A priming piston reciprocating pump 10 has piston guide 14 which encircles piston 16 and is provided a bearing member 22 in the inner diameter of the upper end of the guide 14. The bearing 22 is formed of 25% carbon-filled PTFE and may be fitted without tools into the aforementioned ID. Such a bearing 22 allows a negligible clearance to be utilized between the bearing 22 and the piston 16.