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Ventilation Dampers - Classification

Dampers in ventilation systems may be classified through function, construction or leakage class.

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ventilation damper

Classification by Function

Dampers may be classified according their functional tasks in the ventilation system:

  • adjustment
  • closing, running
  • closing, smoke
  • closing, fire
  • overpressure
  • modulating

Classification by Construction

  • plates
  • membranes

Classification by Leakage Class

  • based on BS EN 1751:1999

The leakage class determines the acceptable air leakage through the damper with a 100 Pa pressure difference.

  • class 0 - No requirements
  • class 1 - less than 0.2 m3/s per m2 valve area
  • class 2 - less than 0.04 m3/s per m2 valve area
  • class 3 - less than 0.008 m3/s per m2 valve area
  • class 4 - less than 0.0015 m3/s per m2 valve area

The air flow rates through the dampers at 100 Pa are in general available from the manufacturers catalogs.

1 2 3
Adjustment x
Closing, running x
Closing, smoke x
Closing, fire x
Overpressure x
Modulation x

Calculating Leakage Air Flow Rate through a Closed Damper

The leakage air flow through a closed damper can be calculated if the the difference pressure through the damper and the leakage air flow rate at 100 Pa (manufacturer data) through the damper is known:

ql = q100 (dpl / 100)1/2                           (1)


ql = actual volume flow per m2 valve area (m3/s / m2)

q100 = volume flow at 100 Pa per m2 valve area (m3/s / m2)

dpl = actual pressure drop through the valve (Pa)

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