Jebao dosing pump draining back into the reservoir

[trustychords]

My Jebao DP-4 is draining calcium and alkalinity back into their respective reservoirs occasionally (e.g., once every 10 doses). I have seen various threads on this issue here, here, and here. The general trouble shooting steps are:

1. Ensure no air is getting into the lines. Suggestions include using 1/8" inner diameter tubing and making sure tubing is secured via zip ties or ideally hose clamps.
2. Installing check valves on the outgoing line to help ensure no back draining.
3. Ensure the rollers are properly pinching the tubing within the dosing head.

My question is about the third point. I am not sure what proper pinching looks like. Below is a picture of the two heads that are back draining. To me, they don't look truly pinched, however, there is pressure on the tube in two spots and based on pictures/videos of other Jebao dosing pumps, look normal. I would just switch out the heads, but all the heads have similar looking pinches. I tried looking at pictures of other higher quality dosing pumps to see what their pinch looks like and I could never get a good look besides the BRS dosing pump, which seems to have a stronger pinch.

I am using the DP-4 with my reef-pi, so getting a new dosing unit isn't an option.

 

[Adamantium]

I have the same problem on the third head, and now the first is starting to develop air bubbles. I can’t figure out the cause. I don’t think any air is getting in, and check valves didn’t help.

 

[Adamantium]

Anybody have ideas about this? It seems almost like, in my case, the air is coming into the outlet of the hose, and building up where it bends over the edge of the tank.

 

[trustychords]

Anybody have ideas about this? It seems almost like, in my case, the air is coming into the outlet of the hose, and building up where it bends over the edge of the tank.

I used 1/8" inner diameter tubing and that creates a really tight seal, especially if you heat it up and slide it all the way up the connector. In fact, it is such a tight seal that it is a pain to remove it. I would start there. I would also ensure that the internal dosing pump tubing is securely connected and in good condition. Finally, ensure that the intake tubing is well below the water line in your dosing reservoir and it isn't sucking in air.

I've never tried it, but you could take all of the tubing out and submerge except for the two ends in a bucket or pot. On one end, connect an air pump and turn it on. If there is a leak in the tubing or connections, then bubbles will come out of that location, and that is where air is being sucked in. If you don't have an air pump, you could try blowing with your mouth, but this will only work if your tubing is short enough.

As for the draining issue, I found a solution that has worked for the last 24 hours. I basically pushed more of the tubing into the internal part of the head. This reduces the space between the roller and head wall, making it more likely there is a good pinch. The picture below shows where I pushed more of the tubing in and I circles the areas I was trying to reduce the space between the roller and wall. I haven't seen this suggested elsewhere and seems to have worked for me. I will update to see if works in the long term.