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About 3.5 weeks ago I bought a new vacuum pump (VEVOR 8 CFM Vacuum Pump 2 Stage). It's started sometimes making a rattling noise for a moment on start, like this morning. I also had a problem when I turned it off this morning, too, with the line still under vacuum, because a little while later I noticed pump oil being pulled up into the line - by the time I noticed, there was probably a tablespoon or two of oil pooled in the bottom of the hose. That also seems bad. It's not doing either thing right now or I'd attach video, but that also makes me think neither are expected behaviors. Is it bad practice to turn your pump off while under vacuum? Is clanking normal, somehow? Or like, should I return this pump or something? (I got the protection plan, also.) Kindof a shame, since it pulled a better vacuum than my previous pump.

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  • $\begingroup$ Unless the manual says otherwise, I would not expect this pump to have a problem starting against vacuum. I would agree with @Ariser about the seizing = broken. If you got the protection plan get it replaced - it could have just been one faulty unit out of 100s made. $\endgroup$
    – J. Ari
    Dec 20, 2022 at 15:20

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So for the oil being pulled into the line you can fit a trap.

As for the clanking you need to get that investigated - maybe a bearing is failing. Bearings fail for several reasons: overloaded, manufacturing defects or lack of lubrication. I would check for the last two.

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  • $\begingroup$ Well, the oil level is near the max (though this pump doesn't have the usual min/max markings on it). How would you check for manufacturing defects? And the pump seized up entirely for a few seconds yesterday, which, again, seems bad. $\endgroup$
    – Erhannis
    Nov 18, 2022 at 17:16
  • $\begingroup$ Oh also - I ran it for maybe 20-30 minutes and it went into (presumably) thermal shutdown. (Started back up again a minute later.) (This was particularly bad because oil started to flow back into the line, automatically.) How long do most pumps run for continuously? I was under the impression they're supposed to run a long time. $\endgroup$
    – Erhannis
    Nov 18, 2022 at 17:19
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I had a similar pump of this style. They are sold all over the globe only differing in the handle and the AC-plug. What you describe sounds like you have too much oil in the pump. If the oil is on max you risk the oil filling the operating volume. As oil can't be compressed the pump will receive heavy blows on every compression of the volume. This can produce the clanking sound and will move the oil to the high pressure side. Furthermore it will draw extra power from the motor.

Take out the surplus oil to have the oil level at the middle of the gauge-glass. Always take care the pump is standing on a perfectly leveled surface when operating otherwise the oil level across the housing will not be what you see in the gauge-glass. Always let the oil settle down some minutes after moving the pump around.

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  • $\begingroup$ Ah, good to know; thanks. The pump seized up entirely a few times, and I returned it. I'm pretty sure the oil was between min and max - probably closer to max, but still within bounds. My new pump started making a slight rattling noise, too, though it's not yet clear it's a symptom of anything. The only thing I'm doing that's likely to be weird is stopping the pump under vacuum, and starting it again under vacuum. Is it bad for the pump, to do that?? $\endgroup$
    – Erhannis
    Dec 3, 2022 at 3:22
  • $\begingroup$ If it seizes, it's broken. Something came loose and blocked. Starting against vaccum sholdn't be a problem for this type of pump. If the pressure at the suction side is low at startup the pump won't move much air but that's just physics. In fact startup should be easier then. Rattling noises to some degree seem to be common with these pumps. After all they aren't high precision machines. $\endgroup$
    – Ariser
    Dec 4, 2022 at 3:02

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