OFITE - Capillary Suction Timer

Capillary Suction Timer

The Capillary Suction Timer (CST) principle was developed at the Water Pollution Research Laboratory in Stevenage, England, for studying the filterability of sewage sludge and for evaluating the effects of pre-treatment chemicals and process conditions of sewage treatment. It has been widely used to study the colloidal properties of clay suspensions. The petroleum industry uses the CST to characterize shales and to optimize the electrolyte concentration in drilling fluids for minimizing its effect on shale formations.

CST studies of filtration characteristics of aqueous systems utilize the capillary suction pressure of a porous paper to affect filtration. When a suspension is filtered under the influence of this suction pressure, the rate at which filtrate spreads away from the suspension is controlled predominately by the filterability of the suspension. The CST automatically measures the time for the filtrate to advance between radially separated electrodes when a fixed area of special filter paper is exposed to the suspension.

The CST consists of two separate components - the acrylic filtration unit with the electrodes and a timer. The method is rapid and easy to use. A sample of the aqueous system to be tested is placed in the sample cylinder and the suction pressure of the filter paper beneath the sample draws out the filtrate. The filtrate progresses radially in an essentially elliptical pattern with the timer starting when the liquid reaches the first pair of electrodes. When the liquid reaches the third electrode, the timing ceases, the finish lamp comes on, and an audible signal is sounded. The CST reading is indicated on a 6-digit LCD counter indicating to tenths of a second.

The filter paper used, Whatman no. 17, chromatography grade, is very important and is available from OFITE. A 9- volt battery provides the power and a flashing "Low Battery" light indicates the need for battery replacement. The complete instrument consists of a timer case, test head, and stainless steel cylinder, which is 1 cm in diameter at one end and 1.8 cm at the other. CST paper must be ordered separately. Other components include an on/off switch and a reset button for resetting the circuits. The unit is powered by a 9-Volt battery.

The following are non-exclusive examples of a variety of industrial processes where the CST instrument is used to evaluate chemicals (e.g. polymers):

Wastewater Treatment
• Mechanical dewatering of thickened slurries from sedimentation basins and filter backwash
• Conditioning of surface and subterranean water in potable water
• Clarification of filter backwash water and thickening of hydroxide slurries from sedimentation basins

Sewage Plants
• Dewatering of raw sludge, digested sludge, and waste-activated sludge on drying beds, rotary vacuum filters, vacuum belt filters, decanter centrifuges, and plate/frame filter presses
• Thickening of biological sludge prior to addition of primary sludge
• Thickening of sludge in Dissolved Air Flotation (DAF) systems
• Improving separation efficiency in mechanical pre- clarification processes
Petroleum Industry
• Borehole stabilization to determine the best electrolyte and polymer to use for maximum shale swelling inhibition
• Evaluating colloidal shale properties to study the reduction of permeability of the formation around the wellbore
• Evaluating the effects of soluble salts and polymers on cuttings

There are many other uses for this versatile instrument in minerals processing, the coal mining and quarrying industries, and the potash, metal, paper, and sugar industries.

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Capillary Suction Timer

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