Operating Parameters

are understood as all variable parameters suitable of being altered during the operation, e. g. the number of revolutions for a rotating centrifugal rotor, or the immersion depth of a filter drum, or the pressing power of a filter press membrane.

Organic Filter Aids

Filter aids for precoat filtration and/or body-feed filtration on the basis of cellulose fibers. In principle organic materials have much less weight than mineral materials i.e. diatomaceous earth, can be burned or used for animal feeding and can be provided in very different quality and price. Wood flour is the most simple and cheap product but contains all ingredients of the wood material, which can be partly eluted while in contact with the slurry to be separated. Much more inert is extract-free cellulose, which is nevertheless relatively cheap. For special applications i.e. in the pharmaceutical industry pure cellulose is needed, which is more costly. By special “fibrillation” the specific surface of cellulose fibers can be increased remarkably.


Selective passage of liquid components through membranes due to a concentration difference. If a liquid permeates a semi-permeable membrane under the force of an outer pressure and the solutes (e.g. ions) are retained on the wall in this manner, then it is called reverse osmosis (saltwater desalination).


limits the fluid level; for example a peeler centrifuge can be operated with an overflow, meaning the suspension drains off over the flange ring during the cake formation and the maximal centrifugal pressure acts. In drum or disc filters the filter trough level can be adjusted with a height-variable overflow pipe.

Overflow Weir

Term often used in connection with clarifiers and thickeners for the overflow rim where the clear liquid evolves. For constant liquid discharge the weir is often toothed or serrated.


Absolute pressure acting against the surrounding atmospheric pressure.

Overpressure Filter

Enclosed filter apparatus, working with an increased gas pressure in relation to the surrounding atmosphere. Overpressure filters work with pressure differences up to around 10 bar; hydraulic or mechanical pressure filters are employed for larger pressures.

Oversize Particles

have a considerably larger diameter than the average solids and appear sporadically as a contamination in a suspension. Oversize particles often have to be separated before the actual separation process, in order not to impair the function of the following separation equipment.

Oyster Filter

Former brand name of the BoHiBar Drum Filter.

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