Proportional directional valve and hydraulic circuit and hydropneumatic suspension system with such a valve

The proportional directional control valve (10) has a single actuator (18), and a control piston (16) moved by actuator starting from first switching position in which working ports (A,B) of valve housing (12) are connected to tank port (T) of housing, via second switching position that directly follows first switching position, into third switching position which successively disconnects working ports from tank port and connects working ports to pressure port (P) of housing. The tank port discharges hydraulic fluid to reservoir. The pressure port feed pressurized hydraulic fluid. Independent claims are also included for: (1) a hydraulic circuit; and (2) a hydropneumatic suspension system for variable suspension loads.