Advantages: 

• Tighter sealing than double louvers.  This means a smaller seal air fan can be used which will result in a cost savings due to lower operating power requirements.. Fan horsepower in only 10-20% of double louvers.
• Shorter flange to flange dimension.  The damper also operates completely within the Guillotine flange to flange dimension.
• Seal Air System can be tested while the system is on-line.  This assures all seals are working.  This can not be done with double louvers.
• Lower operational and maintenance costs.

Disadvantages:

• Clearance is required above, below or to one side of the duct for the drive frame.
• Not recommended for flow modulation.
• Additional structural supports required.

Double Louver Damper

Advantages:

• Can be used for flow modulation in addition to tight shutoff.
• Minimal clearance required outside the duct.

Disadvantages:

• Longer flange to flange dimension is required and clearance is required in the duct adjacent to the flanges.
• Higher operation costs due to larger seal air fans.