met11, RVP seems a right but...
"All models are designed primarily for thermal expansion or low volume relief applications at high pressures
where flow is not critical"
my case isn't thermal expansion
The relief valve won't really care what your case is. What is the relieving scenario? You're going to get an enormous amount of flow at 43,500 psi regardless of how big the valve is. In the past at our company, we've used the RVP series with the published areas by Autoclave, and a discharge coefficient of 0.14. I think the K was back-calculated based on some of the published flow curves in the literature.
Unfortunately I don't know of any other valves that can go up to that pressure. I checked the normal players (Leser, Farris, Crosby, Flowsafe, Consolidated) and none of them even get close to those pressures. Most Autoclaves that I've seen operating in those pressure ranges always have an extruder-style rupture disc, or very small safety head.
The only process I know of which runs that high is high pressure polyethylene- basically a bomb which you use to make a product. Amazing that it works at all...
