Abstract:
A hydraulic fluid circuit for a quick rise type lifting jack positions multiple valves that control two stages of the lifting operation of the jack in the same valve housing machined into a base of the jack and thereby reduces the costs involved in manufacturing and assembling the hydraulic circuit of the jack.

Description:
RELATED APPLICATION DATA 
     This application is a continuation of application Ser. No. 09/431,428, filed Nov. 1, 1999, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention pertains to hydraulic lifting jacks and, in particular, a simplified hydraulic circuit for a quick-rise type lifting jack. The novel construction of the hydraulic circuit positions two discharge valves that control two stages of the lifting operation of the jack in the same valve housing in a base of the jack and thereby significantly reduces the costs involved in manufacturing and assembling the hydraulic circuit of the jack. 
     (2) Description of the Related Art 
     FIG. 1 shows a typical hydraulic jack commonly referred to as a service jack. Hydraulic jacks of this type are well known in the art and examples of the constructions of such jacks are shown in the Tallman U.S. Pat. No. 4,018,421, issued Apr. 19, 1997, and the John U.S. Pat. No. 4,131,263, issued Dec. 26, 1978. Generally, hydraulic jacks of the type shown in FIG. 1 are operated by manually oscillating the lever arm  12  of the jack upwardly and downwardly. The oscillating movement of the lever arm  12  is transferred to a reciprocating pump  14  that draws hydraulic fluid from a reservoir of the jack and compresses the fluid. The compressed fluid unseats a discharge valve of the jack hydraulic circuit causing the pressurized hydraulic fluid to travel through the hydraulic circuitry machined in a base  16  of the jack. The hydraulic circuitry routes the pressurized hydraulic fluid to a lifting cylinder where the pressurized hydraulic fluid acts on a ram or lifting piston of the jack. Extension of the ram or lifting piston of the jack from the cylinder while being acted on by hydraulic fluid under pressure pumped from the pump  14  causes a lifting arm  18  to rise through a mechanical connection between the lifting piston and the arm. In many hydraulic jacks of the type shown in FIG. 1, the lever arm  12  is rotatable in its connection to the jack. Rotation of the arm  12  in a counter-clockwise direction opens a release valve that allows the pressurized hydraulic fluid in the lifting cylinder of the jack to be vented back to the hydraulic fluid reservoir, thereby allowing the lifting arm  18  to be lowered. Rotating the lever arm  12  counter-clockwise after the lifting arm  18  has been lowered reseats the release valve and the jack is again ready for its lifting operation. 
     There are many different types of hydraulic fluid jacks of the type shown in FIG.  1 . In addition, there are similar types of jacks commonly referred to as bottle jacks due to their appearance. These jacks do not employ a lifting arm  18  that raises as the ram or lifting piston is extended from the lifting cylinder of the jack, but instead employ the ram or lifting piston as the lifting component of the jack. Operation of the lever arm of a bottle jack causes the ram or lifting piston to be extended vertically from the lifting cylinder and thus the lifting force of the lifting piston is applied directly to the object to be raised and not through a mechanical linkage such as the lifting arm  18  of the jack of FIG.  1 . 
     All jacks of the type described above employ a circuit of conduits and valves to control the delivery of hydraulic fluid pressurized by the pump of the jack to the lifting cylinder of the jack. The hydraulic conduits and valve housings are commonly constructed by machining or drilling holes into a cast solid metal base of the jack. The conduits and valve housings are then sealed closed at the exterior of the base by screw threaded plugs or set screws that are screwed into internal screw threading of the conduits and valve housings adjacent the exterior of the base. More simplified hydraulic jack constructions require only a few conduits and valve housings machined into the base of the jack and therefore the machining costs of the more simplified hydraulic jacks are relatively small when compared to other jack constructions. 
