Stem Purge Pressure and Valve ASME Pressure Rating

[McT178]

I have a valve with a stream purged stuffing box that is designed and rated for 50 psi, and the maximum purge pressure is 100 psi. Is there a code exemption for the purge pressure being that the flow rate of the purge is insignificant to the flow rate of the valve - like a drop in the ocean with no chance of over pressuring the valve? Or, will the purge line need pressure controls limiting the pressure to MAWP of the valve?

 

[gerhardl]

If I understand you correct here, I believe the answer is quite simple. You can not, in my opinion, pressurize a cavity connected to a total pressurized system, with a source supplying a pressure higher than the allowed for the total system.