if the rotor and stators become contaminated it may not be possible to achieve the desired ultimate pressure rapidly . it will then be necessary to clean the pump in order to remove the contamination . if it is heavily contaminated then the pump may needs to be stripped and cleaned following service instructions . some manufacturers advise that slight contamination can be removed without dismantling the pump . this is achieved by immersing the pump upside down in a vessel filled with cleaning solvent (in a well ventilated location observing all necessary precautions) . this should be an organic solvent chosen to suit the contaminant . suitable trichlorotrifluoroethane .