Abstract: The disclosure is concerned with a filter press for performing a liquid-solid separation or clarification of highly viscous material such as fowl droppings or sea-bottom muds and, more specifically, with a double acting filter press having a function of additional pressing or squeezing of the material which ensures, in combination with the pressing performed by the liquid pressure onto filter cloths, an increased efficiency and capacity of the filtration. Disclosed herein is a reasonably designed arrangement for performing the above mentioned double acting functions.