Three things decide whether a fan does in service what it did on the drawing: how well the impeller is balanced, whether its aerodynamic performance was actually measured, and whether the coating and the motor were chosen against the real air rather than against a default.
Impeller balancing
Every welded impeller is dynamically balanced in two planes on a hard-bearing balancing machine before it is assembled into a casing. The default acceptance grade is G6.3 as defined in ISO 21940-11. Where the fan is mounted on a structure that will carry vibration into occupied space, or where the fan runs above 1 800 rpm, we balance to G2.5 instead.
The grade is a permissible residual unbalance per unit of rotor mass at the operating speed. It is not a quality slogan: halving the grade number halves the permissible unbalance, and on a large impeller that is the difference between a bearing that lasts its rated life and one that does not. Balancing reports are filed against the serial number and can be reissued.
Aerodynamic testing
Performance is measured on a ducted test rig following the method described in ISO 5801, which defines the standardised airways, the flow measurement and the pressure tappings used to produce a fan curve. Because the test method is standardised, a curve measured this way can be compared with one from another manufacturer; a curve produced on a bespoke rig cannot.
Sound power is determined using the ISO 13347 method and reported in octave bands, stated separately for inlet, outlet and casing radiated. We give you all three because the value you need depends on where your acoustic problem is.
[Client to confirm whether the test rig is accredited by a third party, and by which body, before any accreditation is claimed on this page.]
Coating and material selection
Standard construction is mild steel with a powder-coated finish. That is the right answer for clean, dry air and the wrong answer for most extract duties. For humid, saline, solvent-laden or acidic air we select from hot-dip galvanised, stainless, epoxy and specialist coating systems against the analysis you supply. For abrasive duty the question is different again: coating will not survive particle impact, so the answer is a replaceable bolted wear liner.
Motor selection
Motor frame sizes follow IEC 60072, which keeps a replacement sourceable anywhere. Enclosure rating, insulation class, duty type and any classified-area requirement are set from the installation, not from a default. Where a variable speed drive is used, we confirm the cable length, screening and bearing arrangement at order — long unscreened drive cables are the most common cause of bearing currents we are asked to investigate.
What to send us
Volume flow, static pressure at that flow, air temperature, altitude, the airborne contaminant if there is one, and where the fan is mounted relative to occupied space. Six lines of email is usually enough to get a sized model back with the operating point marked on its curve.