to selectively open and close off the intake passage 482.

As the drive piston 222 rises after an uptake of the handle 104 during pumping, the drop in fluid pressure causes the vacuum-to-tank check valve 472 to open, with hydraulic fluid flowing from the reservoir/tank into the fluid cylinder 224. Specifically, hydraulic fluid flows from the reservoir/tank into the intake passage 482, through the open valve 472, and into the second horizontal passage 478, to be sucked into the fluid cylinder 224. When the fluid pressure in the fluid cylinder 224 increases, such as when the handle 104 actuates the drive piston 222, the vacuum-to-tank check valve 472 closes, preventing the flow of hydraulic fluid back into the reservoir/tank via the intake passage 482.

An external port of a diagonal though-bore 584 through the valve block 228 receives the release valve mechanism 226, with a portion of the release valve mechanism being within the diagonal through-bore 584, and another portion being external to the valve block 228. The end of the diagonal though-bore 584 opposite the external port opens into the back of the lift cylinder 480 of the piston assembly 230. Between the piston assembly 230 and the exterior port, the diagonal through-bore 584 intersects a third horizontal passage 486. The third horizontal passage 486 is formed as a bore through the valve block 228, and fluidly connects the diagonal though-bore 584 to one or both of the first and second recesses 560a, 560b.

During lifting, the release valve mechanism 226 closes off the third horizontal passage 486. To lower the saddle base 208, the release valve mechanism 226 is pulled outward, opening the third horizontal passage 486. This creates a pressure-release pathway from the piston assembly 230 through the diagonal though-bore 584 to the third horizontal passage 486, into the tank/reservoir. When open, hydraulic fluid evacuates the lift cylinder 480 via this pressure-release pathway.

As shown in FIG. 5, a fourth horizontal passage 587 through the valve block 228 connects the first recess 560ato the vertical passage 475, intersecting the vertical passage 475 between the ball of the lift cylinder check valve 471 and the first horizontal passage 476. Opposite the connection to the vertical passage 475, the bore-hole forming the fourth horizontal passage 587 widens into a cavity 588 that opens into the first recess 560aas an internal port 589. An adjustable relief valve 590 is disposed in or integrated within the cavity 588 of the fourth horizontal passage 587, and is accessible via the internal port 589.

FIG. 6 is an expanded cut-away view of the fourth horizontal passage 587 and the adjustable relief valve 590. The adjustable relief valve 590 is oriented horizontally in the cavity 588. An externally-threaded hollow relief screw 691 is accessible within the internal port 589 at the back of the first recess 560a. When the first recess 560ais enclosed and sealed by the first reservoir cap 362a, the hollow relief screw 691 is not externally visible nor externally accessible.

The adjustable relief valve 590 includes the hollow relief screw 691, a ball 692, a valve seat 693, and a bias member 694 (such as a spring). Movement of the ball 692 opens and closes the valve 590. Specifically, the ball 692 selectively closes off an aperture in the fourth horizontal passage 587, where the fourth horizontal passage 587 narrows at the back of the cavity 588 to connect to the vertical passage 475.

One side of the valve seat 693 presses the ball 692 against the aperture, while the bias member 694 applies a force against the other side of the valve seat 693. The bias member 694 is compressed between the valve seat 693 and the hollow relief screw 691. The externally threaded hollow relief screw 691 is seated in threads in the sidewalls of a portion of the cavity 588 proximate to the port 589. The compression on the bias member 694 is adjusted by turning the hollow relief screw 691 to thread in or out of the fourth horizontal passage 587.

When the pressure of the fluid in the vertical passage 475 exceeds a threshold limit controlled by adjusting the hollow relief screw 691, the adjustable relief valve 590 opens and hydraulic fluid flows into the tank/reservoir. When the valve 590 opens, fluid from the vertical passage 475 passes through the hollow opening in the axial center of the hollow relief screw 691, and into the first recess 560a.

After the power unit 220 is assembled, the first reservoir cap 362acovers and seals the first recess 560a, restricting access to the relief valve 590. In order to access, adjust, and calibrate the adjustable relief valve 590 by turning the hollow relief screw 691, the power unit 220 is removed from the frame 102, drained, and disassembled, removing the first reservoir cap 362ato expose the internal port 589.

