Patent ID: 6732514
Filing Date: 2004-05-11
Classification: B66F,F04B

Abstract:
A hydraulic jack, comprising:a base frame; a lifting arm having a pivot end pivotally mounted on said base frame and a lifting end arranged in such a manner that when said pivot end of said lifting arm is moved forwardly, said lifting end of said lifting arm is driven to move upwardly; a hydraulic cylinder, having an inner fluid chamber, mounted on said base frame; a piston shank having a driving portion movably disposed in said fluid chamber and a pusher head solidly extended from said driving portion towards said lifting arm to push said pivot end of said lifting arm forward; a first fluid pump system comprising a first fluid reservoir for storing a hydraulic fluid therein and a first fluid circuit comprising a first fluid passing channel extending between said first fluid reservoir and said inner fluid chamber of said hydraulic cylinder, a first pumping means for pumping said hydraulic fluid from said first fluid reservoir to said inner fluid chamber, a first check valve located at said first fluid passing channel for preventing a flow of said hydraulic fluid in a reverse direction, a first fluid returning channel extending between said first fluid reservoir to said inner fluid chamber, and a first sequence valve located at said first fluid returning channel and opening at a predetermined control pressure to enable said hydraulic fluid flowing from said inner fluid chamber back to said first fluid reservoir; a second fluid pump system comprising a second fluid reservoir communicatively connected with said first fluid reservoir and a second fluid circuit comprising a second fluid passing channel extending between said second fluid reservoir and said inner fluid chamber of said hydraulic cylinder, a second pumping means for pumping said hydraulic fluid from said second fluid reservoir to said inner fluid chamber, a second check valve located at said second fluid passing channel for preventing a flow of said hydraulic fluid in a reverse direction, a second fluid returning channel extending between said second fluid reservoir to said inner fluid chamber, and a second sequence valve located at said second fluid returning channel and opening at a predetermined control pressure to enable said hydraulic fluid flowing from said inner fluid chamber back to said second fluid reservoir, wherein said control pressure preset at said first sequence valve is smaller than that preset at said second sequence valve; and an actuation handle pivotally connected to said base frame and arranged to drive said lifting arm from a no load condition to a load condition, wherein at said no load condition, both said first and second pumping means are respectively pumping said hydraulic fluid from said first and second fluid reservoirs to said inner fluid chamber of said hydraulic cylinder to push said driving portion of said piston shank forward, so as to speed up said lifting up of said lifting arm, and at said load condition, said first sequence valve is opened for allowing said hydraulic fluid flowing back from said inner fluid chamber to said first fluid reservoir by means of a loading pressure, while said second pumping means keeps pumping said hydraulic fluid to said inner fluid chamber to substantially lift up said lifting end of said lifting arm.