Abstract: A rotary shredding apparatus having in combination counterrotating cutter supporting shafts operated by a reversible fluid pressure driven motor, and a fluid flow circuit connected to the reversible motor and including a pump supplied source of fluid at a predetermined nominal operating flow rate, a fluid pressure responsive relief valve operative for fluid flow exceeding said predetermined nominal operating flow rate to return fluid to the source, and a fluid flow directing valve connected in fluid flow relation between said relief valve and said fluid driven motor, and control connected to said fluid flow directing valve means; a fluid flow rate detecting sensor disposed in said hydraulic fluid flow circuit between said fluid flow directing valve and said pressure responsive relief valve, whereby upon the fluid flow rate detecting sensing fluid flow reduction at from about 5% to 10% of said predetermined nominal operating flow rate in said fluid flow circuit said fluid flow detecting sensor energizes said c