Food coloring to check for vacuum leaks … crazy idea?

[dvnwvt]

I have a 3/16” natural vacuum run that has never reached it’s ‘full’ vacuum based on 0.88 in. Hg per foot drop. After fixing obvious or suspicious leak points, still no luck. I was thinking about leak detection in plumbing or gas systems that uses soapy liquid to find pressure leaks. Why not do the opposite and saturate tap holes and fittings with water or sap dyed with food coloring to see if/where it’s sucked in to tubing? Haven't tried it yet … am I crazy?

[DrTimPerkins]

Or you could do it the right way and look for bubbles.

I don’t think you want to put dye or soap into your sap.

[dvnwvt]

Dr. Tim, so how to differentiate air bubbles (i.e. from leaks) from natural tree gas bubbles? Speed and periodicity? BTW - I was suggesting a minuscule amount of food-grade coloring mixed with water or sap that would likely disappear in a tankful of sap, and surely be completely invisible after boiling (all my product is consumed by friends and family).

[BAP]

Dr. Tim, so how to differentiate air bubbles (i.e. from leaks) from natural tree gas bubbles? Speed and periodicity? BTW - I was suggesting a minuscule amount of food-grade coloring mixed with water or sap that would likely disappear in a tankful of sap, and surely be completely invisible after boiling (all my product is consumed by friends and family).
Look for lots of air bubbles moving fast. Best bet is to start at the tank on a day where there is fairly good sap flow. Walk up the line watching every inch of the line. When you see a change in the flow and speed of bubbles, find out why. Most likely it is a leak. A tight line should progressively get slower flow as you get towards the top end with less taps feeding into the line. I am not sure how you would introduce food coloring into the line without loosing your vacuum or how it would do anything to find leaks.

[buckeye gold]

I agree with everyone. once you get used to seeing normal flow, it's not hard to find leaks. There are many other things that will effect your vacuum, like fall.

[canaanmaple]

A vacuum leak is air getting sucked in, so adding a dye will show you absolutely nothing. Leaks are easy to spot usually always at a fitting or a loose tap, and sometimes a little micro-chew from an animal. (or maybe the tap went into dead wood or hollow spot and is sucking air from inside the tree)
Look at the pattern of sap bubbles/gas going in and out of each fitting to start. If its not the same going in and coming out, there is probably a leak.

[DrTimPerkins]

...a minuscule amount of food-grade coloring mixed with water or sap that would likely disappear in a tankful of sap, and surely be completely invisible after boiling (all my product is consumed by friends and family).

To make it visible in the lines (tubing is translucent, not transparent), you'd need a pretty good slug of dye...especially since it would get diluted immediately. Yes...it would be diluted greatly, but then you'd be concentrating it again by boiling. In reality, probably not a big deal, but it wouldn't be as helpful as you might think. We've done dye studies to track movement of sap in lines (and in trees), but it takes a LOT of dye to see what is happening. The sap we do that with is always dumped.

https://www.youtube.com/watch?v=D1wQPrgzroA&list=PLZP4fDl-nB99OirKIdJGob1U-_51Sy5Pt&index=4 (in this case the tubing was clear to make it easier to see the movement of the dyed liquid...this example was looking at backflow of sap into trees under vacuum when there is a sudden leak -- without a checkvalve).

[ronewold]

The other thing about this situation that nobody has mentioned is: if you are seeing "low" vacuum at the top of a 3/16 tubing run, you still have vacuum, which is good. In my gravity 3/16 lines, when there is a leak, pretty much all flow uphill from the leak stops. I interpret that as essentially zero vacuum. There might be a trickle from the uphill taps if conditions are perfect (if the uphill section is on a very consistent slope leading to the leak point), but things are visibly stopped in most cases.
You might just have "not quite perfect" conditions in your system, which means you are in the real world! A gravity system is never perfect, of course, and there are a million places to lose a tiny bit of vacuum just because of friction or slope changes or the number of fittings or where the more or less productive trees are located in the line. Without a vacuum pump, there is very little capacity to pull air into the system and maintain ANY vacuum uphill.
If there is really a leak, I can always find it by walking the line and staring at the flow. But if you have visible flow from taps at the top of your line, I would guess you don't have much of a leak, if any. Also, during cold periods where the trees stop running, I often see a tiny icicle at a serious leak in a 3/16 line, but that isn't guaranteed.