Chapter 2

2.1.3 Circular ducts made of galvanised steel Sheet quality

For the manufacture of galvanised air ducts, sheet steel is used with anti-corrosion zinc-based coatings, applied using the Sendzimir process, in the qualities:

  • DX51D Z 275 MAC with a two-sided zinc coating of 275 g/m² according to triangulation test (average thickness of 20 microns per side). Sheetquality/zinc quality according to NEN-EN 10346, tolerances according toNEN-EN 10143.
  • DX51D ZMA140 AC with 140 g/m² double-sided zinc coating according to triangulation test (average thickness of 10 microns per side). Sheetquality/zinc quality in accordance with NEN-EN 10346, tolerances inaccordance with EN 10143. Sheet thickness

The galvanised air ducts are executed with a sheet thickness which is dependent on the diameter, as specified below. Based on the diameter the minimum sheet thickness for standard construction applies:

The thickness of the sheet used for fittings depends on the diameter. Based on the diameter, the minimum sheet thickness for standard execution applies: Connection in pipes

The connection in the spiral wound belt is carried out in a flat flange, where sufficient stiffness and airtightness are obtained. Connection in fittings

The connection of the seams in fittings is executed in such a way that sufficient stiffness and airtightness is obtained. This connection is performed by welding or flanging. Damage to the zinc layer, which could cause rust, should be carefully touched up with an anti-corrosion paint. Length of pipes

Pipes are supplied as standard in lengths of 3000 or 6000 mm. For technical reasons, the length is in principle not less than the diameter of the pipe with a minimum length of 300 mm. Diameters

The pipes are produced in the standard diameters that are indicated in NEN-EN 1506, namely 63 - 80 - 100 - 125 - 160 - 200 - 250 - 315 - 400 - 500 - 630 - 800.

- 1000 and 1250 mm. Additional sizes mentioned in the standard are: 150 - 300 - 355

- 450 - 560 - 710 - 900 - 1120 mm. Bends

As far as the form is concerned, bends are manufactured as standard with a radius measured over the centre of the bend and equal to the diameter, with the exception of diameters 63 and 80, for which the radius is 100 mm. Standard bends are made in angles of 15°, 30°, 45°, 60° and 90°, in a pressed or segmented version with a tolerance of ± 2°. Segment bends ≥45° consist of a minimum of 3 segments. Adapters

Adapters can be symmetrical or asymmetrical and have a top angle of minimum 15° and maximum 60°. For pressed adapters the maximum angle may be 90°. Symmetrical adapters are used as standard. Branches

A branch (split off from an ongoing main duct) can be established by means of a:

  • saddle piece, in combination with straight pipe;
  • T-piece, as a complete fitting;
  • cross-piece, as a complete fitting; and can be executed as standard inangles of 90° and 45°. Designs with an angle < 45° should be avoided fortechnical reasons Splits

A split is a division of a main duct into two continuous ducts. It can be accomplished by means of a:

  • trouser piece;
  • inverted T-piece.

In the case of a trouser piece, the split can take place at an angle α= 90° or 60°. With an inverted T-piece, the split takes place at an angle α= 180°. Connectors

These find their standard application at:

  • connections between pipes; This fitting, made of the same material as the pipes and fitted with abumper, makes an internal connection possible.
  • connections between fittings; This fitting, made of the same material as the pipes, is smooth and makesan external connection possible.

The size of the insertion length of the fittings is attuned to NEN-EN 1506. For the overlap length the following minimum lengths have to be observed:

The connectors are fastened by means of self-drilling parkers and are finished by using:

  • Synthetic rubber tape (= self-vulcanizing shrink tape)
  • PVC tape only for exhaust ducts;
  • Alu-tape only for exhaust ducts;
  • linen tape only for exhaust ducts;
  • reinforced PE tape with acrylic adhesive;
  • two component tape.

The mentioned tapes should be applied according to the recommendations of the supplier. When using circular fittings, provided with a rubber seal (so-called "Safe"), the finish with tape is normally not required when these are installed only once.
For roof ducts, the weather / UV resistance of the sealing material to be used must be taken into account. Adjustment valves

Adjustment valves are manually adjustable and serve to adjust an installation. Perforated valve blades should be avoided. See 3.2.4. Adjustment valve – circular for a detailed description. End caps

The caps are made of the same material as the pipes. Tolerances

The maximum tolerance for the length of a duct is ± 0.005 x L.
The tolerance for diameters is shown in the following table.
The maximum tolerance for angles is ± 2°.

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