Metering piston pump with piston-carried distributor for viscous fluid

A material dispensing and metering piston pump comprising, in combination:

• 1. a cylinder having an axis and defining a chamber receiving the material to be dispensed and metered, the cylinder defining
• a. an inlet for the material,
• b. an outlet for the material axially spaced from the inlet, and
• c. a coaxial cylindrical metering portion extending in the cylinder chamber from the outlet towards the inlet,
• 2. a non-return valve in the outlet, and
• 3. a piston mounted for axial reciprocation in the cylinder chamber between a first terminal position in the metering portion adjacent the outlet and a second terminal position adjacent the inlet, the piston comprising
• a. a piston rod and
• b. a piston head mounted on the piston rod, the piston head including a first member having a peripheral skirt projecting in an axial direction towards the outlet and having a diameter corresponding to that of the metering portion for sealing engagement between the peripheral skirt and the metering portion, the first piston head member defining at least one axially extending aperture therethrough and being mounted for free axial movement on the piston rod between a first axial position and a second axial position, and a second member having a diameter smaller than that of the metering portion and being fixedly mounted on the piston rod adjacent the second axial position, the sealing engagement between the peripheral skirt and the metering portion holding the first piston head member in the first axial position spaced from the second piston head member upon axial movement of the piston away from the outlet and out of the metering portion, whereby the material in the chamber may flow between the piston head members and through the aperture, means on the piston rod for supporting the first piston head member on the piston rod during the axial movement of the piston away from the outlet, and axial movement of the piston towards the outlet and the metering portion causing the peripheral skirt to engage the metering portion and thus to move the first piston head member axially into the second position whereby the second piston head member seals the aperture and prevents flow of the material therethrough into the metering portion, one of the piston head members having a circular ridge defining a knife edge and the other piston head member having a corresponding circular recess for sealing engagement between the knife edge ridge and recess when the first piston head member is in the second axial position.