Doser tubing leaks vs gas bubbles in peristaltic pumps

Greg P · Jul 16, 2020

I'm on a mission to find a solution to some, but not all, of my 1.1ml/min dosers ending up with air in the airline tubing I use for both the suction and discharge sides of my pumps.
I'm using a mix of stock BRS 1.1ml pumps and a couple locally sold similar pumps from my LFS.
These similar pumps are rated the same and are very similar in construction to the original BRS pumps, aside from a power switch and the blue color of the housings. They use the same Santoprene tubing sold by BRS.

The DIY for this is here

I currently use 5 pumps on my Reef; Sodium Carbonate, Calcium Chloride, Mag Sulphate/Mag Chloride, Potassium Nitrate and Monopotassium Phosphate.

Over time, my Big 3 dosers would accumulate air in the airline tubing, but not enough to warrant a problem as every few months I would purge them, and the dosing was consistent with my testing.
However, I recently connected another pair of pumps to dose NO3 and PO4, and found air in the lines within 48 hours - 9" of air within 7' of hose. The product used was Seachem Nitrogen and Phosphorus.
The tubing for all pumps is the same product, and the same length, so my suspicion is the product I'm dosing is causing air in the tubing, or rather gas in the product - the liquid Seachem uses to mix their fertilizers.

First thinking my pump tubes were worn, and not being able to economically source Santoprene locally, I purchased 'Silicon' branded tubing made by New Age Industries, and from a local supplier it was very reasonable. Plus I was able to purchase it by the foot instead of a 50/100 foot roll.
I'm currently awaiting Compression set testing to compare this tubing to Santoprene, and as of now know that my tubing is Shore hardness 50A, versus Santoprene being 73A. This tells me my pumps will last longer as they will not work as hard to compress the tubing.
The only issue I have with this new product so far is the fact its softer, which gives less resistance to the pump motors, thus giving me 1.5ml/min versus 1.1ml/min.
So far, 3 pumps tested have all gone from 1.1 to 1.5, give or take.
Testing was performed over 10 minutes and 3 pumps dosed 14.62, 15.50 and 14.80 ml, so close enough to 1.5ml/min to me.

Suspecting air intrusion, I heat shrinked airline tubing on a pump's nipples. 48 hours later there was a 9" air bubble in the airline after the pump tubing.
This lead me to perform current testing.

I have the suspect doser airline tubing installed in a vial and will see if it leaks overnight/the next day or 2.
I've also set up a doser using RO, with the pump off, and will see if this one either develops air/gas bubbles, or possibly leaks.

Lastly I've put a doser tube under vacuum with airline and check valves. So far, after 7 hours, its holding.
I'll check it after 24 hours and suspect it will hold.

Daniel@R2R · Jul 17, 2020

Interesting issue. I've no idea on it, but I'll bump this up and maybe someone in the #reefsquad will be able to help

dbl · Jul 17, 2020

Interesting indeed and I'm curious to read about your results. Timing is right as I just received the new dosing tubes for my pumps as I discovered they were worn and not holding as before. Took me a while to discover the issue but your thread is a great reminder we should keep an eye on the dosing tubes, if you don't already.

Greg P · Jul 20, 2020

I've performed enough testing and have come to the conclusion that I need to re-locate my dosing equipment lower than it currently is in relation to my sump. Where the 'stuff' is right now was OK when I was just dosing the Big 3 as the pumps ran every 2 hours and was enough to 'chase' air out of the lines, or so I thought.
What my testing has taught me is the fact that my current setup allows my discharge lines to drip approximately 2mls/day. Not a big deal when I'm dosing anywhere from 60 to 100mls/day. But it's a problem when I'm only dosing 2mls/day each of Nitrogen and Phosphorus products.
Not knowing whether this was a gravity issue, or tubing connection leaks, I performed the tests below.

First test was with a spare pump, a small bottle and some RO. The bottle was placed below the pump head and the output line was below the bottle. Over a 24 hour period, the line leaked from the open end, and air developed in the line near the last pump roller. As this is post-rollers and not subjected to any negative pressure, I suspected gravity to be the issue, but there was also a small amount of air in the suction side of the pump tubing. To rule out connection leaks, I started some tests.

I first started off by seeing if my Silicon tubing would hold a vacuum overnight, thus telling me my connections aren't leaking. Unfortunately, somewhere between 10 and 20 hours, it lost all vacuum.
Under vacuum

This lead to an epiphany as I seemed to recall the fact that silicone is gas permeable. So maybe my connections are good, but the tubing is the issue.

