The new filter (Figure 1) is a continuous extended area type of filter using standard Memtec candle filter elements. For optimum uniformity and minimum polymer degradation each element is totally enclosed in its own exclusive housing with sliding spool valves to direct the polymer flow to and from the housing. The individual housings are arranged together in a common structure with common polymer inlet and out ports and common temperature control system. The unit is mounted on a movable stand and can easily be designed with various capacities by varying the number and size of filter elements.

One of the unique features of the Hills filter system is that the polymer cavity in each housing is slightly tapered. This feature is designed such that the inlet polymer flow velocity is varied along the length of the filter to give approximately constant residence times of the polymers as they travel along the length of the filter. This design minimizes the average polymer residence time, but more importantly, it eliminates the polymer "slow zones" which cause some of the polymer to trapped for very long periods of time with conventional extended area filter designs.

Another unique feature of the filter is that individual elements can be added or removed from the polymer streams in order to allow more constant residence times as the polymer flows are changed to obtain different bi-component polymer ratios. This feature also means that when the elements become contaminated and need to be changed that they can be easily changed one at a time without interrupting the polymer process or causing a major disruption in spinning.

When filters in any one of the assemblies 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 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 allow flow to each assembly. A shield is attached to the valve to prevent access to operating assemblies. Several US patents cover specific design features of the system.