Drive arrangement for a pump

A drive arrangement for a pumping plunger (24) of a pump assembly comprises a drive member (30) that is firstly co-operable with the pumping plunger (24) and secondly co-operable with a cam rider (20) so as to impart axial drive to the plunger (24) to perform a plunger pumping stroke whilst permitting lateral sliding movement of the rider (20) relative to the drive member (30). The drive member (30) and the cam rider (20) are co-operably shaped to define (i) an increased volume (44) for lubricating fluid which is variable throughout the pumping cycle and (ii) restricted flow means through which fluid within said volume (44) is dispelled at a relatively low rate as the plunger (24) is driven throughout the pumping stroke. This has the effect of prolonging transient fluid pressure within the volume (44) through that period of the pumping stroke for which return loading of the drive member (30) is a maximum and, hence, provides the benefit that wear of the drive member (30) due to scuffing is reduced.