Hydrostatic noncontact seals are becoming more widely used as shaft seals for high-pressure water pumps. This work shows that the hydrodynamic pressure head (ρ · u2/2), where ρ is fluid density) should not be ignored in such seals where leakage velocity, u, is high. This “inertia” effect causes a change of pressure profile on the seal surface and affects force equilibrium and the seal separation.