One of the advantages of an oil-hydraulic system is that it keeps the value of its oil pressure when the pressurized oil is enclosed in a container. However, when the temperature of the oil changes, it is impossible to keep the value. If a pressure-control sub-system is used to prevent the pressure change, the whole system becomes complicated. In addition, energy is consumed when the pressure is adjusted by the quantity of oil flowing in or out of the container. From these view points, it would be useful if a component were developed which prevented the pressure change caused by the change in oil temperature without controlling the quantity of oil. Therefore, in this paper, a mechanism to prevent the pressure change caused by the oil temperature change is proposed to secure the advantages of the oil hydraulic system even when the temperature of the oil changes. And a component is fabricated to investigate the validity of the proposed mechanism. Its validity is investigated experimentally when the temperature of the oil increases and when the temperature of the oil decreases after it increases.

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