Hydraulic cylinder supply system

A hydraulic circuit comprising:

• a first lift cylinder having a piston separating first and second side chambers;
• a tank providing a fluid reservoir;
• a variable displacement pump connected to draw fluid from the tank and having a mechanism to vary the pump displacement in response to a received load-sensing signal;
• a linkage control valve coupled to receive pressurised fluid output from the pump and operable to output the received pressurised fluid to one of the first lift cylinder first and second side chambers via respective first and second supply lines, and further coupled to deliver the load-sensing signal to the pump;
• at least one switch valve operable to couple the first lift cylinder first side chamber to the tank;
• a relief pressure control valve having a first position providing a connection between the pump output and the first lift cylinder second side chamber, and a second position providing a connection between the first lift cylinder second side chamber and the tank, with a further connection carrying an indication of the pressure in the first lift cylinder second side chamber as the load-sensing signal to the pump;
• a feed line;
• an upper cylinder having a piston separating first and second side chambers, wherein the feed line is in fluid communication with the first side chamber of the upper cylinder and the relief pressure control valve and is downstream of the relief pressure control valve;
• and
• a return line providing fluid communication between the second side chamber of the upper cylinder and the tank.