This 331 Number 6 Pneumatic Damper Actuator for tandem mounting is piloted by a positioning relay which is mounted on a sturdy angle iron frame. This damper actuator has a spring range of 8 to 13 psig, an adjustable spring span and start point and a 1/8" NPT female air connection. This damper actuator is recommended to position inlet vanes on fans or large dampers that use a jack shaft.