a radial pump has a housing with a cylinder ring is pivotally mounted therein . the cylinder ring has a circular aperture within which a cam surface is formed . a cylinder block rotates within the cylinder ring aperture and has a plurality of radially extending cylinders each having port which selectively communicates with a fluid inlet and a fluid outlet as the cylinder block rotates . a plurality of pistons is slideably received within the plurality of cylinders and engages the cam surface . an actuator operably coupled to produce movement of the cylinder ring , which alters the spatial relationship between the cylinder ring and the cylinder block to vary the amount that the pistons move within the cylinders . the amount of movement of the pistons within the cylinders is directly related to the magnitude of fluid flow delivered by the pump and moving the cylinder ring thereby controls the fluid flow . rotation of the bearing ring produces less torsional drag than the sliding motion of the pistons on a stationary ring , which allows for increasing speed of operation and less performance losses .