Vacuum is critical for getting good sap yield on operations where tubing rules. Research from the University of Vermont’s Proctor Maple Research Center in Underhill, Vermont, indicated that an additional 1 inch of vacuum produces an increase in sap yield from 4 percent to 6 percent.

That eye-opening statistic means producers might want to rethink their tubing needs when it comes time to upgrade, change or expand their runs. So, it might seem that big fat lines with super-duty sucking would really boost production. However, the more productive solution seems to lie in really skinny, gravity-powered lines. FARMING covered the advantages of gravity in sap gathering in July 2014. Now, researchers are looking at 3∕16-inch systems with vacuum pumps.

It’s notable that, while the best vacuum pump systems can reliably produce 27 inches of vacuum, a properly installed gravity tubing system using 3∕16-inch tubing can match that. However, preliminary research indicates there may be reason to combine vacuum pumping with 3∕16-inch lines to get an effective sap-gathering system.

“One of the real advantages of using 3∕16-inch tubing with a pump is the ability to improve vacuum without having short lines with few taps and many mainlines, as is currently the trend when using 5∕16 tubing,” said Timothy Wilmot, recently retired Extension maple specialist at the University of Vermont and now researcher for Dominion & Grimm, Inc.

“It should result in a system that is cheaper to set up, and that will add the vacuum derived from gravity to the vacuum produced by the pump,” Wilmot said.

In his new role, he intends to evaluate vacuum pumpbased systems. Wilmot discussed his research at the 21st annual New York State Maple Syrup Conference at Vernon- Verona-Sherrill High School in Verona, New York, this month.

Photo: Spinkle/istock

Using a pump

To date, most research on the 3∕16-inch system has related to using it as a new kind of gravity system. “We have done research at the Proctor Maple Center with quite good results when using a pump in combination with 3∕16-inch tubing,” Wilmot said. “We are adding more 3∕16-inch tubing here (at the Proctor Research Center), and there are a number of producers who are vacuum pump users who are now switching some of their system to 3∕16-inch.”

He noted that, even unassisted by a pump, a 3∕16-inch system adds more vacuum than can be achieved in the traditional 5∕16-inch system with a pump.

Today, there are at least a half-dozen companies that are making the tubing and several of those are making the fittings as well. So a producer making the change to 3∕16-inch is not married to a single firm for supplies. The 3∕16-inch tubing is typically available in 500-foot rolls.

“It integrates very well and sets up almost identically to a 5∕16-inch tubing system,” he said.

Better yet, it weighs considerably less than a similar roll of 5∕16-inch material, making it easier to haul up and down the hills.

Both Wilmot and several commercial producers are experimenting with 3∕16-inch tubing coupled with a vacuum pump system. One of Wilmot’s first projects in his postretirement career with Dominion & Grimm will be to investigate its use when integrated into a system with a vacuum pump.

“A lot of what we need to know about gravity-only systems is pretty well understood,” he said. Now, Wilmot wants to look at the effectiveness of vacuum pumping and 3∕16-inch tubing as contrasted to standard 5∕16-inch systems in similar configurations.

He said the move to have shorter 5∕16-inch lines has proved to be “pretty efficient” but it requires a lot of main lines closer together. Main line is expensive and time consuming to put up, he said. While he still is confirming the numbers and double-checking the efficiency of systems’ length with a vacuum pump, it appears that a move from 5∕16-inch lateral lines to 3∕16-inch lines would allow longer runs with more taps and would require less main line.

“That should result in a system that is easier (and cheaper) to set up,” he said.

Even without a vacuum pump, the argument for a 3∕16- inch system is solid.

Reviewing gravity feed

“In a comparison of gravity sap lines, a 3∕16-inch gravity line should almost always outperform a 5∕16-inch line,” Wilmot said.

A foot of 3∕16-inch tubing will hold only 36 percent as much sap as a foot of the standard 5∕16-inch tubing. This is why a higher vacuum can be established in the smaller tubing. On a slope, the longer length of sap in the tubing extends over a longer elevation. The result is that it exerts more weight on the tap hole.

If a tap hole is tightly connected to a spout and tubing, Wilmot said, then external air cannot enter the system. So the enclosed sap draws a vacuum on the enclosed space within the tubing. Downhill, in the tube, goes the sap.

Setting up a natural vacuum in a sap system is similar to siphoning gas out of a car. One quickly realizes that a drop in elevation makes the system flow better. Extending the length of the line without changing the total drop in elevation will not help the system work better since it is the difference in elevation that provides the impetus. The vacuum is not increased since the weight of the sap is not increased.

The preferred maple tubing arrangement consists of lateral lines going straight up a slope and mains running cross-slope at a shallow angle. Wilmot said a possible method to maximize vacuum on a long but shallow slope might be to jump the lateral lines over the closest mainline, and join them to the next lowest mainline running across the slope. This adds a long section of lateral line below every tree in order to gain a long column of sap.

Whatever the flow system used, Wilmot recommended adhering to standard best practices: good tapping techniques, new spouts, good quality materials, and diligent checking for leaks.

If you are not ready to jump into either a gravity flow or pumped 3∕16-inch tubing setup, Wilmot noted that the 3∕16- inch tubing can mesh nicely with existing systems.

“There is absolutely no reason to change other than on the time schedule a producer wants,” Wilmot said. Most producers replace their tubing on a regular basis, giving them an opportunity to look at the 3∕16-inch system and see how it performs at their operation.

“I don’t get any money from it,” Wilmot said. “I don’t hold any patents. It is what works best for you.”

Cover photo: Marc Dufresne/istock