FIG. 7 illustrates a tamper-resistant cap 795 that may be coupled or disposed over the port 589 and the hollow relief screw 691 as a further precaution, further restricting access to the adjustable relief valve 590. The tamper-resistant cap 795 may be coupled in place, among other ways, by welding it to the valve block 228 over the port 589. The tamper-resistant cap 795 includes a through-hole 796 that has a diameter equal-to or wider than that of the hollow passage through the relief screw 691, with which the through-hole 796 of the cap 795 is aligned. When the relief valve 590 opens, fluid passes through the hollow relief screw 691 and the through-hole 796 of the cap 795, into the tank/reservoir. The presence of tamper-resistant cap 795 further discourages accidental adjustment of the adjustable relief valve 590, even if the power unit 220 is disassembled.

FIG. 8 is a cut-away view of the power unit 221 along the line 8-8′ in FIG. 3. An internal difference between the power unit 220 and the power unit 221 is that the power unit 220 includes a horizontal relief valve 590 in the valve block 228, whereas the horizontal relief valve 890 in the power unit 221 is a cartridge.

The adjustable cartridge relief valve 890 is inserted in a fourth horizontal passage 887 through the valve block 228. The fourth horizontal passage 887 is a bore through the valve block 228 that connects the first recess 560ato the vertical passage 475, intersecting the vertical passage 475 between the ball of the lift cylinder check valve 471 and the first horizontal passage 476. Opposite the vertical passage 475, the fourth horizontal passage 887 widens into a cavity 888 that opens into the first recess 560a. The adjustable relief valve cartridge 890 is oriented horizontally in the cavity 888, and may extend out into the first recess 560a.

FIG. 9 is an expanded view of the fourth horizontal passage 887 and the adjustable cartridge relief valve 890. The adjustable cartridge relief valve 890 includes a cartridge body 998 with a threaded end 999 that mates with threads in the sidewall of the cavity 888. Inside the cartridge body 998 is an externally-threaded hollow relief screw 991 accessible via an axial end-port 989 of the cartridge body 998. When the first recess 560ais enclosed and sealed by a first reservoir cap 362a, the hollow relief screw 991 is not externally visible nor externally accessible.

The adjustable relief valve 890 includes the hollow relief screw 991, a ball 992, a valve seat 993, and a bias member 994 (such as a spring) within the cartridge body 998. Movement of the ball 992 opens and closes the valve 890. Specifically, the ball 992 selectively closes off an aperture within the cartridge body 998 that opens into the fourth horizontal passage 887, where the fourth horizontal passage 887 narrows at the back of the cavity 888 to connect to the vertical passage 475.

One side of the valve seat 993 presses the ball 992 against the aperture, while the bias member 994 provides a bias force against the other side of the valve seat 993. The bias member 994 is compressed between the valve seat 993 and the hollow relief screw 991. The externally threaded hollow relief screw 991 is seated in threads in the sidewalls of a portion of the cartridge body 998 proximate to the end-port 989. The compression on the bias member 994 is adjusted by turning the hollow relief screw 991 to thread in or out of the cartridge body 998.

When the pressure of the fluid in the vertical passage 475 exceeds a threshold limit controlled by adjusting the hollow relief screw 991, the adjustable cartridge relief valve 890 opens and hydraulic fluid flows into the tank/reservoir. When the valve 890 opens, fluid from the vertical passage 475 passes through the hollow opening in the axial center of the hollow relief screw 991, and into the first recess 560a.

After the power unit 221 is assembled, the first reservoir cap 362acovers and seals the first recess 560a, restricting access to the adjustable cartridge relief valve 890. In order to access, adjust, and calibrate the adjustable cartridge relief valve 890 by turning the hollow relief screw 991, the power unit 221 is removed from the frame 102, drained, and disassembled, removing the first reservoir cap 362ato expose the port 989.

FIG. 10 illustrates a tamper-resistant cap 1095 that may be coupled to or disposed over the hollow relief screw 991 as a further precaution, further restricting access to the adjustable relief valve 890. FIG. 11 illustrates a cut-away of the tamper-resistant cap 1095 coupled to the adjustable cartridge relief valve 890. The tamper-resistant cap 1095 may be coupled in place, among other ways, by welding or clamping it to the end of the cartridge valve body 998 over the port 989. The tamper-resistant cap 1095 includes a through-hole 1096 that has a diameter equal-to or wider to that of the hollow passage through the relief screw 991, with which the through-hole 1096 of the cap 1095 is aligned. When the relief valve 890 opens, fluid passes through the hollow relief screw 991 and the through-hole 1096 of the cap 1095, into the tank/reservoir. The presence of tamper-resistant cap 1095 further discourages accidental adjustment of the adjustable relief valve 890, even if the power unit 221 is disassembled.

