The chipper PTH 820 and PTH 1000 series can be equipped with a counter-blade with hydraulic opening

The counter-blade is assembled on a support, fixed to a hydraulic cylinder connected to a lung charged with nitrogen. Should any pieces of metal, stone, or concrete (…) enter into the machine, the lung makes the counter-blade open creating more space for the foreign body; at the same time, together with the opening of the counter-blade, the feeding direction is inverted (in case of independent engine, the friction stops) thus avoiding damage.