Abstract: A piston pump for a backpack sprayer, which operates reliably without damage due to scoring of the wall of the piston cylinder by powders such as wetable solids, which tend to be abrasive and score or scratch the piston cylinder wall which is of plastic material. The pump has a plastic piston cylinder. A liner provided by a sleeve of metal which is not subject to scratching and is of sufficient thickness to maintain a cylindrical shape of the piston wall. The seal of the piston rides on the piston wall liner as the piston reciprocates in pumping the spraying liquid and particles suspended therein from a tank into a pressure chamber in the tank, from which pressure chamber the spraying liquid is extracted for spraying via a hose and a spraying nozzle. The sleeve is molded upon injection of the plastic providing the piston cylinder pump by being mounted on a core having a step which partially overlaps an edge of the sleeve.

Abstract: A sealing structure is provided by an O-ring disposed on a tank, suitable for use in a sprayer, and closed by a cap adapted to carry a pump actuated by a handle which extends into the tank when the cap closes the tank. The O-ring is maintained in a notch between a rim around an open end of a neck of the tank and a shelf extending outwardly from the rim. The cap has a shoulder forming an exterior angle approximately the same as the interior angle between the rim and the shelf on the neck. The shoulder has a chamfered surface which truncates the exterior angle of the shoulder. When the cap is connected to the tank by external threads around the neck and internal threads below the shoulder, the O-ring is compressed in two directions against the rim and against the shelf on the neck of the tank thereby providing an effective compression seal between the cap and the tank.

Abstract: A cap for closing a sprayer tank has integrated therein a pressure relief valve having a tubular member providing a seat with respect to which a valve provided by an o-ring on a stem is displaced in a direction against the seat to close the valve. The stem is connected at one end thereof to a cap and is biased by a spring around the stem at the opposite end thereof into closing position. The cap is guided by a rim around the seat member. The cap defines around the stem a chamber. This chamber communicates with a spout which directs pressurized flow away from the cap when it is rotated to manually open the valve against the bias of the spring so as to relieve pressure in the tank.