US Patent 7930971 Rotary actuator with internal brake mechanism

A vane type hydraulic rotary actuator incorporates a fail-safe brake for preventing movement of the device's rotor relative to a housing in which the rotor is journaled. The brake has a spring-biased piston that is forced to a locked condition whenever applied hydraulic operating pressure acting on the vane falls below a predefined limit. The rotary actuator also incorporates an improved sealing arrangement that prevents egress of hydraulic fluid from a high pressure chamber on one side of the vane to a low pressure chamber on the opposite side of the vane.