ORIGINAL: Heterodox
Would the stuffing support be like a pillow bearing with the brass actually rotating, or just a static/clamp support with the flex/teflon rotating inside the brass? I assume the latter...
Yes, the latter. The stuffing tube will keep the flex from kinking under stress.
ORIGINAL: Heterodox
This looks like a nice coupling for 8-to-10:
Its rated for 19,000 RPM, but my physics knowledge is dusty at best.
The price is certainly right. I don't know what RPM's the HK pump is rated for, but the recommended operational range of my 40mm Powerjet is 10-15K. The smaller units run faster yet. That 19K coupling should handle it fine.