I've used the malleable iron fittings at 500 psi, but I don't advertise that as being safe, and I have no idea how close it is to their failure point. The only one of those on my hybrid is the union, and I really don't care if that fails, as I'm getting a 3000psi one from McMaster in a few weeks anyway.
I definitely wouldn't take this hybrid to 15x unless I was a long way away from it.
And where did you get that ball valve? Even McMaster doesn't have brass ball valves rated that high.
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