Optimizing the Performance of My Vacuum Tubing System: Part I

The goal of these next 3 articles 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 this and the next two posts is a synthesis of past content with some more recent best practice guidance.

When we talk about tubing systems, we have two roads to travel. One is a gravity system and the other is a vacuum system. A conventional 5/16” gravity system is not much different from running sap into a bucket. The yield is much the same as collecting sap in a bucket. When we add vacuum to a tubing system, we increase the sap yield 5% for every inch of vacuum we generate in our system. For example, if we produce 15 inches of vacuum in a line, we should be able to almost double our sap yield.  The first year after installation is always the best. As time on a system accumulates, wear-and-tear hampers performance.

Caption: Year 1 Production with a Brand-New System Should Provide Your Best Vacuum Levels

The definition of vacuum is the absence of air. The maximum level of vacuum achievable on any given day is determined by the barometric pressure. This means that our vacuum level can never exceed the barometric pressure in the location of our sugar bush. There are two way to measure vacuum pump performance, Inches of Mercury (hg) and Cubic Feet per Minute (CFM). Inches of mercury measures the negative pressure produced when air leaves the line. For example, if 50% of the air is removed then the inches of mercury should be somewhere between 14 and 15. At 25 inches of mercury, approximately 85% of the air has been removed from the lines. CFM on the other hand measures the amount of air being evacuated from the lines in units of cubic feet per minute. This is the amount of air that a vacuum pump is pulling out of the system in one minute’s time. Where is the air coming from? The answer is gas that is forming inside the tree and being expelled through the tap hole. As a rule of thumb, there is a 1 CFM requirement for every 100 taps on the line.  However, the biggest contributors are leaks allowing air to enter the system through damaged or aging tubing. This statement emphasizes the importance of managing leaks in a vacuum tubing system.

Caption: Vacuum Gauge Measuring Vacuum in Inches of Mercury (hg)

Speaking of leaks, the most important part of operating any maple syrup system is the time you spend in the woods making sure your vacuum tubing system is leak-free. Much of the rest of the article is spent discussing different technologies and equipment, but the simple fact of the matter is this – the best equipment with poor care in the woods won’t do you a lick of good when it comes to putting more maple syrup on tables of your customers. You must always account for leaks that introduce air into lines. You might be able to maintain peak vacuum on average days, but your system will show its weak points when sap flows are running fast and you need to move as much as air as fast as possible to maintain vacuum levels. Being able to spot and repair leaks quickly is essential. To accomplish this, you should design your system so you can isolate lines to pinpoint problems. This can be done by compartmentalizing your system with valves and vacuum gauges placed at the starting point of each line. The installation of a tubing monitoring system can be a wise investment as well, and the time saved and extra sap produced will pay for the cost of the upgrades in short order.

Back to our lesson on vacuum and barometric pressure. There are factors that have a direct effect on barometric pressure. One is altitude. As the altitude increases the maximum barometric pressure declines (rule of thumb: for every 1000 feet of elevation you lose 1 inch of vacuum). For example, at sea level, or 0 altitude, the average barometric press can be 29 inches; at 2000 feet, the average maximum barometric pressure obtainable is only around 28 inches. In addition, barometric pressure changes under different environmental conditions, and variations in barometric pressure caused by atmospheric changes can occur multiple times in a day. If we are running a vacuum pump under a low barometer at 2000 feet elevation, we might struggle to maintain 28 or even 27 inches of vacuum on a very tight well-maintained tubing system.

Sap moves down the line by gravity on a system of tubes suspended with wire. The basic components are spouts, tees, and drops moving sap from the tree into lateral lines. A lateral line should have no more than 5 to 10 taps per line and should be no longer than 100 feet in length. The lateral lines flow into main lines. In large systems, secondary mains flow into Wet-Dry lines and or trunk lines (large diameter lines) that move the sap to a central collection point.   To properly function, sap lines should be straight, pulled tight, and sloped downhill. To this point gravity systems and vacuum systems are similar, with the gravity system relying on slope and Newton’s law of gravity to move the sap.

