Almost all guillotine dampers require a seal air blower system to make them "0" leakage devices. The exception would be the goggle or spade dampers where the whole blade extends to atmosphere in the closed position.

The seal air fan essentially creates an air barrier around or within the closed blade at a pressure above that of the flue gas. Usually the fan is selected to operate at a static pressure of 2 to 5" WC above the normal operating system pressure.

When the fan is not in operation, it is usually protected by a motorized or manual valve located between the fan and damper. If the valve is not "gas tight", corrosive gases can enter the fan and cause failure if the materials of construction are not satisfactory for the application.

It is not unusual for the customer to specify a standby fan just in case something happens to the primary fan. This "scheme" can get cumbersome and very expensive.

Roughly it looks like the drawing shown below:

Because the fans are introducing ambient air into the damper, a strong possibility of acid condensation can occur. If the damper materials are not selected to withstand the acid attack, obviously we have "more problems". Some recent specifications have called for heating systems to minimize the possibility of the flue gases condensing upon contact with the seal air. This can be a "real barrel of snakes" and we hope the trend "dies a natural death". Not only is the system further complicated, but also the power consumption and space requirements become unreal.

Roughly, it looks like the following: