Duct reducers for industrial dedusting

Duct reducers are used primarily to change the air speed inside the ducting of industrial dedusting systems. The exact shape and design directly influence the uniformity of air flow inside the ducting.

Group I       – small load

Group II     – regular load

Group III  – heavy load

Duct reducers are used primarily to change the air speed inside the ducting from one of two basic reasons:

  1. Decrease of air speed in the ducting
    Is often used to lower the pressure drop inside the extraction ducting. An example is the requirement of the production machines manufacturers to keep the intake suction speed at v = 30 m / s. We place the reducer directly behind the production machine socket and reduce the extraction air speed to the required v = 20 to 22 m / s. This allows us to optimize the ducting pressure drop.
  2. Increase of air speed in the ducting
    This is used with extraction applications where the dedusting cannot result in undesirable suction of the product. The air speeds are set low on purpose to about 7 – 12 m/s, sometimes even lower (dependent on the product granulometry). The reducer is used to increase the speed to the desired v=20 až 22 m/s.

A still-flow places with a minimal airflow should not form in the reduction or in the ducting in front or after the reducer – the extracted dust could form sediments. The Gidly company offers reducers with an angle of 30°.

Proudění uvitř potrubních tras s použitím průběžné redukce 30° - správně
Airflow inside a 30° reducer – no problem here
Proudění uvitř potrubních tras s použitím ostré redukce - špatně
Airflow inside a very sharp reducer – sedimentation spots occur

On the flow visualizations, there can be seen points with a slower air flow (blue paths) in the sharp reducer. The sedimentation of the extracted dust will occur in this place and that is an undesirable phenomenon in the industrial air extraction. The accumulated dust sediments in the ductings are often causes of baghouse ducting burnings. The correct flow is displayed at the reducer branch. The regular flat reducers are not even mentioned, although they are very often seen in air extraction systems in practice. We consider direct flat reducers as absolutely inappropriate.

The reducers change the extraction air speed, this is accompanied  with an undesired phenomenon – abrasion from the extracted material – especially with reducers inducing an increase of air speed. When selecting a reducer (SK I, SK II, SK III) proceed similarly as with branches and wyes.

We have prepared a basic chart for the use of reducers – depending on the extracted dust – by giving examples of the use of different groups for different applications.

Group I  Minimum of particles
Negligible abrasiveness
Welding shops dedusting
Hopper dedusting
Group II Medium amount of particles
Regular abrasiveness
Paper mills
Grinding shops
Coal processing plants
Group III  Large amount of particles
Highly abrasive
Coke dust
Foundry dust
Pneumatic conveying

Offered reducer variants

Dimension variants

Input dimensions DN 80 to DN 1250
Output dimensions DN 80 to DN 1250
Branch dimension DN 80 to DN 1250
Material width 0,5mm – 1mm plumber work – galvanized,
1,5mm, 2,0 mm, 3,0 mm welded

Material design – welded reducers
EN 11 – Sheet metal 11375 with selectable surface finish
EN 17 – Stainless steel 1.4301 for use in food industry
EN 17 – Stainless steel 1.4404 with increased chemical resistance
EN 17 – Stainless steel with increased chemical and thermal resistance

Surface finish for  EN 11 – 11375
Powder coated RAL1015 (ivory)
Powder coated RAL5010 (blue)
Powder coated RAL9001 (cream white)
Powder coated RAL9005 (black)
Powder coated RAL9006 (silver – aluminium)