Abstract: A rotary diaphragm press comprises a revolving drum on the periphery of which a tubular diaphragm is mounted, an endless belt assembly which consists of a cover cloth, a filter cloth, and a back-up belt separately extended and arranged one above the other over said revolving drum, and a series of receiving rollers disposed in parallel with a spindle for said revolving drum so as to press the endless belt assembly against the drum in a contact zone of the assembly. The rotary diaphragm press is further designed so that sludge successively fed to the filter cloth is held between the filter cloth and the cover cloth and is passed through the contact zone.