Those numbers are what close the deal. For most of the technology in service today, they're also the best the machine will ever perform.
We see the proof of this constantly. A customer asks us to replace an ageing screw compressor. We start by measuring what the old machine actually draws — real amps, under real load, on site. Then, to size the replacement, we use the screw's declared flow: the output stamped on its data sheet the day it left the factory, often ten or fifteen years ago. We pick a vane compressor to deliver that full catalogue figure and quote the saving against the customer's current bill.
Almost every time, the real saving lands higher than we quoted.
The reason isn't that our machine beats its own specification. It's simpler, and more telling. That old screw stopped delivering its catalogue flow long ago — years of wear had eroded its real output. The plant's true air demand had been sitting below the catalogue figure, and the tired screw was only just covering it. So by sizing to the data-sheet number, we install a machine comfortably larger than the real demand; it does the same work in fewer running hours, and the bill falls further than we promised.
In other words, we compare against the screw's very best day — the day it was new — and still beat it. The gap that quietly hands the customer a bonus saving is nothing more than the flow a screw loses as it ages. That gap — between the number a compressor is sold on and the number it actually delivers — is the whole story. On day one the two are the same. For most of the technology in service, day one is the closest they ever get.
Over this series we'll walk through exactly why, using wherever possible the screw industry's own research and the laboratories that have measured it: City University London, Fermilab, COMOTI, Texas A&M.
Read the full engineering case → https://www.linkedin.com/pulse/why-screw-compressor-efficiency-declines-over-time-rotary-contaldi-usqkf/