SAFETY VALVE, METHOD FOR DRIVING A CYLINDRICAL DEVICE OF A SAFETY VALVE AND METHOD FOR LOCKING A CYLINDRICAL DEVICE IN A FIXED POSITION

摘要

A blowout preventer comprising a main body (14), a bonnet (12) connected to the main body (14), a ram apparatus (20,30,36) comprising a ram shaft (30) movably disposed in the bonnet (12), the ram shaft having an inner end for a ram block and an outer end (32) movable in said bonnet (12), a locking assembly (62,18) for selectively locking the ram shaft (30), characterised in that said locking assembly (62,18) comprises a locking head (62) having a thread (64) for threadedly engaging an thread (18) about an opening (16) in said bonnet (12), said locking head (62) rotatable within the opening (16) so that the locking head (62) abuts the outer end (32) of the ram shaft (30) to releasably lock the ram shaft (30) in position.