Not all household sprays come in cans. Some kitchen products and perfumes come in plastic orglass containers with squeezy trigger handles that make an aerosol as you pump them back and forth. These sprays (which are called misters or atomisers) work in an entirely different way.
The bottle contains only the liquid ingredient: there's no propellant at all. When you pump the trigger mechanism, you lower the air pressure in the tube running down into the bottle. Because there's air inside the bottle, at the top, the liquid is forced up the tube. The pump mechanism forces some of this liquid out through the tube into a much smaller nozzle, so it turns into a high-speed aerosol of tiny droplets.
The big advantage of misters is that they need no propellant, so they're safer to use. But they generally don't make such a fine or even spray as aerosol sprays, so they're less suitable for products such as paint and polish. They also have to be pumped quite hard to get them going, so it can be quite hard to release small amounts of product with them.
To recap:
- You pump the trigger up and down, forcing air (initially) from the nozzle.
- The escape of air causes a sudden drop in air pressure at the top of the tube in the bottle.
- The air inside the top of the bottle is at higher pressure than the air in the tube, so it pushes down on the liquid.
- The liquid is forced up the tube toward the pump mechanism.
- The liquid leaves as a fine mist of spray.
