WHY BAGS MAY INFLATE DURING THE VACUUM CYCLE?
Once starting the vacuum process, it is important to check that the bag laid on the sealing bar is not folded. By the end of the cycle, as the pressure inside the bag grows, in common machines an inflation of the bag may often be visible. This phenomenon points out the presence of air inside the bag, rather than signalizing a good vacuum quality. By having vacuum inside the chamber and into the bag, the latter inflates as a consequence of the difference of pressure between the two, since air tends to expand towards the vacuum. Once the atmosphere is introduced inside the chamber again, the bag is pressed against the product due to the difference of pressure and it gets compressed. The phenomenon of bag compression doesn’t occur in case inert gas is introduced into the bag, since the air volume is substituted with the inert gas one (modified atmosphere). With chamber vacuum machines it is possible to create vacuum also in bags with liquid products. Even by putting a bag with liquids inside the vacuum chamber, the same physical principle applies: since the pressure inside the chamber equals the one inside the bag, the liquid doesn’t pour out. In fact, there is no external pressure compressing the liquid and pushing it out of the bag.
HOW TO IDENTIFY A GOOD VACUUM QUALITY
The quality of a chamber vacuum machine can be detected thanks to three simple elements:
• By introducing a glass of water inside the chamber at sea level, as soon as the vacuum sensor indicates -99 the water starts boiling (actually degassing). If nothing happens, then the machine doesn’t have a good vacuum quality.
• If the bag inflates during the vacuum cycle, then the final vacuum quality will be poor.
• In case of sealing with liquid products, if these are expelled out of the bag then the final vacuum quality will be compromised.
The expulsion of liquids from the bag is due to the fact that there is still air within it, so the pressure on the inside grows and the bag inflates. The liquid starts boiling and its steam creates even more pressure inside the bag, which escalates and finally expels both steam, air and liquid out of it. In some cases the bag may even explode or get thrown out of the sealing bar. Some manufacturers developed empirical techniques in order to carry out an aspiration cycle in case of liquid in the vacuum bag and do it in several steps. These really are empirical techniques, that do not guarantee an excellent vacuum quality like ELEGEN does. Thanks to its EVOLUTION sealing bar system technology, Elegen can ensure the best possible level of efficiency and performance for chamber vacuum machines.