# Calculate Load carrying capacity of vertically mounted suction cup

• Acenish
In summary, if a suction cup has a weight that is suspended from it and the pressure inside the cup is greater than the pressure outside the cup, the cup will eventually fail because the pressure outside the cup will overpower the pressure inside the cup.
Acenish
TL;DR Summary
Calculate Load carrying capacity of vertically mounted suction cup
I'm looking for means of calculating load carrying capacity of a vertically mounted suction cup.
Suction Cup effective diameter = 90mm
Mounted on a vertical glass surface
Pressure inside the suction cup = 0.75bar
Pressure difference = 0.25bar
Weight is suspended from a rod attached in the centre of the suction cup.
Rod length = 150mm

Need to calculate how much weight can be suspended before the suction cup pulls off the glass surface

Assume, coefficient of friction between suction cup and glass as 0.2

Welcome to PF.
Is this a homework problem?
Have you tried to solve the problem yourself?

Hi
No its not a homework problem, rather a curiosity in suction cup design and load capacity.
This arose while using suction cup phone mounts or clothes line as well as with respect to nerf arrows.

Below is a diagram of the suction cup with a suspended load.

Applying force equilibrium, we get
Fsuction = N (normal force)
now, Ffric = µ x N = µ x Fsuction
& Fsuction = ΔP x A
so, Ffric = µ x ΔP x A = W

Assume, µ = 0.1
Patm =1 bar (0.1N/mm²)
Pi = 0.8bar (0.08N/mm²)
A = π x d² /4 = 6361.73mm² (d = 90mm)

thus, W = 0.1 x (0.1 - 0.08) x 6361.73 = 12.72N = 1.2kg (approx)

However, what has me puzzled is that the Load W will also have a moment acting on the suction cup and this moment if considered in the centre of the cup, will be balanced by the Fsuction till it fails under a 'peeling-off' action (in this case the top end will peel as W is acting downwards.

This gives, W x 150mm = Fsuction x 45 (radius of cup)....... considering moment in the centre.
=> W = (ΔP x π x d² /4) x 45 / 150 = 38.17 N = 3.8kg (approx)

Was hoping to get feedback on whether either of the approaches are correct.
Thanks

Acenish said:
Was hoping to get feedback on whether either of the approaches are correct.
The cup could unstick from the glass, or it could slide down the glass.

Area of cup = Pi*(0.045)^2 = 6.36e-3
Differential pressure = 0.25 bar * 100 kPa/bar = 25 kPa
Cup force against wall = area * pressure = 159 N.

At what vertical load will the cup slide down the wall?
Note that it is independent of the rod lever arm length.
Apply friction; 159 N * 0.2 = 31.8 N.
31.8 / 9.8 = 3.24 kg.

If it did not slide, the cup would break off the surface at;
Assume the length of the rod is measured from the glass.
Fvert = 159 N * (45 mm / 150 mm) = 47.7 N.
47.7 / 9.8 = 4.867 kg.

So the cup will slide at 3.24 kg.

Acenish said:
Assume, coefficient of friction between suction cup and glass as 0.2
Acenish said:
Assume, µ = 0.1

Thanks for response.
Values are arbitrary and I am interested in the approach.

Glad to know, I wasn't off the mark!

## 1. What is the purpose of calculating the load carrying capacity of a suction cup?

The load carrying capacity of a suction cup refers to the maximum weight or force that the suction cup can support without losing its grip. This calculation is important in determining the suitability of a suction cup for a particular application, as well as ensuring safety and avoiding any potential damage or accidents.

## 2. How is the load carrying capacity of a suction cup calculated?

The load carrying capacity of a suction cup is determined by factors such as the size and material of the suction cup, the surface it is being attached to, and the force of the load being applied. The calculation typically involves using a formula that takes into account these variables to determine the maximum weight or force that the suction cup can withstand.

## 3. What are the common materials used for suction cups and how do they affect load carrying capacity?

Suction cups can be made from various materials such as rubber, silicone, and plastic. The material used can impact the load carrying capacity of the suction cup as different materials have different levels of flexibility and strength. For example, a silicone suction cup may have a higher load carrying capacity compared to a rubber one due to its ability to withstand higher levels of force.

## 4. Can the load carrying capacity of a suction cup be increased?

Yes, the load carrying capacity of a suction cup can be increased by using multiple suction cups together or by using a larger suction cup with a higher weight capacity. Additionally, ensuring that the surface and suction cup are clean and dry can also improve the grip and load carrying capacity of the suction cup.

## 5. Are there any safety precautions to consider when using suction cups for heavy loads?

Yes, it is important to always follow the manufacturer's instructions and recommendations for the maximum load carrying capacity of the suction cup. It is also recommended to periodically check the suction cup and its attachment to ensure it is still secure and able to support the load. If using multiple suction cups, make sure they are evenly distributed and properly attached to avoid any imbalances or failures.

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