Wave spring mechanical seal type NV - 3 is very similar to seal types NV - 1 and NV - 2. Main difference is the wave spring instead of multiple springs or single spring. Reason is usage in high viscosity media or media containing solids. Mechanical seal design with wave spring prevents sticking and blocking of small multiple springs. Another advantage of wave springs is more uniform force on the seal face. A steep characteristics curve makes wave springs more sensitive and allow small axial space requirements.