I witnessed the converse of this in the recent Mario Brothers movie. There is a scene where steam piping is about to overpressure and it shows a pressure safety valve lifting. Well that pressure safety valve is an accurately drawn ASME I BPVC open-bonnet PSV with test lever. The open bonnet is to expose the spring to air so it is kept cool and therefore has the correct force downwards on the seat. If you specify a cl…
("Musta been a non-union job." - Super Mario Bros., 1993, looking at some pipework).