In this pump, each sealing ring (14) of the piston (2) consists of two juxtaposed elementary rings (19A, 19B), the gaps of which are straight or angled and are offset, when fitting them, 180° with respect to one another, and of a common expander (21), and the elementary rings are made of a composite which contains more than 50% bronze and about 5% molybdenum disulphide, the rest being PTFE. ;Application to continuously operating variable-capacity pumping of liquid nitrogen at pressures of 850 bar or more.
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