air trapped in dosing pump line

Cment · Jul 7, 2015

I have a pair of BRS dosers dosing 2 part. I have noticed that over time say a week or two, that air pockets begin to build up in the return tubing of each doser. My main conern is the air taking place of the 2 part and not dosing the correct amount. Would this be accurate to say? Is there a way to avoid this from happening? Is this common with the dosing pumps vs others?

Randy Holmes-Farley · Jul 7, 2015

Is the air just trapped in it, or do the air bubbles move along with the liquid?

If they are not moving and are just trapped in place, they are not part of the measured dose and so won't cause any issues.

Cment · Jul 7, 2015

It actually will happen both ways. Is there a way to avoid this?

ThePriceSeliger · Jul 8, 2015

I have the same issue, no resolve yet.

The Kahnasaur · Jul 8, 2015

It is my understanding that as long as the are not exiting the tubing as a "dose" than the pump is still moving the same amounts of fluid around them. I have bubbles in all 3 of my lines and have been ignoring them.

mattvisocky2003 · Jul 8, 2015

Same issue and it definitely misses doses when looking at the exit of the tube. I'm thinking mine is because of the bend/kink where the tubing connects to the john guest fitting. It might be bending enough to not seal. I think I'm going to replace with white water line which is more ridged and see.

kevinsmixed90 · Jul 8, 2015

I have those same pumps from BRS, yes you should use rigid tubing on the intake side and make sure it is properly sealed. I also from time to time see air in the output line but I still seem to get the proper dose so it does not bother me anymore.

Randy Holmes-Farley · Jul 8, 2015

Keeping it tightly sealed and unclogged with solids should prevent air entering it above the water line of the additive.

zesty · Jul 8, 2015

Why not put a liquid measuring cup underneath the output and record what you get for 12 doses and see how much it varies?

I'm going to give it a shot tonight and see, myself!

mcarroll · Jul 10, 2015

Glad I searched....same issue on a peristaltic pump doser. It's also definitely causing missed doses.

These pumps are new to me, so not sure of any tricks to use yet.

I've purged and repurged the lines at least a dozen times.
I installed it with rigid airline tubing to make sure the feed line draws from the bottom of the stock reservoirs.
The airline is tight as h*** on the pump fittings, so no air is getting in there.
And it's happening on both pump heads (ca and alk) about equally.
I've been keeping watch on the delivery tubing to see if they are draining and allowing air in somehow. Nope - always completely full at the ends. Just 1-3" of air collected near the pump - both on the in and out.

Can this much gas just be coming out of solution for whatever reason? I assumed this was what I was seeing...until it kept happening, and happening. Seems an impossible amount.

Thoughts?

Randy Holmes-Farley · Jul 10, 2015

Unless you are creating a lot of vacuum suction, I wouldn't expect gas to be created in the tubing except perhaps by temperature changes.

mcarroll · Jul 10, 2015

I imagine there's a degree of compression/decompression between the pump rollers but that couldn't explain air gathering on the intake side...

Randy Holmes-Farley · Jul 10, 2015

If your suction line is long or your dosing rate is high, that might be an issue. Mine move so slowly that I can't imagine gas that way. I use BRS 1.1 ml per minute dosers for various things.

mcarroll · Jul 10, 2015

Only about 48" of tubing combined on the in and out.

These are only dosing about 20 mL per dose, 4 times a night (~100 mL per day)...and it takes several seconds to dose the 20 mL (haven't timed it), so doesn't seem that fast. Just a dribble from the end of the airline when running.

If there was a leak in the internal doser tubing big enough to allow in air, I'd know it by now, right?

mcarroll · Jul 10, 2015

It's a little bit of a programming hassle, but I was considering breaking up the 100 mL/day into much more than four intervals so the pump would sit idle for shorter periods of time....anyone wanna second that idea for being worth the effort of trying? (About 10 solid minutes of pressing membrane-buttons, so as I said a bit of a hassle.)

mcarroll · Jul 10, 2015

Well "tight as h***" became somewhat relaxed - I was able to fit the airline tubing onto the nipple of the pump tubing 100% of the way just now. It was so tight at installation time that I could only fit it part way on.

I think this is where at least some of my air was coming from. Re-bled the pump lines....watching.

kevinsmixed90 · Jul 11, 2015

something else you can do. for air pumps you can get a small check valve to put inline on your output side the cost around .75 cents. I am however not sure if they would up under the chemicals. something to think about

mcarroll · Jul 12, 2015

There was already a lot of air collected in both sides of both pumps by yesterday...so I made it easier to bleed the lines.

I know this isn't magic, but I can't figure how the air is getting into the line.

The intake is submerged, the outlet is staying full, no evidence of leaks, so....where????

Am I missing something?