Liquid Ring vs. Claw Pumps in Extrusion Degassing: Handling Powder Additives
Plastics compounding lines frequently blend base polymers with abrasive or functional powder additives, such as talc, calcium carbonate, titanium dioxide, or flame retardants. Extracting moisture and volatile off-gases from these twin-screw extruders requires a vacuum system that can handle aggressive process carry-over without frequent mechanical breakdowns.
The Powder Carry-Over Problem in Dry Claw Pumps
More recently, dry claw vacuum pumps have been experimentally used on extruder vents due to their simple dry operation and ease of drop-in installation. However, claw pumps operate with extremely tight internal rotor clearances.
When fine powder additives or resin dust bypass simple suction filters and enter the compression chamber, they act like abrasive sandpaper. This carry-over leads to:
Severe internal rotor abrasion and loss of pumping capacity.
Clogging and thermal lockup of running components.
Constant, unbudgeted pump rebuilds and production downtime
The "Pass Through" Advantage of Liquid Ring Pumps
When dealing with process carry-over, E.W. Klein follows a core design principle: either prevent carry-over from reaching the pump or select a technology that allows it to pass through harmlessly.
Because a Liquid Ring Vacuum Pump (LRVP) uses a continuous ring of seal liquid (typically water) as its rotating piston, it easily ingests fine particulates, liquid droplets, and soft solids without internal mechanical contact or rotor wear. Ingested powders are flushed out with the seal water discharge directly to the plant treatment facility.
Sizing Chilled Water Recirculation Loops
To eliminate wastewater disposal costs, liquid ring systems on extrusion lines are often fitted with closed-loop heat exchangers. The heat removed from the pump by the seal liquid equals the pump's brake horsepower, which can be converted to chilled water heat load using a simple formula:
Heat Transferred (Btu/hr) = Pump Brake Horsepower (bhp) x 2,544.43 Btu/hr
EW Klein Technical Tip
If your claw pumps require constant rebuilds due to powder additive abrasion, consider returning to a liquid ring vacuum pump with a closed-loop heat exchanger. Matching the chiller capacity to the pump's brake horsepower ensures stable operating temperatures and years of maintenance-free degassing.
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