Abstract: A screw press has a friction clutch for coupling the driving flywheel to the press spindle. The clutch is engaged by a hydraulic piston. To maintain a constant piston stroke as the friction clutch wears, a metering piston and cylinder are interposed between the clutch operating piston and the pressure fluid supply to trap pressure fluid in the clutch operating cylinder and to top it up as required, so that the operating piston stroke corresponds essentially to the fixed stroke of the metering piston. Fluid flow to the operating cylinder bypassing the metering piston is controlled by a normally closed valve arranged to be opened positively in dependence on the position of the metering piston, as the metering piston approaches the end of its stroke in the direction for pressurizing the clutch operating piston to engage the clutch. This arrangement ensures that the clutch cannot be inadvertently locked in an engaged condition.

Abstract: A slide is vertically movable in a press frame and supports the upper die. A threaded main spindle is operative between the press frame and the slide. A clutch disc connected rationally rigidly to the spindle is connectable by friction contact to a driven disc flywheel for the operating stroke of the slide. Piston-cylinder units act between the press frame and the slide for returning the slide to the starting position. The spindle is axially clamped between two spring columns, one of which acts between one end of the spindle and the slide and the other of which acts between the other end of the spindle and a counter thrust bearing axially fixed in the press frame.