Official Answer
Answer
In mechanical seal assemblies, the wave spring provides the axial force to keep the seal faces in contact. If the spring is not 'flat' (i.e., its free height varies around the circumference), it will apply an uneven load. This creates a tilting moment on the seal face, leading to non-uniform film thickness of the process fluid and eventual leakage or face scoring. The flatness is controlled during the 'heat-setting' process where the spring is quenched in a fixture. A tolerance of $\pm 0.005$ inches on parallelism is often required. During installation, the technician must ensure the housing is free of debris that could tilt the spring, as even a minor misalignment can double the local pressure on one side of the seal.
