Patent ID: 7150150

Claim:
An open hydraulic circuit including a main pump suitable for delivering a fluid under pressure, a hydraulic motor, two main ducts for the feed and for the discharge of said motor, a selector suitable for taking first and second positions in which said selector connects the main ducts respectively to the main pump and to an unpressurized reservoir for operating the motor, and a neutral position in which said selector isolates said ducts from said pump and from said reservoir for braking the motor, means for connecting a boost duct to the discharge main duct, and two pressure limiters disposed between said main ducts and for limiting the pressure in a respective one of said ducts by diverting excess fluid from said duct into the other duct, the circuit including a relief valve device distinct from said pressure limiters, suitable for taking up a retention position and a relief position in which said device puts one of said main ducts into communication with a relief enclosure, the relief valve device being continuously urged back into one of the said positions thereof by resilient return means and being caused to go into the other position by a control duct connected to one of the main ducts, so that the device is suitable for taking up the relief position thereof when, after the selector has isolated the main ducts from the main pump and from the reservoir, the difference between a pressure in the main duct to which said control duct is connected and a relief pressure higher than a boost pressure changes sign.