Les Ober Geauga County OSU Extensnion
It has been over five years since the first research on 3/16 tubing was published. Since that time there has been ongoing research and also many conflicting opinions about its use. What I am presenting is not based on personal new research but rather my observations of research others have done and previously presented. The topic has been addressed from many different directions by researcher, dealers, manufactures and producers. The result is a massive amount of material assembled on the topic. I will attempt to simplify this in manner that may make more sense to someone who is thinking about using this system in their woods. Keep in mind that this is a short overview of a very complex subject.
The productivity of a 5/16 gravity tubing system is only equal to that of a bucket system. The advantage is that you can bring the sap to a central point of collection, reducing the amount of time and labor required to gather the sap. This system eventually evolved into the modern vacuum tubing system where the tubing system is connected to a vacuum pump and sealed to achieve the highest vacuum possible, given the condition of the lines and the barometric pressure on that day. It will also increase your production by 5% for every inch of vacuum increase in the lines. The problem with these systems is that they are expensive. The cost can run up to 12 to 16 dollars per tap when all of the equipment is included. Also the systems are complex requiring a ton of knowledge on vacuum to achieve maximum efficiency. In 2013 I did a series of articles based on Cornell Maple Tubing and Vacuum Notebook. Those articles are still available in the archive of this blog. There has always been a burning desire to develop a maple tubing system that is simple and relatively inexpensive. For many, the 3/16 maple tubing system has done both.
Tim Wilmot is considered the father of the 3/16 tubing revolution. Tim’s original work was done at the University of Vermont while he was the Extension Maple Specialist for the State of Vermont. He has since retired and is now a researcher for Dominion and Grimm Inc. His latest findings are available in the January 2018 edition of the Maple News. Tim utilized the principal of passing liquid through a narrow tube where vacuum is produced on the back side of that liquid because air and liquid cannot pass each other in the confines of the tube. The weight of that liquid moving downward in the column will determine the level of vacuum on the backside. For every foot of drop there will be .88 inches of vacuum produced. This will continue until you reach a point where the level of vacuum equals the barometric pressure on any given day. If you are at 1500 feet elevation that would be approximately a maximum barometric pressure of 28.5 Hg. To quote Stephen Childs NY State Maple Specialist “in a 3/16 maple tubing system, the weight of the sap below the tap, determines the vacuum level at the tap” . A standard gravity 3/16 system is comprised of 20 to 30 taps extending down a slope to a collector line. The length of the lateral line does not seem matter but the tap count does. The covet here is that you need 30 foot of drop below the last tap on the lateral to the collection point to achieve maximum vacuum on that line. This can be achieved in two ways, a straight drop, or by allowing the lateral to extend down the hill until 30 foot of drop is achieved. Again, the overall length of the line does not matter. On lines where that much elevation is not available, an average vacuum is reached across the line ranging from zero inches at the bottom tap next to collection point, increasing as you move up the hill. The result is an average vacuum for that line that could range between zero to 27 inches depending on the elevation.. In its original form the 3/16 systems were designed to run on a mountain side crating an excellent alternative to the standard 5/16 system used for years. In its original form, it is a system that matches or in some cases exceeds the productivity of a 5/16 vacuum system at a fraction of the cost. I saw 3/16 tubing at work in West Virginia, and I was impressed. They do not worry about 30 feet of fall from the end tap because they often have over100. Most of the tubing in the Mountaineer State is 3/16 and it works. No pumps, only long 3/16 laterals with 25 to 30 taps running hundreds of feet up a mountain. What happens when you move it out of the mountains on to flatter terrain?
One of the biggest misconceptions is that a 3/16 system will work just about anywhere. What producers have to realize is that elevation is key. Many locations that produce sap do not have their systems installed on 10 degree slopes where 30 plus feet of elevation from the top to bottom is no problem. One of the perceived solutions to overcome this obstacle is to add a vacuum pump to the system to boost vacuum in the line. Unless you have elevation, there is a very fine line when it comes to defining the advantage of 3/16 tubing has over 5/16 under these circumstances. In 2017 both Tim Wilmot and Cornell University did research on the addition of vacuum to a 3/16 system. If you run a standard 5/16 line on vacuum up a slope you should have the same vacuum level, top to bottom. The sap moving down the line does not significantly increase the vacuum in a 5/16 line. Also realize that many vacuum tubing systems do not maintain the same vacuum throughout the system. They should, but for multiple reasons they do not. Keep in mind that with 3/16, the weight of the sap moving down the line below the tap determines the vacuum at the tap. For every foot of elevation you gain .88 inches of vacuum and for every inch of vacuum you should increase your sap production by 5%. In many cases, zero at the bottom, 27 inches of vacuum at the top. When you hook a vacuum pump to the line, your bottom tap should now show the inches of vacuum produced by the pump. As you move up the line and the vacuum starts to increase, this can be attributed more to the weight of the sap in the line producing a higher vacuum. Eventually you will surpass the vacuum produced by the pump unless your vacuum pump is doing a stellar job. The real advantage of adding a vacuum pump to a 3/16 tubing is realized at the bottom of slope where you would normally only generate zero or at best minimal vacuum with a 3/16 gravity system. In this case the big advantage to adding vacuum to a 3/16 comes when you increase your average overall vacuum from top to bottom. Take away the slope and you will only get the vacuum you have produced with your pump. There is no real increase of vacuum because there is no elevation to create the weight of the sap in the tube resulting in very little vacuum.
Now let’s look at some more interesting 3/16 research done at the Cornell Maple Program by NY State Maple Specialist Steve Childs and others in 2017. One of the most interesting research projects had to do with sap pullback in a lateral line. This pullback needs to be controlled or bacterial buildup will shorten your season. In 5/16 tubing when the vacuum is shut off, the pullback is only 8 to 14 inches. Bacterial contaminating pull back can be controlled by using check valves or replacing the drop and spout every year. In a 3/16 tubing systems a pullback of 14 feet was documented when the vacuum was cut off for any reason. This could be caused by freeze up or a damaged line. Because of the extended pullback in 3/16, it essentially eliminates any advantage of changing out spouts and drops to control the problem. Right now there is no answer for this in 3/16 tubing but 3/16 check valves may be available soon. The other consideration is the inherent problems associated with running 3/16 tubing. If there is squirrel damage or lose fittings all of the vacuum will be lost below the damage site. The only real advantage is that you only lose vacuum on the damaged line not the whole system. Also, improper cleaning can result in old sap or wood creating plugs in you line inferring with the transfer of vacuum in the line. A vacuum gauge on every line helps to spot trouble before it becomes a bigger problem.
3/16 tubing research continues to evolve and we are learning more every year. Research in 2017 by the Cornell Maple Program and Tim Wilmot continues to clear up the misconceptions. Research has clearly pointed to the best possible use for 3/16 is in sugar bushes with moderate to steep slope. In States like Ohio where 2% grades are common the advantages are becoming harder and harder to justify. In New England and in New York in the foothills of the Allegany Mountains you can see why the development of 3/16 tubing systems has caused such a stir. However, I personally do not see it replacing 5/16 any time soon. Granted there are isolated areas in many Ohio sugar bushes where this system will work. I also see it working for hobbyist that does not have the resources to install expensive vacuum systems. A big thank you needs to go out to Tim Wilmot and Steve Childs, for all of their hard work in this area of maple syrup production.