Hydraulic control systems for mining apparatus

In a hydraulic control system for controlling the operation of pressure-fluid operated support props of mining apparatus;

• said system comprising a common pressure fluid feed line (P), a common pressure fluid return line (R) and manually operated control devices (11, 11') for selectively connecting the feed and return lines to respective first (15) and second (16) working chambers of associated props (10) of which a first working chamber (15) serves to extend and set the prop when connected to the pressure line;
• the improvement comprising setting valve means (18) with opposed first (24) and second (23) pressure-fluid operated control pistons, the setting valve means being settable with the first piston (24) into a first state where connection between the pressure line and said first working chamber (15) is blocked and settable with the second piston (23) into a second state where connection between the pressure line and said first working chamber is established independently of the operating position of the manually operated control devices (11, 11') the first control piston (24) of the setting valve means being connected to said first working chamber (15) and biased with spring force (35) into the first state;
• and control valve means (25) provided with a control piston (29) connected to said first working chamber (15) and biased with opposed spring force (31) to block the pressure line (P) from the second piston (23) of the setting valve means (18) unless a predetermined threshold pressure level prevails in said first working chamber (15) and to connect said second piston (23) of the setting valve means (18) to the pressure line (P) when said predetermined threshold pressure is exceeded in said first working chamber (15);
• whereby the control valve means (25) causes the setting valve means (18) to change from its first state to its second state to connect the first working chamber (15) to the pressure line (8) after an associated control device (11, 11') has connected the pressure line (P) to said first working chamber (15) and the threshold pressure level thereafter is exceeded so that connection between said first working chamber (15) and said pressure line (P) is maintained independent of the operating position of said associated control device, and whereby the setting valve means (18) thereafter reverts to its first state under the action of the first control piston (24) thereof once the pressure in the first working chamber (15) reaches a level in excess of the threshold level and signifying that prop setting has occurred.