This Instructable demonstrates how to make a DIY Maple Sap Reverse Osmosis Unit suitable for processing maple sap. Capacity is suitable for small to moderate syrup operations with 250 - 600 taps. Maple sap comes out of the tree at approximately 2.5% sugar. Finished maple syrup is 67% sugar. Therefore, you have to extract a lot of water to transform sap to syrup - about 39 gallons of water out of each 40 gallons of sap. The traditional method is to boil the water off in a pan over a fire. This works just fine, but takes lots of firewood and time. The RO allows you to take 50% to 65% of the water off before you boil, thus saving time and fuel. Generally I concentrate the sap up to about 8% sugar with the RO. I'll take 100 gallons of sap down to about 40 gallons before sending it to the evaporator feed tank. You still need to boil the sap to make maple syrup as the fire is necessary to create the color and flavor we all love on our pancakes in the morning. The RO just allows you to start the boil with more concentrated sap.

This is a batch process recirculating system that works by running the sap through the RO at high pressure and volume, taking some of the water out, and returning the concentrated sap to the feed tank, where it is recirculated through the RO membrane repeatedly until the total desired volume of water is removed. At that point the RO membrane is flushed with clean RO water (permeate) and set aside for the next sap run. The concentrated sap is pumped into the evaporator feed tank to be boiled. An advantage of this system is that the high flow rate tends to keep the RO membrane(s) pretty clean. You will see commercial single pass systems out there that are capable of extracting 50% of the water in a single pass. These systems tend to use very high pressures in the 500-600 psi range and thus need very specialized pumps, hoses and membrane housings. The RO membranes themselves are identical though.

The system consists of the RO membrane and housing, a motor coupled to a high pressure Procon pump, a low pressure pump, a big water filter, various hoses and pressure gauges and a cart to which to mount the components. The cart in this Instructable I welded together out of steel as it incorporates 2 Unistrut vertical pieces to which to mount one or more membrane housings. However, it is not necessary if you don't have metal working and welding equipment. The first system I built I actually just mounted to a 3ft by 5ft piece of plywood and although heavy and cumbersome, worked just fine. You can build a simple cart out of wood or buy a wagon or garden cart and bolt the Unistrut vertical pieces to it. The cart is handy to move the system around but you can use your creativity appropriate to your construction tools and skills.

I have included a list of components with suppliers and prices.

This is an expensive project. For a system capable of taking off 30 or more gallons of water per hour, you're going to spend around $1300. Although expensive, the end cost is about 1/4 to 1/3 that of comparable commercial systems. The pay back time, especially if you're buying firewood, will be about 2-3 years. Having used an RO I would never go back to full raw sap boiling, I find the convenience and time saving worth the expense.

The system needs a big electric motor (1-1.5hp) to operate the high pressure Procon pump. You will need to wire such a motor to run on 220V and thus will need a 220V circuit and outlet in your shop. Procon pumps require a low pressure pump to pressurize the sap coming in. Thus the sap is pumped out of your tank, through a low pressure pump (I use a portable 125V transfer pump rated at 1500 gal/hr and 50 psi) that brings it up to 40-50 psi in front of the high pressure pump. It then goes into the Procon high pressure pump which boosts pressure to 250 psi as it enters the RO membrane. The low pressure pump must ALWAYS be turned on first and the intake circuit pressurized to 40-50 psi before you start the high pressure pump otherwise you will burn out your Procon pump within a few seconds. I have a big sign beside the switches reminding me to do exactly this and so far I've been lucky.

To some extent this whole use of RO is contrary to conventional RO use. Usually, you use an RO to extract clean, pure drinking water from contaminated or salinated water. Thus the pure water is the end product and the left over concentrated or contaminated water is discarded. With maple syrup it is the opposite - the left over concentrate is the end product you want to process into syrup, and the clean water is a byproduct. I generally store 100 gallons or more of RO water in a tank to clean the RO unit after use. A friend of mine stores 300 gallons in a plastic tote and uses it for drinking and all sorts of things. It's also a good practice to keep 2 or 3 five gallon pails of RO water by your boiler just in case you get over zealous with your boiling and exhaust your feed tank and are in risk of burning up a batch of syrup or your pan. A little RO water can save the day. Most of my RO water is discarded, however, it is excellent to drink and nothing makes a better pot of coffee while you're out in the sap house playing some cribbage and tending the boiler.

