Reoccurring air in the dosing line

[Ziggy17]

I use Randy’s DIY recipe for sodium bicarbonate for alk and AFR for calcium and trace. I’m having issues with air accumulating in the Alk line which is causing erratic dosing. I’ve switched out/ swapped lines,inspected lines, put the tubing directly in the vestibule, looking for a source but can’t seem to put my finger on it. At this point all I can think of is the solution producing gas exchange in the line causing the issue. It’s not occurring in the AFR line, just to ALK. Is this common and or avoidable?

Cheers.

 

[Formulator]

How is the tubing rigged to your system? Can you take some photos that might give us some clues? Sometimes, for example, a long stretch of vertical line going into the tank downstream of the pump can just slowly drip out when the pump is off, leaving a dead volume of air to refill next time the pump turns on.

 

[Ziggy17]

The air is coming from the tubing on both sides of the pump, which is why I’m thinking gas exchange.

 

[Formulator]

The air is coming from the tubing on both sides of the pump, which is why I’m thinking gas exchange.

Peristaltic pumps are closed system fluid path. There is no gas exchange or any way for air to be introduced in the way you are suggesting. I’m suspecting you need to prime the line better and just have air caught in the line at the pump, but the air came from the beginning, not leaking in at the pump.

 

[lakai]

Use zipties at both ends of the pump tubing.

 

[Ziggy17]

Use zipties at both ends of the pump tubing.

I’m going to try that.

 

[Ziggy17]

Peristaltic pumps are closed system fluid path. There is no gas exchange or any way for air to be introduced in the way you are suggesting. I’m suspecting you need to prime the line better and just have air caught in the line at the pump, but the air came from the beginning, not leaking in at the pump.

You would think that was the issue, but I’ve re-primed it 3 times and it’s clear for a day, and then the bubbles start again. I was thinking that the tubing I purchased from Amazon was somehow permeable and allowing gas exchange. Its coming in from somewhere, just need to chase it down.

 

[Waters]

I am sure it is coming from one of the connection points.....doesn't take much for dosers to draw in air. I doubt the airline is permeable to the point where you are seeing air in the lines themselves.

 

[Ziggy17]

The zip ties aren’t working. I can still see the air in the tubing prior to getting to the pump.

 

[Garf]

The zip ties aren’t working. I can still see the air in the tubing prior to getting to the pump.

Is the line getting warm? Or at least, warmer than the reservoir?

Edit - run a calibration test on the pump. Also, stick some one way valves on if possible.

 

[Ziggy17]

Here’s some pics.

 

[elysics]

the tubes are just losely hanging in the reservoirs on those pictures, right? have you looked whether they bob up and down when something is being dosed?

Also those one way valves are produced super cheaply, maybe they or their connections are leaking?

 

[Formulator]

You don’t need a 1 way valve on a peristaltic pump. Might be doing more harm than good. I still think its just not getting a good prime for some reason. How old is the pump? The pump head can wear out and rollers get loose so they can’t hold a prime well. Have yoi tried switching to one of the un-used pump heads on that doser? At the very least you could eliminate that variable by trying it.

 

[slythy]

Those look like the same heads on the jebao pumps. They are notorious for having air in them. The line in the heads dont seal 100% and the doser drops some fluid. You can try using check valves on the draw line.

 

[Ziggy17]

I had the lines initially on the reservoir nipples but then dropped them in to rules out that connection. They do not bob at all, they stay 1” from the bottoms of the reservoir.

The dosing unit is a brand new simplicity dosing pump bought new a month ago. I can try moving the ALK to a different pump to rule out pump head issue. I wasn’t aware the pump could leak air into the system. I too thought it was a closed system.

The one way valves were provided by simplicity but given where they are, I can’t imagine air is getting in there, especially that far up stream and in small bubbles, not long air gaps.

I’ll first try putting the ALK on a separate pump and see if that resolves the issue, but again, if the air is already in the line between the reservoir and the pump, would that be a leaky pump head issue? I wouldn’t think so.

I still think somehow the solution is causing air bubbles to form in the beginning of the system.

 

[Garf]

I still think somehow the solution is causing air bubbles to form in the beginning of the system.

As I previously posted, can you check the pump calibration? I too get gas dissolving out of solution due to a slight temperature difference from reservoir to dosing line location, and fluid retention time in the lines. For me, it is of no consequence.

 

[Ziggy17]

As I previously posted, can you check the pump calibration? I too get gas dissolving out of solution due to a slight temperature difference from reservoir to dosing line location, and fluid retention time in the lines. For me, it is of no consequence.

I’ll check it again later today. My alk starts to dip if I don’t manually dose to top up so I think the bubbles are having consequence. When I manually primes it sometimes the bubbles get to be an inch long.

I was hoping Randy would chime in and advise whether or not the solution itself can and will cause air in the line and how to prevent it from happening.

 

[SomeHappyFish]

I have the same issue..
Primed before use and without bubble, on both side of the line.

So it might be "gas dissolving out of solution" hmmm

 

[Garf]

I’ll check it again later today. My alk starts to dip if I don’t manually dose to top up so I think the bubbles are having consequence. When I manually primes it sometimes the bubbles get to be an inch long.

I was hoping Randy would chime in and advise whether or not the solution itself can and will cause air in the line and how to prevent it from happening.

How much are you trying to dose a day? I wonder how much solution is contained in that line?

 

[Ziggy17]

How much are you trying to dose a day? I wonder how much solution is contained in that line?

I am dosing 28 of ALK bicarbonate solution at and 10 of AFR daily spread into 4 doses 6 hour intervals on each pump. 1 hour apart from each other So not to precipitation.

@randyholmes

Thoughts?