Charge valve for gas, in particular for carbon dioxide, comprising a seat, drilled with a passage, a shaft movable inside the passage against the compression of a return spring bearing against the seat and an elastomeric seal compressed between the seat and the shaft to close the passage when the shaft is moved into a first closed position, called low-pressure position, wherein a thermoplastic seal comprising a polymer that is deformable but has a hardness higher than that of the elastomeric seal, is added onto the seat or onto the shaft to close the passage when the thermoplastic seal is compressed between the seat and the shaft in a second closed position, called high-pressure position, against an additional compression of the elastomeric seal.