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Iris dampers for Circular Ductwork - accurate and quick airflow control

Iris dampers for circular ductwork                  

What is an iris damper? 

Iris damper is a balancing damper used for adjustment and measurement of airflow in the circular ductwork. Its name  “iris” comes from the special construction of the regulation plates mechanism - iris-like - which works similarly to the camera lens shutters, i.e. it minimises the overall dimensions of the damper orifice (opening). 


Quick, silent and efficient – these are the distinctive features of the GBL iris dampers used to adjust and measure air flow.
GBL iris dampers allow for quick and exact regulation and control of the airflow. They work very well wherever accurate airflow adjustment and individual control over the comfort conditions and parameters are required.

Airflow measurement and adjustment = maximum comfort 

Balancing airflow is usually time-consuming and costly during the commissioning of the ventilation system. Linear choking (throttling) of the airflow used in iris dampers simplifies this operation to a large extent.

Iris damper with a spanner

Each iris damper is provided with a spanner for airflow regulation

Owing to the unique construction of the GBL dampers, the airflow may be measured and adjusted within the scope of a single device and a single process, providing a balanced amount of air to each interior. The result is a stable and comfortable microclimate.

Construction of iris dampers

GBL iris dampers are composed of a galvanized steel casing, lens-like regulating plates mechanism which regulates the air flow as well as regulating nut, regulating scale and a spanner (included) which allows to smoothly adjust the diameter of the opening.

Moreover, each iris damper is equipped with two types of connections to fit he air flow measuring unit (manometer).
As a standard, iris dampers are equipped with EPDM rubber gaskets which allow an airtight connection with ventilation ducts.  

Iris damper construction

What sets apart iris dampers from standard air dampers?

Traditional dampers increase the air flow speed along duct walls, which generates a lot of noise.
The iris-type closure of the GBL damper allows throttling of the airflow without causing turbulence or noise in the ductwork
. This allows achieving a higher flow rate and pressure than in a standard damper, without any noise within the ducts.  This solution is much simpler and cost-effective as there is no need to employ additional sound attenuating duct elements. Correct sound attenuation is achieved by proper installation of dampers in the ventilation system.  

For precise measurement and control of the airflow,  iris dampers should be installed in straight duct sections with appropriate spacing no less than:

1.     4 × duct diameter before the damper
2.     1 × duct diameter after the damper.

Using iris dampers is highly advantageous to ensure proper cleanliness of the ventilation system. Since it is possible to fully open the iris damper, cleaning robots can easily reach all duct sections connected by dampers of this type.

Iris damper 100% openedIris damper GBL closed

100% open position allows for easy cleaning, however, the damper cannot be shut closed completely
(the maximum closing ratio is ca. 25% of the nominal diameter orifice).


Advantages of GBL iris dampers:

1.    low noise in the ducts,
2.    easy installation,
3.    perfect balancing of the airflow due to the measuring and adjusting unit,
4.    easy and fast adjustment without the need for additional tools – uses a spanner (included) or an actuator (in a motorized iris damper version),
5.    exact flow measurement,
6.    gradual adjustment – manual, handle-operated, or automatic for versions fitted with the servomotor,
7.    damper construction allows easy access for cleaning robots.  

Iris damper leaflet
Iris Dampers - Benefits and Application
download file in PDF format