How does a spray(spray cans, disinfectant sprays etc.) work?
In: Engineering
There’s two things inside the can…the stuff you care about (paint, hairspray, disinfectant, whatever) and some pressurized gas. The gas is sitting above the liquid, like the “air” space inside a soda bottle.
The key that makes it work is that the nozzle has a straw that goes all the way to the bottom of the can. The gas is pushing down on the liquid but the only way out of the can is through the straw, and that’s in the liquid. So the gas pushes the liquid up through the straw and out the nozzle.
This is why your spray can still “sprays” but doesn’t do anything useful when it’s empty. The liquid has all gone and the gas can finally get to the straw, and now it comes straight out the nozzle.
The product, be it paint or disinfectant, is suspended (chemistry level of suspension, mixed in with but not dissolved) with a bunch of other chemicals called aerosols. Aerosols, like butane, are in gas form at standard room temperature and pressure. They’re put under pressure so that the aerosol is compressed into a liquid form and then put into a spray can.
Now these aerosols and product are mixed together in a can under pressure and pressure wants to equalize. When you hit the spray nozzle, this pressure starts to escape taking with it the aerosol and that carries some of the product along with it. The aerosol evaporates into the air because that’s it’s natural state. The product is still in liquid form of tiny droplets, carried out by the aerosol, which then lands on the surface you’re targeting.
This is one of the reasons you must shake these cans prior to use so the product and the aerosols mix together to get a more consistent spray pattern.
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