A seal for use in a vacuum pump comprises a seal element positioned between inner and outer seal carriers located at the inner and outer surfaces of the seal element. Each of the seal element and carriers is substantially toroidal in shape. The outer carrier comprises retention means to hold the seal element in position. The inner carrier comprises at least one recess located in a surface adjacent to the seal element, and the seal element comprises at least one protrusion on an inner surface, which extends into the at least one recess of the inner carrier. A seal system comprises the described seal and first and second flanges. Methods for enhancing the chemical resistance of a seal system for use in a vacuum pump, and the use of the seal or seal system to connect pipework, are also provided.