When pressing the canister into the actuator, the drug-propellant mixture in the metering valve is released under pressure.
As the liquid propellent ejects from the pressurized valve into ambient pressure, it “flashes,” i.e rapidly expands and vaporizes. This expansion and vaporization shears and breaks the liquid stream into an aerosol.
Propellant vaporization results in cooling of the liquid-gas aerosol suspension. If it is discharged onto the skin, it can be easily felt.
Upon release, the metering valve refills with the mixture of drug and propellant from the bulk of the canister. It is ready for the next discharge.
