Why Spray Can Lids Have A Small Hole On Top?

The hole in the lid of a spray can is necessary to allow air to enter the can and equalize the pressure inside and outside the can. This prevents the lid from popping off when the can is transported to a location with a different atmospheric pressure.

There are many things around us that we look at everyday, but don’t pay any attention to for more than a few seconds. For instance, if you’ve ever carefully observed the lid of a spray can, you would have seen a tiny hole in its lid. Do you know why there is a hole in the lid of these types of cans?

Tight-Fitting Lids

Credit: er ryan/Shutterstock

During their manufacture, the lids are fitted very tightly on top of spray cans, so that the liquid/oil doesn’t ooze out of the nozzle along the sides of the can. Now, suppose a large number of spray cans are manufactured in New Delhi and are set to be shipped to Jammu. The process of transportation is quite easy in itself, but it involves an interesting scientific phenomenon. Let’s assume that a particular consignment of spray cans were shipped from Delhi without putting holes on tops of the cans. In that case, the recipient would be in for a surprise, as all the cans would have their lids popped off!

Why does that happen?

Air Pressure Change

When the cans were being sealed in Delhi, the air inside the lid had a specific pressure that was the same as the air pressure of the surroundings. If they were only being transported to a nearby location, then the lids would have stayed in their original places. However, Jammu is located at a higher altitude than New Delhi, which is why the air pressure in Jammu is lower than the air pressure in New Delhi, as air pressure decreases with elevation. Therefore, the pressure inside the lid would become greater than the pressure outside the lid, resulting in the air inside the lid attempting to expand. This eventually causes the lid to pop off.

Enter the Holes

In order to make sure that the lids don’t pop off when spray cans are being transported over long distances with different atmospheric conditions, manufacturers put a hole on the top of the lid of spray cans. As a result, the air trapped inside the lid gets a “release vent”, so to speak, to seep and allow the air of the surroundings to enter the lid, thus striking a balance and keeping the lid in place.

Therefore, punching a small hole in the lid ensures that the lid stays in place, and guarantees that the liquid inside the can doesn’t ooze out (which would be caused by the absence of a lid).

You can see for yourself how the transportation of goods is not as easy as it may seem at first glance. You have to take care of a number of things, including the climate, atmospheric conditions and other variables, not to mention the process of transportation itself. It’s fascinating how such a simple trick of punching a hole in the lid can maintain the quality of the liquid and ensure the proper delivery of a product, as promised!

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