Abstract

This invention is directed to a valve drive means for a vertical up-down valve of the type having a valve shaft linearly movable within a cylindrical valve bore between a first, normal, valve position and a second, occasional valve position. The drive means includes a vertical rotatable drive shaft with a threaded portion formed between non-threaded portions and a mateably threaded coupler for engaging the drive shaft and transmitting axial force to the valve shaft. The movement of the valve shaft is precisely limited by disengagement of the coupler from said threaded drive shaft portion irrespective of continued rotation of said drive shaft. Means are included for neutralizing hydraulic pressure which would interfere with re-engagement of the coupler with the threading on the drive shaft. Means are also preferably provided for deriving a torque component for rotating said valve shaft within said bore and thus facilitating any "freezing" of seal rings mounted to said valve shaft within said valve bore.