Tag Archives: vacuum
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.
Geauga County OSU Extension
Without a doubt, fall is my favorite time of the year. It is time when all of the hard work of spring and summer comes to together as you harvest the returns for your efforts. It is also a time when the Maple tree goes into dormancy. This means that the maple syrup season is only a few months away. Fall is the best time of the year for planning and making alterations to your maple sugaring operation. You can take the time to carefully plan out what changes are needed before you start the Spring rush.
As soon as the leaves fall you need to get into the woods and take a good look at your operation. Has there been storm damage to you tubing or are your trails blocked. Many producers already have their sugar wood cut for the 2015 season, however the storm damaged wood can quickly be stock piled for 2016. Major damage to your tubing needs to be repaired this Fall. As you look over the situation it might be a good idea to see if you can improve on your current system. This is a good idea even if you do not have damage. Maybe there was a trouble spot last spring that just did not seem to move sap as well as in the other parts of the woods. If it was at the end of a very long mainline maybe there is a way to shorten up that line. It might be possible by extending a wet/dry line further into the woods or increase the diameter of the existing mainline. It is also a good time to look at how you are distributing your vacuum (CFM’s) across the woods. I covered the allocation method used in the NY State Tubing and Vacuum Notebook in an earlier article (How Do I Get Vacuum Where I Need It) posted under the tag “Vacuum”, on the Ohio Maple Blog. One thing to always keep in mind is that if you make a change to your system be sure that you thoroughly research the impact that the change will have on the entire system. Here is an example of a change that could greatly impact the performance of your vacuum system.
Let’s assume you are running 1000 taps on a 35 CFM Vacuum Pump. Under the present system you are able to supply all of the taps with at least 18 inches of mercury out to the longest line in the woods. If you follow the standard rules for vacuum utilization every 100 taps would utilize 1 cfm. The system works because you are using 10 cfm on the pipeline, 5 cfm to run the vacuum releaser and 2 cfm to counteract the distance from the vacuum pump to the releaser. That is only half of your available CFM. This gives you plenty of vacuum (cfm) to overcome leaks and other problems. Now you decide that you can add 300 taps but to do so you will need to install a sap left that requires no less than 7 CFM to run. In this case, you would be taking away another 10 CFM (lift 7 + 300 taps 3) from the main pipeline. We are now up to 27 CFM utilization. Now with only 8 CFM to spare we will have to be very careful to make sure all of the leaks are sealed and that the pipeline is sized correctly. If not you could be headed for a serious drop in Inches of Mercury on your longest lines. One more word of caution, most Vacuum pump CFM ratings are determined at sea level. We do not run our pumps at sea level. Most sugarbushes in Ohio are 500 to 1000 feet above sea level. This means that you may not have as many available CFMS’ as you thought.
All of this comes into play when you are planning to make changes to your maple sugaring operation especially your vacuum system. If you have questions or want to learn more about maple systems I strongly recommend that you plan on attending the 3rd Annual Lake Erie Maple Expo in Albion Pennsylvania, Friday November 7th and Saturday November 8th. On Friday you will have chance to learn from professionals. If you are installing tubing you will want to attend Jason Grossman’s class on Tubing installation Jason is a sugarmaker and a professional tubing installer. He has installed tubing from Minnesota to Maine and several provinces in Canada. His installation technique is considered to be one of the best in the country. Also on Friday you will have a chance to attend a Vacuum Systems Management Class taught by Steve Childs NY State Maple Syrup Specialist and the author of the NY State Tubing and Vacuum Notebook. This is a must read for anyone using and running a vacuum tubing system. Steve will go over many of the topics that he has written about in his notebook. A full list of the Friday and Saturday programs and registration information will be listed on the LEME page of this b
Les Ober; The Ohio State University Extension Geauga County
The 2014 maple season is only 45 to 60 days away depending on where you live in Ohio. The Deer season is coming to an end and it will most likely be safe, to once again enter the woods. Mid-December is a great time to inspect lines and to make adjustments to your tubing system. The work you do before the season will probably determine how well your system will perform during the season. Here are some things to consider and watch for as you work on your tubing system prior to tapping.
