What is the difference between a Safety Relief Valve manufactured to ASME I vs. ASME VIII as far as deign and function? This would be a good question for the safety valve forum. A section 1 valve is certified for a fired pressure vessel. The pop and blowdown are 3% of set pressure. There are TWO rings to adjust to control the pop and the blowdown, and a secton 1 valve usually has an exposed spring to keep it cool. A lifting lever is mandatory. SOme section 1 valves have dual outlets to reduce reaction loads on the piping. Section VIII valves are for unfired pressure vessels. The spring is usually enclosed, but open springs and/or alloy are optional. Rated capacity is at 10% overpressure,16% permissible with multiple valves and 21% permissible for Fire rating. Blowdown is customarily also 10% but I was told recently that the code does not stipulate this and I have not checked to verify. There is only one adjustment ring. A lifting lever is only mandated for air, steam, or water over 140F. Section VIII valves are available with optional bellows-balanced discs so they can be piped to a recovery system with variable backpressure. Section VIII valves are also available with pilots instead of spring-loading, where the process pressure is used to hold the valve closed until the pilot trips. Pilot valves are much more compact and seal tighter as the pressure increases---usually have soft seats. But with the small flow passages to and in the pilot they are not tolerant of contaminants in the process

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