Since last week, we have been applying 40-60 psi of GN2 through rotameter to the bottom sensing line on CP4 in an effort to "erode" the blockage. It appears we have a passage, but the blockage is not completely gone. Today John and I played around at the pump and found the differential pressure transducer reads back 100% on CDS (Beckhoff limit). The Magnehelic had been overpressurized, and wasn't matching CDS, so I swapped it with a new one. When valved in, it slowly creeps up to ~ 30 in. of water (38" = 92% full), along with CDS read back, but there is a leak in the fitting. So we left it valved out. When we combine the two sensing lines, CDS reads 0%. When we isolate them, it reads 100%, but the reading slowly increases from 0-100% rather than an instantaneous jump - even with Mag valved out, so we think we have a partial pathway across the blockage yielding poor conductance.
We canceled the auto overfill today and set the LLCV to 20% open for about six hours (nominal is 41%) hoping to see it come on scale. At around 5pm local we raised it to 38% to sustain over night. We will watch it periodically and revisit tomorrow. We may try to apply up to 200 psi of pressure on sensing line (bypass rotameter) to fully clear the clog.
CP4 was last overfilled yesterday at 11:16 am local.
I fixed the leak at Mag. It now reads 47" which correlates to 114% full. CDS reads 100% full (Beckhoff limit).
Leaving Mag valved in overnight.