Abstract：Seawater and sand may cause serious leak to the marine pumps. A new solution was developed by adapting hydraulic seal combined with mechanical seal,also with the assistance of a system which separate the sand from water.That is to say,clean water separated from seawater by cyclone separating device can be employed to lubricate and cool the mechanical seal.Based on the principle of hydro-dynamical sealing,with the effect of centrifugal force produced by the back vane,water will be thrown to the impeller outlet to ensure the pressure grads of water purify system and prevent sand from coming into shaftend seal.Concrete scheme of design was educed to four steps: study of the characteristic of cyclone device,calculation of cooling flux for the mechanical seal,designing and matching calculation of back vanes.The solution has achieved good effect in many applications in recent years.marine centrifugal pump;sand defend;leak proof; cyclone mechanical seal;vice-leaf
