the seal chamber 17 and the geometry of the seal chamber exit reducer 18 are chosen so as to provide a variable residence time and provide a continuous plug flow of concentrated polymer solids slurry to minimize u201c dead u201d space and reduce plugging tendencies the seal chamber 17 length must be sufficient to allow practical level measurement and control typical residence times of the concentrated polymer solid slurry in the seal chamber 17 are from 5 seconds to 10 minutes preferable residence times are from 10 seconds to 2 minutes and most preferable residence times from 15 45 seconds the continuous plug flow of concentrated polymer solids slurry forms a pressure seal wherein the concentrated polymer solids slurry have an l d ratio inside the seal chamber 17 which is typically 1 5 to 8 preferable l d is 2 to 6 and most preferable is 2 2 to 3 typically the seal chamber exit reducer 18 sides are inclined relative to the horizontal 60 85 degrees preferable 65 80 degrees and most preferable 68 75 degrees the seal chamber exit reducer 18 geometry is defined by substantially straight sides inclined at an angle to that of horizontal equal to or greater than the angle of slide of the concentrated polymer slurry solids and communicates the concentrated polymer solid slurry to a second transfer conduit 19 which communicates with a feed inlet of flash tank 15 in flash tank 15 substantially all of any remaining inert diluent and unreacted monomer in the concentrated polymerization effluent is vaporized and taken overhead via conduit 20 to a second cyclone 21 the major portion of the liquid medium in the polymerization effluent will have been.