Model CD1818-A is an opposed blade volume control damper with 3V style Blades. It regulates the flow of air inside a duct or air handler or other air handling equipments it may be used to cut off the air to an unused room or to regulate the air in different parts of the building depending upon temperature, climate control, occupancy etc. Its operation can be manual or automatic. Manual dampers are turned by a handle on the outside of a duct. Automatic dampers are used to regulate air flow constantly and are operated by actuators which in turn are controlled by a thermostat or building management system.