An hydraulic head features two or three individual radial pumping pistons
and associated pumping chambers, annularly spaced around a cavity in the
head where an eccentric drive member with associated outer rolling
actuation ring are situated, whereby a rolling interaction is provided
between the actuating ring and the inner ends of the pistons for
intermittent actuation, and a sliding interaction is provided between the
actuation ring and the drive member. The respective inlet and outlet
valve trains are also situated in the head, and the head is attachable to
an application and/or customer specific mounting plate. The outside
diameter of the rolling element is barrel shaped, to compensate for any
misalignment of the pistons relative to the drive shaft due, for example,
to either tolerance stack up or deflection.