US2410771A - Hydraulic jack - Google Patents

Description

Nov. 5, 1946.

O. J. BORNGESSER HYDRAULIC JACK Filed Dec. 13, 1944 atentecl ov. 1946E UNETED STATES PATENT @FFECE mesne assignments, to Bristol, Pa., a corporation Kaiser Cargo, Inc., of California Application December 13, 1944, Serial No. 567,996

9 Claims.

This invention relates to hydraulic jacks and particularly to a lapped valve controlled compression jack having a relatively long stroke and adapted for use in testing structural members and for other purposes.

In constructing certain types of structural members such as wings of experimental aircraft, a procedure known as static testing is employed to determine maximum loadings as compared with calculated loadings. One of the most accurate and reliable means for applying test loads of any desired magnitude is the hydraulic jack or series of jacks generally used in conjunction with a device known as a load maintainer valve and with strain gauges applied to the structure being tested. Hydraulic jacks of sufficiently long stroke for the purpose described, as heretofore constructed, have been subject to the disadvantage of inaccuracy arising from friction between the movable members of the jack.

It is the object of the present invention to provide a long stroke hydraulic jack capable of applying a load proportional to the hydraulic pressure available and of avoiding inaccuracies d ue to friction.

Other objects and advantages of the invention will be apparent as it is better understood by reference to the following specification and the accompanying drawing, illustrating a preferred embodiment of the invention, in which Fig. 1 is an elevation partially in section showing the jack in retracted position;

Fig. 2 is a sectional view showing the jack partially extended; and

Fig. 3 is a section on the line 3-3 of Fig. 1.

Referring to the drawing, 5 indicates a cylinder, one end of which is threadedly secured to a plug 6 having an inlet passage 1 and a doughnut type packing 8 -to prevent escape of huid. The plug i has a seat S for a ball It which is mounted in a seat l l provided in a foot l2. Bolts I3 supported in the foot l2 engage springs lll mounted between the heads l5 of the bolts and a i'lange I6. The construction affords flexibility in the support to correct any misalignment of the jack.

Within the cylinder 5, which is relatively short, is a lapped piston valve l'l which is adapted to move through a, relatively short stroke limited by engagement of a flange i8 with a head i9 held by bolts 2D at the top of the cylinder 5. A passage 2l, closed by a plug 22, is provided in the wall of the cylinder 5 and has ports'23 and 2i. When the piston valve ll is elevated by introduction of hydraulic fluid as indicated in Fig. 2, the

uid flows through the port 23 into the passage 2| and thence through the port 2.4i into a transverse passage 25 in the piston valve il, and thence through a longitudinal passage 25 in the valve.

The upper end of the piston valve i7 extends beyond the cylinder 5 and affords a support for a hollow piston 27 threadedly mounted on the end of the piston Valve l1 and provided with doughnut type packing 23 to prevent leakage. The piston 27 is slidable in a sleeve 29 mounted within a cylinder 30 which is threadedly connected to a head 3l with doughnut type packing 32 to prevent leakage. A sleeve 33 with dough nut type packing 34 is disposed within the head 3| forming a bearing for the piston 21. The other end of the cylinder 36 is closed by a head 35 threadedly connected to the end thereof and provided with doughnut type packing 36. The head carries a threaded plug 31 which in turn supports a member 38 held by a set screw '39 having a seat lll for a ball 4l. A bearing member 42, having a seat i3, rests on the ball and is held in alignment by bolts lli extending through openings in the flange 45. The bearing member 42 is thus capable of movement to correct; for any misalignment of the jack.

It will be noted that the internal diameter of I the sleeve 29 somewhat exceeds the internal diameter of the cylinder 5. When iiuid is introduced under pressure through the passage 26 in the piston valve Il, the cylinder Sli will be lifted to extend the jack until the bearing member d2 engages the work. Thereupon pressure will increase until, owing to the difference in internal diameters of the sleeve 23 and cylinder 5, the piston valve H is forced downwardly, thus closing the port 23. This action traps the hydraulic uid in the cylinder 23, whereupon the mechanism operates as a lapped jack. Since the load is constantly floating on the lapped piston valve, the force applied is always equal to the product of the piston valve area and the hydraulic pressure of the fluid, regardless of the amount of extension of the jack.

