(DE19830557-A1)      The lead acid accumulator has a container (2) with at least one hole (4) defining a vent duct for the discharge to atmosphere of gases developed in the accumulator. A porous filtering element (90) is disposed in the duct to allow gases but prevent the electrolyte passing through. The filtering element is constituted by a porous substrate (92) covered by a polytetra-fluoroethylene membrane (94).    Also claimed is a plug or closure element (5) for a topping-up hole of the accumulator, the plug having a central cylindrical portion (50) and an adjacent enlarged end portion (52) defining an annular bearing seat for the filtering element.    ADVANTAGE -   Allows vented gases to escape from the battery whilst filtering electrolyte which may be attached in aerosol form. The membrane covering provides flame proofing, preventing propagation of flames into the accumulator from the exterior. Excessive pressure in the accumulator is discharged locally due to release by the pressure element.    (FR2766014-A1)      The lead acid accumulator has a container (2) with at least one hole (4) defining a vent duct for the discharge to atmosphere of gases developed in the accumulator. A porous filtering element (90) is disposed in the duct to allow gases but prevent the electrolyte passing through. The filtering element is constituted by a porous substrate (92) covered by a polytetra-fluoroethylene membrane (94).    Also claimed is a plug or closure element (5) for a topping-up hole of the accumulator, the plug having a central cylindrical portion (50) and an adjacent enlarged end portion (52) defining an annular bearing seat for the filtering element.    ADVANTAGE -   Allows vented gases to escape from the battery whilst filtering electrolyte which may be attached in aerosol form. The membrane covering provides flame proofing, preventing propagation of flames into the accumulator from the exterior. Excessive pressure in the accumulator is discharged locally due to release by the pressure element.    (US6120931-A)      The lead acid accumulator has a container (2) with at least one hole (4) defining a vent duct for the discharge to atmosphere of gases developed in the accumulator. A porous filtering element (90) is disposed in the duct to allow gases but prevent the electrolyte passing through. The filtering element is constituted by a porous substrate (92) covered by a polytetra-fluoroethylene membrane (94).    Also claimed is a plug or closure element (5) for a topping-up hole of the accumulator, the plug having a central cylindrical portion (50) and an adjacent enlarged end portion (52) defining an annular bearing seat for the filtering element.    ADVANTAGE -   Allows vented gases to escape from the battery whilst filtering electrolyte which may be attached in aerosol form. The membrane covering provides flame proofing, preventing propagation of flames into the accumulator from the exterior. Excessive pressure in the accumulator is discharged locally due to release by the pressure element.    (GB2327141-B)      The lead acid accumulator has a container (2) with at least one hole (4) defining a vent duct for the discharge to atmosphere of gases developed in the accumulator. A porous filtering element (90) is disposed in the duct to allow gases but prevent the electrolyte passing through. The filtering element is constituted by a porous substrate (92) covered by a polytetra-fluoroethylene membrane (94).    Also claimed is a plug or closure element (5) for a topping-up hole of the accumulator, the plug having a central cylindrical portion (50) and an adjacent enlarged end portion (52) defining an annular bearing seat for the filtering element.    ADVANTAGE -   Allows vented gases to escape from the battery whilst filtering electrolyte which may be attached in aerosol form. The membrane covering provides flame proofing, preventing propagation of flames into the accumulator from the exterior. Excessive pressure in the accumulator is discharged locally due to release by the pressure element.