Picture the worst moment for a noise to show up: a drying-systems OEM has just commissioned a brand-new dryer at its customer's plant, with everyone standing around the machine on acceptance day. Two process fans move the air through that dryer — a 75 HP, ~750 mmWC, VFD-driven high-pressure fan and its sister. The fans can't quietly come offline for a week of investigation; the whole new plant is waiting on them. We'll call the OEM the Builder.
Within days of start-up, both bearings on one fan began making a loud, unusual noise. The site did the sensible first thing — topped up the grease — and the noise stayed. Then, two weeks later, the second fan did exactly the same thing. Grease again; noise again. Now it wasn't one odd bearing, it was a pattern on a new plant, with the end customer asking for the bearings to be replaced "at the earliest." A noise nobody can explain, on equipment nobody can switch off, in front of the customer — that's the problem the Builder brought to us.
Start with what wasn't wrong. Before this dryer ever shipped, both fans were performance-tested in-house on our 200 HP VFD test rig, to the IS 4894 / AMCA 210 method — each met its duty, with the test reports and curves on file. On site, when our engineer pulled the removed bearings and checked them, they came out not rusty — no lubrication or contamination story, and no "bad batch of bearings" story either. The fan was on-spec; the bearing was sound. What was left was how the bearing had been fitted — specifically, its internal running clearance. This was a commissioning/assembly setting, not a manufacturing or design defect in the fan.
The educational root cause (generic 5-Why):
Our engineer had already stopped the immediate pain — bearings replaced on both fans on site, run up, and the noise was gone, trial run satisfactory. But the durable fix for the cause isn't a better bearing; it's correct internal clearance, set and verified at assembly. We set the clearance right, and the fans ran clean.
Because the fans were rig-tested to their duty before dispatch, when a later airflow question came up we could hand over the same test report and curves and show the fan met its specification.
Honest note: this case is reported on what was measured — the fix was verified by an on-site trial run and formal closure. We don't publish vibration or temperature deltas we didn't record.
A fan that turns noisy right after commissioning — and shrugs off fresh grease — is usually telling you about how it was fitted, not whether the fan is any good. Here the fan tested on-spec and the bearing was sound; the answer was in the running clearance set at assembly. The value isn't only replacing the part; it's proving what's actually fine, finding the real cause, and closing it so the next fan doesn't do the same thing.
Running a fan that went noisy soon after start-up, and a grease top-up didn't fix it? Send us the details for a root-cause investigation — you'll get a written corrective action, not just another bearing.
— Jitamitra Electro Engineering · Technical Services
Engineered for Every Application.
Flow, static, gas temperature, application — or attach a spec, GA drawing or a multi-fan schedule. Engineer to engineer.
ISO 9001:2015 quality system · performance-tested to IS 4894 / ISO 5801 / AMCA 210 method · witnessed FAT on request, at no cost.
*For our standard range, additional days required for special projects
