Whether startup and shutdown operation of mechanical seals goes on smoothly directly influences its reliability and life span.A transient dynamic model was developed by taking into consideration the effect of liquidsolid force coupling between end faces

microcavitation and face contact.Seal parameters

such as axial displacement of floating ring

film thickness

contact pressure and leakage rate

etc were computed.Transient seal behavior of mechanical seals during startup and shutdown operation was investigated.The influence of axial runout on seal performance was analyzed.The results showed that due to the effect of axial runout and change of velocity during transient operation

key seal parameters varied correspondingly with axial runout

and large runout led to big disturbance.The model and numerical methods could be used to improve the product design method and to assess design rationality.