The invention is based on the technical problem of improving the pressing in of large press fittings, said problem being solved by a device for transmitting a mechanical force for driving a pressing device for press fittings, having a storage container (4) for hydraulic fluid, having a pump cylinder (8), having a working cylinder (12), having a first line (14) for connecting the storage container (4) to the pump cylinder (8), having a second line (16) for connecting the pump cylinder (8) to the working cylinder (12), and having a third line (18) for connecting the working cylinder (12) to the storage container (4), wherein means (20) for preventing a return flow into the storage container (4) are provided in the first line (14), wherein means (22) for preventing a return flow into the pump cylinder (8) are provided in the second line (16), wherein switching means (24) for opening and closing the third line (18) are provided, and wherein the swept volume (VA) of the working cylinder (12) is configured to be greater than the swept volume (VP) of the pump cylinder (8). The invention also relates to a corresponding method.