Resistance arises from the filter cloth, mesh, or bed, and to this is added the
resistance of the filter cake as it accumulates. The filter-cake resistance is obtained
by multiplying the specific resistance of the filter cake, that is its resistance per unit
thickness, by the thickness of the cake. The resistances of the filter material and precoat
are combined into a single resistance called the filter resistance. It is convenient
to express the filter resistance in terms of a fictitious thickness of filter cake. This
thickness is multiplied by the specific resistance of the filter cake to give the filter
resistance. Thus the overall equation giving the volumetric rate of flow dV/dt is: