What's measured
The fan is the engine of an LEV system, and like any engine it fades. Fan decline is rarely dramatic - it is a slow loss of airflow that creeps across every hood at once, which is exactly what makes it dangerous.
The short answer
The fan is the engine of an LEV system, and like any engine it fades. Fan decline is rarely dramatic - it is a slow loss of airflow that creeps across every hood at once, which is exactly what makes it dangerous and easy to miss.
The detail
A fan moves less air as it wears, and it wears in several ways at once. Drive belts slip or perish, bearings tire, and the impeller wears down, corrodes or clogs with dust so its blades no longer bite the air the way they did. Changes elsewhere - a new damper setting, an extra hood spliced in, a loading filter - shift the fan's operating point and pull it away from the duty it was set up to deliver. None of these announce themselves; the motor note barely changes, so the loss is measured, not heard.
Because the fan sits at the heart of the system, its decline pulls down airflow everywhere at once. Every hood loses a little capture together, so nothing looks obviously broken - there is no single dead hood to point at. A fan running backwards after a motor rewire, or freewheeling on a slipping belt, can look and sound perfectly healthy while moving a fraction of its designed air. Reversed rotation is the classic trap, because a backward-spinning centrifugal fan still moves some air and still sounds busy.
What it means for you
At a thorough examination the examiner measures airflow and static pressure and compares them against the fan's commissioned duty, checks the direction of rotation, inspects belts and bearings, and looks at the impeller for wear and dust build-up. The whole point is to find the gap between a fan that runs and a fan that performs - two very different things that sound identical from across a workshop. Belt tension and bearing play are quick to check and quick to put right, but only if someone looks for them rather than trusting the hum.
Because the loss is gradual and system-wide, it is precisely the kind of drift that benchmarking against commissioning figures catches early, and precisely the kind that a running fan hides from an untrained eye. The reassuring hum of a motor is not evidence that the air is still being moved at the rate the system needs.
The service behind the guide
We measure airflow and static pressure against the fan's commissioned duty and check rotation, belts, bearings and the impeller, with a clear report and remedial actions.
Questions
Drive belts slip or perish, bearings tire, and the impeller wears, corrodes or clogs with dust. Changes elsewhere in the system, such as a new damper setting or a loading filter, also shift the fan away from its designed duty.
Because the fan sits at the heart of the system, its decline lowers airflow at every hood at once. There is no single dead hood to notice, so nothing looks obviously broken.
Yes. A fan running backwards after a rewire, or freewheeling on a slipping belt, can look and sound healthy while moving only a fraction of its designed air.
Airflow and static pressure against the commissioned duty, the direction of rotation, the belts and bearings, and the impeller for wear and dust build-up.
By benchmarking the readings against the commissioning figures. A slow, system-wide drop in airflow shows up as falling numbers long before anyone notices contaminant escaping.
Phoenix Duct Clean · by the numbers
We measure airflow and static pressure against the fan's commissioned duty and check rotation, belts and the impeller, with a clear report.