How many times have you said to yourself, this system just does not perform as well as it did when we installed it? You have to realize the first year of maple tubing system’s life will be its best year, simply because it is brand new. The spout and drops are new and everything is tight and working properly. After the first year a systems performance will depend on how well it is maintained. Leaks will develop and those leaks can expose flaws in the system. Finding and repairing leaks is the first step to achieving high vacuum. The problem with doing work on lines prior to tapping is that you are not running a vacuum pump making it almost impossible to find all of the leaks. However, with careful inspection you can spot and repair many potential trouble spots that can cause problems later.
The first step is to walk the wood making sure that all of the lines are up and running tight and straight. Inspect all the tubing that is in contact with tree. These areas are where you will find the highest percentage of squirrel chews. If the critters have been chewing this should be easy to spot. Make sure you not only look for chew holes but also scrapes where the little vermin start to chew and back off for whatever reason. Next you need to look for old connections on tees that have been stretched and twisted, replacing old tees where they are needed. If your system has some age then this year may be a good year to start replacing drops and spouts. Research out of the Cornell University maple program states that you can improve your production by over 50 % when you install new spouts and drops. A couple of interesting side notes are that you can come very close to this by keeping the old dropline and installing a new check valve adapter on that line every year. Many producers are finding it more convenient to replace the spout every year and the drops every third year. Use a different color tubing on new drops so that you can quickly identify the drops that need to be rotated out.
Three areas to check on main lines are the saddles, boosters and line connectors. Check for old worn or stretched saddles. If the loop line going to the saddle has become disconnected and is pulling hard on the saddle itself replace the saddle immediately. Once the seal on the saddle is twisted you will more than likely not be able to properly reseat the saddle without leakage. Saddle leaks are hard to detect and can quickly become the site of major vacuum lose. Another trouble spot are the boosters on a wet dry line. Most of these are made of PVC plastic. PVC plastic was developed for indoor plumbing in buildings. It is not designed to be left in direct sunlight for long periods of time. The result is a total breakdown of the plastic due to Ultra violet light from the suns rays. The UV Light and exposure to hot and cold will also breakdown the glue in the joints. Any PVC fittings should be inspected and replaced on a regular basis. If you use a PVC line from your vacuum pump to your releaser, including your moisture trap, make sure you inspect this area for loose or cracked joints. These areas are not only exposed to UV light but experience major vibration that can cause damage to the line.
The other location where vacuum leaks can occur is where lines are joined together with Cam Lock couplings. Producers need to replace the rubber gaskets on the inside of these couplers on a regular basis. Also try not to exert a lot of outward force on these connections. The work best when they couple together with little force.
Most of the above locations can be inspected without have to run the vacuum. Of course the final inspection will need to be made once the taps are in and the vacuum is running. If you can flush lines with water prior to using them many leaks will appear during this process. However, this may not be possible due to weather conditions. Early inspections and maintenance can offset hours of costly repairs and down time once the season starts.
By Les Ober, Geauga County OSU Extension
You have just bought a new vacuum pump and you have spent some time making sure that your vacuum lines are sized properly but for some reason one or two lines are just not preforming the way you want. Is there a solution to this problem? Yes there is! It is all about distributing the vacuum to where you want it.
If all of the vacuum lines are the same size and all of them run directly to the releaser all of the CFM’s for each line will be distributed equally across the system. If you have 4 1 inch lines coming to the releaser that is powered by a 60 CFM pump each line would receive 25% of the vacuum or 15 CFM. According to theory that would be enough vacuum to run 1500 taps on each line. However, based on previous articles in this blog you realize that due to line loss this is not entirely true but each line would receive 25 % of what is available. What happens when you have 1 1 ¼ line used in a wet dry system hooked to the releaser along with 3 1 inch single lines. This is where vacuum distribution comes in and the math starts.
Each pipe diameter has a cross section area
Knowing this will give you the cubic feet capacity per minute for the pipe.
It will also allow you to assign a percentage of a vacuum pipes capacity to each pipe.
