Gas injection valve for liquid e.g. PVC suspensions - having a perforated truck piston with a head sealing against the wall of the suspension container

摘要

A container for a liquid suspension, eg. a PVC suspension, is provided with a gas injection valve having a gas injection tube (3) extending through the wall (6) of the container and terminating flush with the inner surface (9) of the wall. A piston rod (5) is reciprocable within he tube and has a trunk piston (2) secured to one end, the tracking end of the piston carrying a soft ring (4) which seals with the gas tube. The rear end wall and side wall of the trunk piston contain apertures (15,14) and the leading end of the piston comprises a solid disc (1) having a rearwardly extending bezel (16) which in the valve closed position sealingly engages the end surface (17) of the gas tube. If desired a resilient ring, adapted to absorb 50%-80% of the closing force, is located under the disc adjacent the bezel. The valve is of use in introducing a gas eg. water vapour into a PVC suspension to degas it. With the valve even only slightly open the degassing gas flows through the piston and out of the small gap between it and the tube at high velocity to prevent ingress of particles into the piston.