Actuation is extremely important to damper reliability and performance. As requirements for elevated temperatures increase, manufacturers must search for different and creative ways to power machines. Depending on how they're tested, dampers can be actuated in various fashions, but most require a fail-position device. Dampers switch to an open or closed fail-safe position when losing its electrical power or pneumatic air supply. This is inherent with fire rated apparatus, but may not be applicable with modulating or smoke control TVCDs. Additionally, dampers can be fitted with many ancillary devices such as pressure switches, smoke detectors and position indicators to isolate and solve system problems. Single actuators may power multiple sections of each damper or there may be only one per section. In either case, engineers must remember if a single actuator powering multiple sections fails, all section control is lost. This could be detrimental if the failed section supplies or exhausts a high air percentage from the system. Commonly, actuators are directly coupled to damper drives. Attention should be given to the heat transfer through the coupler and into the actuator. Heat sink couplers or protective shields are used to extend actuator life during elevated temperature exposure. Getting a pneumatic operator to pass the 250 degrees C requirement is usually not difficult and the price of this actuation is very economical. However, initial costs for compressors, piping, dryers and maintenance have encouraged some designers to choose electric actuators. Pneumatic actuators have great durability while providing affordable power. Installation and mounting is similar to electric but the overall envelope is generally smaller. Although not always most economical, the initial cost of electric actuation is less than pneumatic actuators. Electric units mounted in the air stream and requiring 250 degree C exposure for more than one hour may require enclosures such as thermal blankets in addition to heat sink couplers. Again, actuation selection depends on location and function.