     More complex jack constructions, for example, a hydraulic jack that has a quick-rise feature where the ram or lifting piston is extended quickly from the lifting cylinder on oscillation of the jack lever arm until it encounters a resisting load, and then is extended more slowly from the lifting cylinder as the hydraulic fluid is pressurized by the lever arm and pump to lift the load require a more elaborate hydraulic circuit in the jack base. The more elaborate circuit of a quick-rise lifting jack requires additional conduits to be machined into the base of the jack and additional valve housings to control the two stage lifting function of the jack. Jacks of this type will have increased manufacturing costs over that of more simplified jacks due to the additional machining steps needed to construct the hydraulic circuit and the additional assembly steps needed to assemble the valve elements into the valve housings of the hydraulic circuit. 
     FIG. 2 shows a schematic representation of a hydraulic circuit for a prior art quick-rise lifting jack. The circuit is formed into the base (not shown) of the jack in the known manner of machining conduits and valve housings into the base from the exterior of the base. All hydraulic circuits of this type basically operate by drawing hydraulic fluid from a fluid reservoir into a pump, and then pressurizing the fluid forcing it through the hydraulic circuit to the lifting cylinder where the pressurized fluid causes a ram or piston to be extended from the cylinder. As explained earlier, the lifting piston is mechanically connected to a lifting arm of the jack or acts directly on the load being lifted by the jack. In operation of the circuit shown in FIG. 2, the lifting piston is quickly extended out of the lifting cylinder until it encounters the load to be raised. On subsequent operation of the pump of the hydraulic circuit, the lifting cylinder is raised at a slower rate but exerts a greater force on the object to be raised. 
     The hydraulic circuit shown in FIG. 2 includes a pump  22  comprised of a pump cylinder  24  and a pump plunger  26  mounted in the cylinder for reciprocating movement therein. The reciprocating movement of the pump plunger  26  is caused by oscillating movements of the arm  12  shown in FIG.  1 . 
     The pump cylinder  24  communicates through a conduit  32  with a relief valve  34 . The relief valve  34  includes a cavity machined into the base (not shown) of the jack that contains a relief ball valve  36  that is held against a valve seat by a spring  38 . The cavity is sealed closed by a screw threaded plug  42 . The cavity also communicates with the hydraulic fluid reservoir R of the jack through a conduit  44  that is behind the relief ball valve  36  when the ball valve is positioned on its valve seat as shown in FIG.  2 . 
     The pump cylinder  24  also communicates through a conduit  46  with a discharge valve  48 . The discharge valve  48  includes a discharge ball valve  52  that is biased against a valve seat by a spring  54  that is contained in a cavity machined into the jack base. The cavity is closed by a screw threaded plug  56 . At the bottom of the discharge valve cavity is a suction valve cavity containing a pump suction ball valve  58  that seats on a valve seat separating the suction valve cavity, the pump cylinder  24  and the conduit  46  communicating the pump cylinder with the discharge valve cavity and suction valve cavity from the reservoir R. 
     A further length of conduit  62  extends downstream from the discharge valve  48 . This length of conduit  62  communicates with the release valve  64 , a gravity valve  66 , a second stage ball valve  68  and an interior ram  72  of the jack lifting mechanism  74 . 
     The release valve  64  contains a release valve element  76  that is shown in FIG. 2 seated against a valve seat that is machined into the base. The release valve element  74  is permitted to move away from the valve seat when the lever arm  12  of the jack is rotated in a counter-clockwise direction as explained earlier. This unscrews the release valve element  74  away from its valve seat and opens communication of the downstream conduit  62  to the hydraulic fluid reservoir R. Rotation of the lever arm  12  in the clockwise direction causes the release valve element  74  to be screw threaded into the downstream conduit  62  closing the valve against its valve seat. 
     The gravity valve  66  includes a gravity ball  78  that seats on a valve seat machined into the base. The gravity ball  78  is not spring biased against the seat. When the release valve  64  is opened, a difference in hydraulic fluid pressure on opposite sides of the gravity ball  78  causes the ball to unseat from its valve seat, opening communication through the gravity valve  66  to the release valve  64  in a manner that will be later explained. 
