Opposed Blade Damper (OBD)

Opposed Blade Damper (OBD)




The OBD opposed blade dampers are commonly used in supply and exhaust air systems to achieve volume control.

Located directly behind the supply air or exhaust air outlet, the damper should only be used for fine trimming of air quantities (no more than 37 Pa) if quiet conditions are required.


Manufactured from aluminium or zincanneal construction with a matt black finish.


When an opposed blade damper is closed or partly closed, it restricts the flow of air by decreasing the available area and in doing so, increases the pressure drop and reduces the amount of air passing through. It also increases the noise level.

As a guide, closing a damper to the point where the area is decreased to 70% of fully open, will double the pressure loss and adds approximately 7dB to the NR level.

Closing the damper to the point where the area is reduced by 50% increases the pressure loss to four times the full open value – and could add 20dB to the NR level.


Marine or hospital grade.