Greiner caps popping off in centrifuge

[SMILLER 844]

We are in the process of switching our specimen collection tubes to Greiner Vacutte (previously we used BD).    For some reason, with one of our STAT fuges, the stoppers keep coming off while being spun.  Not all the time but enough to be annoying. 

The centrifuge in question is a Hitteck EBA200.  The vendor has recommended a certain insert for these Greiner tubes, but they still keep popping off at random.  The stoppers are slightly different from the BD tubes, but we cannot see what is causing this.

If anyone has any ideas for fixing this they would be appreciated.  We are trying to see if Greiner has any ideas.

Scott

[A. DeRossett 1]

We had to use tube lifters in some of our centrifuges to prevent the tubes from sinking down into the holders.  If we didn't use the tube lifters, the cap of the tube would hit the lip of the holder and pop the cap off.  Once we used the lifters, we stopped having caps pop off.