How does a suction cup work?
A suction cup adheres to a surface as the surrounding pressure (atmospheric pressure) is higher than the pressure between the suction cup and the surface. To create the low pressure in the suction cup it is connected to a vacuum pump. The lower the pressure (higher vacuum), the greater the force on the suction cup.
Material handling with suction cups is a simple, inexpensive and reliable technique. It is therefore a solution worth considering before going over to more complicated methods. Suction cups can lift, move and hold objects that weigh just a few grams up to several hundred kilograms.
Low service requirements
Does not damage the material handled
Quick attachment and detachment
|Limited force (atmospheric pressure)
Sizing suction cups
Suction cups have quite different capacities depending on the design. Please see the values in the tables for respective suction cups.
Energy requirements at different vacuum levels
A deep vacuum means that the suction cup has to work harder and thus wears out quicker; also the energy requirements increase at higher vacuum levels. If the vacuum level increases from 60 to 90 – kPa, the lifting force increases by 1.5 times but with ten times the energy requirement. It is better to maintain a lower vacuum level and instead increase the suction cup area. In many applications, a good target for the vacuum level could be 60 -kPa; at this level you get a high lifting force with relatively low energy requirements.
Consider the height above sea level
Atmospheric pressure decreases with increased height. This means that the available force decreases at the same rate. An application designed for lifting 100 kg at sea level, can only manage to hold 89 kg at 1,000 metres. A vacuum gauge is normally calibrated with atmospheric pressure as a reference. This means that the gauge shows available vacuum levels at different heights.
Lifting force in different directions
A suction cup can be used irrespective of whether the force is perpendicular or parallel to the surface. If the force is parallel, it is transferred through friction between the suction cup and the surface. A suction cup with cleats is most suitable in this case because it is rigid and provides high friction.
- Cylindrical metric thread: designated with the letter M. Example M5.
- Cylindrical Inch thread (also called Unified thread): designated with the letter UNF. Example 10-32UNF.
Dry seal thread (American system of pipe threads):
The dry seal system consists of cylindrical and conical pipe-threads. The threads have a 60′ profile angle andare sealed without packing or seal rings (please note that when these are used in other combination of thread systems, that “sealing” is not applicable). The dimensions are given in inches and Piab’s catalogue uses the letters NPT and NPSF:
- Conical thread is designated NPT. Example: 1/8″ NPT.
- Cylindrical thread is designated NPSF: Example: 1/8″ NPSF.
BSP thread (British system of pipe threads):
- The threads have a 55′ profile angle and are dimensioned in inches.
- Cylindrical thread is designated with the letter G. Example: G1/8″.