Inside the Aerosol Can
Posted by smculp on November 12, 2008
The two systems that are used in aerosol cans to spray the ingredients inside are the compressed-gas system and the liquefied-gas system.
Compressed-gas System: First, the liquid product is poured into the can. Then the can is sealed, and a gaseous propellant is pumped through the valve system at a high pressure in order to push the product down. A plastic tube runs from the bottom of the can to a valve system at the top of the can. The valve system has a small headpiece with a channel running from an inlet near the bottom of the headpiece to a small nozzle at the top of the can. A spring pushes up the headpiece to block the channel inlet. When the headpiece is pushed down, the inlet slides open, creating a passage. The high-pressure propellant gas drives the liquid product up the tube and out the nozzle, and the nozzle atomizes the product (breaks it up into tiny drops).
Liquefied-gas System: The liquefied-gas system is similar to the compressed-gas system, but is the more popular of the two aerosol can systems. The propellant is a liquefied gas and remains a liquid at all times. The set up of the liquefied-gas system has the same design as the compressed-gas system. The product is poured in, and the can is sealed. Then the propellant is pumped in under high pressure so as to prevent the propellant from expanding into gas. Then the valve opens; the pressure on the liquid propellant decreases, causing the propellant to boil. Particles break free to form a layer of gas at the top of the can. This pushes the liquid product and propellant up the tube to the nozzle. When the liquid goes through the nozzle, the propellant expands to gas to either create a fine spray with the product or form foam.
