Abstract: A reciprocating pump (10) comprises a body (11) configured as a cylindrical pressure vessel defining an internal space (13). The body (11) comprises a wall (17) having an opening (18) therein. The pump (10) further comprises a reciprocating plunger (25) having a cylindrical side face (26) and an end face (27). The plunger (25) extends into the internal space (13) through the opening (18) within the wall (17). A seal means (40) is provided for establishing a fluid seal between the body (11) and the plunger (25) at the opening (18). The seal means (40) is adapted to accommodate limited tilting movement of the plunger (25) with respect to the body (11). The seal means (40) comprises a bush (43) with which the plunger (25) is in sliding and sealing engagement. The bush (43) is supported in a mount (45) and is moveable with respect thereto to accommodate the limited tilting movement of the plunger (25).