A belt filter press having a wedge zone which can be adjusted during operation of the filter press to prepare a sludge or other material to be deliquified in the most efficient manner for high pressure deliquification also includes a sealing arrangement for sealing the marginal edges of the upper and lower belts, a tapered slide cam assembly on either side of the belts for adjusting the wedge angle in a controlled manner, rack and pinion assemblies associated with hydraulic cylinders on either side of the belts to ensure the uniform movement of the lower belt supports, and the staggered arrangement of upper and lower belt support members where the lower belt support members are concave-like in shape to facilitate the sealing of the marginal edges of the belts, as well as to form a confined pocket which will facilitate the shearing action induced in the material to be deliquified.