Abstract: In the process for reducing the residual vinyl chloride monomer in an aqueous polyvinylchloride dispersion comprising the steps of depressurizing an aqueous polyvinylchloride dispersion containing emulsifiers and/or protective colloids as obtained from pressure polymerization in a polymerization zone, subjecting the same to a vacuum with heating, passing the gasses and foam of liquid constituents resulting from said depressurizing step and said vacuum treating step to a confined space wherein said gasses are separated from liquid constituents, and recovering an aqueous polyvinylchloride dispersion having a reduced residual vinyl chloride monomer content, the improvement consisting in passing said gasses and foam of liquid constituents to a confined space having a volume of not more than 331/3% of the volume of said polyvinylchloride dispersion and returning said foam of liquid constituents to said polyvinylchloride dispersion in said polymerization zone through an elongated zone of small cross-section below s

Abstract: A valve arrangement for injecting a gas into a polyvinyl chloride fluid suspension, through an inlet port in the bottom of the suspension tank. The valve includes an overhanging upper disk with a hollow foraminated cylinder, so that the gas exits the cylinder under pressure through the foraminations, thus keeping the operating portion of the valve free of the suspension, with the valve disk overhang providing additional protection against intrusion of suspension material into the clearance space between the valve cylinder and surrounding injection tube. The valve disk overhang terminates in a pointed ridge which engages the top of the injection tube to form a seal.

Abstract: In the process for steam-stripping residual monomer from an aqueous polymer dispersion comprising injecting steam into an aqueous polymer dispersion containing residual monomers and the customary amounts of emulsifiers and/or protective colloids, said dispersion having a solids content of from 15% to 55% by weight with simultaneous evacuation of the gas space above the dispersion whereby said gas space is maintained at a subatmospheric pressure and said residual monomers are volatilized, the improvement consisting of injecting a sufficient volume of steam into said aqueous polymer dispersion whereby from 5% to 50% by weight of the injected steam passes through said dispersion uncondensed, thereby substantially preventing formation of foam above said dispersion.