fuel stage c 2 staging valve 236 is closed and c 2 purge valve 222 is opened after approximately two minutes purging of c 2 ring 204 is complete and c 2 purge valve 222 is closed as power is further decreased fuel is supplied to only u201c b u201d ring group 56 and fuel is purged from c 1 ring 202 initially u201c c u201d ring group shut off valve 242 is closed and c 1 and c 2 purge valves 220 and 222 c 2 staging valve 236 and u201c c u201d ring group drain valve 248 are opened for approximately two minutes to complete the purging after the purging is complete c 1 and c 2 staging valves 234 and 236 c 1 and c 2 purge valves 220 and 222 and u201c c u201d ring group drain valve 248 are closed whenever fuel flow to u201c b u201d ring group 56 is shut off u201c b u201d ring group 56 is purged after u201c b u201d ring group shut off valve 166 is closed u201c b u201d ring group drain valve 180 and u201c b u201d purge valve 174 are opened for purging after approximately two minutes u201c b u201d ring group 56 is purged and u201c b u201d ring group.