An hydraulic head features two, three, or four 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. The piston shoe or foot smoothly enlarges from the piston stem, thereby avoiding the concentration of stress at the interface. Another improvement is in the capture of the piston foot through beveled holes at the ends of a C-band spring such that the bevel substantially conforms to the contour of the foot and thereby reduces stresses and wear. Yet another improvement is that the C-band spring is retained within a guide channel of the cavity wall thereby permitting apparent reciprocating displacement of the spring in parallel with the reciprocation of the pistons, while avoiding axial movement or tilting within the cavity.