Siemens SFA71U ZONE VALVE ELECTRONIC ACTUATOR, 24 VAC, 2-POSITION, NC, SR.Siemens SFA71U Zone Valve Electronic Actuator, 24 Vac, 2 Position, NC, SR. SF Series electronic zone valve actuator, 24 Vac, normally closed, 2 position, with spring return. Works with Siemens 599 Series zone valves with 1 10 inch (2. 5 mm) stroke. UL listed for plenum installations, manual override. Additional Information Actuator TypeElectronic Control or Fire Smoke TypeControl Damper Force105 N Fail SafeYes Control Signal2 position Positioning