1,022,469. Advancing mine roof supports. DOWTY MINING EQUIPMENT Ltd. Feb. 2, 1965 [Feb. 11, 1964], No. 5687/64. Heading F1P. An advanceable mine roof support 3, Fig. 2 (not shown) is released slowly by draining fluid through a line 19, an aperture 34 in a piston valve 26, a lever-actuated pilot valve 36 in parallel with valve 26 and through a line 22 leading to a main return line 23 and the prop is then released more quickly by the valve 26 being lifted from its seat 27 following the pressure drop across orifice 34 when the roof bar is clear of the mine roof the pressure drop across aperture 34 decreases which results in valve 26 closing and rate of release being slowed. If during advancement the roof bar re-engages the roof the resulting pressure build-up in valve chamber 29 lifts valve 26 to re-establish quick release of the prop. The pilot valve 36 is held open by a rod 39 when lifted by a lever 42 pivoted about its fulcrum by the rod 49 of a piston 47 subjected to main pressure supply from a line 12. The valve 36 is closed prior to resetting the prop by the lever being displaced by a record piston 52 when a valve 14 in a branch 13 of line 12 is opened by the conveyer advancing jack 5 at the end of its stroke.