Any leakage around the lapped piston valve I l escapes through a port 46 to a passage 47 closed by a plug 48 and extending to an outlet passage G9 connected to the pressure fluid return line (not shown). When the line pressure of the pressure fluid is relieved, the piston valve l1 returns to the position indicated in Fig. 1 of the drawing. Thereupon uid drains from the cylinder 3B and piston 2 through the passages 26 and 25 into the passage 2l and through the port 23 into the outlet passage 4S. The same result follows when the load applied to the jack increases beyond the load which can be supported by the pressure on the lower surface of the lapped piston valve ll. In that event, the piston valve Il is forced downwardly to the position indicated in Fig. l, and the fluid drains from the jack without flowing back through the pressure line.

Since the piston valve Il is relatively short and the lapped surfaces thereof of relatively small area, the amount of friction introduced in the operation is negligible. At the same time, the entire stroke of the jack is limited only by the length of the cylinder 3B, which may be of any desired dimensions. The friction introduced through movement of the cylinder Sil upon its piston is also negligible. Hence it is possible to afford the necessary stroke to accomplish the desired purpose and at the same time ensure the application of a load which is directly proportional to the pressure of the iiuid. As indicated, overloading, that is the attempt to apply a load beyond the capa-city of the apparatus, results in immediate collapse without danger of forcing fluid backwardly through the fluid pressure line.

Various changes may be made in the form and construction of the apparatus without departing from the invention or sacrificing the advantages thereof.

claim:

l. A hydraulic jack comprising a relatively flxed valve cylinder, a piston valve slidable therein and having a portion extending beyond said cylinder, a second cylinder mounted for longitudinal movement cn and relative to said extending portion of the piston valve, means to admit fluid under pressure to the valve cylinder to actuate the piston valve, and a fluid passage adapted to place the interiors of the two cylinders in communication and controlled by the piston valve, whereby when fluid is admitted to the valve cylinder and actuates the piston valve to open said passage some of the fluid will be admitted to the second cylinder to move it longitudinally on the piston valve extension and thereby extend the overall length o the jack.

2. A hydraulic j ack comprising a valve cylinder, a piston valve slidable therein with a relatively short stroke, said piston valve having a relatively long portion extending beyond said cylinder, a second cylinder mounted for longitudinal movement on and relative to said extending portion of the piston valve with a relatively long stroke,

means to admit fluid under pressure to the valve cylinder to actuate the piston valve, and a fluid passage adapted to place the interiors of the two cylinders in communication and controlled by the piston valve, whereby when uid is admitted to the valve cylinder and imparts the relatively short stroke to the piston valve to open said passage some of the iluid will loe admitted to the second cylinder to impart the relatively long stroke to it and thereby extend the overall length of the jack considerably more than accomplished by the relatively short stroke of the piston valve.

3. A hydraulic jack comprising a relatively short valve cylinder, a piston valve slidable therein with a relatively short stroke and having lapped surfaces of relatively small area, said piston valve having a relatively long portion extending beyond said cylinder, a second cylinder mounted for longitudinal movement on and relative to said extending portion of the piston valve with a relatively long stroke, the area of contact between the second cylinder and the piston valve extension on which it slides being relatively small, means to admit fluid under pressure to the valve cylinder to actuate the piston valve, and a fluid passage adapted to place the interiors of the two cylinders in communication and controlled by the piston valve, whereby when fluid is admitted to the valve cylinder and imparts the relatively short stroke to the piston valve to open -said passage some of the fluid will be admitted to the second cylinder to impart the relatively long stroke to it and thereby extend the overall length of the jack considerably more than accomplished by the relatively short stroke of the piston valve.

