Pressure relief device for high-pressure vessel

A pressure relief device for a high-pressure vessel, the pressure relief device, which is mounted on a mounting part formed between an inlet passage through which gas from a valve body flows and a discharge passage through which gas is discharged to the outside to open and close the inlet passage, the pressure relief device comprising:

• a cap member mounted on the mounting part to be able to seal and having a space part formed therein;
• a piston member inserted into the cap member to be linearly movable, having a first chamber part with an open lower side, sealing the inlet passage by being inserted into the inlet passage to be sealed, and dividing the space part of the cap member into a second chamber part and a third chamber part;
• a spring installed between the piston member and an inner surface of the mounting part to provide an elastic force in a direction in which the piston member is retracted;
• and
• a fusible alloy which is mounted on the third chamber part so as to support the piston member so that the piston member is not retracted, and is molten to retract the piston member and to open the inlet passage when a surrounding temperature is greater than or equal to a set temperature, wherein,
• when the fusible alloy is molten, the molten fusible alloy is sequentially introduced into the first chamber part and the second chamber part to be prevented from being discharged to the outside.