     The second stage valve  68  comprises a ball valve  82  that is biased by a spring  84  against a valve seat machined into the base of the jack. As explained earlier, the cavity that contains the second stage ball valve  82  and its spring  84  is machined into the base by drilling the cavity from the exterior of the base. The second stage ball valve  82  controls communication of fluid between the downstream conduit  62  and the interior of a lifting cylinder of the lifting mechanism  74  to be described. 
     The interior ram  72  is a long hollow tube that is mounted in the base of the jack. The interior  86  of the ram  72  communicates with the downstream conduit  62  through a ram conduit  88  machined into the base. 
     The lifting mechanism  74  of the jack includes a lifting cylinder  92  secured to the base of the jack. The tubular interior ram  72  extends through the center of and is coaxial with the lifting cylinder  92 . An outer ram or lifting piston  94  is mounted in the lifting cylinder  92  over the interior ram  72 . The lifting piston  94  has a cylindrical interior bore  96  into which the interior ram  72  extends. A seal  98  in the interior bore  96  of the lifting piston seals around the exterior of the interior ram  72  and defines a first chamber in the interior bore  96  of the lifting piston. An interior surface  102  of the lifting piston  94  in the first chamber of the interior bore  96  functions as a first stage reaction surface or lifting surface of the lifting mechanism as will be explained. 
     The lifting piston  94  has a cylindrical exterior surface and an annular seal  106  extends around the exterior surface and engages in sliding, sealing contact with the interior of the lifting cylinder  92 . The seal  106  also defines a second chamber  108  in the lifting cylinder  92 . Inside the second chamber  108  is a second surface  112  or second stage reactive or lifting surface of the lifting piston  94 . 
     Communicating with the second chamber  108  of the lifting cylinder  92  is a suction valve  114 . The suction valve  114  is comprised of a suction ball valve  116  and a spring  118  that biases the suction ball valve against a valve seat machined into the base. When a vacuum is created in the second chamber  108 , the suction ball valve  116  is pulled against the bias of the spring  118  and unseats from its valve seat communicating the second chamber  108  with the hydraulic fluid reservoir R of the jack. Also communicating with the second chamber  108  of the lifting cylinder  92  is the gravity valve  66  and the second stage valve  68 . 
     In operating the hydraulic circuit of the two stage lifting jack shown in FIG. 2, the lever arm  12  of the jack is first manually oscillated causing the plunger  26  to be retracted in the pump cylinder  24 . This creates a vacuum in the pump cylinder that unseats the pump suction valve  58  and causes hydraulic fluid to be drawn from the reservoir R into the pump cylinder. On subsequent movement of the plunger  26  back into the cylinder  24  while manually oscillating the lever arm  12 , the fluid in the pump cylinder is pressurized. If the pressure of the fluid in the pump cylinder  24  becomes excessive, the relief ball valve  36  will unseat from its seat against the bias of its spring  38  and allow the fluid under pressure in the pump cylinder  24  to pass through the relief valve  34  and return to the jack reservoir R. In normal operation of the jack, the fluid under pressure in the pump cylinder  24  travels through the conduit  46  communicating the cylinder with the discharge valve  48 . The pressure of the fluid causes the discharge ball valve  52  to be displaced from its valve seat against the bias of its spring  54 . This allows the fluid under pressure to pass into the downstream conduit  62 . 
