Diaphragm valve actuator - has sleeve with coarse external and fine internal thread between hub and core

The diaphragm valve has a threaded spindle working in a tapped bore in the housing. A sleeve-type hub (2) coupled to a drive (3) turns but cannot slide in the housing (1). The spindle (5) inside the hub comprises a sleeve (6), and a core (7) which cannot turn in the housing. The sleeve engages via a coarse-pitch external thread (8) with the hub, and via a fine-pitch internal one (9) with the core. In its end position retracted into the sleeve, a stop face (11) on the core bears against a mating one (12) in the sleeve, generating friction torque. By turning the hub, the sleeve is movable into an end position protruding from it, in which a threadless portion (13) of its outside surface bears against a similar inside one (14) in the hub, generating a coupling friction torque between the two. ADVANTAGE - Rapid closing combined with high closing pressure.