next up previous contents
Next: Trouble Near Base Up: Trouble During Pre-Cool Previous: Misc. Heatload   Contents

OVC Pressure Bottoms Out at $ 10^{-3}$

During the pre-cool, the OVC pressure should drop to $ \lesssim
10^{-6}$ mbar as N$ _2$ condenses. Occassionally, a problem arises where the pressure will bottom out at $ \sim10^{-3}$ mbar and sit there indefinitely.

Symptoms: OVC pressure bottoms out at $ \sim10^{-3}$ , even while pumping with the pump cart or temperature less than $ 70$ K.

Diagnose: Pump directly on the OVC pressure gauge with the pump cart. Pressure should drop below $ 10^{-6}$ mbar easily. If pressure bottoms out around $ 10^{-3}$ mbar, pressure gauge needs cleaning.

Solution: Clean the OVC pressure gauge.

Jonathan Ouellet 2014-08-26