Hydraulic jack assemblies

A hydraulic jack assembly, comprising:

• a hydraulic cylinder including a ram;
• a hydraulic fluid tank;
• a hydraulic unit base having therein a piston cavity, a small piston outlet channel, and a medium piston outlet channel, the small piston outlet channel and the medium piston outlet channel each connected to a respective fluid inlet and a respective fluid outlet;
• a dual pump piston slidably disposed in the piston cavity, the dual pump piston comprising a small piston and a medium piston connected to the small piston along a longitudinal axis of the dual pump piston, the small piston having a smaller displacement volume than a displacement volume of the medium piston, a small piston fluid space formed at a periphery of the small piston and a medium piston fluid space formed at a periphery of the medium piston, wherein the small piston outlet channel is connected to the small piston fluid space and the medium piston outlet channel is connected to the medium piston fluid space;
• a small piston low-pressure one-way outlet valve and a small piston high-pressure one-way outlet valve disposed in series in the small piston outlet channel between the fluid inlet and the fluid outlet connected to the small piston outlet channel to form a small piston temporary storage cavity between the small piston low-pressure one-way outlet valve and the small piston high-pressure one-way outlet valve, wherein the small piston low-pressure one-way outlet valve and the small piston high-pressure one-way outlet valve are oriented in the small piston outlet channel such that a fluid can flow from the fluid inlet to the fluid outlet of the small piston outlet channel but cannot flow in opposite direction from the fluid outlet to the fluid inlet of the small piston outlet channel, and wherein the small piston temporary storage cavity is connected to the small piston fluid space of the small piston;
• and
• a medium piston low-pressure one-way outlet valve and a medium piston high-pressure one-way outlet valve disposed in series in the medium piston outlet channel between the fluid inlet and the fluid outlet connected to the medium piston outlet channel to form a medium piston temporary storage cavity between the medium piston low-pressure one-way outlet valve and the medium piston high-pressure one-way outlet valve, wherein the medium piston low-pressure one-way outlet valve and the medium piston high-pressure one-way outlet valve are oriented in the medium piston outlet channel such that a fluid can flow from the fluid inlet to the fluid outlet of the medium piston outlet channel but cannot flow in opposite direction from the fluid outlet to the fluid inlet of the medium piston outlet channel, and wherein the medium piston temporary storage cavity is connected to the medium piston fluid space of the medium piston,
• wherein the respective fluid inlets of the small piston outlet channel and the medium piston outlet channel are connected to the hydraulic fluid tank,
• wherein the respective fluid outlets of the small piston outlet channel and the medium piston outlet channel are connected to the hydraulic cylinder.