In all the aerosol cans that we have, we will see a series of warnings about its use, among which are, for example, that the can should not be punctured or that it should not be brought close to heat sources, which is why it is important to know how the pressure of an aerosol works, we will tell you about it in this article. Romar Global Care, you aerosol packaging company.
How does a spray work?
Aerosol cans are now a staple in our daily lives, whether they contain cosmetics, food, insecticides, paint, etc. These cans make product application much easier and are very practical, whether used industrially or at home.
Aerosols have evolved quite a bit since they were invented. They are basically a pressure vessel where liquids and gases are stored. They are composed of various elements such as: push button, valve, spring, canister, liquid and gas.
More than 95% of manufactured aerosols use liquefied gases as propellant., such as hydrocarbons, dimethyl ether and 1,1 difluoroethane, which although they offer better performance for spraying the aerosol product, these liquefied gases can become flammable and with increasing temperature, their vapor pressure and the thermal expansion of the liquid increase.
How an aerosol works
As for the how aerosols work It hasn't evolved much since its invention. Let's take a step-by-step look at how an aerosol works:
- The propellant It is kept at high pressure inside the canister, so it is in a partially liquid state. When it is in a partially liquid state, the propellant mixes with the liquid to be vaporized.
- Once tightened the push button and since there is much more pressure inside the can than outside, the liquid tends to rise through the plastic tube until reaching the nozzle Up to this point, the liquid has not been sprayed.
- When the mixture of liquid with propellant comes out through the nozzle changes its pressure. The propellant, being inside the boat, is under high pressure and in a liquid state. When it comes into contact with the atmosphere while passing through the nozzle, the pressure is much lower and the propellant becomes gaseous, pulverizing in such a way that the liquid spreads into the atmosphere in the form of rain.
How does pressure affect aerosol?
To discuss aerosol pressure and its importance in performance, we'll first mention some important aspects of aerosols; for example, their definition tells us that:
An aerosol is a non-refillable packaging system consisting of a container and a metering valve, where the product and a propellant have been impenetrably sealed.
Taking this definition into account, we know that the propellant is a fundamental part of the aerosol system, but then, What is propellant? It is precisely the gas responsible for supplying the pressure necessary for the active ingredient to emanate from the container when we operate the dosing valve.
The gases most commonly used as propellants are currently classified as follows:
Compressed gas
- Air, Nitrogen, Carbon Dioxide (when compressed, its pressure decreases depending on its volume and it is difficult to empty the contents completely).
- Hydrocarbons (petroleum-derived gases that are economically accessible. They are the most commercially used).
Liquefied gas
- Chemical synthesis gases (they have a higher cost than hydrocarbons and are used mainly in countries where the VOC limit is regulated).
- Mixtures of hydrocarbon gases and chemical synthesis (state-of-the-art blends used primarily to maintain VOC limits and reduce costs when using hydrocarbons).
Characteristics of liquefied gases
- Toilets. In order to modify the aroma of the active product.
- Reduced pressure variation. During the use of aerosol, provided there is equilibrium with its vapor phase, because the Pv is independent of the liquid volume.
- Wide range of Pv according to the requirements of the product and packaging. (Between 22 psi and 110 psi for hydrocarbon gases).
- Soluble in the concentrate for most uses.
- Commercially available and economically viable.
- Toxicologically acceptable and non-corrosive.
- Adequate environmental impact with a minimal effect on ozone, minimal contribution to the greenhouse effect and air pollution.
- The lowest possible flammability.
- Pure and stable. To avoid side reactions.
What relationship existsbetween the propellant gas and the pressure from the packaging of an aerosol?
This list highlights the features of relationship between the propellant gas and the vapor pressure term, which is exerted by the vapor of a liquid when it is in equilibrium with the liquid.
From the method for determining the vapor pressure in liquefied gases we can highlight some important points for said determination:
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- The test of the water bath, It is carried out in line with a 50-degree bath for three minutes.
- Additionally, another test is carried out with a temperature set at the aerosol industry of 21°C, which must be set, corroborated and maintained during the test using a water bath, because temperature is a determining factor in the measurement of Pv.
- The unit of pressure established to express the results is psi.
- It is important to express the Pv value with reference to sea level, which requires an altitude adjustment; for example, if the determination is made in Mexico City (located at 2,240 meters above sea level), the adjustment is made by subtracting 3.4 psi from the Pv value obtained.
- The pressure gauges used must be calibrated and have the appropriate measurement scale.
- We must ensure that the device used for this test is filled correctly and that it is leak-free.
- The test device must basically consist of an upper chamber and a lower chamber (the volume ratio of the upper chamber must be 3 times greater than that of the lower chamber), and both interconnected by a valve as shown below.
Which the proper way of filling of aerosols?
Below we will show you the proper way to fill aerosol:
- Connect the empty device with all valves open directly to the tank/trailer/tank truck containing the gas sample to determine the Pv.
- Fill the device completely with liquid.
- Close the end valves (keep the valve connecting the chambers open).
