There is disclosed a cryogenic tandem pump system comprising a cryogenic reservoir for storing cryogenic liquid, a first pump engaged with a first actuator and configured with a sump. The system further including a second pump engaged with a second actuator and is also configured with a sump. The reservoir, sumps and pumps are fluidly connected via piping and are configured with a pump controller. The pump controller is configured to dynamically control displacement, velocity and acceleration of the first and second pumps. The pump controller regulates the flow and pressure of cryogenic liquid between the first and second pumps to produce zero return to the reservoir.

Piston for a fluid machine, the piston being configured to be mounted at least in part inside a liner of the machine with a relative back- and forth movement with respect to the liner, the piston extending in a main direction and comprising a head, which has a first end of the piston, and a shaft, which has a second end of the piston, the first end of the piston being configured to delimit, with the liner of the machine, a fluid expansion and/or compression chamber, the shaft comprising a lateral wall which is provided with at least one annular groove defined between a first crenelation and a second crenelation, the at least one annular groove being equipped with at least one gasket seal configured to cooperate in a sealed manner with a lateral wall of the liner of the machine, the at least one gasket seal being provided with a through-orifice configured to allow a stream of fluid to flow from the expansion and/or compression chamber towards the second end of the piston, wherein the at least one gasket seal comprises at least one cavity separate from the through-orifice, the cavity being configured to accommodate a pressing system for pressing the gasket seal against the first crenelation and against the second crenelation, in the main direction of the piston.

Piston for a fluid machine, the piston being configured to be mounted at least in part inside a liner of the machine with a relative back- and forth movement with respect to the liner, the piston extending in a main direction and comprising a head, which has a first end of the piston, and a shaft, which has a second end of the piston, the first end of the piston being configured to delimit, with the liner of the machine, a fluid expansion and/or compression chamber, the shaft comprising a lateral wall which is provided with at least one annular groove defined between a first crenelation and a second crenelation, the at least one annular groove being equipped with at least one gasket seal configured to cooperate in a sealed manner with a lateral wall of the liner of the machine, the at least one gasket seal being provided with a through-orifice configured to allow a stream of fluid to flow from the expansion and/or compression chamber towards the second end of the piston, wherein the at least one gasket seal comprises at least one cavity separate from the through-orifice, the cavity being configured to accommodate a pressing system for pressing the gasket seal against the first crenelation and against the second crenelation, in the main direction of the piston.

A cryopump apparatus defines an open interior cavity with a process assembly received within the open interior cavity. The process assembly includes a refrigerant passage having a refrigerant inlet end to receive a refrigerant therein and a refrigerant outlet end to output used refrigerant. A process passage has a process inlet end to receive a process gas and a process outlet end to output a product gas. A heating element is thermally coupled to the process passage and a cap seals the open interior cavity.

A cryopump apparatus defines an open interior cavity with a process assembly received within the open interior cavity. The process assembly includes a refrigerant passage having a refrigerant inlet end to receive a refrigerant therein and a refrigerant outlet end to output used refrigerant. A process passage has a process inlet end to receive a process gas and a process outlet end to output a product gas. A heating element is thermally coupled to the process passage and a cap seals the open interior cavity.