Abstract: End face width is a significant design parameter of mechanical seal, which numerical value is an important factor affecting end face specific pressure and tribological characteristics. The furan resin-impregnated graphite and microporous atmospheric sintered silicon carbide were adopted as the sealing friction pairs to investigate the influence of end face width of mechanical seal on the limit p_cv value (i.e. the product of specific pressure p_c and average linear velocity v). The limit p_cv values of friction pairs with five different values of the end-face width were obtained by means of variable load with a constant speed (namely PV method) and variable speed with a constant load (namely VP method) in water medium environment. According to the PV method, two rotational speeds of 3000 r/min and 6000 r/min were selected, corresponding to the average linear velocity of the sealing end face were 7.84 m/s and 15.68 m/s, and which were defined as PV₃₀₀₀ method and PV₆₀₀₀ method respectively. The sudden increase of friction coefficient was used as the basis for judging seal failure. The time-varying characteristics of friction coefficient and sealing medium temperature with different widths of end faces were analyzed with the above three methods. The surface wear morphologies of the friction pairs were measured with scanning electron microscope and three-dimensional (3-D) measuring laser microscope, and the failure mechanism when the seal reached the limit p_cv value was revealed. The results showed that the friction pair with a narrower end face can reach a greater limit p_cv value with the same measuring method, corresponding to a smaller friction coefficient and a greater temperature rise in the sealing medium until the failure of the seal. Under the condition of given end-face width, the limit p_cv value measured by VP method was similar to that measured by PV₃₀₀₀ method, but obviously smaller than that measured by PV₆₀₀₀ method. Under the condition of given end-face width and the PV method, the friction pairs with the speed of 15.68 m/s had a higher limit p_cv value and a lower limit p_c value than those with the speed of 7.84 m/s. The reason was that the increase of friction linear velocity intensified the friction heat generation of end face, which was not conducive to the friction pair reaching a larger end-face specific pressure. When the limit p_cv value was reached, the sealing surfaces of graphite rings with five different values of end face width all had the phenomenon of large-area material peeling off, and the main wear mechanism of the friction pairs was adhesive wear, which was mainly due to the overheating of the end faces and the vaporization of the liquid film caused by the sudden increase of friction torque. Both the PV and VP method can be used to determine the limit p_cv value of the mechanical seal. Compared with the PV method, the sudden increase in friction coefficient corresponding to seal failure was relatively insignificant, and the damage to the graphite surface was weak through the VP method. Therefore, it was recommended to adopt the means of variable load with a constant speed, and the average linear velocity of the sealing end face was recommended to be 7.84 m/s. On the premise of meeting the requirements of material strength, the reduction in the end face width can effectively avoid overheating of the end faces, which was beneficial for the mechanical seal to reach a greater limit p_cv value. It provided a theoretical and experimental basis for designing the end-face width and prolonging the service life of mechanical seals in the future.