PF-18L LIW w differential


Alternative to twin screws.
A forward feed helix and a reverse
feed helix concentrically mounted to
the same shaft.

Differential Feed Screw Design Benefits

  • Large diameter screw prevents “boring” through product. Defeats product bridging over feed screw.
  • Differential action between fights produces low flow rates with a high screw RPM.
  • Discharge from feeder is uniform and pulse free.
  • Multiple screws having common diameters eliminate feed tube changes and resulting dead zones.


  • Small capacity feed screws with small diameter (and pitch) prevent uniform and reliable filling of screw flights.
  • Large feed screws with large pitches provide uniform filling of screw flights but create large material discharge pulsation when feeding at low feed rates.
  • Small feed screws installed in a feeder designed for large feed screws create material “dead zones” where stagnant material builds up resulting in flow blockage and preventing complete clean out of the feeder.
  • Typical small diameter feed screws of both single and twin screw design are fragile, easily damaged and generally unreliable in heavy industrial process applications.

Solution: Thayer Scale’s Patented Compound Flight Feed Screw

  • Large pitch of screw’s outer winding assures reliable and complete filling of screw flights.
  • Screw’s differential feeding action assures consistent, precise and reliable feeding of material without pulsation.
  • Large over-wind matches (screws) feed chamber and tube diameter eliminating dead zone areas. No material build-up occurs. Assures reliable flow and complete clean out of material.
  • Solid flight screw with robust over-wind assures reliable performance and
    long term durability in harsh process environments.