## How To Choose The Right Style & Size Vacuum Cup

When you are using vacuum to pick and place different objects, how do you know which style vacuum cup and size you need?  EXAIR offer’s (3) different styles of vacuum cups in a variety of sizes to cover a wide variety of applications.

The first is the round cup, they are suited to smooth, flat surfaces.  They grip and release quickly, hold their shape with frequent use, and grip well when used with vertical loads.  Also, round cups are offered with cleats for a better gripping power when the load is heavy.  Vacuum Cups with cleats provide extra rigidity that lends itself to heavy loads.  The extra rigidity prevents the cup from peeling away or deforming when a heavy load is required.

Next we have the Oval Cup, they provide the most gripping power due to their larger surface area.  They naturally lend themselves to heavier loads.  They are ideal for flat rigid sheet materials such as wood, glass, cardboard and composites.

Last but not least we have the Bellows Cup, they are best suited for curved, uneven or textured surfaces.  The bellows or more accurately called “convolutions”, provide a collapsible area that allows the cup to quickly compress when it contacts the surface of item to be moved.  Please know that the grip/release time is greater due the the larger internal volume of the cup.

Here is an example: If we want to pick up a sheet of glass that weighs 20 lbs, what size vacuum cup(s) do we need?  Fortunately we have published charts in our catalog with the math already completed, but this is how we arrived at the answer.  Using the formula below:

D = Cup Diameter
W = Weight of item
N = Factor of safety ( We recommend a safety factor of 2 for horizontal lifting and 4 for vertical lifting).  For this exercise we will use a safety factor of 4.
U = # of cups (Remember it takes a minimum of 3 points to make a plane)
V = Vacuum level (psi) – Exair Porous E-Vac’s are rated to 21″ HG, Non – Porous 27″ HG and the Adjustable E-Vac 25″ HG.   (Each inch of HG equals .491154 PSI)
π = 3.14159
μ = Vertical surface friction coefficient (.5 for typical non-porous materials such as metal, glass, stone, etc..)

The calculated diameter is 2.26″ so we would choose the next standard size which is 2.5″ diameter.

When you are looking for Vacuum Cup application assistance or expert advice on safe, quiet and efficient point of use compressed air products give us a call.   We would enjoy hearing from you!

Russ Bowman, CCASS

Application Engineer
EXAIR Corporation
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