Apparatus for continuous polymer filtration

Abstract

An improved continuous large area polymer filter employs a single valve to control molten polymer flow into and out from at least two but preferably three or more filter assemblies. In a neutral position the valve apportions flow equally to each of the filter assemblies. When filters in any one of the assemblies becomes clogged and requires cleaning or replacement, the valve is repositioned to prevent flow into and out from the clogged assembly while continuing to apportion flow among the remaining assemblies. A small amount of polymer is bled from the selected assembly to effect depressurization and the assembly is removed, restored to function and replaced. The valve is repositioned to allow a slow bleeding of polymer into the restored assembly and the bleed valve is opened to allow air and air entrapped polymer to be removed from the assembly before returning it to service. When the bleed valve flow has stabilized the valve is once again repositioned to allow full flow into and out from the serviced assembly and to apportion flow to each assembly. The valve has mechanical stops to prevent flow from being blocked to all of the assemblies simultaneously and a shield is attached to the valve to prevent access to operating assemblies. The shape of the filter cavities is tapered toward the output end to reduce the volume of molten polymer entrapped stagnantly between the cavity and the filter therein.