Screw Grit Classifiers (SGC) from Napier Reid offer a solution to removing, washing, and dewatering grit and sand, in addition to protecting downstream mechanical equipment and improving the performance and reliability of drainage systems.


Napier-Reid SGC with Hydro-Cyclone 3D Rendering

Napier-Reid SGC with Hydro-Cyclone 3D Rendering


Screw Grit Classifier Process

A mixture of water, organics, grit, and other solids is fed directly into the grit classifier through the influent box and diverted into the classifier tank.

The influent enters the classifier tank horizontally, creating a hydraulic jump that allows water and light weight organics to skim over a weir plate and into the effluent trough.

Grit and other heavy material settle to the bottom of the detention trough and are transported up an inclined plane by a low speed conveying shaftless screw.


As the grit and other heavy materials are transported up the inclined plane, the specially designed conveyor tumbles and washes the grit in order to remove the organics from it. The washed organics are returned to the effluent connection by an organic return connection.

Once the grit and heavier material is elevated above the classifier’s water level, the solids are further dewatered by transferring them to a convenient discharge height. The grit falls through the grit discharge chute into a grit collection box or into a screw conveyor for disposal.



  • High efficiency equipment: Removes up to 95% of 150 mesh grit having specific gravity of 2.65 or higher
  • Low organic content: Typical discharge from the classifier is 90-95% dry weight with less than 5% organics
  • The shaftless conveyor design maximizes grit recovery
  • No underwater or intermediate bearings
  • Low speed of the conveyor, resulting in longer trough liner life
  • Compact and robust unit
  • Low power consumption
  • Virtually maintenance free
  • Easy to install
  • Low installation cost


Constructional Features of Napier-Reid Screw Grit Classifier

  • Efficient and proven design washes and removes grit and other heavy materials from wastewater. Organics are washed from the grit and returned to the wastewater treatment plant.
  • Various models with different screw diameters and trough sizes to cover a wide range of flow and grit handling requirements.
  • Material of construction: Carbon steel or stainless steel, depending upon application or requirement.
  • Shaftless screw can be of carbon steel, alloy steel or stainless steel.
  • Specially designed high quality UHMW liner provides years of smooth operation.
  • Robust gear drive unit with oversized bearings for long life.
  • High or premium efficiency electric motor.
  • Trough liner designed for easy removal and replacement.
  • Robust design and high quality components for a long life.
  • Free standing design. Needs no extra support for stable operation.
  • Compact design leading to smaller footprint.
  • There are no intermediate or end bearings under water.
  • Drain connection with valve provided for complete draining of the classifier.
  • Optional features like hydro-cyclones (to effectively handle large volumes of water without increasing the classifier size), heat tracing, variable speed drive, and explosion proof motors can be provided if required.