CLOSED LOOP "Pressure Override™" Controls for Melt Filtration


Screen feed controls regulate the movement of the filter screen based on our proprietary algorithm that has been developed and refined over decades of use in thousands of installations.  Directed by this logic, our screen changers become a fully integrated element of the extrusion process, delivering optimum performance.




The CLOSED LOOP algorithm uses our proprietary  Screen Guide & Resolver Assembly™ to monitor and ensure a consistent rate of screen movement.

‘CLOSED LOOP’ “PRESSURE OVERRIDE™" controls incorporate all the features of the TIME CYCLE™ algorithm, i.e., a constant rate of screen advancement  is maintained via a feedback loop.  The additional PRESSURE OVERRIDE™ (or Differential ΔP Pressure) feature automatically increases the rate of screen advancement by continuously monitoring the pressure before the screen (P1) - or the differential pressure across the screen (ΔP) -  to maintain uniform processing pressure (head pressure). The distance of screen advancement in both Time and Pressure Cycles is programmable to achieve a precise rate of movement, allowing for fine tuning to the specific parameters of a given application.

This type of control is best suited for applications where the processing parameters can vary more often, the level of contamination could be unpredictable and with medium to fine filtration.



closed loop pressure override control panel for screen changer melt filtration polymer extrusion

 Features of the Closed Loop – Pressure Override™ algorithm:

  • Operational modes:  OFF/AUTO/TEST/MELT

  • Password protected

  • Screen advancement based on Time and Pressure (P1 or ΔP) cycles:

    The Closed Loop-Time algorithm is used to maintain a steady incremental rate of screen travel.  Simultaneously, the system continually monitors the melt pressure. If the pressure rises above the preset value (e.g. 300 psi/20 bar above the clean screen value) due to excessive contamination or other changes in polymer processing conditions, the Closed Loop - Pressure Override™ algorithm automatically speeds up the rate of screen movement.
    Once the polymer pressure (upstream of the screen P1 or across the screen ΔP) drops below the preset value, the controls automatically revert to the Closed Loop - Time Cycle™ algorithm. 

  • The rates of screen movement both by Time and Pressure cycles are operator selectable and adjustable.

  • If the melt pressure (upstream of the screen: P1 or across the screen: ΔP) reaches a much higher value, a secondary alarm stops the automatic cycling of the screen. The information can be further used to interlock the operation of the extruder.

  • Screen movement is verified by the controls.  Immediate indication of an malfunction of screen advancement is given by means of the NO FEED alarm. The automatic cycling is stopped, and the operational mode is turned to OFF.

  • A variety of operational patterns for the heaters and coolant flow can be selected to customize the controls for a range of polymer and processing conditions.

  • All the heating zones are monitored by temperature controllers. Power consumption indicators are also included

  • Door handle is interlocked with a disconnect switch inside the enclosure.

 Alarms (visual and audible) supplied for:

  • NO FEED:  in case screen movement cycle is not completed

  • NO COOL:  in case of accidental loss of coolant flow to the line

  • HIGH PRESSURE – indicates high upstream pressure above the Pressure Override™ set point

  • Optional LOW PRESSURE – indicates that the head pressure is below the level that can activate a screen  movement (AUTO) cycle.

  • NO HEAT alarm:  stops operation of the controls and returns to OFF mode, prevents the screen from advancing without adequate heating conditions

 Protections supplied for:   

  •  TEST mode has max time protection.

  • BOOSTER and EXILT LIP heater(s) have separate protection limits against overheating in all modes.

  • To prevent incorrect settings of the timers

  •  MELT mode has an additional protection against overheating of BOOSTER and EXIT LIP by allowing the  cooling system to expedite the drop of temperature (mainly for low flash point polymers).

  • To prevent incorrect mode selection when properly interlocked with the extruder / equipment.     

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HITECH™ The Leaders in Continuous Melt Filtration since 1969