T-Slim or T-Flex and Occlusion Alert


I hear you. I switched to the X2 partly because I love my dexcom CGM and the 2 companies have a history, partly because uploading data is way easier with Tandem (although now I upload everything to Blip/Tidepool which is not perfect but I love having all devices’ data in one place) also partly because the X2 is quite a bit smaller than the new medtronic pumps. I may be guilty of willful ignorance myself. If I had dug deeper on these forums I might have noticed these false “occlusion alerts” as a thing. Here’s my amateur guess as to the cause: Tandem does not use a syringe and plunger mechanism to push insulin like most pumps do. Inside their cartridge is a bag that you fill with insulin. That bag gets squeezed to push insulin out. Tandem estimates volume by measuring the pressure left in the bag (Boyle’s law). So this is a lot more complex than just pushing a plunger 1mm to deliver 10 units of insulin which is what medtronic and others do. Instead Tandem is, by design, much more sensitive to pressure changes and therefor throwing out false alerts all the time. It gets them a smaller mechanism (the small pump holds 300units) but it also gets them a lot of false occlusion alerts. It sort of annoys me that the only error message I see is “occlusion alert.” It would be much more honest and easier to diagnose if they said “pressure alert” because there is clearly no occlusion.


Thanks for that detailed explanation, @Zardoz (love the screen name, btw. A SF classic!). That also explains why people say the reservoir-filling process makes it more of a challenge to eliminate all the bubbles/vacancies. Big problem I had with the Snap occlusions was that they mostly occurred during sleep times, maybe because lying on the side with the infusion set was causing just enough back pressure to set it off even though there was no real problem. So I was always getting jangled awake and not able to sleep through the night. Do you find you get more of these alerts overnight than in waking hours?


Ive been on the X2 one month–my first pump. I get an occlusion alert about once/week but it’s not due to the set. It’s a kink in the tubing. So i straighten out the tubing, tell the pump to resume delivery and all is ok. I’m not sure what I’m doing to the tubing to get it to kink so often and i fear the alarm going off at the theater or someplace else embarrassing.


I’m sorry to hear that the X2 still occludes. I got tired of the TSlim occlusions and the frequent, 10 minute change-outs of my infusion sets and purchased a pump I had heard good things about - the Vibe. I have since found it to be extremely reliable, with no occlusions to date (over a year) and accurate display of my CGM numbers. So, DrBB if you’re looking for something as reliable as Medtronic, I’d suggest the Animas Vibe. I’ve had two other Animas pumps before, with equally solid results. I have had to sacrifice the gorgeous Tslim interface and connectivity, because the Vibe isn’t quite so advanced in these areas. It takes several minutes to upload the Vibe to Diasend each time I do it. But I’ll deal with that inconvenience in exchange for perfect insulin pumping, fast change-outs (2 min) and an accurate CGM display any day.


@Zardoz , does the insulin bag inside the cartidge really get squeezed? I thought the insulin was pumped out. The big difference between the two (pump or squeeze) would be the necessity for air to get into the space left by the collapsed insulin sack. And the more I work with my t:slim, troubleshooting occlusions, the more I find it’s imperative the 6 little vent holes need to be free to breathe.


I’m looking at my T-slim and don’t see little vent holes. Where are they?



Ah!! Thank you!1 I’ll see if that is causing my problem.


I’m no engineer and I’ve never taken a cassette apart so I’m approaching this occlusion issue (both silent and with alarms) by trial and error. And what I’ve found works best to minimize my issue is to make sure those holes aren’t “sealed” against either my skin, in a very tight pocket, or in a snuggish case. I first noticed that if I put the pump in a small zip bag, mostly sealed, and then in my pocket, that it was a recipe for trouble. I’d do this while on a windy beach or when playing in sand. Bad idea. It seems my pump did better when it could “breathe”. Over the last six months or so I tend to only get occlusion alarms when the sites are bad or I’ve compressed the tubing in some manner.


Are they ok for larger guys? I’m a bigger guy about 300 lbs


Like everyone else commenting on this post, I keep looking for explanations for these occlusion alarms. IMO it is a pump problem and probably related to pressure and faulty sensor mechanism. Kind of surprised and disappointed that the X2 didn’t fix the problem that was obvious with the first generation of Tandem pumps.


I had the choice between the Medtronic Minimed 630g and the T:slim. Does anyone have any advice this will be my first pump I’ve been doing so much research and still can’t decide between the two. As I’m not getting a CGM or sensor I will just be using the pump as is. Any advice is appreciated. Thank you!


