Tag Archives: Maple Tubing Sytems

The Quest for High Vacuum in a Maple Tubing System (Part 1)


Les Ober
Geauga County
OSU Extension

The variety of vacuum pumps on todays market is very extensive. Although vacuum has become a mainstay in maple production our utilization of vacuum pumps and equipment is very small compared to their use in the industrialized world. Maple production is just on the tip of the iceberg when it comes to vacuum utilization. Even though vacuum is used extensively in the maple industry we have only been at it a very short time. For this reason there is a lot of misunderstanding about the laws of physics (Quantium Mechanics) that govern the science of vacuum. The online encyclopedia Wikipedia definesthe word vacuum as “void of matter”. In fact it stems from the latin word vacuus which means vacant. The study of vacuum goes back to the Greek Age and the time of Aristotle. Several basic scientific principals apply when it comes to vacuum. Due to pressure exerted by the earth’s atmosphere (15 lbs per sq. in.) you can only achieve a maximum vacuum level of 29.92 inches of mercury. You actually can only achieve a vacuum level equal to the barometric pressure on any given day at any given location. Barometric pressure changes with the elevation above sea level. Another principal is how we measure vacuum. The level of vacuum is a negative measure (because you are creating a negative pressure inside of a vessel) and is read in inches of Mercury. The rate of air being removed from a vessel by a vacuum pump is measured in cubic feet per minute on an English measurement scale.

Even though it has become the Holy Grail, in the maple industry, the term “High Vacuum” is largely misunderstood. High Vacuum or perfect vacuum exists only at 29.92 in. Hg. This is the highest level of vacuum achievable in our atmosphere and occurs only when every molecule of matter is removed from a vessel. This is extremely hard to achieve because once all of the air is removed there are still other gases that qualify as matter and are very hard to remove. In fact the closest thing to a perfect vacuum only exists in outer space and we are not producing syrup on the moon. Wikipedia states “There are three levels of vacuum achievable with modern vacuum pumps. Low vacuum (vacuum cleaners), Medium Vacuum (achieved with a single pump) and High Vacuum (achieved with multi-staged pumps and measured with an ion- gauge).” As you can see the vacuum we use falls in a range of somewhere between low and medium. Obviously the average maple producer does not live in the scientific world of vacuum, nor does he need to. The reality is that we are not dealing with a closed vessel but rather miles of tubing where the introduction of air occurs at every tap, fitting and squirrel chew. The range that most maple producers should be comfortable with is around 20 in. to 27 in. of vacuum depending on their system and the pump they are using. The reason being is that, this is that all vacuum pumps are not created equal and vary greatly in their ability to produce vacuum. Now this is where the discussion and the debate begin. As I have stated in an earlier post (March 25, 2013 Is it The Pump or The Mainline Size That is Effecting the Performance of Your Tubing System?) the producer must consider the entire system before he decides on the type and size of vacuum pump to use. Even though we are increasing the volumn of sap being produced by increasing the level vacuum closer to 29.92 we need to be more concerned about the ability of the whole system to remove air from the system efficently. Rather than concentrating on achieveing the maximum depth of vacuum we should be paying closer attention to the systems ability to overcome leakage and everyday wear and tear.

There is a wide variety of vacuum pumps that can be used to apply vacuum to a maple tubing system. In fact with the use of 3/16 tubing (based on the research of Tim Wilmot at the Proctor Maple Research Center) you may not even need a vacuum pump to achieve your vacuum goal. Most of the pumps used in the maple industry are adapted from some other type of use. The first pumps came from the dairy industry and were used to milk cows. These were rotary vane pumps that were designed to produce around 16 inches of vacuum. The vacuum was produced as the air trapped between the vanes held in an offset rotor was expelled to the outside via the exhaust. As the vacuum level increases heat is builds as a result the system needs some kind of lubrication to absorb the heat. The pump is lubricated with oil that was contained in an oil reservoir. Once you went above 16 inches the strain on the pump produced more heat that it was designed for. For that reason oil coolers and oil-reclaimers were used to make them more efficient. Bearings need to be lubricated with a precise amount of oil to maintain function. When running above 20 in hg, if any of the above are neglected you are headed for a Chernobyl type melt down. There are commercial rotary vane pumps (running a flood vacuum) on the market that are capable of achieving up to 27inches of vacuum. One of the most popular pumps being used is the liquid ring pump. The liquid ring pump uses an impeller running in a ring of liquid producing close to 29 inches of vacuum. As the air is drawn in it becomes trapped in a compression chamber that is formed between the impeller veins and the liquid. The air is expelled to the outside as the liquid (oil or water) is recycled. These pumps achieve as close to 29 inches of vacuum as any pump on the market. The down side of this type of pump is that a water source is needed and that source needs to be kept above freezing. If oil is used then there are environmental considerations.

One of the most recent pumps to come on the maple scene is the rotary claw pump. The rotary claw will produce 27 inches of vacuum, just under a liquid ring. This is a pump that is designed for continuous duty and one that requires minimal maintenance during the season. The claw runs at a very close tolerance to the chamber and traps air in-between the claws and the chamber and expels it to the outside. A small amount of oil is used lubrication. The downside is that these pumps are very expensive. They are designed to be run year round. Long layover periods may allow the pump to develop a rust layer inside to the pump resulting in excessive air. Because they run at a very close tolerance this may lead to early breakdowns. If you buy a rotary claw you need to fog the pump with anti-oxidation oil in the off season to prevent premature wear.

The last pump is the new age rotary vane pumps that are designed to run continuously and to produce a vacuum of 29 inches. This appears to be a very efficient pump. These pumps are similar in design to the older rotary vane pumps but have very close tolerances. They lubricate with oil but total requirement is minimal. So let’s rate the pumps on their ability to produce high vacuum from top to bottom. At the top is the liquid ring and the new age rotary vane with the edge going to the liquid ring especially one of the two stage models on the market at this time. These pumps will consistently reach 27 to 29 inches of vacuum. Not far behind is the rotary claw which will produce 27 to 28 inches of vacuum. Next is the improved rotary vane with a flood system at 27 inches. At the bottom is bossy’s favorite the old style rotary vain used in milking systems. She liked it because it produced no more than 16 inches of vacuum. Any more and she would send it across the room with one swift kick. No matter what you use you will get more sap from you trees. Collecting maple sap with a vacuum system not only saves time and labor but the vacuum will increase your sap yield by up to between 50 % and 150%. In the next post I will cover things you need to consider before you hook your pump into the system.

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Filed under Maple Education, Maple Production Tips, Tubing & Vacuum Systems