     The fluid in the downstream conduit  62  is directed to the release valve  64 , the gravity valve  66 , the second stage valve  68  and into the ram conduit  88  and the interior bore  86  of the interior ram  72 . The force exerted by the second stage spring  84  on the second stage ball valve  82  is much greater than that of the discharge valve spring  54  on the discharge ball valve  52  and therefore the second stage ball valve does not open. With no load applied on the lifting piston  94  of the jack, fluid pressure builds up quickly in the first chamber defined by the interior bore  96  of the piston and acts against the first reaction surface  102  of the piston. This causes the piston  94  to be extended quickly from the lifting cylinder  92 . As the piston is extended from the cylinder, a vacuum is created in the second chamber  108  of the lifting cylinder. This vacuum causes the suction valve ball  116  to unseat from its valve seat against the bias of its spring  118  and draws hydraulic fluid from the reservoir into the second chamber  108  behind the annular seal  106  of the lifting piston. The quick extension of the lifting piston  94  is continued in this manner by continued manual oscillating movement of the jack lever arm  12 . 
     Once the lifting piston  94  reaches the object to be raised and a load is exerted on the piston, the force of hydraulic fluid pressure in the first chamber  96  defined by the piston interior bore acting on the first reaction surface  102  of the piston will eventually become insufficient to further extend the piston from the lifting cylinder  92  and lift the object. This causes the hydraulic fluid pressure in the downstream conduit  62  and in the ram conduit  88  to increase, eventually to the point that it displaces the second stage ball valve  82  from its valve seat against the bias of the second stage spring  84 . This allows the hydraulic fluid to then pass through the second stage valve  68  and enter the second chamber  108  of the lifting mechanism. The increased pressure of the hydraulic fluid in the second chamber  108  acts against the larger surface area of the second reaction surface  112  of the piston  94 . This results in a greater force exerted on the lifting piston  94  by the hydraulic fluid and the further extension of the lifting piston out of the cylinder, although now at a decreased rate. 
     Once the object has been lifted by the jack and it is desired to lower the object and retract the lifting piston  94  back into the lifting cylinder  92 , the release valve  64  is opened by rotating the lever arm  12  of the jack in a counter-clockwise direction. This causes the release valve element  76  to be rotated in its internally threaded bore and to back away from its valve seat, opening communication between the downstream conduit  62  and the fluid reservoir R. This relieves the fluid pressure in the downstream conduit  62  and the fluid in the first chamber  96  defined by the piston interior bore is forced through the interior  86  of the first stage ram  72 , through the ram conduit  88  and the downstream conduit  62  bypassing the release valve  64  to the reservoir R. With the fluid pressure in the downstream conduit  62  being relieved, the fluid under pressure in the second chamber  108  displaces the gravity ball  78  of the gravity valve  66  and flows past the release valve  64  to the reservoir R. In this manner, the lifting piston  94  is retracted back into the lifting cylinder  92  of the jack. 
     From the description of the prior art two stage lifting jack hydraulic circuit described above, although with reference to a simplified schematic representation of the circuit, it should be appreciated that a complex hydraulic circuit of the type shown in FIG. 2 requires a significant number of machining operations at several different locations in the base of the lifting jack to form the hydraulic fluid conduits and the valve housings of the circuit. The number of machining steps required to drill holes into the base of the jack and the number of different locations of the holes in the base of the jack required to produce a complex hydraulic circuit such as that described above with reference to FIG. 2 significantly contributes to the overall costs involved in manufacturing a two stage lifting hydraulic jack. If the manufacturing process could be simplified by reducing the number of conduits and/or valve housings required for a hydraulic circuit and thereby reducing the number of machining steps and the number of different locations on the base where machining steps are to be performed would significantly reduce the costs of manufacturing two stage lifting jacks of the type shown in FIG.  2  and described above. 
