A 510 MeV high luminosity @PHI@-factory is operating at INFN Frascati National Laboratory, Italy. The accelerator complex consists of a full energy Linac, a small damping ring and two electron-positron high current storage rings. The behaviour of the vacuum under operation, the dynamic pressure and the beam conditioning versus beam dose will be presented. A desorption efficiency below 1x10@super -6@ molec./phot. has been reached in some sections of the vacuum chamber, while a value in the range of some times 10@super -5@ molec./phot. has been reached in other sections. Possible reasons that could explain these differences will be also presented.