Vacuum and positive-air circuits must not oppose each other unintentionally. Overlap can occur through controller timing, slow valve exhaust, a sticking spool, shared manifolds, or incorrect hose routing. The pressure curve may flatten, oscillate, or reverse briefly.
Electrical output status alone is insufficient because a valve can remain open after its command changes. Mold pressure, valve position, and pilot pressure should be observed through the transition. A short overlap that is invisible on the HMI may still consume most of the available pressure differential.
Sequence interlocks, exhaust capacity, valve response, and manifold separation should be corrected. Intentional staged pressure transitions must be documented and validated; accidental overlap should not be used as a soft-start method.