Function
A silencer is used in an air transport system to absorb and reduce installation noise so that permissible sound levels are not exceeded.

Material quality and thicknesses

For normal comfort ventilation, silencers are manufactured from the following materials:

• Rigid silencers:
  • Outer layer: Sendzimir galvanised steel;
  • Inner layer: perforated Sendzimir-galvanised steel;
  • Absorption/damping material: mineral wool, glass wool or polyester(usually 50 or 100 mm);
  • Coulis (optional): finished mineral wool sheets to prevent the fibres fromentering the air flow;
• Semi-flexible silencers:
  • Aluminium flanged flexible pipe;
• Silencer in duct:
• Plastic, polystyrene foam;
• Other choice of material, depending on the application, in consultationwith the supplier.

Connections
The silencer is available with circular and rectangular connections.

Dimensions
The available nominal dimensions of the intermediate silencers are standardised to NEN-EN 1505 (rectangular connections) and NEN-EN 1506 (circular connections) and can be chosen as shown in the tables for standard dimensions given in this Guide under chapters 2.1.1.6 (rectangular connections) and 2.1.3.6 (circular connections). They refer to the internal dimensions with a tolerance of +0 to -5 mm. The dimensions depend on the manufacture.
The length of a circular silencer depends on its function in the air duct system. The most common silencers are available in lengths of 300, 500, 600, 900, 1000 and 1200 mm.

Assembly instructions
Silencers must be fitted in accordance with the manufacturer's instructions. If present, these should at least comply with the requirements according to section 3.1.4.

Installation of semi-flexible silencers
A minimum bend radius results in a large pressure drop. The aim should therefore be to achieve as wide a bend as possible. For semi-flexible dampers, a minimum bending radius of R= d + 2 x insulation thickness should be observed.
Suppliers recommend a minimum bending radius of twice the diameter (d). Double bends should be avoided.

Insulation
Specifically in the case of fibrous material (internal insulation), seams and the like must be finished in such a way that the fibrous material cannot be carried away by the air current.

Sustainability aspects
Silencers with circular connections can be connected to the air ducts more efficiently than silencers with rectangular connections and contribute to the airtightness of the air duct system, if these fittings possess sufficient airtightness according to NEN-EN 15727.