A positive displacement pump especially designed for home use comprises a crankcase housing and a cylinder block joined thereto, the cylinder block containing a cylindrical bore whose longitudinal axis is at a predetermined angle relative to the longitudinal axis of the pump's drive shaft journaled in the crankcase housing. A piston having a central longitudinal bore formed inward from one end thereof and which includes a timing window extending through its side surface, is fitted into the cylindrical bore and coupled to the drive shaft by a pin which is journaled in a spherical bearing. A suction port is formed through the wall of the cylinder block on one side surface thereof and on the opposite side surface, 180.degree. away, is a high pressure discharge port. When the pump is driven, the piston both rotates and reciprocates causing the timing window in the piston to sweep by the inlet or suction port where a charge of liquid at low pressure is allowed to enter the hollow piston. As the piston rotates, the timing window moves to a point where it is ultimately in line with the discharge port when the piston is at a top dead center position. By canting the pin of the piston relative to its longitudinal axis compensation for the unequal hydraulic forces acting in the transverse direction on the piston results. An improved lubrication system incorporating grease as the lubricant is also employed.
C.Richard Gerlach; Edgar C. Schroeder