3/8" tubing making my pump noisy? Possible cavitation?

[JWFokker]

Now I realize Mag 3's are rather noisy as far as pumps go, but mine's fully muffled and doesn't vibrate at all. What I'm experiencing is a fluid noise coming from the pump itself. I know I should have larger ID tubing going from my reservoir to my pump to improve flow, but am I possibly experiencing cavitation as a result of it? I'm eventually going to be making a large acrylic tube reservoir for in the bottom of my case that will mount to the pump inlet, but if the 3/8" ID tubing at the inlet is definitely causing cavitation, should I put my watercooling setup on hold until I get larger inlet tubing to prevent damage?

[Kobuchi]

Try kinking the inlet tube for a moment. This will not increase water pressure on the suction side, but will reduce flow. If that reduces the sound, you can rule out cavitation.

[JWFokker]

It actually made no difference at all. The noise remained the same. What's odd is that if I position the pump higher, lift it up to the level of the reservoir and waterblock, still a couple inches below the radiator, it gets louder momenarily, like there's air being released from the pump but there isn't any coming out. It finished bleeding days ago and there's definitely no air in the pump.

[Kobuchi]

Raising the pump lowers water pressure (in this case weight of water) around it. Cavitation appears when pressure (usually at suction side) drops so much water vaporises. So it sounds clear enough your pump is cavitating, and lifting it just made that worse.

I guess you can eliminate the cavitation by increasing fluid volume in your system or by... Well, we're both over our heads *ack* so try Google and good luck.

[JWFokker]

I guess I'll be making that reservoir sooner rather than later.

[JWFokker]

Well it turns out in my haste putting everything together in my new case I mistakenly crossed my reservoir outlet and radiator inlet lines on the pump inlet and outlet respectively. My loop was going radiator-pump-reservoir-cpu instead of reservoir-pump-radiator-cpu as it should. Whoops. I didn't notice until I went to switch my zip ties for some hose clamps I got and said WTF? I guess pumping into the reservoir would explain things. I'm still going to make a reservoir for my pump inlet to attach to, but at least now I've got this taken care of. There's still a tiny bit of cavitation going on that I can barely hear (probably due to the 3/8" ID inlet tubing) but the reservoir is coming so I don't have to worry about it so much now.

[bobkoure]

Originally Posted by Kobuchi

Try kinking the inlet tube for a moment. This will not increase water pressure on the suction side, but will reduce flow. If that reduces the sound, you can rule out cavitation.

You meant "outlet", right? Increasing inlet restriction is going to increase the potential for cavitation...

[JWFokker]

It's all sorted out now. I still need larger inlet tubing or ideally a reservoir that will attach to the inlet of the pump, but until then, paying proper attention and putting things where they're supposed to be has done the job well enough.

[Kobuchi]

Originally Posted by bobkoure

You meant "outlet", right? Increasing inlet restriction is going to increase the potential for cavitation...

I did mean inlet. It's a test to rule out cavitation, poorly worded.

[bobkoure]

Originally Posted by Kobuchi

I did mean inlet. It's a test to rule out cavitation, poorly worded.

So, poorly worded or not, you're saying that restricting the inlet of a pump can alleviate cavitation?
This is totally contrary to my experience - I've observed that restricting the inlet can cause cavitation - not alleviate it.
If you think about it, this makes sense (at least to me).
I'm overloaded right now - anyone else want to step in with pointers to theory and fact around cavitation (feel free to tell me I'm wrong - I'm glad to find out if I min-know something, so I can fix it...)

EDIT: "min-know" was supposed to be "mis-know" - as in Banks' famous "It ain't what a man don't know that make him a fool - it's the things that he do know that ain't so" (I may have the wording somewhat wrong - but you get the idea...)

[Kobuchi]

Originally Posted by bobkoure

So, poorly worded or not, you're saying that restricting the inlet of a pump can alleviate cavitation?

I think we have the same understanding of cavitation. JWFokker was concerned about a "fluid noise". Kinking the inlet was a test to rule out cavitation. The test was not meant to reduce cavitation (more likely to exacerbate it) but to modify or eliminate any other noises caused by flow.

The result was negative: JWFokker reported "the noise remained the same".

[JWFokker]

Oh, it was definitely cavitation, much reduced now that I have things reconnected in their proper order, and I've still got a bit of it, but not nearly as much as there was. I'll be switching to either larger ID tubing from the reservoir to the pump or fabricating a reservoir to attach to the pump inlet to eliminate it completely.