Topping off is needed if the level of the cryo buffer goes below 75% ( the second level meter in the middle of the control rack)
1. Set the cryopump frequency to 20 RPM (Use the arrow up and down buttons on the square blue controller above the level meters).
2. Close V6 and diaconnect the outlet of the constant pressure module (the black device mounted on the gas outlet of the side dewar ) from the inlet of V6. If the pressure in the buffer builds up above 30 PSI open V6 briefly to release the extra gas.
3. Raising the low pressure probe (S2 LN2 vessel) until the automatic low pressure fill is on (the red light on vessel level meter module will come up) and wait until liquid starts flowing (check that the level is going up in the vessel) .
4. Close the low-pressure intake (V4 LP fill). Open the high-pressure intake (V3 HO fill) and V6 vent.
5. Continue the refill until the buffer level meter reads between 90% and 100%.
6. Close V6 and V3 and open V4. Lower the low pressure probe (S2 LN2 vessel) back to its permanent position.
7. Increase the frequency of the cryopump from 20RPM to the desired value.
8. Connect the outlet of the constant pressure module (the black device mounted on the gas outlet of the side dewar ) to the inlet of V6. Make sure the pressure builder of the dewar is set at 60 PSI.
10. Open V6 and make sure the differential pressure in the buffer is equal to the desired value. If not adjust the constant pressure module by turning the black knob very slowly.