the solenoid valve is not actuated work port 86 communicates with work port 100 through line 102 to the driving chamber of cylinder 22 the driving chamber of cylinder 24 is connected directly to motion control valve 80 through line 104 work ports 106 and 108 of spool valve 78 may be alternately shifted by operation of the valve spool to discharge oil into tank 110 as will be explained below coupling is initiated with both cylinders 22 24 fully retracted after the tool 42 has been picked up and swung against the frame 14 so that the bevelled locking trunions 26 28 are in alignment with the shouldered pivot pins 52 54 the hydraulic controls are actuated to extend the piston rods of cylinders 22 24 one after the other into locking engagement with the pivot pins oil may be first introduced through lines 82 84 and 102 to engage trunion 26 with its pin 52 and then introduced through lines 84 and 104 to engage trunion 28 with pin 54 once locked to their respective pins the rods of both cylinders remain so engaged until it is desired to detach the tool from the frame to accomplish detachment of the tool by appropriate adjustment of the several valves oil is fed through lines 82 84 port 88 and line 90 to the lower chambers of the cylinders this causes the cylinder pistons to simultaneously retract the oil in the upper end of cylinder 22 being discharged into tank 98 and the oil from the top of cylinder 24 being discharged through lines 104 and 84 into tank 110 which may be the same tank as tank 98 in.