Mechanihal CAV - constant air flow question

[martinakenic]

Can anyone explain how it works mechanical CAV (Manual) like

http://www.trox.es/---kvs-controlador-de-caudal-de-aire-/type-rn-a62db21c628cdb93.pdf

I know that have some aerodinamics force, but is it possible explain via formulas and sketch, How this device maintaining constant air flow, and how it look mechanic inside and pressure in this device.

Thanks!

 

[danw2]

Sometimes the story is right in the manufacturer's documentation:

The volume flow controller is a mechanical self-powered unit and works without external power supply. A damper blade with low-friction bearings is adjusted by aerodynamic forces such that the set volume flow rate is maintained within the differential pressure range.

The aerodynamic forces of the airflow create a closing torque on the damper blade. The bellows extends and increases this force while at the same time acting as an oscillation damper. The closing force is countered by a leaf spring that unrolls over a cam plate. The shape of the cam plate is such that a change in the differential pressure leads to an adjustment of the damper blade in a way that the volume flow rate is maintained almost exactly.