Kyle, Gerardo 

Today we wanted to quantify the gas load "contribution" of the known leaking all-metal 2.5" Vent/Purge valve at the X-end station.  

SETUP 
X-end open to BT (GV19, GV20 open)
Main Turbo backed only by the leak detector (no parallel pumping)
 

RESULTS 
LD helium baseline < 10-10 torr*L/sec before valving turbo into X-end volume
Helium background signal = 3 x 10-8 torr*L/sec after valving turbo into X-end volume 
Valved-out IP12 
Removed NW50 blank from closed Vent/Purge 2.5" all-metal valve (i.e. vented air side of closed metal valve) 
X-end pressure responded by rising to low 10-7 torr 
Sprayed audible flow of helium on air side of closed valve while monitoring helium signal 
Helium signal rose rapidly then leveled-off and peaked at 2 x 10-5 torr*L/sec (signal peaked after ~10 seconds of spraying but I continued spraying until ~30 seconds) 
Spent the next few hours pumping system with the turbo pump to remove introduced helium.  We also added an O-ring valve in series with the leaking valve and evacuated the air side of this valve 

CONCLUSION 
Traditionally we have only used the vendor supplied hand knobs to open/close these Vent/Purge 2.5" metal valves (1 per isolate-able volume).  The allowable torque specs far exceed what can be applied using these knobs.  As such, our valves are likely under-torqued as a rule and, as was demonstrated yesterday, this leak could likely be eliminated by tighing this valve using a wrench.  As this particular valve has a "gappy" conflat joint on the vacuum side, we didn't want to "fix" it using a wrench (long lever) while we are open to the BT and while commissioning time is at a premium.  The main take away is that all of our poor pressure level at the X-end can be attributed to this under-torqued metal valve and that we have no reason to suspect GV19 or GV20.