Fountain Pen Filling Mechanisms

There are several filling mechanisms used in fountain pens today. The main types of filling mechanisms include Cartridge, Converter, Eyedropper, Piston, Sac, and Vacuum. Each has its own method for how to fill the fountain pen with ink, as well as how to clean it out. There are pros and cons to each type of filling mechanism.

Main Types of Filling Mechanisms:

Cartridge

An ink cartridge is a small, disposable, sealed plastic reservoir that holds fountain pen ink. Some pen brands use their own proprietary style, though many use a standard international (short or long) size cartridge. A cartridge-style fountain pen is filled by inserting one of these prefilled ink cartridges.

A disassembled brass fountain pen with an ink cartridge on a white background

Pictured: Kaweco Brass Sport fountain pen with ink cartridge

Converter

A converter is a detachable, refillable ink reservoir that allows you to use bottled ink in a cartridge pen. Fountain pens that have this option are often referred to as Cartridge/Converter pens.

A dark blue fountain pen disassembled with a converter on a white background

Pictured: LAMY Studio fountain pen with converter

Eyedropper

This type of fountain pen utilizes the entire barrel as a reservoir for ink. Ink is filled directly into the barrel, allowing for a high ink capacity. This can be done with an eyedropper or an ink syringe. Some pens are eyedropper-only, meaning they do not accept a cartridge or converter, while others allow for these methods too.

A clear fountain pen filled with ink, on top of a drawing and writing

Pictured: Kaweco Sport fountain pen, eyedropper-filled with ink

Piston

A type of filling system that uses a retracting plunger inside a sealed tube to draw ink into the pen. A piston filling mechanism can either be screw or push operated, though the screw/twist type is the most common.

A clear fountain pen with a black cap, open, and showing the internal piston

Pictured: TWSBI ECO fountain pen with piston mechanism

Sac

Primarily found in vintage fountain pens, a sac is an ink reservoir typically made of silicone or latex. The pen is filled by first collapsing the sac to release the air, and then it fills with ink. It can be attached to the pen such as in the style of crescent-fillers or level-fillers, or as part of a converter, called aerometric.

A black Pilot fountain pen, disassembled, on a white background

Pictured: Pilot Metropolitan fountain pen with CON-B squeeze-style converter

Vacuum

These fountain pens have a push-style piston that uses vacuum-pressure to fill the large pen body with ink. They seal the ink chamber when closed, making it more ideal for flying (air pressure changes) without risk of the ink leaking.

A translucent brown Pilot fountain pen with the cap off and vacuum rod extended

Pilot Custom 823 fountain pen with vacuum-filling mechanism

How to Fill Each Type of Fountain Pen:

In this video, I'll show you how to fill the basic types of fountain pens, as well as the pros/cons of each one:

Cartridge (:28)/Converter (1:20)
Eyedropper (2:30)
Piston (4:08)
Vacuum (5:28)

There are certainly some other filling mechanisms like bulb, lever, crescent, blow, and button fillers, but those are mainly in vintage pens and not my area of expertise. This video should cover about 95% of pens you'll see, especially newer ones.