Advanced Valve Designs' LD style dampers are intended for use in HVAC systems and low pressure (<10" wc) industrial applications. 

http://www.advancedvalve.com/images/light-duty-damper.jpg

• These valves should be used in clean gas systems where particulate matter is not a concern. 
• These dampers offer light weight, economy and durability in low pressure systems.
• Standard material is carbon steel but are available in a wide variety of alloy materials (304 S/S, 316 S/S aluminum, etc.).