Monday, May 19, 2014

Lab Book 2014_05_19 Second Fiberglass Dewar Looks Good!

Lab Book 2014_05_19     Hamilton Carter
Started work on leak checking a second fiberglass Dewar.  So far, the jacket seems to be holding vacuum well.  The auxiliary roughing pump was pumping more vapor into the system than expected.  Once it was taken out of the circuit, the diffusion pump quickly pulled the jacket back down to a reasonably good vacuum.  No leaks were detected in any of the vacuum junctions, or anywhere on the jacket.

Testing a different fiberglass Dewar.  I wire brushed the old Teflon tape off the vacuum port and and attached the lead detector after putting on new Teflon tape.
Just pumping the hose up to the Dewar, it looked like there might be a leak.  When the rouging pump was taken out of the system after a minute or two, the pressure went back up from about .05 to above .1 rather quickly.  However, after letting the roughing pump work for 28 minutes, when the valve was closed removing the roughing pump, the vacuum held at .05.

The helium leak detector was used to find no leak in the hose or the fitting on the new Dewar.  The Dewar valve was opened and the vacuum gauge moved to > 2.  The roughing pump was left on the volume for several minutes and the vacuum reduced back down to 1.48.

Once the roughing pump was disconnected, the vacuum improved very quickly.  At 17:20, the vacuum read 0.9 on the bottom scale, (all previous readings were on the top logarithmic scale).


The liquid nitrogen trap was filled at 21:05, and required two and a half Styrofoam cups of liquid nitrogen.  It will be filled again in the early morning.  The trap requires about six cups to fill from room temperature.

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