Hydraulically operated lifting apparatus and pump therefor

Portable hydraulically operated lifting apparatus comprising:

• a wheel mounted chassis;
• a mounting base supported on said chassis and defining first and second pivot mounting locations and a cylinder pivot mounting location;
• said cylinder pivot mounting location being below the first and second pivot mounting locations;
• a raisable element defining a planar supporting surface;
• first and second support elements pivotably coupled to said first and second pivot mounting locations respectively and to said raisable element;
• a hydraulically operated cylinder pivotably coupled to said cylinder pivot mounting location and to said raisable element;
• and
• means for supplying a pressurized flow of hydraulic fluid to said cylinder for providing extension thereof and consequent lifting of said raisable element, said supplying means comprising
• a hydraulic pump including;
• a reservoir for hydraulic fluid;
• a cylinder bore communicating with said reservoir via a supply opening and having a first inner diameter;
• first one way valve means disposed at said supply opening for permitting entry of hydraulic fluid into said bore and preventing exist of hydraulic fluid therefrom at said supply opening into said reservoir;
• and
• second one way valve means communicating with said cylinder bore at an outlet location located at the opposite end of said cylinder bore from said supply opening;
• piston means comprising
• a piston rod coupled to an operating handle and defining an intermediate portion having a second outer diameter and an end portion disposed within said bore, said end portion having a third outer diameter;
• first and second piston elements slidably disposed about said end portion, having an outer diameter slightly less than said first inner diameter and having inner diameters slightly greater than said third outer diameter and defining a hydraulic fluid passageway between said end portion and the inner diameters of said first and second piston elements;
• a cap element mounted onto said end portion adjacent said second piston element;
• and
• an annular seal associated with said cap element and being operative during outward motion of said piston rod with respect to said bore away from said supply opening when said cap element and said second piston element are forced together by the hydraulic fluid pressure between said cap element and said outlet location, to seal said hyraulic fluid passageway from the portion of said bore lying between said cap element and said supply opening, and thereby to force hydraulic fluid from said cylinder bore via said second one way valve means,
• said annular seal being operative during inward motion of said piston rod with respect to said bore towards said supply opening, when said cap element and said second piston element are not forced together to permit hydraulic fluid communication from said cylinder bore via said hydraulic fluid passageway thereby forcing hydraulic fluid from said cylinder bore via said second one way valve means as said piston rod displaces hydraulic fluid in said cylinder bore.