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The cold head temperatures should be averaging about 4-5K. If they are warmer it may be due to a flow dynamic of warm gas and there may be an adjustment of the NV501 needed. There may also need to be some balancing of flow performed by closing some of the helium gas delivery ball valves down. We have not yet needed to do this. The pressure on the dewar can be 6-7 psi and the flow in and out should generally be continuous. Some hiccups and periodic fluctuations are normal but long times with the inlet closed are not good. When everything is tuned right we should expect 4L/hour on each liquefier.
Vacuum pump out:
The vacuum of the dewars should in principle shouldn't need to be pumped out for a long time but we have already seen that Liq A performs better if it's pumped out at least every 2 months. When doing this make sure to pump down to at least low 10^{-3} torr and then close the turbo valve and check how fast it climbs (leak rate test). After all is well with the vacuum perform a pump and purge on the helium space of the dewar without going down much below atmosphere (can cause problems, or close all connections and remove stinger) and also perform the level pressure sensors cleaning procedure before starting the dewar cooldown.
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