Filling the tslim cartridge

Why is it that sometimes when I pierce the cartridge using the needle that the tip of the needle doesn’t stop half way and pierces straight through the rubber?

If the valve is open it will go all the way down. If not it will stop half way. It doesn’t matter though because you are injecting into the resivoir and not through the valve.

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Thanks so are you saying even if it goes all the way in, it won’t damage the cartridge?

Correct. It won’t. It’s mentioned in the instruction manual.

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During training for my Tandem pump this happened to me on my first cartridge fill. My trainer had described to me what to expect but having the needle bury itself to the hilt was not what she described. She quickly explained that this sometimes happens and that no harm to the cartridge occurred.

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Here’s what the top of the cartridge looks like if you open it. The insulin fill port is the larger circle on the right; the white rubber seal sits on top of the C shape, with an open well in the center, and a small hole to the right, below the open part of the C shape. (The smaller round port to the left is where the tube comes out of the cartridge.)

The smaller circle in the middle of the C is the solid platform at the bottom of the well, which you normally hit with the needle, which stops the needle half way in. But if you point the tip of the needle too far towards the right side of the cartridge it goes down into the hole in the C-shaped opening, which is how the insulin goes into the pump. To my knowledge, that doesn’t cause any damage.

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Thanks that’s very interesting. But it usually happens when I poke it smack bang into the center. Not on the side where the c opening is located.

The needle can’t go through the solid center of the well. Perhaps you saw the needle enter the top of the white rubber seal exactly at the center, but the syringe or cartridge had a slight lean, sending the needle’s point slightly towards the side of the cartridge. The dimensions here are small multiples of the width of the needle, so it’s subtle. A countermeasure is to lean the syringe slightly toward the center of the cartridge.