Abstract: A plate-type filter press has sidebars carried on fixed frames, and the filter press plates, the queen end and the king end are all supported on the sidebars by means of pins projecting laterally from the plates and the king and queen ends and resting on the bars. The plates and the queen end are able to slide along the bars on their pins, and even the king end is allowed a limited amount of float between stops on the bars. The press is opened and closed by means of double-acting hydraulic piston-and-cylinder units which are mounted on the king end and are coupled to the queen end by longitudinally extending tie rods so as to close the press by pulling the queen end towards the king end.

Abstract: A plate type filter press, which is opened and closed by at least one hydraulic piston-and-cylinder unit, has a mechanical lock to lock the press in the closed position so that it is not necessary to maintain a high hydraulic pressure to keep the press closed. The mechanical lock may be a set of claws on the hydraulic cylinder to co-operate with a locking ring on the piston rod, with a hydraulic lock cylinder to retract the claws for unlocking, or a lock gate that is introduced into or retracted out of the path of a lock collar on the piston rod by operation of a lock cylinder. The press is first closed with a predetermined high hydraulic pressure that compresses the filter press pack sufficiently for easy movement of the mechanical lock into locking position, and then operation of a lock limit switch automatically stops the hydraulic pump and energizes a bleed valve to reduce the closing pressure to a level at which the press pack compression is relaxed enough to give firm lock engagement.