Abstract: A hydraulic control system for controlling the orientation of a material handling unit on a lift boom. The control system includes a flow divider/combiner valve operative in a boom-raise, unit-leveling mode to pass a portion of the fluid displaced from the rod end of the boom cylinder to the base end of the unit cylinder, and operative in a boom-lower, unit-leveling mode, to combine the fluid stream displaced from the base end unit cylinder in a preset ratio with pressurized fluid, and pass the combined stream to the rod end of the boom cylinder. A modulating valve controls flow to and from the base end of the boom cylinder and is pilot actuated to inhibit descent of the boom until the pressure in the unit cylinder reaches a level at which the unit cylinder initiates levelling of the unit.

Abstract: A control system for a lift boom pivotable with respect to a vehicle by a boom cylinder and material handling unit pivotable with respect to the boom by a unit cylinder when the control of a boom control valve and a unit control valve. The control system includes a flow divider/combiner valve and operative in a boom-raise, unit-leveling mode to pass a preset portion of the fluid displaced from the rod end of the boom cylinder to the base end of the unit cylinder. The flow divider-combiner valve is operative in a boom-lower, unit-leveling mode, to combine the fluid stream displaced from the base end unit cylinder in a preset ratio with pressurized fluid, and pass the combined stream to the rod end of the boom cylinder. The control system can be disengaged from the automatic leveling mode to enable the boom unit to be operated manually under the control of the boom and unit control valves.

Abstract: A hydraulic control system for controlling the orientation of a material handling unit on a lift boom. The control system includes a flow divider/combiner valve operative in a boom-raise, unit-leveling mode to pass a portion of the fluid displaced from the rod end of the boom cylinder to the base end of the unit cylinder, and operative in a boom-lower, unit-leveling mode, to combine the fluid stream displaced from the base end unit cylinder in a preset ratio with pressurized fluid, and pass the combined stream to the rod end of the boom cylinder. A modulating valve controls flow to and from the base end of the boom cylinder and is pilot actuated to inhibit descent of the boom until the pressure in the unit cylinder reaches a level at which the unit cylinder initiates levelling of the unit.