External Box, 30RZT Cavitating

[Styyn]

I should preface this by mentioning I have done quite a bit of searching and reading on forums and have done some of my own diagnosing, but I could still use some help from the gurus.

I've just finished an external box with a 30RZT pushing into three 2-342's in series and an RBX with the #5 plate in it. I plan to add a Fusion HL to the loop, eventually, but the journey from Aus to the US is a long one, apparently (almost 3 weeks now).

This post got kind of long so I'll cut to the chase right here for those who hate all the gory details, but I'll leave them below for those who do

-- Are the three 2-342's, RBX (and eventually the Fusion) capable of creating enough backpressure? I've restricted the outlet manually and it didn't seem to reduce that "sand in the system" noise at all.

-- Or is it more likely that my 3/4" inlet barb, combined with ~1' of 3/4" ID tubing feeding off of a 64oz. res, again with a 3/4" barb, is the culprit? The lid of the res does cave in, slightly, while the pump is running.

-- If it is inlet restriction that is still the problem, what next? Do like Moony and fashion a custom acrylic res directly on the inlet? I'd like this to be a last resort, as the thought of permanently bonding something to a brand new $250 pump is pretty off-putting.

-- Is it possible that the sound I'm hearing is just the tiny bubbles in my system? I don't leave the pump run for more than a minute or so at a time because I don't want cavitation to damage it. That coupled with all the posts talking about how fast these things clear air from the system worries me (I think I saw Cathar say something about clearing his system in 15 seconds?) The combination of a T-line and a res (albeit a res at the lowest point in the system) I'd think would clear the loop pretty fast...


And here's the nitty-gritty. Sorry I couldn't just take pics and let them do the talking, but I don't have a digicam, as yet.

The 2-342's are mounted vertically in the 30x20x24 box. The outlet on the Iwaki feeds up to a T just before the inlet on the highest HC, making it the highest point in the system. All tubing from the inlet of the pump to the inlet on the last HC is 3/4" ID. The outlet on the last HC in the series feeds out to ~6' of 1/2" ID tubing and the RBX. The outlets on the RBX then Y back together to another ~3' of 1/2" tubing.

For testing purposes, I'd initially had the last 3' after the RBX on a 1/2-3/4 adapter that connected to ~1' of 3/4" ID before the inlet of the pump. This cavitated like crazy so I made a quick'n'dirty res out of a 64oz., 4.5" diameter tupperware container with a 5/8" barb inlet and 3/4" barb outlet. This quieted things quite a bit, but I still get that "sand in the system" sound, slightly, and the pump is creating enough negative pressure to collapse the lid of the tupperware container slightly.

I should also mention that the nozzles on the inlet and outlet are identical 3/4" ID barbs (plastic, unfortunately). All the 3/4" tubing is braided vinyl and the 1/2" is Tygon.

Thanks much for any advice you guys can give me

[brucoman]

my MD30RZ always has a bit of "turbine" noise....
suggest larger inlet hose, 1" ID or bigger even (#1 issue IMHO)
is the T line off the T at the pump outlet?
suggest you pump water from bottom of RAD's to the top, not top to bottom (clears air much better, you may have air pockets still)
do you see any bubbles (small & fast moving)?

[Styyn]

Yeah, extremely fine bubbles that move so fast they're barely visible. Currently there's ~3' of tubing after the outlet on the pump before the T, with about 6" of hose from the other side of the T to the inlet of the first HC.

Have any suggestions on getting larger inlet tubing to fit? I haven't been able to find any 1" or larger nozzles that also have 3/4" threads.

As for the HC tubing order, I'll give that a shot, thanks for the tip

[brucoman]

[quote=Styyn]Yeah, extremely fine bubbles that move so fast they're barely visible.

Have any suggestions on getting larger inlet tubing to fit? I haven't been able to find any 1" or larger nozzles that also have 3/4" threads.

QUOTE]

the bubbles will make noise in the pump, need to make sure all air is out, look to see if any place you can see bubbles entering stream

use copper plumbing fittings. don't really need barbs, can heat tubing to stretch over bigger fittings.

[JWFokker]

My Mag 3 had a bit of cavitation coming off a res with anything less than 1/2" ID tubing, and the 30RZT is considerably more powerful. I'd try to get 1" ID tubing on there if I were you. I'm moving up to 5/8" ID tubing just to improve flow on my Mag 3 since that's the biggest that will fit. The best thing for flow is to put the inlet inside the reservoir if at all possible though.

[Turbokeu]

Originally Posted by Styyn

Is it possible that the sound I'm hearing is just the tiny bubbles in my system? I don't leave the pump run for more than a minute or so at a time because I don't want cavitation to damage it.

I'm convinced that pump cavitation cannot occur at the pressures we're dealing with in PC watercooling.

Anyway, when the filter compartiment in my fishtanks clogs up badly the pumps start to suck half water, half air, producing that typical noise (my pumps are in the last filter compartiment, therefore the water level goes under the intake level of the pumps).
Sometimes (i'm actually not that ponctual in my fishtank maintenances...) the pumps work that way for months without issues (except the noise).

CD

[pauldenton]

Originally Posted by Turbokeu

I'm convinced that pump cavitation cannot occur at the pressures we're dealing with in PC watercooling.

Anyway, when the filter compartiment in my fishtanks clogs up badly the pumps start to suck half water, half air, producing that typical noise (my pumps are in the last filter compartiment, therefore the water level goes under the intake level of the pumps).
Sometimes (i'm actually not that ponctual in my fishtank maintenances...) the pumps work that way for months without issues (except the noise).

CD

well a 30z on 60hz power is pretty high pressure (11M H20)

hmm - surely the T is at best redundant now you have a res?

[killernoodle]

Have you tried just putting distilled water in there? Maybe the additive is what is causing the bubbles. I'd remove all the water in there now, put in distilled water, then add whatever additive you want after all the bubbles are gone.

[Styyn]

Yes, I had plain distilled water to start, but I've since corrected the problems and it's leak-testing right now.

First I re-routed the HC order, per brucoman's recommendation and that fixed the bleeding problem--these things really do clear all the air in 15 seconds After that I was still getting that slight "sand" noise, and the top of the res was still caving in slightly. I scrounged up a couple of 1" copper fittings for the pump inlet and res outlet and have connected them with a net length of ~1" of 1" tubing. This cured the "sand" noise, and the new taller, skinnier, one gallon res seems to give better separation between the inlet and outlet for the small bubbles to come out without being sucked back in by the pump inlet.

Can't thank you all enough for the tips, they sped up my set-up time considerably and saved me a helluvalotta grief.

Thanks again