Here is my experience with this doser. In a nutshell, you might want to inspect the pump head assembly because it appears that mine were installed in reverse.
Here are the events that led me to this conclusion;
I acquired my unit about a month ago. During calibration, pump head number two began to slip (motor was still going but the three rollers were not rotating). I could hear the sound change as it slipped on and off. I could also confirm this visually. Even if I managed to complete calibration with no slipping events, when I set the doser to dose, the heads would slip around five or six times out of ten tries. This resulted in under dosing. I returned it and got another unit. During calibration of this second unit, three out of the four heads slipped on multiple attempts. Needles to say, I had lost confidence in the dosing heads and thought I had wasted my money. I went on-line and did some searching and while doing that, I found someone disassembling one of these dosing heads. It was not the exact one installed in the Jebao doser but the design was the same. I took apart the dosing heads in my unit and I noticed that the way the roller heads were inserted in the pump housing was reversed when compared to the one I saw on-line. I reversed mine to look like the one on-line, I calibrated and tested and tested and tested... It’s been over two weeks and I have not seen one failure in any of the four heads. I have monitored the dosages and they are all spot on. At this point my confidence has been restored.
I did a search on-line to look for an illustration to attach to this response to provide a visual and I found this RC link which supports my finding as well. This is a Marine Magic doser but the design for the dosing head is the same.
(To be clear assembly A in the link below is the way I have installed the rollers in my pump heads)
http://www.reefcentral.com/forums/showthread.php?t=2123530
I don’t know who I can contact to confirm that this is the proper installation but it seems that assembling them this way allows the dosing tubing to tighten/wrap down on the roller heads better against the motor axis and prevent slipping and also possibly create a better seal against the tubing thus preventing the fluid to back siphon.
I don’t know if Jebao assembles all the doser heads in this manner or if this was just a case of one assembler that was miss instructed or not paying attention. Or maybe Jebao received them this way from their source…
I hope this helps someone.
I would also like if possible, for those of you that open your pump heads to compare which way they are assembled and let us know your findings. Specially if you have other brands but with similarly designed pump heads.