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Grit Classifiers

Designed for grit separating and washing.

A grit classifier is typically designed to precipitate grit and debris from the influent stream settling it into the conveyor trough for removal. 

During the removal process it is possible to remove organic matter from the grit and debris by spraying the material with plant water during the transportation (nocking back the lighter organic material into the effluent stream). The dewatering of the grit and debris starts once the material moves above the water line, gravity pulls the water back the grit into the tank section. For better dewatering the combination of spiral speed and the length of the conveyor above the waterline play a key role. 

atara equipment grit classifier photo

 There is a number of benefits of a Shaftless Screw being used in a grit classifier:

Low cost operation

  • Shaftless screw, no submerged bearings or seals.
  • Compact and robust design.
  • Direct coupled, easily accessible gear-drive.
  • Complete with hydro-cyclone where required.


  • The combination of the inlet design, tank and conveyor shapes all contribute to minimize turbulence in the quiet zone and increases efficiency.
  • Overflow weir design, helps to avoid blockage by floating debris, such as organics.


In both: Municipal and Industrial water and waste-water treatment.


ATARA Grit Classifiers come equipped with:

  • Bolted lids, (over the tank section) and the free length of conveyor
  • Hinged inspection coverts over both the overflow weir and discharge
  • The conveyor trough is lined with removable wear bars of hardened steel, stainless steel bars or grooved UHMW
  • The gear drive is coupled to the endplate using a gear drive adaptor
  • The drive shaft extends from the hollow shaft through a packing gland and is direct coupled to the coupling disc of the spiral
  • The ATARA Grit Classifier is delivered with supports designed to suit installation on an even floor surface.


  • Mild steel painted
  • Stainless Steel (304), (316) or (316L)

Design Data

grit classifier rendering atara

ATARA Type SA 260 320 355 420
Dim. Flow L/sec 5 - 12 12 - 20 20-27 27 - 35
Water Area m² 2.3 3.0 4.0 5.0
Water Volume m³ 1.2 1.8 3.3 4.2
A 3850 4400 5900 6300
B 1250 1500 1500 1800
C 1500 1700 2150 2150
D 1500 1700 2350 2600
E (overall height) 2050 2350 2950 3300
L1 (Length of trough underneath hopper) 3000 3000 4000 4000
L2 (Length of trough above waterline) 1000 1500 2000 2500
Connection in / mm 100 150 200 200
Connection out / mm 150 200 250 250
Engine Output kW 0.25 0.37 0.55 0.75
RPM (conveyor spiral) 4.2 4.2 4.6 4.2

Note: the measurement C,D,E and L2 are min. measures. If C and L2 are increased, the A,D and E measurements will also be increased. When ordering, please state type and length of Conveyor (L1+L2).

Operating under Normal Conditions as described above, the following is an approximate percentage of grit particle sizes removed:

Size: 0.2 mm (0.0079 in) 50%
  0.25 mm (0.098 in) 75%
  0.3 mm (0.0118 in) 90%
  0.4 mm (0.0157 in) 98%
  0.5 mm (0.0196 in) 99%
  1.0+ mm (0.0394 in) 100%

This data was collected from a W.W.T.P. The grit was contaminated with organic material standard at W.W.T.P. It is possible to improve separation of smaller particles, by pre-washing.


New style Shaftless grit classifier

The grit and debris precipitate out of the flow, into the horizontal shaftless screw transport conveyor. The shaftless screw horizontal transport conveyor discharges into the vertical conveyor via a axial connection. The vertical shaftless screw conveyor transports the girt and debris vertically and exits through the discharge port. The advantage to transporting the grit vertically the grit dewaters more efficiently once the grit breaks the water line in the shaftless screw vertical conveyor. 

shaftless grit classifier atara equipment


Questions? Want a quotation? Feel free to contact us, we will be pleased to help you!