Capillary Suction Time Apparatus

Capillary Suction Time Apparatus

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The Capillary Suction Time has been used since the 1970s as a quick and reliable method for characterising sludge filterability and conditionability.

It is sludge filterability that, predominantly, governs the output of nearly all the various types of dewatering equipment including: drying beds, belt press, vacuum filters, filter presses and centrifuges. The capillary suction pressure generated by standard filter paper is used to ‘suck’ water from the sludge. The rate at which water permeates through the filter paper varies depending on the condition of the sludge and the filterability of the cake formed on the filter paper. The CST is obtained from two electrodes placed at a standard interval from the funnel. The time taken for the water front to pass between these two electrodes constitutes the CST.

The force generated by capillary suction is much greater than the hydrostatic head within the funnel, so the test is independent of the amount of sludge, as long as there is sufficient to generate the CST. Each test can be completed in a few minutes.


  • AC switching across the CST head to improve life and reliability.
  • Over 100 hours continuous use from readily available PP3 9V batteries.
  • LCD display
  • Audible indication of start, stop and fault conditions
  • Unit and accessories are supplied in a strong plastic case
  • The unit has been designed and tested to comply with
  • European and USA EMC standards.


Each unit comprises of

  • CST meter
  • Perspex block assembly and stainless steel funnels
  • Filter papers for immediate use
  • Spare PP3 9V battery



Case dimensions33 x 26 x 5.5 cm
Weight1.75 kg


Order Information

304BCST Capillary Suction Time