CV versus 5/16 drops on gravity system

[Tapper705]

Anyone have any experience with 5/16 drops on a 3/16 gravity system. I am expanding this year and am considering installing 5/16 drops or check valve spouts. Any input would be appreciated.
Jason

[fred]

I would not recommend using CV on gravity there's not enough pull for the ball. many studies have been done on the 3/16 vs 5.16 drops going to 3/16 and 5/16 lines. Cornell and UVM have plenty on it

[bmbmkr]

I started with 3/16 about 6 years ago. The first year I used 3/16 drops. Second year I doubled # of taps and switched out to all 5/16 drops. I did use a few cv taps that second year, but even with 25"/Hg natural vacuum on steep slopes, some of the balls stuck shut later in the season. I'm guessing because of sticky sugar. I observed sap sucking all the way back to the tap hole in 30" 3/16 drops at night when it froze. With the 5/16 drops, I've never seen it draw more than 10", usually 6-8".

[maple flats]

For every year since I first started using any 3/16 tubing for my laterals, I used cheaper seasonal taps in year 1 on any system, but in years 2 -5 I used CV taps. All had 5/16 drops after year 1. In my first year I used 3/16 drops, but after that all used 5/1 drops on old and new systems alike.
I also fought conventional wisdom on 3/16 laterals, I actually used 3/16 laterals on flat and even below the mainline laterals, just because it was cheaper and quicker to install. I had 26-27" vacuum on the mains but I only once put a vacuum gauge at the end of a lateral. It had 20-22 taps and was about 250' long, I still got 15" vacuum on medium flow days but only about 10-11" on high flow days. My thinking was that even 10" was better than 0 vacuum and I was getting as much sap as I could easily process using an RO (250gph) and a 3x8 evaporator running at 75-80 gph, on 400 taps. I at the time was a one-man operation during the season. I did get help during tapping. I had more help back in the days when I had 1320 taps, but that was before I started using any 3/16 tubing.

[maple flats]

Remember, 3/16 laterals on good slope is not called a gravity system but rather a natural vacuum system. (Yes, gravity IS generating the vacuum).

[BAP]

I have a lot 110 taps on 3/16 with 5/16 drops on natural gravity vacuum. I run CV adapters for spouts. Don’t have much problems with them. Get really good yields, better than my other lot which is fairly flat that I use 5/16 going into a mainline using a Shurflo pump for vacuum.

[DrTimPerkins]

Remember, 3/16 laterals on good slope is not called a gravity system but rather a natural vacuum system. (Yes, gravity IS generating the vacuum).

Dave is correct. A 3/16" system installed correctly with proper slope IS a vacuum system. That's the whole point of 3/16" tubing.

The opposite is also true. A 3/16" system installed on flat ground or low slope is NOT a vacuum system. Often it is more like a pressure-building system, which can lead to very poor sap flow. In flat/low slope areas a 5/16" tubing system (unvented) will perform better.

[Sugar Bear]

Dave is correct. A 3/16" system installed correctly with proper slope IS a vacuum system. That's the whole point of 3/16" tubing.

The opposite is also true. A 3/16" system installed on flat ground or low slope is NOT a vacuum system. Often it is more like a pressure-building system, which can lead to very poor sap flow. In flat/low slope areas a 5/16" tubing system (unvented) will perform better.

Due to my experience over the past 6 years ( very little compared to yours ) and for the protection of the "little" guy just starting out and reading this. I would add here that even though "In flat/low slope areas a 5/16" tubing system ( unvented ) will perform better" It will not perform better than if these taps were on individual drops to buckets. I.E. no natural vacuum will be generated and no back pressure will be generated. I call it a Free State Tap.


As compared to the same taps being on individual drops to buckets, even with 5/16 tubing, the drop off in efficiency of these same taps being on a flat ground tubing sequence is immediate with beginning with even just a second tap added to a tubing run. The "pressure-building system" easily prevails, impedes and corrupts flow even on 5/16 tubing.

And it even takes forever to drain a garden hose on flat ground in the fall. Although not once the hose is stowed away in the house or garage :o

Again in my humble painstaking experience over the past 6 years I believe the most effective flat ground efficiency neutralizer from taps on individual drops to buckets VS taps on runs is through the use of a mechanical pump. The mechanical pump can easily make the taps on the run more efficient then if these same taps were on drops to buckets as you will go from a pressure state into a vacuum state inside the tubing run.

Its important to be clear here that flat ground and tubing work very poorly whether 3/16 or 5/16 ( even if 5/16 is the better of the two "bad" choices ) , unless mechanical vacuum is added.

Somehow these threads leave the impression to the beginner, that there is a way to get good flow on tubing runs on flat ground without mechanical support.

There is not or we would be powering our cars on it.

[Sugar Bear]

Dave is correct. A 3/16" system installed correctly with proper slope IS a vacuum system. That's the whole point of 3/16" tubing.

The opposite is also true. A 3/16" system installed on flat ground or low slope is NOT a vacuum system. Often it is more like a pressure-building system, which can lead to very poor sap flow. In flat/low slope areas a 5/16" tubing system (unvented) will perform better.

While we are on the topic of "unvented" I wanted to ask a question, I have had on my mind for some time. Have you guys ever considered venting with a Microbial filter attached to the vent? And or would that possibly be effective for flat ground venting?

[maple flats]

Venting by any normal method yields less sap.

[DrTimPerkins]

Somehow these threads leave the impression to the beginner, that there is a way to get good flow on tubing runs on flat ground without mechanical support.

While that is not what is stated anywhere, anyone who leaves with this impression would be wrong as you say. Getting sap to run in tubing on flat ground requires a great deal of effort to ensure that the installation is very, very good just in order for it to run OK. Using a pump will certainly help, but many people in this situation (small operations) can't justify the cost of a pump.

I think one of the key misconceptions out there is that 3/16" tubing will help generate natural vacuum in ANY circumstances, including low slope and flat ground. It does not and is only indicated on sloped land.

[DrTimPerkins]

Have you guys ever considered venting with a Microbial filter attached to the vent? And or would that possibly be effective for flat ground venting?

We could complicate the story by putting in a bunch of caveats, but the bottom line is that venting of tubing serves no useful purpose.