US2539739A - Two-speed hydraulic jack - Google Patents

Description

Jan. 30, 1951 E. P. GRIME 2,539,739

Two-SPEED HYDRAULIC JACK Filed Sept. 23, 1946 Patented Jan. 30, 1951 'invention relatesvto a hydraulic fiack and more specifically toa two-speed jack. In the vopy eration of hydraulic jacks, the original load on the jack is usually very light and if the fluid enters the main hoisting cylinder, it requires a great number of strokes to force this cylinder out.

It is, therefore, an object of my invention to provide a small auxiliary cylinder which will actuate the jack while the load is light and lift the piston in the main cylinder, but when the load passes a certain point, the fluid is automatically ported into the main cylinder to actuate the larger piston.

Other objects and advantages of my invention will be apparent from the following description andpreferred embodiments thereof.

In the drawing:

Figure 1 is a longitudinal section of my hydraulic jack.

Figure 2 is a cross-section, taken on the line 2-2 of Figure 1. v

A hydraulic jack constructed in accordance with the preferred embodiment of my invention comprises a housing I, to which a cylinder 2 is threaded at 3. Carried in the cylinder 2 is a large piston II, which has sealing devices 5 to close off a cylinder head 6. Carried by the piston 4 is a ram 1, which can have any of the usual attachments fastened to its head 8 to lift or move said attachments. The ram 1 hasguide members 9 to keep the same centered in the cylinder 2. A cylinder ID in the center of the ram 'I has therein a sleeve II, which is threaded at I2 to the housing I.

Preferably formed at the opposite end of the housing I from the cylinder 2 is a cylinder I3, in -which is positioned a piston I5, which has attached thereto a connecting shaft I6, which can be connected at I1 to a handle orfgother means for reciprocation.

A chamber I8 in the housing I provides a storage chamber for hydraulic fluid-'such as oil. A bore I9 passes through the housing I and is closed at one end by a plug and at the other end by av mechanism, tobe hereinafter described. A bore 2I connects the end of the cylinder I3 with the bore I9 and passage 22ginthe sleeve II. A bore 23 connects the bore 2IV with a port 24 entering ,the chamber I8. A ballvalve 25 is positioned inthe bore 2I to close off the bore 2l from the bore I9, while a ball valve 26 closes the bore 23 from the bore 2I.

In the operation of my device, when the piston I5 is reciprocated in the cylinder I3 on its suction stroke, it lifts the ball 23 fromyitsseat, opening thefbore 23 to thebore 2| and sucks oil -from the chamber I8 into the-'cylinder I3. At the'same time, this suction and any pressure in the passage 22 or the bore I9 forces the ball valve 25 closed.

vUpon the opposite stroke of the piston I5, the

pressure forces the ball valve 26 closed and opens the valve 25, forcing the oil into the passage 22 and the cylinder head/IBB, thus causing movement of the ram 1. I prefer to have the cylinders I0 and I3 of substantially the same diameter, thus one stroke of the piston I5 will move the ram 1 the same distance. When, however, the pressure upon the head 8 becomes so great that the pressure developed in the head IIIa by the piston I5 can no longer be increased, the ball valve 21 is forced open and the oil then passes through the bore I9 into the cross port 28 into the main cylinder head 6, which then drives on the greatly expanded area of the piston 4, increasing the mechanical advantage upon the ram '1, thus automatically permitting the same size piston I5 to lift greater loads as the diameter of the cylinder 2 is substantially larger than the diameter of the cylinder I3. A spring 29 maintains 25 the ball valve 21 closed until the load is high enough to require the extra mechanical advantage. In the preferred form of my invention, I have found that the spring 29 should not be compressible until a load of 500 pounds is placed upon the ball valve 21, which should be approximately a closure for a 1%" diameter valve seat.

While the ram 1 is being actuated only by the pressure in the head ma, a back pressure would result in the cylinder head 6. I therefore provide a port 30, communicating with the port 24 and the bore I9 and closed by a ball valve 3|. As long as there is no pressure in the bore I9 below the valve 21, movement of the ram 1 moves the piston 4 outwardly and will suck open the ball valve 3l, allowing hydraulic fluid to pass from the chamber I8 into the cylinder head 6, thus preventing any back pressure in the cylinder.

To allow my hydraulic jack to return to its original position, I provide a lever 33, which is pivoted at 34 to the housing I and contacts a push rod 35, which strikes a ball valve 36. When the lever 33 is depressed, it forces down the push rod 35, opening the ball valve 33, allowing the hydraulic fluid in the head IIIa and the passage 22 to be ported through the bore 31 back to the 'l l chamber I8. A second push rod 38 is in contact with the ball valve 35 and the ball valve 21 and forcing open of thelball valve 36 causes the push rod 38 to push open the ball valve 21, permitting the iluid in the cylinder head 6 to port out through the port 31 into the chamber I8. A spring 39 is positioned to act against the projection 40 and maintain the push rod 35 and the lever 33 in a normal position to allow the ball valves 36 and 21 to remain normally closed.

While I have described the preferred embodiments of my invention, I am not limited to any of the details herein set forth, except as described in the following claim:

I claim:

In a hydraulic jack, a body, a lifting piston slidable in a primary cylinder attached to said body, a secondary cylinder in said piston, a reciprocating piston pump in the said body having a pump cylinder substantially the diameter of said secondary cylinder, an enclosed source of hydraulic fluid, a port connecting said pump cylinder with said fluid supply closed byacheck valve when said pump is compressing, a port connecting said pump cylinder with said primary cylinder closedlby a check valve when said pump is in its suction stroke, a port connecting said primary and said secondary cylinders and closed by a check valve until the pressure in said secondary cylinder rises to a predetermined point, a check valve normally held closed by the pressure in said secondary cylinder adapted to be opened by a push rod to bleed off the uid from said secondary cylinder to said i'luid supply, a push rod connecting said bleed off check valve and said check valve between said primary and said secondary cylinders.

EDWARD P. GRIME.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date `617,135 Weeks Jan. 3, 1899 2,284,228 Page May 26, 1942 2,398,558 Reimuller Apr. 16, 1946

Images