Next test;
I used a factory tube assembly and attached a couple airline check valves, then I pressurized it with my home compressor, and submerged it. I installed a loop of airline connecting the 2 check valves together to rule out their reed valves leaking.
At 10 minutes, you can see there are hardly any bubbles on the outside of the Santoprene, and again at 30 minutes. So Santoprene isn't overly permeable to gas.

Not the same for the Silicon tubing.
The following 4 images are; pressurized, initially under water, at 10 minutes and at 30 minutes.

So as you can see, silicone tubing is much more gas permeable than Santoprene.
For this reason, I believe I've found out why I've seen some 'air' in the pump tubing before the first roller. The liquid is under negative pressure caused by the rollers sucking fluid up the supply line. This pressure is pulling gas/gasses through the silicone tubing and the fluid is returning to the container.
As I stated earlier on, this wouldn't be a big deal if the pumps were all dosing large enough amounts daily to 'flush' the air bubbles.

My dosing equipment for the Big 3 has been above my sump for over 8 years, with the pumps about 1-1/2 feet above the containers and about 4 feet above the waterline.

I'm about to perform a test where they will be moved to a new home next to the Chiller. This will allow me to have the pumps just below where the dosing lines are suspended over the last section of my bubble trap.
I see no reason why this will not allow me to keep the airline tubing full at all times - minus what gas bubbles decide to show up in the solutions and possibly small amounts of air before the first pump roller. We'll see ...

Crashnt24 · Jul 20, 2020

Following. I'm running Triton and I only dose 2ml a day. Lines are filled with air less than 24 hours after a dose. This makes me miss doses constantly. I have to manually dose everyday. Makes my two Neptune Dos pumps a complete waste of money

Greg P · Jul 21, 2020

Crashnt24 said:
Following. I'm running Triton and I only dose 2ml a day. Lines are filled with air less than 24 hours after a dose. This makes me miss doses constantly. I have to manually dose everyday. Makes my two Neptune Dos pumps a complete waste of money

Are your containers and pumps above your tank/sump?
Post pics of your situation and another writeup. I'll try to help.

Greg P · Jul 21, 2020

Here's my test today with RO. The pump is parked at 12 and 6, and will sit this way while I run this for 24 hours to see if it holds.
I'm looking for 2 things;
1 - Will the suction side develop air inside the pump tubing?
2 - Will the output stop dripping and hold it's own against gravity?

Question 1 I will not speculate, but hope having the bottle above the pump helps.
Question 2 will only be answered with time. I have the output end essentially at the same point as where it will eventually end up.

Reefer Reboot · Jul 21, 2020

Nice experiment with interesting and informative results. Thank you for posting this. I had a similar problem a while back and found a simple solution. By putting a check valve at the very beginning of the dosing line (submerged in the dosing fluid) and one at the end where it drips into the tank/sump, it negates any back draw siphon pressure differential and drippage. (Be sure the check valves are both orientated so the flow is towards the tank/sump.) For informational purposes, my reservoir/pump/sump orientation is just like what you had in post #4, picture #8.

Greg P · Jul 21, 2020

Interesting to hear check valves worked for you. I thought about using them but am concerned about them becoming clogged over time. I usually change out my doser airline tubes annually as they become clogged with alk and ca deposits.

Greg P · Jul 21, 2020

19 hours and the RO test setup has no air in the lines nor has the tip been dripping.
I'm going to call this setup a success and start moving things over to this new location.

Greg P · Jul 31, 2020

Over 10 days now and I see bubbles forming in the lines. I'll assume these are gas bubbles coming out of solution.
With my testing I'll suggest running tubing below or level with your containers to alleviate bubbles in your lines.

I run my containers below my pumps, but this runs the risk of a leak allowing a siphon.

Running my pumps below my sump allows air to be pumped out of the lines.

Regardless, I'm happy enough with my tubing setup and hope what I've posted here helps others.

Reefer Reboot · Jul 31, 2020

I had thought of one other thing that may or may not be having an impact on your situation, so take it with a grain of salt. I believe I read earlier that you had replaced the pump head tube. If so, if the wall thickness of the replacement tubing is less that the OEM tubing, could you be losing enough squeeze from the pump head rollers that allows the fluid to slowly leak back past the rollers. Maybe this is a moot point if the pump head rollers are spring loaded to compensate. Like I said, just a thought that I'll throw out there.