Which type of vane pump utilizes an oval rotor in a concentric housing?

The type of vane pump that utilizes an oval rotor in a concentric housing is the external vane pump. This design features an oval-shaped rotor that allows for efficient fluid movement through the pump. The concentric housing provides a controlled environment that enhances the operational stability and performance of the pump.

The oval rotor creates varying volumes in the pump chambers, which helps to draw in fluid at the intake side and push it toward the discharge side. This unique design enhances the pump's ability to handle varying flow rates and maintain consistent pressure, making it suitable for various applications where reliability and efficiency are essential.

Other types of vane pumps, such as flexible, balanced, and unbalanced, use different configurations and mechanisms that do not involve the oval rotor in a concentric housing, thus distinguishing the external vane pump as the appropriate answer in this context.