A rotary vane actuator comprising: a rotor assembly including: a rotor hub having a longitudinal axis, said rotor hub having: first and second opposing vane assemblies disposed radially on the rotor hub, each of the first and second vane assemblies comprising: a first vane disposed on the rotor hub and having a first side and a second side; and a second vane disposed on the rotor hub, with a valley member between the first vane and the second vane, a continuous seal groove formed on a peripheral edge of the first and second vanes and the valley member; and a continuous seal disposed in the continuous seal groove; a stator housing having a central chamber having an interior surface adapted to receive the rotor assembly; wherein the rotor assembly is assembled with the stator housing, so that the first and second opposing vane assemblies and the stator housing form a pair of opposing first pressure chambers and a pair of opposing second pressure chambers inside of the central chamber, and wherein the pair of opposing second pressure chambers are in fluid communication with each other through a fluid passage formed between the continuous seal and a rotor wall. a rotor assembly including: a rotor hub having a longitudinal axis, said rotor hub having: first and second opposing vane assemblies disposed radially on the rotor hub, each of the first and second vane assemblies comprising: a first vane disposed on the rotor hub and having a first side and a second side; and a second vane disposed on the rotor hub, with a valley member between the first vane and the second vane, a continuous seal groove formed on a peripheral edge of the first and second vanes and the valley member; and a continuous seal disposed in the continuous seal groove; a stator housing having a central chamber having an interior surface adapted to receive the rotor assembly; wherein the rotor assembly is assembled with the stator housing, so that the first and second opposing vane assemblies and the stator housing form a pair of opposing first pressure chambers and a pair of opposing second pressure chambers inside of the central chamber, and wherein the pair of opposing second pressure chambers are in fluid communication with each other through a fluid passage formed between the continuous seal and a rotor wall. a rotor hub having a longitudinal axis, said rotor hub having: first and second opposing vane assemblies disposed radially on the rotor hub, each of the first and second vane assemblies comprising: a first vane disposed on the rotor hub and having a first side and a second side; and a second vane disposed on the rotor hub, with a valley member between the first vane and the second vane, first and second opposing vane assemblies disposed radially on the rotor hub, each of the first and second vane assemblies comprising: a first vane disposed on the rotor hub and having a first side and a second side; and a second vane disposed on the rotor hub, with a valley member between the first vane and the second vane, a first vane disposed on the rotor hub and having a first side and a second side; and a second vane disposed on the rotor hub, with a valley member between the first vane and the second vane, a continuous seal groove formed on a peripheral edge of the first and second vanes and the valley member; and a continuous seal disposed in the continuous seal groove; a stator housing having a central chamber having an interior surface adapted to receive the rotor assembly; wherein the rotor assembly is assembled with the stator housing, so that the first and second opposing vane assemblies and the stator housing form a pair of opposing first pressure chambers and a pair of opposing second pressure chambers inside of the central chamber, and wherein the pair of opposing second pressure chambers are in fluid communication with each other through a fluid passage formed between the continuous seal and a rotor wall.