A pump unit comprises a primary piston pump, a secondary piston pump, and a flow path adapted for fluidically connecting in series the primary piston pump and the secondary piston pump. The pump unit's duty cycle comprises a delivery-and-fill phase, in which the primary piston pump supplies a flow of liquid to the secondary piston pump, and during the delivery-and-fill phase, the flow of liquid supplied by the primary piston pump is partly used for filling up the secondary piston pump and partly used for maintaining another flow of liquid dispensed across the secondary piston pump. The flow path comprises a heat exchanger, wherein liquid supplied by the primary piston pump passes through the heat exchanger before being supplied to the secondary piston pump. The heat exchanger is adapted for reducing a temperature difference between a temperature of liquid supplied to heat exchanger and a temperature of the secondary piston pump, in that the heat exchanger is kept at a temperature of the secondary piston pump, so that after having passed the heat exchanger, liquid supplied to the secondary piston pump has substantially the same temperature as the secondary piston pump itself.

A mass spectrometer or ion mobility spectrometer is disclosed comprising means for detecting a blockage in an inlet orifice arranged between an ion source and a vacuum chamber. The blockage is detected as a result of a reduction in pressure within the vacuum chamber. This change in pressure is detected indirectly by monitoring the amount of power that a vacuum pump is using, the amount of current that a vacuum pump is drawing, the temperature of a vacuum pump or a region in proximity to the vacuum pump, or the flow rate of gas out of a vacuum pump.

A pressure increasing system includes a plurality of stages of compressors configured to compress carbon dioxide to a pressure higher than a critical pressure; intermediate coolers cooling the carbon dioxide discharged from a compressor in a preceding stage; a subcooler provided between a seventh stage compressor in the final stage and a sixth stage compressor in a preceding stage and cools the carbon dioxide; a bypass line through which the carbon dioxide in the inlet of the seventh stage compressor is extracted, depressurized and supplied to the subcooler as a refrigerant; a flow rate adjusting valve provided on the bypass line; and a control unit configured to regulate a degree of opening of the flow rate adjusting valve so that at least one of a temperature and a pressure of the carbon dioxide in the inlet of the seventh stage compressor remains constant.

A pressure increasing system includes a plurality of stages of compressors configured to compress carbon dioxide to a pressure higher than a critical pressure; intermediate coolers cooling the carbon dioxide discharged from a compressor in a preceding stage; a subcooler provided between a seventh stage compressor in the final stage and a sixth stage compressor in a preceding stage and cools the carbon dioxide; a bypass line through which the carbon dioxide in the inlet of the seventh stage compressor is extracted, depressurized and supplied to the subcooler as a refrigerant; a flow rate adjusting valve provided on the bypass line; and a control unit configured to regulate a degree of opening of the flow rate adjusting valve so that at least one of a temperature and a pressure of the carbon dioxide in the inlet of the seventh stage compressor remains constant.