GB1350082A - Cartridge pistons - Google Patents

Abstract

1350082 Pistons ADSHEAD RATCLIFFE & CO Ltd 15 Nov 1971 [17 Oct 1970 27 Oct 1970] 49407/70 and 50911/70 Heading F2T A piston for use in dispensing viscous substances, such as mastic sealant, from a cartridge comprises a crown 5, skirt 6 and one or more grooves 10 formed in the outer surface of the skirt, the grooves, when the piston is mounted for co-operation with the cartridge wall, providing a passage which permits escape of air past the piston but does not permit appreciable leakage of the viscous substance. The piston may be made of synthetic plastics material with a concave crown and a skirt strengthened with internal circumferential ribs 11. The grooves 10 may be parallel with the piston axis, angled or helical. When the piston is first inserted into the cartridge, the air trapped between the crown and substance to be dispensed flows past the piston through the grooves 10. The skirt may be tapered towards the crown as shown so that during a dispensing operation when force is applied by a plunger 9, the leading edge of the skirt is expanded into sealing engagement with the cartridge wall due to the flattening out of the crown. In a modification, the grooves stop short of the rear edge of the skirt and the rear edge is in sealing engagement with the cartridge wall; when the piston is first inserted, the trapped air passes along the grooves and lifts the rear edge of the skirt to permit its escape.