Clean at the works, shaking at site: three installation faults behind a cone rub

At-a-Glance

The Setup

The fan went through an OEM partner to a plastics-machinery plant in Gujarat — a straightforward centrifugal blower on a new installation. The kind of unit nobody is supposed to think about once it is bolted down and running.

Which is why a vibration complaint on a new install carries weight out of proportion to its size. Vibration is how an installation quietly destroys itself: it walks fasteners loose, chews bearings, cracks the ductwork the fan is bolted to. And when it appears in the first weeks of life, the conclusion on the shop floor is the uncomfortable one — you sold us a bad fan. At stake was the OEM's credibility with their end customer, and ours with the OEM.

The Complication

The complaint named two symptoms in one line: cone touching, and vibrations.

"Cone touching" means the inlet cone — the bellmouth feeding air into the impeller eye — was fouling the rotating shroud. A running-clearance failure: the gap between a stationary part and a spinning one had been lost.

Here is the trap. A cone rub is itself a vibration source, so the obvious path was to treat the rub as the disease: an out-of-true impeller, a fan that came out of the works wrong. That path is wrong. The rub was a symptom — something had pushed cone and impeller out of concentricity, and it had happened after the fan left our floor.

The Diagnosis & Fix

We worked it in the only order that settles an argument like this: prove or disprove the fan first, then look outward.

Step one — rule out the fan. The blower had been run and measured before despatch: V 2.8 / H 2.4 / A 3.8 mm/s. Under ISO 14694 for a rigidly-mounted fan, BV-3 accepts up to 4.5 mm/s (alarm 7.1, shutdown 9.0). Every axis sat comfortably inside acceptance. Whatever was shaking at site had been acquired after despatch.

Step two — read the site. Seven photographs came with the complaint, and they did the rest of the work. Three faults, all at the installation stage:

1. No proper foundation. The blower was not bolted down — anchor bolts had simply not been used. An unrestrained base cannot absorb running forces; it amplifies them.
2. The transit spacer was still fitted. The yellow-painted C-spacer that supports the inlet and outlet flexible flanges during transport had never been removed before start-up — hard-linking the fan to the very ducting it was meant to be isolated from.
3. Misalignment. The assembly centreline and the fan centreline did not match: the direct mechanical route to a cone rubbing an impeller.

Cause chain: spacer left in, no foundation bolts, misalignment → running clearance lost at the cone → contact and unrestrained running forces → high vibration at site, from a fan demonstrably within tolerance at the works.

The Result

Reported honestly, so it is worth something to you:

• We proved the fan was good at despatch. The works record — V 2.8 / H 2.4 / A 3.8 mm/s, inside BV-3's 4.5 mm/s acceptance — is objective evidence the machine was within tolerance when it left us.
• We found three specific, correctable installation faults in the site photographs: transit spacer not removed, no bolted foundation, assembly-to-fan misalignment.
• We issued the corrective actions: remove the yellow C-spacer from the inlet and outlet flexible flanges; provide a properly bolted foundation; correct the alignment of the assembly to the fan centreline.
• We changed our own process. This case is why transit-spacer removal, anchor-bolt sign-off and a running-clearance check are commissioning-checklist lines — and why the works vibration certificate travels with the fan, so any site can separate a works issue from an erection issue immediately.
• What the record does not confirm: our file documents the diagnosis and the instructions issued. It does not contain a post-fix vibration re-check or a customer closure sign-off. We will not claim an outcome we cannot evidence. What we stand behind is the finding and the corrective action delivered.

The Takeaway + Call to Action

The lesson is a diagnostic discipline, not a fan fact. When a new installation vibrates, the fan is the last suspect — but only if you can prove it. That proof has to exist before the argument starts, which is why a works vibration record travelling with the machine beats any amount of debate on site. Get the certificate, then go and look at the foundation, the transit restraints and the alignment — the photographs usually give you the answer before anyone opens a casing. And if a spacer painted bright yellow can survive to first start-up, so can yours: make its removal a signed line, not a memory.

We service centrifugal fans and blowers of any make — vibration investigation, alignment and running-clearance checks, balancing to ISO 21940, and performance testing to IS 4894 / ISO 5801 / AMCA 210 method. If a fan on your plant is shaking and nobody can tell you why, we will come and find out.

— Jitamitra Electro Engineering · Technical Services

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