An electrically actuated valve for regulating a working pressure of a closed volume load includes an inlet valve (24) for controlling fluid flow between a supply port (16) and a working port (18) and an outlet valve (26) for controlling fluid flow between the working port (18) and an exhaust port (20)....http://www.google.de/patents/US5318354?utm_source=gb-gplus-sharePatent US5318354 - Proportional control valve with differential sensing area