Step 1: RO Component List

Attached is a pdf of the components you'll need. I have no particular relationship with the suppliers or brands listed, they just happened to be the ones I used. You may be able to find other similar components from other suppliers at other prices. One thing to keep an eye on, if you choose a motor other than the one listed be sure they have the ability to mount to the Procon pumps, as the mounting hardware is somewhat proprietary and unique. The high capacity Procon pumps bolt on to a 56C motor frame using a special adaptor that you must purchase.

Reverse Osmosis Parts List copy.pdf
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Step 2: The Cart and Frame

The frame is a rectangular base welded from 1 1/2 in angle iron. It measures 18 inches wide by 24 inches long. It has a mounting plate for the high pressure motor and pump. At one end I drilled holes through the sides through which I put a piece of 5/8 rod as an axle for a couple of little wheels. At the other end is a simple handle for moving the system around. Rising from the center of frame are two 3 ft pieces of 1/1/2 inch Unistrut channel. As you'll see, the RO membrane housing will mount horizontally to the Unistrut with some special clamps.

From 1 1/2 inch angle iron stock cut 3 pieces 24 inches long and 2 pieces 18 inches long. In two of the 24 inch pieces drill a 5/8 inch hole for the axle 1in from the end and 1/2 inch from the lower border. Make a rectangular frame by welding two 24 inch and two 18 inch pieces together. Make sure the axle holes are aligned with one another on the side of the frame. Weld the third 24 inch piece in the middle of the frame parallel to the sides.

Cut two 3 ft pieces of Unistrut. Weld the Unistrut pieces to the middle piece of angle iron 5 inches from each end so that they are vertical and parallel.

Cut a 24 in and 6 in piece of 1 inch square tubing. Weld the short piece at right angles at one end of the long piece - this is your handle. Clamp it against the center strut so it sticks up at about 45 degrees and weld the other end to the center strut in the frame.

Put your 5/8 in steel rod through the side holes in the frame and slip the wheels onto the axle with 5/8 washers on each side of the wheels. Mark the axle so that you have about a 1/2 in sticking out on either side of the wheels. Remove the axle and cut to length. Drill a 5/32 inch hole 1/4 inch from each end. Cotter pins will go through these holes to hold the wheels on. Reassemble the axle and wheels and lift the front end of the frame until it is level with the ground. Measure the distance between the ground and the bottom of the frame. Cut 2 pieces of angle iron or 1 in pipe to that length and weld them vertically at the front end of the frame to serve as leveling feet.

Cut a piece of 3/16 in plate to approximately 8in by 10in, the specific size isn't important as long as it's big enough for the mounting holes on your high pressure motor. Position the plate at the front corner of the frame, it is fine if it hangs over a bit. Position the motor on the plate and see how the mounting holes line up. Move the plate and motor around until the motor holes will clear the frame. Mark the position of the frame and the mounting holes with a sharpie. Remove the plate, drill the mounting holes in the plate, and weld the plate to the frame on the marks you made.

Cut a piece of 1/8 inch plate 24 inches long by 6 inches wide. Weld this to the the top of the Unistruts parallel to the ground. You will mount your switches and water filter to this. Alternatively, you can just bolt a piece of 2x6 24 inches long to the Unistrut.

Spray paint the frame with some enamel paint.

You are done with the cart

Step 3: High Pressure Procon Pump and Motor

You will need to attach the high pressure Procon pump to your motor.

Before you mount the pump, wire the motor for 220V temporarily so you can test the rotation. Make sure the motor is wired so the rotation is the same as the arrow on the Procon pump. If not, then consult the wiring diagram in the motor to change rotation to the correct direction. Leave a 4 ft piece of wire coming out of the motor to run to a switch. Shaft couplers attach to the end of motor shaft and the end of the Procon pump drive shaft. There is a cone that bolts on to the 56C motor frame. The Procon pump then slides in so the shaft couplers align and bolts to the other end of the cone.

Seal all pipe connections with teflon tape. To the intake of the Procon pump attach a short piece of 1/2 inch pipe with a T-fitting that has a 1/4 in pressure gauge that will measure up to 100 psi or more. Attach a hose fitting to the end of the pipe. This is where the sap will come into the high pressure pump from your water filter. The pressure gauge will let you know when the low pressure side as 40-50 psi before you turn on you high pressure pump. ALWAYS pressurize the low pressure circuit before you turn on your high pressure pump or you'll burn out your Procon pump.

