Why my tool is sinking?

A Reason for the sinking is the Valve 6 is stuck or are not able to close good engough. 

Please turn the valve completely in until you feel resistance. please do not use force with feeling.

If this does not help and the tool still goes down, then you have to do another test.

Move the machine completely to maximum opening. Switch off the machine and loosen this screw connection:

Is oil coming out of this valve?

In the appendix also the hydraulic diagram of the machine. 

I would like to ask you for feedback when you have done the test.