the casing of a pump defines a threaded hole into which is inserted an outer block for reacting radially directed forces transmitted by a second inner block from a movable , pressurized cam ring surrounding the pump rotor . the blocks have mutually parallel mating surfaces arranged generally parallel to a plane tangential to the ring . onto one of such surfaces is bonded an anti - friction bearing material , such as a woven fabric or metal , to facilitate sliding action between them . the eccentric position of the cam ring is partly established by the action of system pressure acting on control pistons while the guided motion of the inner block further positions the ring to optimal adjustments made to the outer block .