Air compressor resonating/ringing sound

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hudstr

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So I got an air compressor at an auction for probably too much money and it makes a weird resonating sound.

It is a California air 9010d and it has an air dryer built in, which is why I bought it. I couldn't test it because the pressure regulator switch and gauges were broken, I'm guessing it got knocked over and broken. I've replaced that but now I have the weird sound issue.
9010D_0_600.jpg


The sound only occurs when it is building pressure into the tank. In the video it only happens after a few seconds of the motor spinning, I think this is because the electric solenoid is open at startup and closes after a second. I've tested it every way I could think of to isolate the sound. It still happens with just the compressor unit plumbed directly into the tank so I am confident it either the compressor unit, check valve and solenoid switch, or the tank itself.

Has anyone seen anything like this? My current ideas are the oil-less pistons and cylinders are worn and are resonating when under load building pressure, or the check valve is faulty somehow, or the air going into the tank is causing the resonating. Its hard to tell where the sound originates from because the tank just amplifies everything.

Does this actually matter? Probably not because I don't think it will explode, but I would like an ultra-quiet compressor to be ultra-quiet, and not a musical instrument.
 
That sounds like a bearing that is in some serious need of oil.
 
Sounds like a bearing. As soon as it gets the slightest bit warm, it starts to yell "replace me!"
 
Yep, sounds like worn dry bearing.
 
That was it, one of the connecting rod bearings makes noise. I wrote that off at first because I would have thought it would make the noise at all times but it only happened when it got up to speed under load I guess.
 
I've changed the connecting rod bearings but it still made the exact same sound so I tore it down again to the rotor bearings but they seemed fine so I put it back together again. One of the connecting rod bearings was on its way out but that wasn't the source of the noise. I'm still convinced it is somehow resonating when it enters the tank. The sound isn't present when you start from an empty tank, and it grows louder as more pressure builds, and when you start and stop it will run for a second before the sound returns.

I wish I had one of those portable air tanks so I could plumb it in really easily to see if it is the tank but I don't have one.
 
To me, that sounds like an air leak ,once it build up some pressure it comes on, I wanted to mention it when you first posted it because it sounded like loud whistle.
 
I took apart the last thing I didn't touch which was the check valve and solenoid. Didn't seem like anything is wrong with it, there was a indented witness mark where the rubber piece seals but I don't think that would be an issue. I reinstalled it and the sound is a bit quieter so repositioning the check valve made it quieter. I think I'm done messing with it.

For fun I stuck a boroscope into the tank and there is only a spec of surface rust. I would have hoped it be like this considering the air goes through a column of desiccant before going into the tank.
20220128190818.jpg
 
can you disconnect the compressor from the tank, and see if it still happens while venting to air. Do it before the check valve.
lets isolate one thing at a time.
if it still happens, I would ask California air..

I wonder if you have a bad teflon ring.
 
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