What is a flow-regulator

The different branches of ventilation or air-conditioning ducting networks can be subject to variations of airflows and pressure. As a result, it is necessary to balance the different branches in order to achieve the desired air supply or extraction. The balancing process can become increasingly difficult as the number of branches and number of diffusers increases.

Constant flow regulators can offer a simple and reliable way of resolving such problems and can provide precise regulation that ensures hygiene and thermal comfort for the occupants while optimizing the performance of fans and of the HVAC system as a whole.

What is a flow-regulator?

A flow regulator is an aeraulic element placed inside the ventilation or air-conditioning duct. It is calibrated to the requested airflow and will maintain a constant flow over a large pressure range. It can be used both in extraction or supply air ducts.

How does it a flow-regulator work?

The flow regulator is composed of a flap which constantly regulates the available cross section of the air passage according to pressure variations upstream and downstream of the regulator.

When the difference of pressure increases, the flap reduces the air passage section and inversely, when the pressure decreases the flap opens wider.

The flow regulation is factory calibrated at a requested airflow, but it can also be adjusted on-site according to the requested airflows. In the case of the RDR, there are scale markings on the front side of the regulator.

The flap will always return to its set position by return spring action.

What are the different types of flow regulators?

There are 3 types of RDR flow regulators:

  • Low pressure = RDR LP: The pressure range is between 20 and 100 Pa
  • Standard RDR: The pressure range is between 50 and 250 Pa
  • High Pressure = RDR HP: The pressure range is between 150 and 600 Pa


The flow regulator is simply fitted into a vertical or a horizontal duct. In a horizontal duct, respect the « DOWN » sign indicated at the front of the product. A seal ensures the airtightness of the installation.

When the flow regulator is installed close to a diffuser, the minimum distance between the diffuser and the regulator must be at least one diameter in extraction mode and 3 diameters in blowing mode.


The flow regulator must remain accessible to help its maintenance.

Tests standards

The aeraulic characteristics of the RDR meet the requirements of the norm NF E 51-776-2.

The flow regulators are characterized by their sound power levels Lw dB(A) according to the difference of pressure, measured at the duct.

The tests are carried out according to the standard NF EN ISO 3741 and NF ISO 5135.