Why is a safety factor applied when sizing vacuum cups?

Leaks, surface roughness and the acceleration of the load all reduce the real holding force. A safety factor of at least 2 stops the load being dropped.

Which surfaces suit vacuum lifting?

Smooth, flat, non-porous surfaces such as glass, sheet metal and plastic suit vacuum cups. Porous materials such as rough card and fabric leak air and lose grip.

How is a load released from a vacuum cup?

The vacuum is switched off and the cup is vented to atmosphere. A short blow-off pulse of air can release the load quickly.

CCEA A-Level Technology and Design 8900

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Mechanical and Pneumatic Systems

Vacuum handling, proximity sensors and 5/3 valves

3 things to know
A2 1

Overview

Vacuum cups and the force they hold with a worked example, safety factors, inductive, capacitive and reflex proximity sensors, and closed-centre and exhaust-centre 5/3 valves.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

How is a vacuum produced for a pneumatic lifting cup?

Key term

How does a vacuum cup hold a load?

Numbers

A vacuum cup of 60 mm diameter works at 0.6 bar below atmospheric pressure. Calculate its theoretical holding force.

Questions from this subtopic

Each one with the model answer underneath.

1
How is a vacuum produced for a pneumatic lifting cup?
Model answer
A motor-driven vacuum pump or an air-driven vacuum generator removes air from the cup. A vacuum generator uses the venturi effect of compressed air rushing through a nozzle.
2
How does a vacuum cup hold a load?
Model answer
The cup seals against a smooth surface and the air inside is removed. Atmospheric pressure outside then presses the cup and load together.
3
A vacuum cup of 60 mm diameter works at 0.6 bar below atmospheric pressure. Calculate its theoretical holding force.
Model answer
The theoretical holding force is about 170 N. Area = π × 30² = 2827 mm², and 2827 × 0.06 N/mm² = 170 N.
4
Why is a safety factor applied when sizing vacuum cups?
Model answer
Leaks, surface roughness and the acceleration of the load all reduce the real holding force. A safety factor of at least 2 stops the load being dropped.
5
Which surfaces suit vacuum lifting?
Model answer
Smooth, flat, non-porous surfaces such as glass, sheet metal and plastic suit vacuum cups. Porous materials such as rough card and fabric leak air and lose grip.
6
How is a load released from a vacuum cup?
Model answer
The vacuum is switched off and the cup is vented to atmosphere. A short blow-off pulse of air can release the load quickly.

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