Post a copy of the P&ID and highlight the valve in question.

GE LSTG design steam seal systems used two relief valves.

the R1 would be on the large pipe diameter supply header. given the supply header is normally 2 to 4 psig, the relief was set for >20 psig. the exact lift pressure not that importaint as the piping could withstand even greater pressure, but if SSH was operating at 20 PSI, something in its control had failed and protect this piping and devices.

the R2's (could be multiple) would be near the main steam source supply bypass valve, in the small diameter piping to the SSH. these reliefs were set for >200 psig, again exact lift pressure not important. in the event the steam feed into the SSH through the bypass valve became excessive, the piping restriction to the SSH would cause this R2 to open indicating something had failed in the SSH control. by relieving R2, this should limit the available pressure that the SSH devolps to <20 psig and thus protectes this piping and devices

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