Scroll pump having bellows providing angular synchronization and back-up system for bellows

A scroll pump has a metallic bellows that angularly synchronizes the stationary and orbiting scroll blades of the pump, and a hack-up system for the bellows. The back-up system consists of pins integral with and fixed relative to one of the stationary and orbital parts of the scroll pump, and a guide part that is integral with and fixed relative to the other of the stationary and orbital parts. The back-up system may be a non-contacting hack-up system in which there is no contact between the pins and guide part during normal operation of the pump. Therefore, no particles are created by a wearing away of such parts which would otherwise have the potential to contaminate the fluid being worked by the pump and reduce the useful life of the pump.