Expression is on operation of separating liquid from solid liquid mixtures which has long been used on a universal scale in widely divergent fields. In fruit pulps processing and fermentation industries. removal of a portion of the liquid in filler cake is essential to the maximum yields of products. In sewage sludge treatments, dewatering of filter cakes is important to disposal by incineration. transportation. and landfill. In the chemical process industries, drying of wet cakes increases cost, and it is desirable to eliminate as much liquor as possible by non-thermal methods. This paper is mainly concerned with the development of a simplified equation for constant-pressure expression.