Caption: 65 CFM Bush R-5 Vacuum Pump

When vacuum is added to the system, sap flow is aided by the movement of air.  The components of a vacuum tubing system are the vacuum pump, which is connected to lines via a sap releaser. Even though it is called a vacuum pump, it is not a pump in the conventional sense of the word and that is a bit confusing. A conventional pump moves liquid creating pressure ahead of the liquid and suction on the backside of the liquid. There are other types of pumps used in maple production. For example, a diaphragm pump is a conventional pump and that creates enough suction (secondary vacuum) to draw sap from a tree. However, if liquid is not present in the lines that suction can be lost.  A true vacuum pump moves air, not liquid and it creates a higher level of vacuum (absence of air) as the air is removed from the lines. That level of vacuum can be maintained with or without sap in the lines and will only drop if a leak allows outside air to enter the line.  Because the pump is designed to move only air, the liquid must be separated from the pump. This separation process is performed by a sap releaser. If sap enters the vacuum pump severe damage to the pump can occur! To prevent this from happening, a moisture trap is placed between the pump and the releaser.

Caption: Sap house releaser (right) with Vacuum Piston Pump (left)

A properly sized vacuum pump with a proper CFM rating will be capable of removing air faster than it is introduced. However, there is one factor that can interrupt and slow that process – line size. Vacuum lines are designed to conduct air to the pump. If your line diameter is too small, the air movement will be restricted requiring more time for the pump to clear air from the lines. This phenomenon is referred to as line loss. The smaller the line the more the air flow is restricted resulting in higher line loss. As an example, a 60 CFM pump set at 15 inches of vacuum hooked to a 3“ line can maintain over 40 CFM out to 5000 feet. However, that same pump hooked to a ¾” inch line is incapable of delivering 15 inches of vacuum at 2500 feet from the pump. Line loss increases the time (recovery time) needed to evacuate air from the line and restore peak vacuum level.

What is missing from this equation? The capacity of the line to conduct liquid. Every diameter of pipe has a maximum liquid capacity. The size of the pipe that is needed is determined by the number of taps flowing into the pipe. Each tap during a peak flow might contribute upwards of 0.2 gallons of sap per hour. Once you calculate the amount of sap flowing in you can determine the size of the pipe that is needed. There is however one caveat, the steeper the slope the faster the sap moves through the line thereby effectively increasing the capacity of a given-sized line on steeper slopes. Slope can also influence sap flow in other ways. The portion of the line, 50 feet or longer with the least amount of slope, will strongly influence sap flow. Examining this critical portion of your line might dictate a necessary increase in line diameter to allow for adequate air and liquid flow. Remember, you need to move air as well as liquid through a maple pipeline. To do this you must maintain the proper ratio of air to liquid inside the line so as not to inhibit sap movement. If you look at a working cross section of tubing it should contain 60% air and 40% liquid. This is a primary consideration when determining what size of line to use in your sugarbush.  If the liquid level increases beyond that ratio or is uneven (wavy), the air movement will be restricted resulting in a drop in vacuum.

Caption: Whip Connection to a Wet-Dry Line.

There are two ways to solve this problem. The first would be to increase the size of your main lines but 1 ½” inch and 2” tubing is expensive, and it adds to the overall expense of the tubing system. Still, increasing tubing size may be justified if you have a large number of taps coming into a trunk line. The other alternative is to install a dual-line conductor commonly known as a Wet-Dry Line. Composed of two lines of equal size (or a dry line slightly larger than the wet line), a Wet-Dry system can excel at moving sap across flat areas or areas where multiple secondary mainlines merge. Secondary mains may enter the Wet-Dry line at a booster, or a line configuration called a whip. This allows sap to move down the wet line without impeding the airflow in the dry line. This set-up is particularly useful in flat areas where slope in minimal and sap flows slowly which may inhibit the necessary amount of air flow. Wet-Dry lines can be a cost-effective way to move sap through areas of minimal slope.

Stay tuned for Part II in a couple of days and be sure to leave questions or comments!

Author: Les Ober, Geauga County OSU Extension

When the Season Comes to an End

The season has come to an end and now you are faced with the arduous task of cleaning up you maple operation. Where do you start and what do you use? For most equipment, the answer is simple – lots of hot water and elbow grease. A good place to start is with the tanks that hold both sap and syrup. Most are stainless steel and are easy to clean with a pressure washer. We found that a tank washing nozzle that fits your pressure washer is a valuable tool. The specially-designed nozzles enable you to spray to the side and reach areas that a standard spray tip cannot reach. There is no substitute for stainless steel equipment if you can afford it.

Plastic totes and poly tanks have become popular because they are relatively inexpensive but they are harder to clean. Plastic totes, while affordable, may only last about two or three seasons if you get off your cleaning schedule. It does not take long for the plastic to become so contaminated with bacterial spores that you have to discard and replace. However, if you keep poly tanks cleaned they will last for years. Another simple tip is to clean as soon after the season ends as possible. Allowing totes and tanks to sit dormant allows bacteria to build and grow making cleaning more difficult.

