Here are the numbers. Two tests, both on Mattei rotary-vane units, both run from commissioning to the end of the ~500-hour run-in window:
55 kW unit, Intertek (independent, third-party laboratory). Specific energy measured at commissioning and again at approximately 500 hours of operation. The improvement: 3.8%.
75 kW unit, Mattei in-house parallel test. Same protocol, same window. The improvement: 5.5%.
So the typical run-in gain on a Mattei vane compressor sits in the 3–6% range, depending on machine size — measured, repeatable, and externally verified on the 55 kW unit by an internationally accredited testing laboratory. The mechanism is straightforward: in the first 500 hours, the blade flanks polish smooth against their rotor slots, internal friction drops, and the power drawn for a given delivered flow decreases.
Three precisions are worth stating, since this is the first time these specific numbers have been put forward publicly in this campaign.
The improvement is in specific energy — the kilowatts drawn per cubic metre per minute of delivered flow — not in raw flow. The machine doesn't get bigger; it gets more efficient.
After the 500-hour run-in, the curve doesn't keep climbing. It locks in and holds. We've followed units across many years of service: post-run-in specific energy stays flat. There is no continued-improvement claim, and there is no decline either.
The gain comes from the blade flanks polishing in their rotor slots — not from the tips bedding into the stator wall. The tips never contact the stator at running speed. Hard tip contact at speed under operating pressure would seize the surfaces; the hydrodynamic oil film is precisely what keeps them apart.
Now set those numbers against a clearance-sealed machine. At zero hours, a good screw and a vane are broadly comparable on specific energy. Mattei has never rested its case on a dramatic day-one gap. But by around 500 hours the vane has moved 3–6% ahead, before the screw has even begun to age. From there the two technologies move in opposite directions: the vane holds flat, the screw declines as its clearances open. The gap between them doesn't close across the working life. It widens.
That's the case in measurable terms. The screw side of the curve still needs the kind of industry-wide independent testing the original article calls for. Until then, the inference from manufacturing tolerances and the overhaul schedule does the work.
The full sealing-physics case→ https://www.linkedin.com/pulse/why-screw-compressor-efficiency-declines-over-time-rotary-contaldi-usqkf/