An improved shaft sealing ring (16) for a portable paint gun (1). The sealing ring has a truncated frustro-conical surface (20) tapering from a radially extending retaining surface (30) toward a front end (22) of the sealing ring (16) and a radially extending flange (24) at a back end (26) of the sealing ring (16) with an outer peripheral groove (28) in an outer surface (21) of the ring body (17) between the flange (24) and the retaining surface (30). The ring (16) is installed by urging the front face through an opening having a diameter smaller than that of the face. The flange (24) is resiliently deflected to form a seal when the ring (16) is installed. A central bore (18) of the seal is sized to receive a shaft (14) with a seal between the shaft (14) and the ring (16) provided by a ridge (32) extending radially into the bore of the ring (16) at the back end thereof. The ridge (32) is urged against the shaft (14) by deflection of the flange (24).