- The valve connecting both chambers is closed and the purge valve opens to allow the lower chamber to empty completely.
- Once the lower chamber is empty, close the purge valve and open the valve that connects the chambers to allow the liquid to descend and generate the space where the liquid-vapor equilibrium necessary for determining the Pv of the liquefied gas is achieved.
- After the aerosol can has been filled correctly, it must be immersed in a water bath at the set temperature (21°C) for approximately 30 minutes.
- During that half hour, the aerosol can must be removed from the water to shake it vigorously and return it to the water every 2 minutes. Once the 30 minutes are up, the pressure gauge must be connected to take a reading.
As previously mentioned, temperature is a determining factor in the measurement of Pv. In the results of vapor pressures at different temperatures, the values obtained at the temperature already established for the determination should be highlighted.
Pv readings at other temperatures should also be included to demonstrate the variation obtained between the results and the importance of maintaining a constant temperature.
Ensure aerosols are not overfilled
One of the risks associated with the aerosol filling It is the thermal expansion of gases. An aerosol can can burst if not left sufficient space to allow for free thermal expansion.
If an aerosol is filled above 85 µl, it could cause an accident. For example, if it were filled to 91 µl at a temperature of 15°C and heated to 50°C, its volume would expand by 100.6 µl, which could cause the container to explode.
For this reason, Aerosol containers should never be overfilledWhen heated, they can burst and cause an accident during manufacture, handling, storage, transportation, or use.
From Aerosol Romar Global Care, a third-party aerosol packaging company, we ensure that all the aerosol cans comply with regulations to ensure the maximum security in our products.
Overfilling of an aerosol container is due to carelessness or human error. Another safety measure to prevent overfilling is weight control. This measure should also be mandatory for the aerosol filling.
The function of a weight control is identify high and low aerosol contents and automatically reject from the line aerosols that do not comply with the established content.
This way, you can prevent overfilled cans from entering the hot water bath and bursting.
Aerosol Romar Global Care, guaranteed safety in our products
In Aerosol Romar Global Care We adapt to the necessary safety measures as well as the needs of our clients. We strive to fully adapt to your requirements, always seeking to be flexible and adapt our costs as closely as possible to remain competitive.
We take care of adapting your products to the appropriate aerosol, so that aerosol pressure is not a problem. Our goal is packaging aerosols with the best value for money. We have 40 years of experience to ensure you the best service in the aerosol sector.
We want to offer you the most effective and innovative solution, always thinking about how to improve your product.
How to prevent accidents with the aerosol can
Every year there are accidents with the aerosol cans, so we must always keep these warnings in mind. Not only is approaching a heat source dangerous, but exposure to the sun also causes boats to explode like bombs, which can lead to dangerous accidents.
There have been multiple accidents reported due to ignoring these warnings, so it is extremely important to always keep them in mind when handling aerosol cans. Therefore, if you are looking for a company that handles aerosol cans, packaging aerosol products, it is essential that you verify that said company ccomply with regulations during the packaging process.
How much pressure is there in a spray can?
To understand why aerosols end up becoming potentially deadly weapons, you should know that the canisters have a pressure of between 2 and 8 atmospheres. That's the equivalent of between 2 and 8 kilometers per cubic centimeter. This would cause a potentially deadly explosion.
For this reason, only part of the container is filled with liquid, leaving room for possible expansion through the concave base and top.
In addition, the aerosols are tested individually before leaving the factory by passing them through a hot water bath, as mentioned above, which increases the pressure of the can, thus verifying its strength and integrity.
Therefore, the manufacturer must take this into account and ensure that the aerosol can is not overfilled.
Did you know that cosmetic products can be packaged in aerosol? Romar Global Care We have the perfect pressure for this type of aerosol. Learn more at the following link: Cosmetic products that can be packaged in aerosol
Prevention of bad practices in aerosol pressure
Finally, some suggestions already mentioned are listed in order to prevent bad practices in the determination of vapor pressure.
- It is important to perform the determination at a temperature of 50°C and 21°C, continuously checking that there is no variation, using calibrated thermometers.
- Always use calibrated pressure gauges with the appropriate scale, remembering that the unit of pressure is psi.
- We must not forget to adjust for altitude and thus assume that the expressed Pv values are always referred to sea level.
- During the determination we must ensure that the device does not have any leaks.
- We must ensure that the necessary liquid-vapor balance is achieved to generate the PV by filling the device correctly. Therefore, we recommend avoiding performing the determination directly from the aerosol can or using a device that doesn't meet established standards.
Romar Global Care, your best choice in aerosol packaging
In Romar Global Care We take care of having the best packaging service company, always taking into account safety measures for the use and handling of aerosols, ensuring you get the best product so that the pressure of one or more aerosols is not a problem.
We package all types of aerosols, from cleaning products, air fresheners, and party supplies to cosmetics, beauty products, and food.
We focus on your recommendations to ensure you have the best experience with us as your spray manufacturer.