Area of the Pipe
¾” .44 sq. inches 1 ½” 1.77 sq. inches
1.0” .78 sq. inches 2.0” 3.14 sq. inches
1 1/4 .1.23 sq. inches 3.0” 7.07 sq. inches
How do I determined what percentage of my vacuum is going to each line?
Let’s say in your woods you have 4 line, three 1 inch lines with 1/3 of my taps on them and one 11/4 over 1 inch Wet / Dry with 2/3 of the taps. Here is a simple formula determine vacuum
: For the 1 inch lines .78 + .78 + .78 = 2.34
For the 1 ¼ line = 1.23
.78 ÷ 3.57 = .22 or each 1 inch line receives 21 % of the CFMS
All together the 1 inch lines in this system are receiving 63% CFMS
That leaves the remaining 37 % (32CFM) capacity for the 1 1/4 line.
Now you have 2/3 of the taps on the 1 ¼ wet /dry line only receiving 1/3 of the CFM”s. You need to redistribute the CFM’s to the largest number of taps. To correct the problem you need to reduce the number of CFM’s going to the 3, 1 inch lines or you need to increase the size of the dry line on the wet dry system. If you apply the math using the above information you can obtain the most economical solution;
You could install a 2 inch line in place of the 1 ¼ this would apply 60% of the CFM’s to that line and 40 % to 3, 1 inch lines. You could also bring all three 1 inch lines together into a vacuum booster with a 1 ¼ outlet going to the releaser. What you end up with is two lines coming into the releaser of the same size, each with 50 % of the CFM’s. Remember the wet line does not count as a vacuum line; its only function is to transfer liquid. The only other considerations are to avoid line loss from the vacuum pump to the releaser by using a 2 or three inch line and to account for all the CFM’s used by releasers and other equipment on the system.
All of this information is available in more detail in the New York State Maple Tubing and Vacuum System Notebook from Cornell University, written by Stphen Childs, New York State Maple Specialist. To obtain a copy contact Cornell University, College of Agriculture and Life Sciences, Department of Natural Resources.
Les Ober, Geauga County OSU Extension
When you start to install a vacuum tubing system you need to understand a few basic principles that determine how air moves through a mainline. First you must consider the line loss. Line loss is caused by the friction of air moving through the line. A general rule of thumb is that the narrower the diameter of the mainline, the slower the air removal at long distances. The line will restrict the pumps ability to quickly remove vacuum and recover from leakage. If you have a 1000 foot, 1 inch mainline attached to a 60cfm pump you will lose 50% of you CFM’s within the first 200 feet. If you attach the same pump to a 2” line you will lose 50% of your CFM at 1500 feet. Air moves easier through a larger diameter line.
You need to consider how a vacuum pump works. The measure of vacuum pumps efficiency is not how many inches of mercury it can obtain but how many cubic feet of air it can remove from the line in one minute. Remember even the smallest vacuum pump can remove the air from an air tight system and obtain high vacuum if you give it enough time to work. Also remember there is no such thing as an air tight maple tubing system, ability to recover from leakage quickly is critical. Bigger pumps can remove air from the line faster but only if that air can move down the mainline quickly. If the diameter of the mainline is too small the air flow will be restricted by line loss.
Using the same 1000 ft. mainline, how many taps will it run? Let’s consider a 1 inch line, 1000 feet long hooked to a 60CFM pump. The 1 inch line will only allow 8 cubic feet of air to move through the line in one minute’s time at 1000 feet. If you follow the rule of 1 CFM for every 100 taps that would mean that you could not exceed 800 taps on that line, even though you have a vacuum pump capable of running 6000 taps. The only way to solve this problem is to go to a larger diameter line. If you move up to a 1 1/4 line of the same length hooked to the same pump you would have 12 CFM available at 1000 feet into the woods. You could theoretically run up to 1200 taps on this line. The major problem here is that many producers feel that they can solve their vacuum problems by buying a bigger vacuum pump. The truth is that at 1000 feet, with a 1 inch line, hooked to a 15 CFM, pump is capable of transferring 7 CFM. If you replace the smaller pump with a much larger pump (60 CFM) it will only be able to transfer 8 CFM. A larger pump under these circumstances will not transfer any more CFM’s.
