A fountain pen is a very cool tool to have, but many users don’t apply it often simply because they don’t know how to refill a fountain pen. It’s a very important aspect to find out for you because if you use it every day, you’ll need to do this operation somehow.
To what features of the instrument you should pay attention? Is this procedure different for different pens? Let’s figure this out.

 Make a well-thought-out choice of your instrument. To avoid further difficulties when you will need to refill your fountain pens, we suggest exploring various types of pens with different filling mechanisms and choosing the one or several that seem the most appropriate for you in terms of price and usage. Basically, we divide the charging mechanisms into three categories: Built-in; Cartridges; Converters.
You can find out which mechanism your pen applies very simply – try to twist two pieces of the pen apart. If you succeed, you are dealing with a hand-installed mechanism. Here is the explanation of how to fill ink in a fountain pen, depending on the filler type.

 Built-in filling mechanisms are more popular than hand-installed ones because they can contain more ink and there will be no need to refill fountain pens very often. This is very helpful for those who write very often and need a pen that would be capable of working as long as possible. However, tools with this filling mechanism also have some considerable disadvantages. The first one is that they are expensive. If you have one pen it will, probably, last long. But if something happens to it, you will have to purchase another one, which may cost more than the majority of options. Additional expenditures are caused by the need to buy bottles of inks. You cannot refill such pens with cartridges. Moreover, refilling the pen with the ink from a bottle might be a messy task.
All in all, these options are quite popular because of their usability. Here are the most popular built-in mechanisms you should consider.

Piston fillers take time to be crafted, that’s why if you see a fountain pen with this refilling mechanism, it might mean that the pen costs a bit higher than the average tool. The first step to take here is to twist the piston until the resistance point. Don’t try to push it too hard if you don’t want to break the pen. After this, you should put the nib into the ink and start twisting the piston in the opposite direction. And that’s it. The ink fills the tank, and you can start writing unless it’s empty again.
The benefit of this mechanism is that your liquid won’t leak from the reservoir. This is because the piston is retracted in the end and there is no way for ink to leak.

Vacuum fillers. Production of pens with vacuum fillers also requires effort from a manufacturer. Similar to all other tools with built-in mechanisms, they are a bit more expensive than other options. Nevertheless, we can say that the price corresponds to the quality of the mechanism and to the ease of its usage.
The first step is to completely untwist the knob at the top of the pen. The second step is to gently pull this knob and put the nib into the bottle of ink. Then, you press the knob and the liquid goes to the chamber of your pen under low pressure. Usually, it takes up to 10 seconds to fill the pen completely.

Crescent filler. At first, the principles of the crescent filter work might seem complicated to you. However, you will quickly understand how this mechanism works after you do it step by step and pay attention to every following stage.
First of all, you need to turn the locking ring so as to place it into the opening position. Then, put the nib into the inkpot. The liquid should cover the nib completely. The third step is when you are pressing the crescent. This is done in order to make a vacuum inside the chamber. Then, you release the crescent and the ink goes up into the reservoir. The final step is to prevent discharging – turn the crescent back into the locking position.

Cartridges. Refilling cartridge fountain pens is an extremely simple process that includes fewer steps than charging the tools with the built-in filling mechanisms. However, simplicity comes with a considerable disadvantage. Well, at least some users find it so. It’s possible to apply only those cartridges that suit your pen. This means you won’t be able to enjoy using the whole diversity of inks sold only in bottles. Nevertheless, despite its disadvantages, there is still a solution. But you must be careful because refilling fountain pen cartridges with a syringe might be messy and inconvenient. So,  twist two pieces apart and put the cartridge inside the piece with the nib on the tip. Then, press it down and put your tool into a proper position. This way, the ink will flow down the barrel and fill in the nib. It might take up to an hour in some cases.

Converters. How to fill a fountain pen with ink if it applies converters? This works much similar to the variant described above. In the store, you can find both piston or squeeze converters. Since the principle of charging is very common for these mechanisms, we will describe this process on the example of a piston converter.
-First of all, install the converter. 
-Then, put the nib into the bottle of ink and start doing what you would do with the built-in piston filler – twisting the knob.
-Then, you should twist back to let the ink flow into the reservoir.
-Make sure to insert a converter correctly. This way the ink won’t be leaking during the process.