The European XFEL facility in Hamburg is comprised of a linear accelerator and three Free-Electron-Laser beamlines covering the energy range from 250 eV to 24 keV. It will provide 2700 pulses in trains of 600 microsecond duration at a repetition rate of 10 Hz. For the photon beam diagnostics, several gas-based devices have been developed and placed in the beam transport system. They operate with different noble gases (Xe, Ne, Ar) with pressures up to 1·10-4 mbar. Having a windowless photon beam transport system, and a limited capability for noble gases that can be provided by the distributed array of ion pumps sustaining the UHV environment, a turbomolecular based differential pumping section has been developed. This modular system is able to minimize the gas flow to the rest of the beam transport system, also offering a large optical clear aperture between pumping stages, and enabling the required installation and alignment flexibility in all the tunnel locations (up to 10), including variations as floor and ceiling-mounted versions. A general overview of the vacuum system analysis, performance validation procedures, and structural and alignment concept, as well as installation status is reported.