Power plants – Pressure fluid source and motor – Ram driven by fluid pumped from reservoir
Reexamination Certificate
2000-05-09
2001-10-02
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Ram driven by fluid pumped from reservoir
C091S029000, C254S0930HP
Reexamination Certificate
active
06295812
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a jack, and more particularly to a hydraulic jack that can adjust the lift capacity to lift quickly and lower slowly.
2. Description of Related Art
A conventional jack includes a lift arm and a handle mounted on a movable base seat. A hydraulic driver is mounted on the base seat and has a base member with a compound path. A container to hold hydraulic fluid, a release valve and a drive piston to drive a lift arm are mounted on the-base member. The conventional jack employs hydraulic power to extend the drive piston which has a lift arm connected to the distal end. The lift arm can engage an object such as the frame of a car, so that the lift arm can lift the object by extending the lifting piston.
However, the lift capacity of the conventional hydraulic jack is fixed so that the user must choose a jack suitable for the weight of the object to be lifted. Consequently, a jack may not be able to lift an object because of inadequate lift capacity or lifts a light object too slowly due to excessive lift capacity.
The present invention has arisen to mitigate and/or obviate the disadvantages of the conventional hydraulic jack.
SUMMARY OF THE INVENTION
In accordance with the present invention, a hydraulic jack has a compound piston assembly and a hydraulic driver with fluid path by which the jack can adjust the lift capacity so as to lift quickly and lower slowly.
Further benefits and advantages of the present invention will become apparent after a careful reading of the detailed description with appropriate reference to the accompanying drawings.
REFERENCES:
patent: 5937647 (1999-08-01), Hung
patent: 6042985 (2000-03-01), Tang
Hedman & Costigan ,P.C.
Lazo Thomas E.
Look Edward K.
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