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These filling systems have in common the use of the presence of a ''[[breather tube]]'' which allows to perform the refill by repeating several times some mechanical action (different depending on the different filling systems) which allows to create a compression of the air inside the pen tank. The variety of ways in which this compression is carried out has been extremely wide, but in most cases provides some mechanism that acts on a flexible bulb.

These filling systems have in common the use of the presence of a ''[[breather tube]]'' which allows to perform the refill by repeating several times some mechanical action (different depending on the different filling systems) which allows to create a compression of the air inside the pen tank. The variety of ways in which this compression is carried out has been extremely wide, but in most cases provides some mechanism that acts on a flexible bulb, even if there are alternative mechanisms, such as the one found on some [[Ancora Lusso]] in which the depression is done with a very short running piston.