Tandem Tslim Pump Cartridges

Thank you for stepping in. We are all trying to help each other out based on the information we have.

As I have said, I am committed to the Tandem Tslim because my amazing Animas pump is discontinued.

Is it possible for me to redirect the conversation back to the question about how it measures the amount of insulin and how one can know whether air bubbles have been removed from the cartridge.

Thanks to all.


So I am flagged yet blatant personal attacks are allowed.

If I felt you actually wanted input from me than I would.

But I assume this is going to be flagged and hidden anyway.

Drive on.

I have been using my t.slimx2 (without the basal IQ until I get my Dexcom g6) for 2 weeks now and have had no problems with bubbles nor occlusions since the first time I made a cartridge change and goofed it up royally. Since then the process has gone smoothly, although quite slowly because I very, very carefully read the instructions as I go about the cartridge loading.

Curiosity got to me as to how exactly the cartridge operates and I tried, unsuccessfully, to open one to see the mechanics of it. Didn’t have the time to get a hammer to whack it open but was very much impressed that it would not budge to finger pressure. Will persevere. The next BANG you hear will be a Tandem cartridge being whacked open. Of course, it will be a used cartridge and won’t be inside the pump. :smirk:


thanks for your post. I would love to see what it looks like inside–Tandem should include an illustration to explain how it works so that we don’t have to imagine what the darkened chamber contains. I just want to know where my unaccounted insulin is hiding.

Here is a link to the Tandem YouTube clip that shows how they recommend filling a cartridge. This is essentially what I do … except I only pull about 50 units worth of air when I do it.

Good luck,



I follow those instructions slowly and precisely. No bubbles. No occlusions. No problems. Knock on wood! I must admit that this is more intricate and time consuming than the cartridge change was on my Animas Ping. But that took me a while to learn as well. One thing I learned a long time ago though was to never, never change the site and cartridge before bedtime. If anything is going to go wrong it will be then at the end of the day when I am tired and distracted and hurried.


That’s correct.

Here’s a brief video clip showing how the pump operates. Before I retried I was involved in designing micro pumps for laboratory use. The X2 pump mechanism was a big factor in my decision to go with Tandem. The slow delivery speed and isolation between me and the insulin reservoir were very appealing. I often had stinging at the infusion site from the relatively fast bolus delivery on all my previous pumps.

The cartridge fill process is definitely more cumbersome than other pumps. But once you do it a couple times it’s quite easy. I follow the directions in @John_S2’s post and never have an issue with bubbles. I routinely use the pump until 4-5 units are left in the cartridge with no problems.

Thank you for this post.
I too follow these instructions and I do not see many air bubbles (except a couple tiny ones at the beginning when I am filling the tube). I also never get occlusion alarms, I just feel like I am using far more insulin with this pump.

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Indeed, never at night. I will often fill it the earlier in the day if I think I will need to change it out before bed.

I am also following the official instructions and do not have much in the way of air bubbles or occlusions but I am just wondering why it does not register all the insulin I put in (and yes, I do calculate for priming and the “20” unit reservoir).

Will continue to observe, I am only one month in and must admit I am unnerved by not seeing what is inside.


This is the video that I used to train on filling the cartridge. Will continue to work on perfecting my technique. I do not get any occlusions or have many air bubbles, I am just baffled with how it doesn’t seem to register the full amount of insulin that put in there (even when I consider the priming and the “reserve” of 20 units).

That is especially true if you are using a cannula type of set. Steel sets aren’t likely to cause you any non-delivery issues at any time of the day or night, so it’s quite safe to change out a steel-set in the evening.

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See my post above, directed at Willow.

That’s a common complaint of Tandem pump users. Some say that after you use a certain amount, it will correct the amount of insulin remaining. Sounds kinda annoying, if you ask me.

My trainer indicated that it was not recommended to prefill the cartridges. Not sure why. Didn’t ask because I never prefilled.

I’d be interested to know if they “think” that the insulin would be degraded by prefilling. As if the insulin could go “bad” in 6 days as opposed to being in a reservoir for 3 days. Or go bad in 10 days. Assuming one isn’t leaving them in a hot car. :slight_smile: Is the material that the bladder is made from causing insulin deterioration?

That would be my assumption, or maybe my question. I have been told that degradation due to interaction with the plastic is a factor in limiting rigid reservoirs to 3 days’ use. But I’ve also seen people say they fill the reservoir up with six days’ worth of insulin so they can keep the same reservoir going when they rotate the infusion set, with no apparent loss of potency. Could be it’s one of these things that lives on in official documentation because of some study or other but that doesn’t actually obtain any more in practice.


Once the set change is done and insulin delivery has been resumed, the insulin reservoir indicator shows 240+. After a few hours it will then show the actual amount of insulin minus 20 units. The pump subtracts and doesn’t count 20 units from the reservoir supply for some reason. This probably has something to do with the pump relying on pressure readings from the bag instead of a plunger to estimate reservoir capacity.

Is that because you can’t totally empty the reservoir during normal pump use? Does it retain 20 units that is not deliverable?

That is my understanding. I have run the cartridge completely empty a few times but never checked to see how much insulin was really left. At 5 units, the pump has stopped delivery and told me to replace the cartridge.

I suspect it may be because once removed from the vial and not inserted into the pump, the insulin is in uncontrolled condition. Could also be a matter of contamination since the cartridge is now taken out of its antiseptic covering. Just speculation, of course.