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