Your evaporator needs to be sugared off and flushed out as soon as possible. I often flush the pans with clean water and then refill them with permeate from the RO and let them soak. If permeate is not available, use water. I will drain and refill the pans with clean water and then add the proper amount of pan cleaner following label directions. Once the pan cleaner has done its job, I drain the pans and use a high pressure washer to finish the job. Do the process correctly and your pans will look brand new. Make sure all your float boxes are clean, replace gaskets if needed. Soak your auto draw off temperature probe and your hydrometer in a 5% vinegar solution to remove any residues or films. The thermocouple in the auto draw off probe works best when there is no niter on the probe. Clean your filter press thoroughly and lubricate parts with a food grade lubricant. It is good practice to remove all extra filters from your sugarhouse and store them in your house, somewhere dry and rodent-free. If you use a filter tank, you will need to clean filters and make sure they are completely dry before story to ensure no mold will develop over the off-season. Any filters with problems, even minor, should be discarded, and you should purchase new inventory for the next season.

Reverse osmosis units (RO) should be soap washed and thoroughly rinsed immediately after the last time you use them. Make sure all of the permeate is drained out. Once you break down the RO, return your membranes to the storage vessels with a cup of permeate in each one. Once everything is clean, you should send the membranes in to your dealer for cleaning and testing. There is nothing worse than starting a season with a bad membrane that is passing sugar. Make sure your high pressure pump and your feed pump are free and fully drained. Inspect the membrane housings and get them as dry as possible. Many times with the recirculating motors and pumps on the bottom of the membrane towers, dampness can cause the pump shafts to seize and seals to deteriorate. Because evaporators and ROs require the use of chemicals that are incompatible – phosphoric acid and basic soap – keep them separate and out of reach of children. Be careful when you mix pan cleaner and always follow the directions on the label.

The most controversial portion of a maple system to clean is most certainly the tubing. It seems everyone has his or her own way of dealing with the miles of tubing stretching through the woods. I have cleaned tubing just about every way possible over the years. We have sucked water, pumped water and air, water only, air and tubing cleaner, and just plain did not clean at all. In my experience, using water and air worked well until we tried to pump up too steep of slope and had a blowout that may have had enough force to launch a satellite. Sucking water through the lines left a lot of liquid in the lines that eventually turned to green snot. The method we now use seems to work. We pull taps with the vacuum, nip off each old spout, and immediately use a Stars Company (out of Quebec) line plug to seal the drop line and maintain vacuum on the system. Done properly, the sap in the lateral line will not suck back into the drop line. We then use a paint marker to mark the old tap hole which greatly speeds up next season’s tapping process. Once all of the taps are out, we back flush the mainlines with clean water. Next we close all of the main lines and open the end of each lateral opening long enough to pull air through the lines and keep vacuum on the system. Doing this should remove 80% of the liquid from the lateral and main lines. At this stage, we successively open the ends of each main line and let air in with the vacuum on. Once the vacuum on the entire system drops to zero shut off the pump. At some point before the next season, we then install new spouts on all the drops and let the lines air out completely. This method may seem excessive but it does work. We have a small amount of green sap at the start of the season, but nothing we could not easily filter and could possibly have been avoided by flushing the system again before the season.

A word of caution when it comes to using tubing cleaners. They have to be completely flushed from the lines before the next season. Never use Isopropyl alcohol – it is illegal in the United States. Also be aware that some cleaners attract Mr. Bushy Tail and his friends – never a good thing for tubing operators.

Once your system is cleaned, bring in all releasers and clean and sanitize them thoroughly. They are made of PVC which makes a good home for bacteria. Go over the mechanism and use lubricant provided by the manufacture to lubricate all of moving parts. The last task is to care for your vacuum and transfer pumps. Change the oil or drain out the water on liquid ring pumps. On the new rotary claw pumps change the oil and fog the pump with a pump oil. You need to make sure rust does not build up. The same is true for rotary vane pumps which are more maintenance-free but putting some oil on the vanes never hurts. All gasoline motors should be drained and the gasoline replaced with SeaFoam or a similar product. Never leave gas with ethanol in the tank. Drain the crank case oil and replace it with fresh motor oil and you will be ready to go for next season. Lastly, make sure you transfer pumps are drained and stored somewhere that will not fall below freezing.

Author: Les Ober, Geauga County OSU Extension