If your client wants to know the airflow rate of our silent fans (or any fan for that matter) in CFM (Cubic Feet per Minute), firstly you can remind them that South Africa converted to the Metric (or SI) system in the 70's.
In accordance with the "Systeme International d’Unites" (SI system), volumetric flow rate (airflow) is used in South Africa, using the SI unit of cubic metres per hour (m³/h). The SI unit can easily be converted to cubic feet per minute (CFM): One m³/h is ~0.589 CFM and one CFM is ~1.699 m³/h.
For example, our (older) 150 silent fans have two settings, with the quietest one (28dB) using 0.22A (46W). This moves air at the rate of 520 cubic metres per minute. Using the above formula, 520 * 0.589 = 306 CFM (approx). The slightly louder (32 db) – but more powerful – setting uses 0.27A (58W), moving air at the rate of 650 cubic metres per minute. Using the above formula, 650 * 0.589 = 383 CFM (approx).
Our new 200mm fans are a bit different in that they require two reducers to fit the 150mm pipes that go with our CO2 lasers, and they do not have adjustable speed. They are still relatively quiet at 43dB, and use 0.53A (about 130W) while moving air at 900 cubic metres per hour (m³/h).
Fairly critically, these types of fans do require a bit of maintenance. They need to be kept clean because of the burnt material that flows through them. And while cleaning, the shaft retainer nut should be checked for tightness. You will need to undo the hose clamps to see inside the fan.