OK, so this is an adventure! Make sure you have some coffee, it's a long one!
When we last spoke, I had 6 clean flow control screws. They first had 10 minutes in ultrasonic with ~3% phosphoric acid and a little Dawn (less than 1/4 tsp in 10oz). Light check. Those that were still clogged had another 10 minutes. When I was done, I could see light through all of them. Great! So time to test.
A few notes about testing. I tested the first one with the first stage end cap tightened properly. That gave me an IP of 125psi (these are Blizzards and tuned for icewater). I then re-tested with the end cap hand tight, which left it about 1/16" from fully screwed down. Turns out that this doesn't make a difference at all: same IP, same flow results. Good to know: it's a lot faster testing without using a big wrench...
Also, hitting the purge button on the reg for, say, a full second or so causes the bubbles to completely stop. It takes a good 5+ seconds for the bubbles to start again. Interesting: it seems that in normal operation that one-way valve will need to keep the water out for at least a little bit.
Back to the results. Of the six, one performed well below spec (7cc/min), three performed slightly below spec (17cc/min), one performed within spec (25cc/min) and one was actually past spec (35cc/min).
I decided to work on the three slightly below spec They were all within 16-18cc/min and would give me an opportunity to see how more cleaning affected them. I ran them through 10 minutes of ultrasonic in the phosphoric acid again. Pulled them out and rinsed them. Put then back into the reg: no bubbles on two, and very weak bubbles on the third (well below what it was before and didn't even bother to measure)!
What was the difference? Well, for one thing, I had quickied out on the rinse. So, I redid them, this time going through my full O2-style process (which I did last night). Another thing: I hadn't dried them. Last night they air-dried. Today, there might have been a droplet in them. I wouldn't normally think of that as a problem, but that is a *really* tiny hole to try to push air *and* water through... So I blew them out with tank air.
Somewhat better: one was at 17 cc/min, one at 20 c/min, and one was clogged, and I couldn't see light through it (which I could when the rinse was done). So maybe there's a reason Sherwood put a filter upstream of these?
For the two clogged ones, I whipped up a new batch of cleaning solution, this time 1:5 (or ~6% phosphoric acid) and less than 1/4 tsp Dawn to 10oz solution. Another 10 minutes, then full O2 rinse process, then quick blow dry. I can see light.
After testing: better results! One was 20cc/min and one was 22cc/min. Nice!
So I now have six unclogged flow elements! The process seems to have worked. But it's really picky. Seeing as I had six of them, it was well worth the effort. If I only had one? I'd be tempted to simply buy a replacement -- especially once I had bought a spare one on the shelf that I could use immediately and not have to wait on the replacement.
For the future, I'd go with: 1:5 Klean Strip to Hot water (10oz total), <1/4 tsp Dawn. 10 minutes ultrasonic. Look for light. Repeat if no light. Full O2-style rinse process. And it does work!
Hopefully I can simply keep these guys bubbling and won't have to go through this for a while!