A valve operator (10) which includes a ball screw (28) in constant engagement with the output shaft (24) of an air cylinder for automatic operation of the valve, and which includes a manual drive means (20) engageable with the ball screw (28) in any position thereof. The manual drive means (20) includes...http://www.google.com/patents/US4429592?utm_source=gb-gplus-sharePatent US4429592 - Valve operator
