Filling a cartridge without bubbles
Hold the cartridge upright and level, put the needle tip against the inside wall of the glass, and push slowly so the liquid runs down the side. Filling at an angle, or fast, is what forces air in ahead of the liquid and leaves you tapping bubbles out for five minutes.
What you need in front of you
- A sterile 3ml cartridge, still sealed until this moment
- A syringe, large enough to do it in one pass
- An alcohol wipe
- Somewhere flat, clean and well lit
- A filling tool, if you have one, or a steady hand
The order that works
Wash your hands, then wipe the tops
Both the vial stopper and the cartridge stopper. Give the alcohol a few seconds to dry rather than wiping it straight off, because the drying is what does the work.
Draw the full amount in one go
Two half-fills means two chances to introduce air and two punctures through the rubber. Use a syringe big enough for the whole volume.
Stand the cartridge upright
This is where a filling tool earns its money. Both hands free, cartridge dead level, no wobbling. Held at an angle, air gets in and stays in.
Needle in against the wall, not the middle
Enter through the stopper and angle so the tip touches the inside of the glass. The liquid runs down the wall instead of dropping through the air inside.
Push slowly
Slow enough to watch the level rise. Speed makes turbulence, turbulence makes bubbles, bubbles cost you five minutes.
Withdraw, then check the glass
Hold it to the light. A few pinhead bubbles clinging to the wall are normal and harmless. A large pocket at the top wants clearing before you load it.
Load and prime
Cartridge into the pen, screw on a needle, dial two clicks and expel them pointing upward. That clears the needle and confirms the pen is delivering before it matters.
Prime every time. Two clicks costs almost nothing and it is the only way to know the mechanism is engaged and the needle is clear before you have committed to an injection.
The four mistakes that cause almost everything
- Filling at an angle, which traps air at the top of the glass
- Pushing fast, which whips bubbles through the liquid
- Filling in two goes, doubling the air and the punctures
- Skipping the prime, so the first dose is short by whatever sat in the needle
How full is full
A 3ml cartridge holds 3ml, but do not aim for the brim. Leave a few millimetres. A completely full cartridge has nowhere for the plunger to sit properly and tends to weep at the stopper when the pen is dialled.
Questions
- Do I need to vent the cartridge while filling?
- Not usually. As the plunger is free to move, displaced air escapes on its own. If you feel real back pressure, you are pushing too fast or the plunger has jammed.
- Can I fill a cartridge while it is in the pen?
- No. The pen mechanism holds the plunger, so there is nowhere for the liquid to go. Fill it out of the pen, then load it.
- How long can a filled cartridge sit?
- That depends entirely on what is in it and how it is stored, which is outside what we can advise on. As a matter of equipment, a sealed filled cartridge kept cold and out of light is fine mechanically for weeks.