Official Answer
Answer
Out-of-roundness (ovality) causes the wave spring to apply uneven pressure to the seal face. Mathematically, the load $P$ becomes a function of the angular position $\theta$, i.e., $P(\theta)$. This leads to non-uniform wear of the seal carbon and eventually to leakage. This is often a manufacturing defect or the result of improper handling. For high-speed centrifugal pumps, we specify a maximum ovality (e.g., 0.1 mm) and use a nested wave spring which, due to its continuous coiling, inherently maintains better circularity and provides more uniform loading than several stacked single-turn springs.
