Abstract: A housing block with a first passage and a second passage extending parallel to the first passage is attached to each membrane filter plate. A piston is mounted slidably in the first passage and a spacing bolt is positioned slidably in the second passage. A first circumferential groove which is connected with a compression compartment between elastic membranes extending radially exteriorly is introduced into the center of the first passage. The piston has a plurality of, advantageously four, axially extending piston grooves which connect with the circumferential groove in the open configuration and because of that the above mentioned compression compartment is connected with the surrounding atmosphere. The operation of the pistons is positively actuated by a counterweight and the sealing bolts are positioned in succession in a row. The motion of these spacing bolts is bounded by a stop piece.