     SUMMARY OF THE INVENTION 
     The hydraulic circuit of the present invention overcomes disadvantages of prior art hydraulic circuits of the type employed in two stage lifting jacks by the design of the circuit which positions several valve elements coaxially in line with each other. The simplified hydraulic circuit of the invention positions three valve elements in the same valve housing where cavities in the valve housing containing each of the valve elements are extensions of each other. The coaxial alignment of the three valve elements and their associated three valve cavities enables the three cavities of the valve housing to be formed in a single bore machined into the base of the jack, thus eliminating additional manufacturing steps required in machining three separate valve housing cavities in three separate locations on the exterior of the base of the jack. In this manner, the simplified design of the hydraulic circuit of the lifting jack of the invention significantly reduces manufacturing costs of the jack. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further objects and features of the invention are set forth in the following detailed description of the preferred embodiment of the invention and in the drawing figures, wherein: 
     FIG. 1 is a perspective view of one type of lifting jack with which the simplified hydraulic circuit of the invention may be employed; 
     FIG. 2 is a schematic representation of a hydraulic circuit for a two stage, quick rising hydraulic jack; 
     FIG. 3 is a schematic representation of the simplified hydraulic circuit of the invention employed in a two stage, quick rising jack; 
     FIG. 4 is a cross-section view of a portion of a jack of the type shown in FIG. 1 employing the simplified hydraulic circuit of the invention; and 
     FIG. 5 is a cross-section view of a portion of the jack shown in FIG. 4 taken in the plane of line  5 — 5  of FIG.  4 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The hydraulic circuit of the invention functions in basically the same manner as the prior art two stage hydraulic circuit of FIG.  2  and many component parts of the circuit of the invention shown in FIG. 3 are given the same reference numerals as the like component parts shown in FIG.  2 . Basically, the improvement over the prior art two stage hydraulic circuit of FIG. 2 provided by the circuit of the invention shown in FIG. 3 is in a multiple valve element valve housing  122  that replaces both the discharge valve  48  and second stage valve  68  of the prior art circuit of FIG.  2 . As in the prior art, the conduits and valve housing cavities shown in the schematic representation of the hydraulic circuit of the invention in FIG. 3 are machined into a base of the jack by drilling holes into the base from the exterior of the base. The multi-element valve housing  122  of the invention permits several valve elements to be positioned into coaxially aligned cavities machined into the base, thus eliminating separate cavities machined into the base for each of the valve elements of the prior art hydraulic circuit, eliminating machining steps required by the prior art circuit and reducing manufacturing costs from that of the prior art circuit. 
     The hydraulic circuit shown in FIG. 3 includes a pump  22 , a relief valve  34 , a pump suction valve  58 , a downstream conduit  62 , a release valve  64 , a gravity valve  66 , a lifting mechanism  74  and a lifting mechanism suction valve  114  that are the same in construction and operation to the like component parts of the hydraulic circuit shown in FIG.  2  and having the same corresponding reference numbers. However, in the hydraulic circuit of FIG. 3, the second stage valve  68  is absent and an additional fluid conduit  124  provides communication between the second chamber  108  of the lifting mechanism  74  and the multi-element valve housing  122  of the invention. 
     The valve housing  122  is machined into the base coaxially aligned with the pump suction valve  58 . The valve housing is formed with a first cavity  126  and a second cavity  128 . The first cavity  126  is an extension of the cavity of the pump suction valve  58  and communicates with the pump cylinder  24  through the first conduit  46 . The first cavity  126  is drilled into the material of the base in line with the cavity of the pump suction valve  58  and with a larger circular cross-sectional area than that of the cavity of the pump suction valve  58 . This forms an annular valve seat  132  at the bottom of the first cavity. The valve seat  132  separates the first cavity  126  from the cavity of the pump suction valve  58  and from the first conduit  46  communicating the pump suction valve with the pump. Positioned inside the first cavity  126  is a first stage ball valve element  134  and a first spring  136  biasing the valve element against the first cavity seat  132 . The first cavity  126  communicates with the downstream conduit  62  behind the first stage valve element  134 . When the first stage valve element is displaced from its valve seat  132 , fluid communication is established between the pump  22 , the first conduit  46 , the first cavity  126  and the downstream conduit  62 . 
