Abstract: A hydraulic platform lift, having hydraulic pump means and first and second hydraulic cylinders each having a piston member therein, each operatively coupled to a respective side edge of a platform to permit raising and lowering of the platform. A positive displacement valve is further provided, with the hydraulic platform lift and comprises a pair of juxtaposed cylinder members, each containing a longitudinally-movable piston, such pistons operatively coupled to each other so that movement of one piston causes an equal movement of the other. The positive displacement valve is adapted, when the pump means provides pressurized hydraulic fluid via a respective aperture to a first side of each of the pistons, to cause the pistons to be displaced an equal distance causing an equal egress of hydraulic fluid from the cylinder members via a respective aperture.

Abstract: A hydraulic platform lift for use with a truck or trailer, having hydraulic pump means and first and second hydraulic cylinders each having a piston member therein, each operatively coupled to a respective side edge of a platform to permit raising and lowering of the platform. A positive displacement valve is provided, alone and in combination with the hydraulic platform lift, which permits powered raising and lowering of the platform, and comprises a pair of juxtaposed cylinder members, each containing a longitudinally-movable piston, such pistons operatively coupled to each other so that movement of one piston causes an equal movement of the other, each cylinder member having a pair of opposite ends, one end of which having an aperture to permit ingress of hydraulic fluid from the pump means and another aperture at an opposite end to permit egress of hydraulic fluid from a corresponding cylinder member to one of the hydraulic cylinders.

Abstract: A hydraulic platform lift for trucks, having hydraulic and electrical circuitry to provide automated, or automated with manual override, platform levelling capability in the event the truck is tilted. Three embodiments are claimed where levelling may be accomplished in three separate ways; a first embodiment where levelling is accomplished by stopping one side of the platform and allowing the other side to "catch up", a second embodiment where levelling is accomplished by reversing the direction of movement of one side relative to the other to allow rapid levelling, and a third embodiment where the rate of movement of one side is slowed relative to the other, to allow the other side to "catch up" and thereby level the platform.