4. A'hydraulic jack comprising a valve cylinder, a piston valve slidable therein and having a portion extending beyond said cylinder, a second cylinder carrying a work-engaging portion and mounted for longitudinal movement on and relative to said extending portion of the piston valve, means to admit motive fluid under pre-ssure to said valve cylinder to produce a forward stroke of the piston valve, a fluid passage adapted to place the interiors of the two cylinders in communication and having an entrance port in the wall or the valve cylinder arranged to be opened for admission o some of the motive fluid during the latter part only of the forward stroke of the piston valve and to be closed during the first part of the return stroke thereof, whereby when motive fluid is admitted to the valve cylinder the piston valve is actuated to open said port for admission of some of the motive iiuid to the second cylinder to move it longitudinally until its work-engaging portion :contacts with the work, the effective pressure area in the second `cylinder which is responsible for relative movement between it and the piston valve extension being greater than the efective pressure area of the piston valve so that aiter pressure is applied to the work by the jack the piston valve will be moved in the opposite direction by the fluid pressure in the second cylinder to close said port and thereby trap the motive uid in the valve cylinder.

5. A hydraulic jack comprising a valve cylinder, a piston valve slidable therein and having a portion extending beyond said cylinder, a second cylinder mounted for longitudinal movement on and relative to said extending portion of thel piston valve, means to admit motive fluid under pressure to said valve cylinder to produce a forward stroke of the piston valve, a fluid passage adapted to place the interiors of the two cylinders in communication and having a port in the wall of the valve cylinder arranged to be opened by the piston valve during its forward stroke i or admission of some of the motive fluid to the second cylinder to move it longitudinally, and an exhaust port in the wall of the valve cylinder, the piston valve when in normal position serving to place said exhaust port in communication with said firstnamed port so that when the line pressure of the motive uid is relieved and the piston valve returns to normal position the motive fluid will be exhausted from the second cylinder through said first-named port and said exhaust port.

6. A hydraulic jack comprising a valve cylinder, a piston valve slidable therein and having a portion extending beyond said cylinder, a second cylinder carrying a work-engaging portion and mounted for longitudinal movement on and relative to said extending portion of the piston valve, means to admit motive fluid under pressure to said valve cylinder to produce a forward stroke of the piston valve, a uid passage adapted to place the interiors of the two cylinders in communication and having a port in the wall of the valve cylinder arranged to be opened by the piston valve after it has moved a predetermined distance on its forward stroke for admission of some of the motive fluid to the second cylinder to move it longitudinally until its work-engaging portion contacts with the work, the eiective pressure area in the second cylinder which is responsible for relative movement between it and the piston valve extension being greater than the effective pressure area of the piston valve so that after pressure vis applied to the work by the jack the piston valve will be caused to start a return stroke by the fluid pressure in the second cylinder and will close said port and thereby trap the motive uid in the valve cylinder, and an exhaust port in the wall of the valve cylinder, the piston valve having a passage adapted to place the exhaust port and said rst-named port in communication upon further return movement of the piston valve to exhaust the motive uid from the second cylinder when the jack is overloaded or when the line pressure of the motive fluid is relieved and the piston valve thereby returned to normal position.

7. A hydraulic jack comprising a relatively xed valve cylinder, a piston valve slidable therein and having a portion extending beyond said cylinder, a second cylinder mounted for longitudinal movement on and relative to said extending portion of the piston valve, means to admit fluid under pressure to the valve cylinder to actuate the piston valve, and a iiuid passage adapted to place the interiors of the two cylinders in communication, said passage having one portion located within the wall of the valve cylinder and another portion extending through a portion of the piston valve and its extension and opening directly intothe second cylinder, the portion of the passage within the valve cylinder wall entering the valve cylinder at one point where it is opened and closed by movement of the piston valve and entering the valve cylinder again at a second point where the piston valve has a recess adapted in all positions of the valve to establish communication between the two portions of the passage, whereby when fluid is admitted to the valve cylinder and actuates the piston valve to open said passage some of the uid will be admitted through the passage to the second cylinder to move it longitudinally on the piston valve extension.

8. A hydraulic jack in accordance with claim 1 having a work-engaging member associated with the second cylinder, a ball-and-socket connection between said member and the second cylinder, and a ball-and-socket support for theV valve cylinder.

9. A hydraulic jack comprising a short stroke cylinder and piston valve, a long stroke piston and cylinder supported on the piston valve, the cross-sectional area of the long stroke cylinder being slightly greater than the cross-sectional area of the short stroke cylinder, and the short stroke cylinder and piston valve having passages and ports whereby fluid under pressure is delivered to and trapped within the long stroke cylinder to extend and maintain it in extended position.

OTTO J. BORNGESSER.

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