Abstract: A pump having a piston tip member which fits a cylinder bore sufficiently loosely that abrasive particles in fluid being pumped do not excessively wear away the cylinder walls and piston tip member, the fit being sufficiently close, however, as to provide substantial and effective pump pressure, the liquid that by-passes the tip member being retained by a sealing assembly surrounding the piston rod for assuring that substantially all of it returns to the forward side of the piston during a return stroke.A paint spraying assembly using the pump described.