I haven’t been around lately but I wanted to post an update to my occlusion issues on the X2. It’s been 4 months since I posted about the regular “occlusion alerts” i’d been having. The good news is that I now have them very rarely. Maybe once every 5 infusion sets/ 20 days.

Here’s what I had been doing for years on Medtronic as well as on the X2:

  • CGM and infusion sets on my “love handles” aka just above my hips (I am relatively thin like many type 1s so I don’t have a lot of site choices)
  • I would put CGM on the front of my hips and inset slightly back on my hips, rotating each from left side to right side.
    inset moves every 4 days CGM moves every 2 weeks.

that worked great for medtronic and terribly for Tandem X2. Here’s what I changed to:

  • moved cgm to my upper arms (this was a big leap for me and I was worried about it but it works great and after 2 times I had it down. it even works for 3 weeks per arm now) I keep it on with Skin-Tac and remove with Tac-Away
  • moved infusion set farther back on my upper hips to a spot never used before (still change sides every 4 days)
  • I now ALWAYS fill the Tandem cartridge completely full. I actually slightly overfill it just barely beyond 300ml)
  • I spend lots of time tapping out and sucking out bubbles when I’m filling a cartridge. I really take my time and commit to getting nearly all the air out of that cartridge before pushing the insulin into it.
    *after 4 days I change the infusion set only (to the other hip). I keep the same cartridge and tubing since I’ll have about 150 units left at that point.

What I’m doing here is 2 things:
*moving the infusion set to virgin territory where there is likely less scarring or build up (although I can’t see or feel anything in my old spots)
*taking great pains to have more insulin and less air in the cartridge.

I’m not sure which part of this change is most significant but I rarely have occlusion alerts anymore. When I do have them they are almost always when I have between 50-0 units of insulin left. and just like before- when I do get the alert I simply re-bolus (which always works fine) and chalk it up to an imprecise and overly cautious pressure reading.

I’d like to thank @Laddie . You’re posts here and on your blog made me feel like I was not crazy and pointed me towards some fruitful experiments. Hopefully this post will help others.

Oh and I’m using T-90s just because I had a lot of them from my original order and with my first round of experiments I got the same results on all the infusion sets.


Thanks for the shoutout and glad that I was of help. And glad you seem to be avoid constant occlusion alarms.


Just a question: what do you do to do this? What do you do that is different from the instruction Tandem gives us?


Hi all–I’m new to TuDiabetes, and just wanted to say I found this thread really helpful. I’m a frustrated Omnipod user thinking of switching to a traditional pump for the first time. I was considering TSlim b/c of it’s iphone-like style but hearing about the occlusion problems is giving me pause. A friend suggested the Animas Ping (I don’t want the Vibe b/c I don’t want my CGM and my pump integrated) so I’m now going to search for any discussions about the Ping.
Anyway, I’m really glad a place exists for these conversations!


RachelRose, I have used Medtronic (twice), Deltec Cozmo (My favorite and why I hate Medtronic due to their lawsuit that chased Deltec out of the Insulin pump business in the USA), Animas and now the TSlim.

I will be posting a full review of the TSlim very soon, but I’ll say that I’ve had NO occlusion alerts at all. None… I am giving it a 4 out of 10 rating for other reasons. That iPhone interface was designed by Lawyers, not User Experience Design pros…

The Ping drove me nuts with the occlusion alerts. I felt lucky if I went a day without at least one. I hated that pump, and threw it hard against walls, tables, and probably other things in the two short years I tried to live with it.

IMHO, if occlusions are a concern, the Ping is a pig.


Currently we use the Tandem t:slim X2. Not a single occlusion problem yet. No complaints.

Is the Animas Ping still available for new pump requests? The Ping is/was a nice pump but it was FDA approved in 2008 so there might be some newer technology you could find interesting.


I don’t actually do much that is different than what my Tandem rep taught me. I just do more of it; lots and lots of tapping and lots and lots of pulling back on that plunger when sucking out air bubbles from the cartridge. I keep that up unilt there are nearly no tiny “champagne” bubbles coming out of the cartridge. I also think that it helps to put as much insulin in the cartridge as it will hold. I figure that more insulin = less air and I’m guessing that since liquids are effectively incompressible while air is very compressible, the pump ought to be able to judge “occlusions” better if there is less air in it. I may be kidding myself with all of this but somewhere in this mix of stuff I’ve changed, something is working better. call it faith based troubleshooting I guess.


When priming be sure to hold the Tandem upright. Yes - this is in the directions but this step could easily be missed.