     The second cavity  128  of the multi-element valve housing  122  is also machined into the base by drilling the cavity into the base coaxially with the first cavity  126  and the cavity of the pump suction valve  58 . The second cavity  128  is formed with a slightly larger circular cross-sectional area than that of the first cavity  126 , thus forming a second cavity valve seat  138  between the first cavity  126  and the second cavity  128 . A second stage ball valve element  142  is positioned in the second cavity  128  on the valve seat  138 , and a second spring  144  is positioned in the second cavity on the second ball valve. The opening of the second cavity  128  to the exterior of the base is machined with internal screw threading into which a high pressure plug  148  is screw threaded sealing closed the cavities. 
     The additional second stage conduit  124  communicates with the second cavity  128  behind the second ball valve element  142 . This additional or third conduit  124  extends from the multi-element valve housing  122  to the second chamber  108  of the base. 
     FIGS. 4 and 5 show cross-section views of the base  146  of the jack of the invention with FIG. 4 being a side cross-section of the base and FIG. 5 being a cross-section taken through the plane of line  5 — 5  shown in FIG.  4 . Because the hydraulic fluid conduits and valve cavities are drilled into the base  146  of a jack in various different planes through the base, for simplicity only two cross-section views of the jack of the invention are shown in FIGS. 4 and 5, with FIG. 5 showing the multi-element valve housing  122  of the invention formed into the base  146  of the jack. It should be understood that the hydraulic circuit of the jack shown in FIGS. 4 and 5 is the same hydraulic circuit of the invention shown in the schematic representation of FIG.  3 . Several of the hydraulic fluid conduits and the component parts of the jack shown in the schematic representation of FIG. 3 are also shown in FIGS. 4 and 5 with their same reference numerals. 
     As seen in FIG. 5, the multi-element valve housing  122  is machined into the base  146  with the pump suction valve  58 , the first stage discharge valve element  134  and the second stage discharge valve element  142  in axial alignment in their respective cavities. It can be seen in FIG. 5 that as the cavities of the respective valve elements extend further into the base  146  from the exterior surface of the base, their cross-sectional areas become smaller. Thus, the three valve element cavities can be drilled into the base in coaxial alignment with a valve seat formed at the bottom of each cavity separating it from the next lower cavity as described earlier with reference to FIG. 3. A spacer  152  is positioned in the pump suction valve cavity limiting the movement of the pump suction valve  58  within the cavity. The first cavity valve seat  132  is machined into the base  146  just above the pump suction valve  58 . The first stage discharge valve  134  rests on the first cavity valve seat  132  and the first stage spring  136  is positioned on the first stage valve. The first stage spring  136  extends upwardly from the first cavity  126  slightly beyond the second cavity valve seat  138  where it engages with the second stage discharge ball valve element  142 . Because the first spring  136  engages against the second stage valve  142  to bias the first stage valve  134  against the first valve seat  132 , there is no need to provide an annular shoulder or stop surface in the first cavity  126  for the first spring  136  to act against when biasing the first valve against the seat. The second stage discharge valve  142  is shown seated on the second cavity valve seat  138 . A spacer  154  is positioned on top of the second stage valve element  142  and the second stage spring  144  is positioned between the spacer  154  and the screw threaded plug  148  that closes the valve housing  122  of the invention. 
     In operating the hydraulic circuit of the two stage lifting jack shown in FIGS. 3-5, the lever arm of the jack is first manually oscillated causing the plunger  26  of the pump to be retracted in the pump cylinder  24 . This creates a vacuum in the pump cylinder that unseats the pump suction valve  58  and causes hydraulic fluid to be drawn from the reservoir R into the pump cylinder. On subsequent movement of the plunger  26  back into the cylinder  24  while manually oscillating the lever arm  12 , the fluid in the pump cylinder is pressurized. As in the prior art hydraulic circuit, if pressure of the fluid in the pump cylinder become excessive, the relief ball valve  36  will unseat allowing the hydraulic fluid in the pump cylinder to pass through the relief valve  34  and return to the reservoir R. In normal operation, the fluid under pressure in the pump cylinder  24  travels through the first conduit  46  communicating the cylinder with the first stage discharge valve cavity  126 . The pressure of the fluid cause the first stage discharge valve element  134  to be displaced from its valve seat  132  against the bias of the first spring  136 . However, because the second spring  144  exerts a greater downward force on the second stage valve element  142  than the force exerted by the first spring  136 , the second stage valve element  142  remains in place against its valve seat  138 . The movement of the first stage valve element  134  away from its valve seat  132  allows the fluid under pressure to pass into the second conduit or downstream conduit  62 . 
