Optimizing the Performance of My Vacuum Tubing System, Part III

The goal of the previous two articles (Part I, Part II) and this final installment is for you to realize that there are many factors that go into installing and running a maple vacuum tubing system. All the factors are interrelated and each one needs to be careful considered on the part of the operator.  The below information is contained in the Cornell New York State Tubing and Vacuum System Notebook (NSTVN) written by Cornell University’s Maple Specialist Steve Childs.  Much of the information is these three posts is a synthesis of past content with some more recent best practice guidance.

Part I introduced basic concepts of vacuum in a tubing system, some different variants within vacuum systems, and the different factors (most well within the control of the producer!) that influence vacuum levels throughout a system.  Part II walked you through how to calculate vacuum levels within your system and how to ensure your production needs are met by your system’s capacity.  The final installment will help direct you towards a vacuum pump that will do the job you need it to do.


When someone brings up the subject of vacuum, one of the first questions producers ask is, “What size vacuum pump will I need to run my system?” They will also sometimes ask, “Will the old rotary vane pump my grandfather abandoned in the barn 10 years ago (or longer…) do the job?” The question I also ask back is this, “What vacuum level do you want to run at today and into the future?”

We should get the second question out of the way first. Grandpa’s pump was designed to milk cows, and Bessy would get a little fussy if the vacuum level were to jump above 15 Hg. So the simple answer is that Grandpa’s pump will work, but it is not designed for optimizing maple production. But if you are happy with a modest increase in production beyond simple gravity-fed lines, dust off the old rotary vane pump and run it at the recommended RPM. Moving on to where the maple industry has evolved.

To review, vacuum pumps are designed to remove air from the system, and we already know that vacuum pumps are rated in terms of their ability to remove cubic feet per minute (CFM) from the system. Two additional factors come into play when comparing vacuum pumps. One is the horsepower rating, or the power required to remove air at high levels of vacuum. As the air is removed from an enclosed area the molecules of air in that area become very sparse. A pump must work very hard to remove the remaining molecules of air in the system. The pump must also overcome the force of the negative pressure inside that enclosed area, and this challenge requires more horsepower. A larger pump with a higher CFM rating has a higher capacity to accomplish this task but bigger pumps also require higher horsepower motors. The final factor is pump speed. If you turn a pump faster your will move more air thereby increasing the pump’s capacity. However, over-speeding a pump can cause excessive wear on the pump. This becomes a critical factor when sizing a gasoline of diesel motor driven pump. Pullies need to be sized correctly or performance is sacrificed.

Caption: Vacuum gauge measuring 26+ inches of vacuum

Most of today’s liquid ring, flood vacuum, rotary claw and new age rotary vane pumps are designed to run at vacuum levels up to 29 inches. An important thing to remember is that all pump ratings and vacuum level capacities are preformed using a standard test at the factory removing air from a sealed vessel and a performance curve is developed. This is done in a controlled environment. Now the question becomes what happens when you lower the air temperature and increase or decrease the barometric pressure? The result is confusion. Today, many maple equipment companies are simply listing pump sizes by motor horsepower instead of by CFM capacity. I have personally never seen optimum conditions out in a sugarbush in February and March, and as pointed out above, motor horsepower is only one factor determining pump capacity.

Another question I have is this – “What is the likelihood of that pump reaching 29 inches of vacuum in your sugarbush?” How many times have you heard producers tell you that the pump gauge mounted somewhere near the inlet of the pump is reading 28 inches of vacuum and therefore he must be producing 28 inches of vacuum at every tap in his woods? The harsh reality is that out in the woods he might be struggling to produce 15-20 inches of vacuum. What has the producer not factored in? First, line loss because line diameter can be restricting flow and impairing the ability of the vacuum pump to remove all the air from the system. Second, the producer might have an abundance of leaks in his or her system. The reality is that the only vacuum reading that counts is the reading that is taken out in the woods at the last tap. Today in the age of maple tubing system monitors, producers can know exactly what level of vacuum they have at the end of each line. They can also monitor the level of vacuum at the releaser and make the comparison to the end of their lines and isolate and correct problems as they occur.

To determine what sized pump your operation requires, you should begin by constructing an evaluation like the one used in the NY State Maple Tubing and Vacuum System Notebook. Start by calculating the proper line size for the number of taps you have now and do not forget to think ahead regarding possible expansions you may make in the future. Factor in your equipment such as the releaser you want to run, whether you have lifts in your system and other CFM consuming features. Do not forget to build in some reserve performance to allow for possible leaks and for keeping up with your during peak runs. At this point, you should have a good idea of the right-sized pump for your operation. If you are right on the edge of meeting CFM demand, you should strongly consider buying a pump one size or even two sizes bigger than you planned especially if expansion is in your future. What’s the old adage? Buy once, cry once.

The Bottom Line

You have now made all the calculations and are beginning to understand the logic and principles behind setting up a vacuum tubing system. So what is the return on investment (ROI) for spending money on a bigger pump and increasing the size of your lines? For that answer, let’s look at yield research done at UVM Proctor Research Center. For the UVM study, the goal was to determine yields in systems up to 25 inches of vacuum. The results showed that sap yield doubles when vacuum is taken from 0 to 15 inches (8 gallons per tap). From 15 to 20 inches, the payoff was a 3 gallon increase, and pushing vacuum another 5 inches to 25 Hg resulted in an additional 2.5 gallons. At 25 inches vacuum, you have added nearly 14 gallons of sap per tap.  Even at 20 inches of vacuum, the additional yield is still over 10 gallons. In today’s market you can add a modern vacuum pump, a releaser, and moisture trap for less that $10,000. If you increased your production by 75% on 1000 taps, you would go from 250 gallons a year to 400. If those 150 extra gallons sold on the retail market for $50.00, your return would be $7,500 dollars. At that rate, you have paid for your vacuum upgrade in two years. What are you waiting for?!

This is the final installment in the 3-part series dedicated to optimizing your vacuum tubing system.  Be sure to leave questions or comment below.

Author: Les Ober, Geauga County OSU Extension

Leave a Reply

Your email address will not be published. Required fields are marked *