{Kyle, Gerardo, Chandra}

Today we capitalized on short-notice unscheduled maintenance day to remove and replace a legacy turbo station at mid-X station. Removal and installation went smoothly and we were leak checking by 3:15 pm when we discovered a large leak at the 12" flange of CETEC gate (turbo side). We replaced the gasket but flange still leaks at a rate of e-3 Torr-L/s. We concluded that the seal weld on turbo-side GV flange is cracked from bottoming out studs via double nutting, due to poor GV design. The tapped holes in flanges go all the way through the flange and the flange is weakly stitch welded to the GV body (see attached photo). Side note - Gerardo found that the 14" CETEC valves on ion pumps have partially threaded thru holes to prevent this from happening.

We will need to vent the MX spool at next opportunity to replace the CETEC valve. Meanwhile, the new turbo is bolted to the valve and volume is isolated via foreline safety valve. We are currently more vulnerable than normal operation with near atmospheric pressure on the other side of turbo isolation valve. The good news is the o-ring is seated in favorable direction so that atmospheric pressure pushes it in closed direction.

Note that we have replaced all legacy CETEC valves on site except at midstations' turbo and ion pumps (and EY turbo which will be replaced next time we vent EY).