A hydraulic pressure intensifier (1) is described comprising a housing (2) having a low pressure chamber (3) and a high pressure chamber (4), force transmitting means (5) between the low pressure chamber (3) and the high pressure chamber (4), and a switching valve (8) connecting the low pressure chamber (3) to a first pressure or to a second pressure different from the first pressure. It is intended to have a large volume on the high pressure side of the pressure intensifier. To this end the switching valve (8) is controlled by a pilot valve 18.

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 hydraulic pressure intensifier (1) is described comprising a housing (2) having a low pressure chamber (3) and a high pressure chamber (4), force transmitting means (5) between the low pressure chamber (3) and the high pressure chamber (4), and a switching valve (8) connecting the low pressure chamber (3) to a first pressure or to a second pressure different from the first pressure. It is intended to have a large volume on the high pressure side of the pressure intensifier. To this end the switching valve (8) is controlled by a pilot valve 18.

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.

The present invention provides a technique that enables liquid feeding with small pulsation by reducing the volume of a liquid feeding pump. Disclosed is a liquid feeding pump comprising: a first plunger pump that has a first plunger; a second plunger pump that has a second plunger and is connected to the first plunger pump in series; a pressure sensor that is disposed on the downstream side of the second plunger pump; and a control unit that accepts an input of the discharge pressure of a liquid measured by the pressure sensor to control driving of the first plunger and driving of the second plunger, wherein when the first plunger pump compresses the liquid, the control unit drives the first plunger at a first speed, and then decreases the speed to a second speed slower than the first speed before the compression is completed, and wherein the control unit discharges the liquid from the second plunger pump by driving the second plunger in parallel with the driving of the first plunger.