Another factor to consider is that most modern vacuum pumps are capable of maintaining a high level of hg mercury or inches of vacuum. Once a leak develops the vacuum level declines. At that point it is up to vacuum pump to overcome that leak by removing the incoming air. The pump must be able to do the job quickly to maintain an optimum level of performance (high vacuum) . As demonstrated in the above example a big pump can only be as efficient as the line capacity behind it.
Up to this point we have only considered air flow through an empty line with no sap in it. What happens when we add sap? The optimum goal is to maintain 60% air and 40% liquid inside the vacuum line. What happens during peak flow when the ratio is often reversed? Under low flow conditions there is very little liquid inside you mainline and air can move freely. Under peak flow conditions sap builds up and air blockage often occurs. This blockage could be in the form of waves or even worse slugs of sap that seal off a portion of the line. This is real problem especially on slopes of 2 % or less. The solution to this problem, especially on flat ground or where large volumes of sap are entering the primary mainline from secondary main lines is a dual-line conductor or wet dry line. The bottom line conducts the sap and the top line removes the air from the system. The bottom line is sized based on its liquid capacity and the top line is sized based on air flow and CFM capacity. When figure the CFM capacity for a Wet-Dry system only consider the capacity of top line. The advantage of a wet-dry system is that you should never have liquid in you top line, that means that it will transfer air at full capacity and the bottom line will have more capacity to transfer sap. To get a more in-depth description of how to install a vacuum system, including line loss charts for both single and wet-dry mainline purchase a copy of the New York State Maple Tubing and Vacuum System Notebook from Cornell University, Stephen Childs Author.
Les Ober, Geauga County OSU Extension
The concept of vacuum is the exact opposite of what most people think of when they see a pump and some lines. Most people think of air being pushed though a line, similar to a compressor with an air line. Air can be compressed to an infinite level as long as what is holding that air does not explode. With vacuum it is the exact opposite .Vacuum is pressure based on the force that the earth’s atmosphere exerts on all of us. This amounts to about 15 pounds per square inch of surface or 29 inches of mercury. This pressure is also referred to as barometric pressure. As the atmosphere fluctuates it will go up and down with atmospheric air movement (weather fronts). If you remove air from a container you will produce a vacuum inside that container. That lack of air creates a negative pressure that is measured in inches of mercury (hg.) and will never exceed the outside barometric pressure. As molecules of air are moving toward the pump and that air is ejected at a volume over a period of time. In this case Cubic Feet of air per Minute (CFM) . The capacity of the pump will determine how fast this will happens. What we are trying to create inside our sap lines is the absence of air or a perfect vacuum. Most producers grasp these basic concepts they also realize that there is no way to maintain a perfect vacuum inside their sap lines. Damage from wildlife and age introduces air into the system. Even the tree allows air to be introduced. For this reason we always allow for 1 CFM of air movement for every 100 taps. The problem with most systems is that we are getting way more air into the system than we want. This puts a greater burden on the pump to remove the air. The speed at which this is accomplished is largely determined not only by pump capacity, but how the tubing system is constructed. Line length and diameter in relation to the pump and the amount of liquid in the lines has as much to do with it as pump size. Couple this with the fact that most producers are attempting to run at high vacuum ( as close to the daily barometric pressure as possible). The problem with this is that it is counterproductive to pump efficiency. To go from 12 to 15” vacuum requires 20% more system capacity, 12 to 18”Requires 50% more system capacity and from 18 to 20” requires 80% more capacity. Research says you can get more sap per tap, up to 50 % increase. However, this greatly increases the demand on your pump and everything behind the pump has to be in optimum condition. You can see in one short paragraph there is more to running a vacuum system than hooking a line to a pump.
