Patent ID: 7220515

Claim:
A pressure-variation preventing tank structure for a tank in which electrolyte circulated for use is stored, comprising: a gas phase portion within the tank in the region above the upper surface of the electrolyte in the state in which the electrolyte is stored in the tank; a breather bag arranged in said gas phase portion of said tank and inflating/deflating in communication with outside air; and a breather bag attaching portion attaching said breather bag to the tank, including a communication hole for said breather bag to communicate with outside air; wherein said breather bag has air-blocking, acid-resistant and expandable characteristics, and has a three-layer structure formed by a metal film and two film-like resin layers arranged so that said metal film is interposed therebetween, and the breather bag is arranged to avoid contact with the electrolyte in the state in which the electrolyte is stored in the tank.