Cryogenic Pump Performance

"The pump is installed on a tank"

I don't think that you have mentioned the pump is installed on a tank and this pump lifts the liquid. This means negative suction?

Unlike oils, liquefied gases like Argon are non-lubricating by themselves.

Negative suction or blockage at suction side leads to 'vapor formation (cavitation)'. Such cavitation in a positive displacement pump would lead to partial dry running. Which intern leads to whole lot of complications like 'loss of throughput, accelerated wear on suction/discharge valves, plunger and packing'.

Please provide more details like:

1. Does the pump works on negative suction. If so, what is the lift?
2. If 'flooded suction' how much is the suction head? In essence, "what are NPSH_A and NPSH_R?"
3. Is there objectionable restriction on suction side? Strainer, valves on suction side etc.
4. Air getting in through stuffing box element will lead to: loss of throughput and excess wear on plunger. Less or excess tightness of glands or improper selection of plunger packing would lead to this wear.
5. The velocity and pressure drop across the pump's suction and discharge valve will lead to cavitation and accelerated wear on suction/discharge valves, plunger and packing. Presuming the pump is from a reputed manufacturer, we would look in this problem as the last, but not the least.

Some of the screen shots from our CBT on: Positive Displacement Pumps' are pasted herewith, to give some ideas for troubleshooting.