Liquid-pressure driving system

A liquid-pressure driving system in which a main circuit thereof forms a liquid-pressure closed circuit together with a liquid-pressure actuator,

• the liquid-pressure driving system comprising:
• a liquid-pressure pump connected to the liquid-pressure actuator through two pressure liquid passages and configured to suck a pressure liquid through one of the two pressure liquid passages and eject the pressure liquid through the other of the two pressure liquid passages;
• pressurizing mechanisms interposed on the respective two pressure liquid passages and configured to apply pressure to the operating oil returning from the liquid-pressure actuator;
• a low pressure selector valve connected to parts of the two pressure liquid passages, each of the parts being located at one side of the corresponding pressurizing mechanism which side is close to the liquid-pressure actuator, the low pressure selector valve being configured to introduce to a cooling passage the operating liquid having lower pressure between the operating liquids flowing through the two pressure liquid passages;
• a restrictor mechanism interposed on the cooling passage;
• a cooler apparatus interposed on the cooling passage so as to be located downstream of the restrictor mechanism, the cooler apparatus being configured to cool the operating liquid flowing through the cooling passage;
• and
• a pressure liquid returning mechanism connected to parts of the two pressure liquid passages, each of the parts being located at one side of the corresponding pressurizing mechanism which side is close to the pressure liquid pump, the pressure liquid returning mechanism being configured to return the operating liquid, cooled by the cooler apparatus, to the two pressure liquid passages.