The best way to approach designing a vacuum system is to start with the tubing system and put a pump in place that will run that system. To do this, you need to determine how many taps will be on each mainline. You need to know the slope of those mainlines. Sap flowing in a relatively flat wood will move more slowly than sap moving down a mountain side. Each line has a capacity for liquid it is conducting. For example a 1 inch line on gravity will conduct 50 gallons per hour on a 2% slope and 75 gallons per hour on 6% slope. Remember that you want no more than 40% of the space inside the tubing holding liquid. The rest of space is needed to move air. The vacuum line is dual purpose, but its main function is air movement. If the sap level rises to the point that it blocks that air movement then the vacuum level quickly drops off. This along with excessive leakage is the main reason for vacuum level drop from the pump out into the woods. Using too small a diameter line will result in lines running full of liquid and a drop in vacuum. One of the best ways to overcome this problem is to use dual-line conductors, using the top line for air movement and the bottom line for liquid. The use of this type of system is vital in flat woods with very little slope. Getting your lines sized correctly is the first step in creating an efficient vacuum system. In the next post we will discuss the importance of vacuum line sizing and distribution.
LesOber Geauga County OSU Extension
Looks like Ohio Maple Producers may be headed into another sugaring season with unusual weather patterns. As of February 5th there has already been a significant amount of new syrup made in NE Ohio. The real challenge is setting up your production system so that it can deal with the changes in the weather. You may say that there is nothing we can do about the weather; we have to accept what comes. That is right, however you can change the way you produce syrup to take advantage of every opportunity that comes our way. If you take a look at what happened in Ohio over the past several seasons you will notice some definite trends. Yield per tap dropped from .286 gallons of syrup per tap in 2008 to .169 in 2010. Last year we once again lead the nation in Yield per tap (.244). One of the main reasons for this a favorable weather pattern for producers on vacuum tubing systems, collecting a greater volume of sap, on more days, ending up making more syrup per tap, over the course of the season. How you manage that system during the season is key.
Taphole sanitation has become the buzz word of the industry. It is all about keeping your drop lines and spouts free of bacterial contamination. The piece of technological equipment that may have started it all is the Check Valve Adapter Spout. The warm weather in Ohio over the last several years has proven to be a good test for the new spout that is designed to prevent a back flow of bacterial laden sap back into the tree. It works well in warmer climates like Ohio. It also left a lot of maple equipment companies scrambling to address taphole sanitation issue. All of this is based on research done at Proctor Lab in Vermont and the work done at Cornell University. What it comes down to is that you need to be replacing your spouts every year. You should be replacing your drops every other year. If you shut off your vacuum for extended periods of time during the season when it is not frozen, then you should consider using the Check Valve. The newest model goes directly on the line without the stubby adapter and looks very promising. If you run your vacuum continuously then one of the new polycarbonate spouts may be the answer. Check your drops frequently looking for bacterial buildup. Also this is a prime where squirrel damage occurs. Watch for leaks. At the end of the season make sure you get all of the sap out of the drops. The best way to do this is to clean under vacuum if you can. This removes the maximum amount of liquid out of the lines.
One question that comes up a lot is whether you should shut down your vacuum pump during extended periods of warm weather or let it run? Many producers are finding out that when you run the vacuum pump continuously, you will continue to collect sap even when the temperatures remain above freezing for several days. In most cases the sap you collect will produce enough syrup to offset the cost of running the pump. In fact it is better to keep the pumps on and keep something moving through the lines. This cuts down on bacterial growth in the lines and the moving sap will keep the lines cooler. It takes a good vacuum pump to run under warm conditions. The average vane pump (dairy pump) struggles in this environment. They are not designed to producer high vacuum over long periods of time. They are designed to work comfortably at 16 inches of vacuum. This is the vacuum that you use to milk cows. The best pump choice for extended high vacuum use is a liquid ring pump. They are cooled by water or oil and they hold up well under long periods of continuous use.
The last several years should have convinced everyone that tubing on vacuum pays. The Financial analysis released last winter in The Ohio State University; 2012 Maple Syrup Enterprise Budget shows that the cost of production can be improved by installing and running a vacuum tubing system. One thing that is certain is that the maple industry is now driven by technology and it is helping us deal with Mother Nature.