Cfm is a misleading figure, ask the manufacturer for the the pump’s performance curve chart. It will state the pump’s flow rate at various vacuum depths, this is the information you want to know. Two different brand/model pumps can have an identical cfm rating but their flow rates at a given vacuum depth can differ.
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Absolutely right
@spdking gave a nice explanation of this some time ago
Reason I always recomend the big brand vacuum pumps for laboratory use and not havc pumps
Leybold trivac and Edwards M lines have good curves
Even Alcatel,Welch and pheiffer do well
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Ive had a few of those tbey came with our wiped film skids years ago, always sounded like they were gonna blow up. I just tossed tbem and out a real ohmp on there