To selecting an appropriate mechanical seal , first you should consider its rotation part , and then you should evaluatee its stationary surfaces. factors like the pressure of seal environment , temperature and the speed of rotor shaft (rpm) , type of pumped fluid and the diameter of rotor shaft should be considered and after paying attention to these factor , appropriate mechanical seal will be selected for the pomp . because when a seal failed , most of expenses will be for its subsitution , and in the most cases , components of the process will be out of work in order install new mechanical seal so selecting appropriate mechanical dam with respect to its working conditions , can lead to better performance of producing process.