Contrary to popular opinion, there really is no pressure or vacuum inside a Kayfun Lite. They have open air and juice channels, so neither the chamber nor the juice tank are really pressurized. The only vacuum created is when the user draws on the mouthpiece. This creates a differential, and juice is replenished to the wick as the vaporozed juice is drawn off. It is actually a supply and demand system; sort of like those self feeding water bowls people have for dogs. The hole is specifically sized so that as the dog drinks water, the level in the bowl lowers, and the tank replenishes the water to a specific level. In the Kayfun lite, the juice channels are carefully sized, so that the only time juice is fed to the coil is when the user draws it off. If the channels were larger, it would constantly flood. If they were smaller, the juice wouldn't be fed fast enough. That's why it's important not to cover the channels with the wick. It will result in dry hits. Conversely, if you remove the top cap, it would be the same as having the juice channels too large. The chamber will flood, because the level of the juice in the tank would equalize in the chamber.