The bores, ports, and cavities within the power units 220/221 may be formed in the valve block 228 by machining the valve block. Integrated valves, such as valves 471, 472 and 590 may then be assembled and adjusted within in the valve block 228. With the jack power unit 221, the adjustable cartridge relief valve 890 may be separately assembled in the cartridge body 998, and then coupled into the power unit 221.

From the foregoing, it can be seen that there has been described improved jack power units 220/221 which improves the safety of the jack 100 by internalizing and limiting access to the relief valves 590/890. An added benefit of the adjustable cartridge relief valve 890 is that it can be set to the proper pressure prior to being inserted into the power unit valve block 228 during assembly of the power unit 221. The ability to calibrate the power unit valve block 228 separate from the power unit 221 means that the adjustable cartridge relief valve 890 be manufactured and calibrated separately from the power unit 221, and distributed as a pre-calibrated replacement part. The ability to pre-calibrate the adjustable cartridge relief valve 890 prior to insertion into the power unit 221 allows it to be shipped into the field for repairs by qualified technicians without requiring further calibration in the field.

ESCO Professional Aluminum & Steel Jacks (Cylinders) are known for their quality and lightweight durable design. With a variety of lifting capacities, from 55 Ton to 100 Ton Plus, the ESCO Professional Line of Hydraulic Jacks (Cylinders) is must-have for heavy lifting applications.

Jacks are pieces of material handling equipment that uses force multiplication to lift or move heavy loads. The term jacks can refer to a variety of lifting devices that employ leverage and other methods of mechanical advantage to amplify an applied force to provide the ability to transport a load. Hydraulic jacks are distinguished by their use of an incompressible liquid, such as hydraulic fluid or jack oil, as the means by which force multiplication is achieved. The primary mechanism by which force is applied varies, depending on the specific type of jack, but is typically a screw thread or a hydraulic cylinder. Jacks may be categorized based on the type of mechanism used to generate the lifting force, typically mechanical power, hydraulic power, or pneumatic power.

Mechanical jacks, such as the commonly used car jacks, lift heavy equipment and are rated based on the lifting capacity, which is typically expressed in terms of the number of tons that the jack can handle. Hydraulic jacks tend to have higher lifting capacities than mechanical jacks owing to the amount of force that can be generated by the hydraulic cylinders which produce the lifting action. Common forms of hydraulic jacks include bottle jacks and floor jacks.

To illustrate the components that are used in a hydraulic jack, a typical manually operated hydraulic jack will be considered. The primary components are discussed below. Note that other smaller components are also used to create the hydraulic jack, such as o-rings, pins, but the primary components shown will be helpful to understand the operation of the jack.

The reservoir or buffer tank is a vessel that holds hydraulic fluid or pump oil which will be used to transfer applied pressure from the pump to the ram. The pump is typically a piston pump that is mechanically activated by moving the pump lever or handle up and down. The handle movement builds up pressure in the hydraulic fluid which transfers that pressurized fluid through a check valve and into the main cylinder. The main cylinder, sometimes referred to as the ram, is driven upwards extending out of the hydraulic jack body by the pressure of the hydraulic fluid, creating the needed lifting force and lifting the load. A release valve is included to release the pressure so that the ram can retract and the load can be lowered.

Some rams are equipped with a threaded extension so that when fully retracted the ram extension can be unscrewed. This feature extends the lifting range for the jack and can eliminate the need to add blocking underneath the jack when the load surface to be lifted is higher than the retracted height of the ram and the jack body.

Hydraulic jacks function based on a concept in fluid mechanics known as Pascal’s Principle. Essentially, if two cylinders (a large and a small one) are connected by an incompressible fluid, and a given amount of pressure is applied to one cylinder, that same pressure is imparted to the second cylinder through the fluid connecting them. However, because pressure is equal to force per unit area, the cylinder that has a larger area will experience a force multiplication effect. Even though the pressure on both cylinders is the same, the force which is produced on