Importance

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Abstract

A drain plug is disposed in a drain hole through which oil is discharged from a high-pressure chamber formed in a valve block. Within the drain plug there is arranged a drain pin that slidably opens and closes the drain hole. A fixed pin serves to restrict a displacement of the drain pin. A thermo-switch is located within a low-pressure chamber behind the drain pin in such a manner as to be urged by a return spring so that the drain pin is pressed to keep the drain hole closed. When a predetermined temperature is reached, the thermo-switch allows its head pin to extend, with the reaction force as a result of abutment of the head pin against the fixed pin causing the thermo-switch to retreat to release the pressing force exerted on the drain pin. In consequence, the drain pin is displaced by a high pressure toward the direction in which the drain hole is opened, allowing high-pressure oil to be drained into the low pressure side.

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First Claim