Apparatus for controlling a hydraulic single acting cylinder

An apparatus for controlling a piston continuously subjected to a constant unidirectional force within a hydraulic cylinder, said apparatus comprising:

• a first solenoid operated valve disposed in a supply line through which working fluid is supplied from a hydraulic pressure source to a working chamber defined in the hydraulic cylinder by the piston, said first solenoid operated valve movable between a first position to open said supply line and a second position to close the supply line;
• a second solenoid operated valve comprising a proportional pressure control valve disposed in said supply line for regulating the pressure of fluid in said supply line;
• a third solenoid operated valve disposed in a return line through which working fluid is returned from the working chamber to a hydraulic tank, said third solenoid operated valve comprising a proportional pressure control valve for regulating the pressure of fluid in said return line;
• a control unit operatively connected to said first solenoid operated valve for moving said first solenoid valve between said first and said second positions, the control unit operatively connected to said second and said third solenoid operated valves for inputting a variable exciting current to the solenoid of the second and the third solenoid operated valves respectively which causes the second and the third solenoid operated valves to restrict the supply line and the return line respectively in proportional amounts over a range of values corresponding to the magnitude of the exciting current input thereto thereby controlling the piston speed.