Patent ID: 7373869

Claim:
In a hydraulic system having a first control valve that couples a hydraulic actuator to a supply line containing pressurized fluid, and a second control valve that couples the hydraulic actuator to a return line connected to a tank; a method comprising: receiving a command indicating desired motion of the hydraulic actuator; determining a first pressure differential that exists across the first control valve; determining a second pressure differential that exists across the second control valve; ascertaining from at least one of the first pressure differential and the second pressure differential whether a trapped pressure condition exists in the hydraulic actuator in which case an active indication is produced; when the indication is active: (a) opening one of the first control valve and the second control valve to release the trapped pressure, and (b) determining from a change in at least one of the first pressure differential and the second pressure differential when the trapped pressure condition no longer exists and thereafter opening the other of the first control valve and the second control valve to produce the desired motion of the hydraulic actuator; and when the indication is inactive, opening both of the first control valve and the second control valve to produce the desired motion of the hydraulic actuator.