Help troubleshooting 3/16 gravity line

[cmeudaly]

It’s my first season using tubing. I’m in Eastern Kansas and I’ve only learned what I know from you folks here and other online resources.
My season here is early and I tapped 1/8/22.

My setup:
Five lines of 3/16 averaging 500’ long with 17 taps on each using 5/16 drop lines with stainless spouts.
I’m using the green CDL fittings.
They all run from the top of a hill (which I’m estimating by the looks of it is a 50-60’ elevation from the collection tank)

I also have 14 sap bags in another stand of maples 1/4 mile away, mostly as a control group because I don’t know what using tubing is supposed to be like.

The weather has been weird and everything is starting late, but just this last weekend through today we got a real sap run. Proportionally, the bags have been outperforming the lines, and I’ve had suspicions that my lines aren’t set up right, but the weather HAS been weird, so I’ve been giving the lines the benefit of the doubt, while continuing to research and look at videos/photos of other people’s gravity setups to double check I did things right.
Here’s why I have questions:
With this sap run we got, I went this evening to collect and the 14 bags combined had 25 gallons, and my collection tank from the lines had 50 gallons.

The tank should have 6x the amount that the the bags total, as there are 6x the number of taps on the lines. So there should have been 150 gallons in my tank instead of just 50. There has to be something not right with my lines.
Here’s a list of facts that might be significant in helping you help me:
1. I do not have “end of line hooks”. I just used my tubing tool to force the end of the 3/16 tube into the 5/16 dropline tube for the very end (or beginning?..the dropline from the highest tap). It looks very airtight...maybe it’s not?
2. I do not have a vacuum gauge. I was curious at some point and pulled a tap out way upstream when the line was full of sap and immediately all the sap flew down the tube and I heard a sucking gurgling noise and putting my finger over the end of the tap felt like a little vacuum hose until there was no sap in the line anymore. After that I learned what the fine, soapy looking airleak bubbles look like. They took forever to move all the way down and out, but once they were out, sap in the line started moving faster again which leads me to my next question...
3. The sap in the line moves slow. Like 3”/sec. Is it supposed to creep along like that? The most I’ve seen come out of the end into the tank is like when you crack a faucet open enough where it goes from a drip to a little stream. There’s bubbles that come too, like big sputtery bubbles though.
4. After the lines get to the bottom of the hill, the slope shallows out in route to the tank. Not flat, but not as steep as the hill is. It still picks up 4 or 5 taps in this shallower area before it gets to the tank.
5. I’m pretty sure the tubing system is to be totally sealed except for the end that runs into the collection tank, but since I’m asking questions I have to get this out of the way: Is it really? Is there such thing as too much vacuum/everything being too tight? Like how a straw you plug the top of doesn’t allow the liquid do fall out of the bottom. Could this be what is happening? So what happens if both ends are open?
6. There is currently no squirrel damage
7. All the taps are above the laterals
8. I tried to run the line in an S rather than a W, but it’s really more like a W.

I’m just disappointed in how little production has come out of the tubing vs the bags and I want to fix it before I lose the next sap run.

Long post, sorry. Thanks for reading. See you in the comments. Happy to clarify anything I did not explain well there.

[DrTimPerkins]

Venting (when you pull the spout at the top) will cause all the sap in the lines to run out quickly, but then it'll settle into a 1 drop in-1 drop out situation. The idea behind 3/16" tubing is to create natural vacuum, so that is what you want....a really tight (leak free, so not vented) system where the weight of the sap running down will create a vacuum. A good deal of research from the 1950s on to the 2000s has shown venting to be a BAD idea unless your goal is to get less sap. Venting pulls air containing microbes into the system that result in premature taphole drying. But that isn't your problem right now...it is clearly something different.

Are the trees up on the hill facing a different direction? Are they all tapped on the cold (north or west) sides compared to the trees on bags? Taps should be spread all around the stem (all directions) to even out the flow timing.

How long is the flat area at the bottom of the hill? 3/16" is not the best option for flat ground as it will create pressure rather than vacuum due to the friction in the line. Secondly, when you say the lines are W shaped...how much so. Does the 3/16" still have a good slope or by doing all the turns did you cut way down on the slope (and thus make the runs fairly flat)? That too would create pressure. The tubing needs to be running downhill, the more slope the better.

Alternatively, maybe your lines are sagging or alternatively stretched too tight?

[cmeudaly]

Both stands are on North facing hills, however, the trees I have bags hanging on are at the bottom of the hill, and of course many of the trees that have tubing running to them are on the side and on the top of the hill if that matters. But your point on which way the actual tap holes are facing is interesting and I’ll have to check on that. When I was running all bags I would purposefully try and tap on the shadier side of the tree to help extend my season because it can get very warm here in KS very fast, so out of habit I probably put most of them to one face of the tree.

About the W bends, nothing’s more than 90° but that’s probably too much. I thought I could get away with tighter bends since my hill was pretty tall.

Length of the shallower run to the tank is maybe 40-50’. What kind of slope is too shallow for 3/16?

[buckeye gold]

patience grasshopper, patience

What is your prime season? A lot of variables to consider. Maybe it's just not time for the others to run.

If your bags are on edges or open woods, yards, roadside etc. they are going to run before woods trees.

I think you need to get some end line fittings. Plastic ones are dirt cheap. Seal up those starting taps, they are probably the most critical taps on your whole lateral, screw them up and you've screwed the whole line.

[cmeudaly]

Will do.
Prime season here is mid January through end of February. I’ll be interested to see if the tubing does better than bags arter it gets warmer. Bags usually start showing mold after 6 weeks of being hung.

[buckeye gold]

Your season is close to mine. I'm all 3/16 and my lines aren't running big yet either.