30 is preferably compressed between end pieces 34 36 via a packing nut 38 it is to be understood that packing nut 38 and housing 16 are each threaded and engaged together retaining the packing nut 38 to housing 16 and allowing axial compression of end piece 36 against the v ring packing set 30 an enlarged bore 42 provides clearance between the internal diameter of nut 38 and the piston rod 12 in this design any side loads on rod 12 must be taken up by end pieces 34 36 and the packing set 30 referring now to fig2 the piston pump assembly of the prior art and that of the present invention are each intended to be driven by an eccentric 44 driving a connecting rod 46 which is shown in solid lines in a bottom dead center position and in phantom in a top dead center position connecting rod 46 is coupled to piston rod 12 via the yoke 48 it is to be understood that connecting rod 46 and yoke 48 are secured together by a yoke pin 50 to maintain alignment of yoke 48 and piston rod 12 a drag link 52 is connected between yoke pin 50 and stationary pump frame 54 link 52 is shown in a bottom dead center position in solid lines and in a top dead center position in phantom in fig2 it is to be further understood that pump housing 16 is secured to the pump frame 54 via a set of threads 56 and a lock nut 58 as drag link 52 reciprocates it will be apparent that yoke pin 50 will travel in.