     The fluid in the downstream conduit  62  is directed by the hydraulic circuit to the release valve  64 , the gravity valve  66  and into the ram conduit  88  and the interior bore or first chamber  86  of the lifting mechanism  74 . As with the prior art two stage lifting jack, with no load applied to the lifting piston  94  of the jack, fluid pressure builds up quickly in the first chamber  96  of the piston and acts against the reaction surface  102  of the piston to cause the piston to be extended quickly from the lifting cylinder  92 . As the piston is extended from the cylinder, the vacuum created in the second chamber  108  of the lifting cylinder causes the suction ball valve  116  to unseat from its valve seat against the bias of its spring  118  and draws hydraulic fluid from the reservoir R into the second chamber  108  behind the annular seal  106  of the lifting piston. 
     Once the lifting piston  94  reaches the object to be raised and a load is exerted on the piston, the force of hydraulic fluid pressure in the first chamber  96  acting on the first reaction surface  102  of the piston will eventually become insufficient to further extend the piston from the lifting cylinder  92  and lift the object. This causes the hydraulic fluid pressure in the second conduit  62  and in the ram conduit  88  to increase. As the pump  22  continues to force hydraulic fluid into the hydraulic circuit of FIG. 3, the increasing hydraulic fluid pressure developed by the pump eventually reaches the point where it displaces both the second stage discharge valve  142  and the first stage discharge valve  134  from their respective valve seats  138 ,  132 , against the bias of the second stage spring  144 . This allows the hydraulic fluid under the increased pressure to pass through both the first cavity  126  and the second cavity  128  to the third conduit  124  and through the third conduit to the second chamber  108  of the lifting mechanism  74 . The increased pressure of the hydraulic fluid in the second chamber  108  acts against the larger surface area of the second reaction surface  112  of the piston  94 . This results in a greater force exerted on the lifting piston by the hydraulic fluid in the second chamber  108  and the further extension of the lifting piston out of the cylinder, although now at a decreased rate. 
     Once the object has been lifted by the jack and it is desired to lower the object and retract the lifting piston  94  back into the lifting cylinder  92 , the release valve  64  is opened by rotating the lever arm  12  of the jack in a counter-clockwise direction just as in the prior art hydraulic circuit. 
     Thus, the hydraulic circuit of the invention shown in FIGS. 3-5 provides a more simplified hydraulic circuit for a two stage, quick rising lifting jack. This is accomplished by machining the valve housing  122  of the invention into the base  146  of the jack with a pump suction valve cavity  58 , a first stage discharge valve cavity  126  and a second stage discharge valve cavity  128  that are axially aligned and extensions of each other. This also positions the pump suction valve element, the first stage discharge valve element  134  and the second stage discharge valve element  142  in axial alignment with each other. The hydraulic circuit of the invention locates the drilling position for the pump suction valve, the first stage discharge valve and the second stage discharge valve at one location on the base  146  of the jack, thus eliminating multiple drilling locations in the jack for the multiple valve elements. The hydraulic circuit of the invention also locates the assembly point of the pump suction valve, the first stage discharge valve  134  and its associated spring  136 , the second stage discharge valve  142  and its associated spring  144  and the sealing plug  148  at one location on the base  146  of the jack, thus eliminating multiple assembly locations on the base for multiple valves. 
     While the present invention has been described by reference to a specific embodiment, it should be understood that modifications and variations of the invention may be constructed without departing form the scope of the invention defined in the following claims.