In case of insufficient intensity of airflow check following sense of rotation; remember, that fan with radial rotor, when spinning in wrong direction, pushes out some amount of air from circulation spinning speed and tension of belts determine intensity of airflow using Pitot head determine static pressure of air suction and blow-out.
The difference between static pressure of air suction and blow-out determines static pressure of fan.
Check, if tension and pressure answer to values from specification.
If tension is low and pressure is equal or higher than in specification the causes of unstable work are connected rather with a machine, than with fan.
In this case check losses of tension in circulation, but at the same time control the static pressure of most important parts of machine.
If intensity and static pressure are low then there is a problem with a fan and accompanying devices
In this case
✔ check for presence of foreign bodies
✔ check if some flexible connections are damaged (maybe they are cause of narrowing of air channels)
✔ check leaking
✔ check if the fan has a proper suction measuring nozzle
✔ check for possible obstacles in air sucking (curves, rapid changes is airflow direction)
✔ check for possible obstacles at air outlet (curves, rapid changes is airflow direction)
Change of rotation speed
Intensity changes relatively to rotation; Intensity V = V1 x (n/n1)
Changes of pressure: Pt = Pt1 x (n/n1)^2
Changes of power: P = P1 x (n/n1)^3
If the noise comes from movement of airflow, the cause of noise is connected with foreign bodies laying in suction point or air outlet. The solution is to remove them.
But more frequent the cause of noise is connected with inappropriate selection of fan.
In this case we suggest to replace the fan with other one, which is more quiet (usualy with bigger diameter and lower speed) or use some silencing material.
If noise is of mechanical origin the cause is connected with physical contact between moving parts, wrong bearing or vibrations of metal sheets.
If noise is of electric origin the cause is connected with eccentric between rotor and stator or vibrations of winding.
In each of these cases we suggest using antivibration supports (pendulum-type vibration damper supports) and antivibration connections made of rubber, both in suction point and air outlet.
Vibrations can appear because of lack of balance or inappropriate construction of supports or because of both reasons.
The construction can be strenghtened or change its resonance grequency adding some ballast.
Very effective solution is to use antivibration supports (pendulum-type vibration damper supports).