Pump and Flush Main Bath

To prepare the main bath (MB) for transferring LHe, you must evacuate it so there is no air within. Also, you need to make sure no LN2 is left inside. You will evacuate the main bath by pumping on it with the He-4 pump and fill the MB with He-4 gas. With the MB over-pressurized with He4 gas, you prevent air from rushing in when you open the exhaust port to do the LHe transfer. Also, we want the mixture to pump into the dump so that it stays out of the fridge while the transfer is going on.

1. Check the He-4 gas tank to make sure there's enough gas to flush the MB.
2. Pump mix to dump: Open V9, V5, V1, the gate valve, the condenser valve, and then V6. (Actually we have changed this: we now usually let mixture into fridge before initial transfers.)
3. Make sure all openings to the MB are closed (needle valve, plugged exhaust ports, Speedivalve for He recovery line). These should already have been closed.
4. Make sure that all He recovery lines on the wall are closed and the yellow valve is switched to exhaust.
5. Turn on He-4 pump, or scroll pump hooked up to He-4 line.
6. Open V4A, V1A to pump on the MB until P2 reads < 1 mbar. This will take a few minutes to register on the Pirani gauge.
7. Close V1A, V4A (blocks off the MB).
8. Open V5A, V2A, and the rear Speedivalve to evacuate the clear hose (pumps out Vent).
9. Close V2A, V5A; turn off the He-4 pump.
10. Open the He-4 gas supply - gas is now flowing through regulator and the copper gas lines.
11. Open the blue valve that connects gas line to IGH - gas is filling the clear hose now.
12. Open V2A, V5A, V4A. When G3 starts to rise (> 70 mbar), open V1A - at this point, He-4 gas will be flowing through to the MB.
13. G3 will decrease in pressure when you open V1A - when it rises again above 70 mbar, close V2A, V5A, V4A, V1A.
14. Close the Helium valve on the gas line and shut off He gas supply.