The Young 4081 Round pneumatic damper is ideal for pressure dependent VAV zone control, air inlet, and exhaust vents, although it may be used to control air in any branch duct. Damper is designed to work with low pressure systems up to 1″W.C., and is driven by a 5 to 10 lb. spring range pneumatic actuator installed in the factory. Damper operation is direct-acting, normally closed. The actuator can be operated from a pneumatic thermostat or static pressure controls. Units are simple to understand and install while providing the comfort of modulating VAV. This damper is perfect for retrofit. Actuator change is quick and easy and the noise level and air velocity changes are kept to a minimum. The minimum position stop is easily adjusted.