Vacuum capacity is inadequate when the system cannot remove the required air volume quickly enough to form the sheet before it cools. The result is often acceptable broad shape with weak corners, shallow texture, or incomplete deep features.
Pump nameplate flow is not a complete sizing method. Effective performance depends on mold and box volume, receiver volume, starting pressure, line conductance, valve response, leakage, altitude, and the time available before the sheet stiffens.
Verify the system dynamically
Pressure should be recorded at the receiver and near the tool during an actual cycle. If the receiver begins each cycle at a different condition, recovery time or pump condition is involved. If the receiver remains stable but the tool pressure changes slowly, restrictions, valves, or dead volume are more likely.
The receiver and pump should be sized from the enclosed volume and required pressure-time curve rather than a universal volume multiplier. Reducing unused tool-box volume and moving fast valves closer to the mold can improve response without changing the pump. Additional heat should not be used to compensate for a system that is fundamentally too slow.