What causes the flexible membrane of a vacuum cup to seal itself to the load and enable lifting without damage?

• A. Airflow
• B. Ambient humidity
• C. Pressure difference
• D. Temperature difference

Answer: (C)

The key idea is the pressure difference. When the vacuum cup and its membrane evacuate air, the inside of the cup becomes lower in pressure than the surrounding ambient air. That higher outside pressure pushes the flexible membrane tightly against the load, forming an airtight seal across the contact area. The seal plus the negative pressure inside creates a suction force that holds the load and lets the cup lift it without applying damaging clamping forces. The membrane can conform to surface irregularities, improving the seal, and the suction is maintained as long as the internal pressure remains lower than the outside. Airflow is used to remove air, but the actual cause of adhesion is the difference in pressure, not humidity or temperature differences.