To the outlet of the Procon pump use a piece of 1/2 pipe with a T fitting and another pressure gauge. This gauge needs to be able to measure up to 300 psi. Attach the flexible high pressure metal hose to the outlet from the T fitting. This will run to the intake on your RO membrane housing.

Bolt the high pressure pump motor to the mounting plate on the cart.

Step 4: Water Filter and Low Pressure Hoses

I generally have used garden hose to connect the low pressure system components together. It's universal, it's cheap and readily available. It's also easy to take apart for cleaning at the end of the season. I have friends who have used PEX or clear PVC hose and bayonet fittings. All those are fine if you prefer. I still like my garden hoses.

Attach the water filter bracket to the back side of the horizontal plate you have at the top of your Unistruts with self tapping metal screws or small bolts. The intake and output of the filter housing is 1 in. You will need 2 reducers to adapt from 1 in intake/ouput to a garden hose intake and output fitting from the filter housing. Attach the filter housing to the mounting bracket. Using a 6 ft piece of 3/4 inch garden hose attach the output of the filter to the input of the Procon pump. Attach a 10 ft piece of 3/4 inch garden hose from the low pressure pump to the input of the filter. Install a new 1 micron 4.5 x10 in house filter each time you run the unit (some use a 5 micron filter but 1 micron is better). This keeps the membrane clean. Buy a case of them before maple season starts. It is important to use 3/4 inch garden hose on the input side as the high pressure Procon pump needs a lot of volume and it is easier for the low pressure pump to supply the volume through short lengths of 3/4 inch hose. I have run into trouble using long narrow hose, so avoid my past mistakes and use short lengths of 3/4 in hose. On the output side going back recirculating back to the tank and sending RO water to a holding tank it is fine to use 5/8 inch garden hose.

Step 5: Optional Pump On/Off Switches

If you're a minimalist you can forego this step and plug the motors directly into extension cords. But I like the convenience of having an off/on switch for the low and high pressure pumps side by side. Attach two switch boxes to the cross piece at the top of the Unistruts.

Take the 4 ft pigtail coming out of the high pressure motor and run it to a double pole 220V switch. Attach a length of wire long enough to get to your 220V outlet to the other side of the switch. Attach a 220V plug on the end of the feed wire to go into your 220V outlet.

For the low pressure pumps I wired a switched 120V plug that the low pressure pump plugs into. I attached a short piece of wire which plugs into an extension cord long enough to reach a wall socket. Attach a 3 prong 120V plug to the short piece of wire,

Attach a sign by the switches reminding you to turn on the low pressure pump before the high pressure pump. The general process would be open the feed from the tank, turn on the low pressure pump and check the pressure gauge at the inlet of the high pressure pump to make sure it is showing 40-50 psi. Then turn on your high pressure pump switch.

Step 6: RO Membrane and Membrane Housing

Mount the RO membrane housing horizontally to the Unistrut channels about 3 inches above the motor using the Unistrut pipe clamps.

There are two cap ends for the membrane housing with 1/2 in threaded holes - one in the center of the end cap and one at the periphery. The sap will enter through the hole at the periphery. Clean RO water (also known as permeate) will flow out through the center hole. On the left hand cap just above the high pressure pump, using teflon tape to seal the threads, attach a 3 inch piece of pipe and a 1/2 pipe union to the peripheral hole. Attach the flexible high pressure hose coming from the high pressure pump to the pipe union. The pipe union makes it easy to disconnect the end cap for cleaning. Tighten very well - if you're going to get leaks, it's right here. You'll notice in the photos I have another T-fitting with a shut off tap and hose attachment. I was going to use this for backwards flushing of the system. But I haven't used it and probably wouldn't add it again. But it is there and you will see it in the photos. Plug the center hole with a 1/2 pipe plug, we're going to extract the RO water from the other end of the housing.

In a single membrane system, on the other (right) cap end on the peripheral hole attach a small piece of 1/2 in pipe with a simple 1/2 in gate valve. Coming out of the gate valve should be a garden hose fitting. The concentrated sap will come out of the valve into a hose that will be returned to sap tank while the RO recirculates. On the center hole attach a small length of 1/2 pipe that runs to a garden hose fitting. Pure water will come out of this hole and run to your RO water storage tank.

The gate valve will be used to set the pressure in the RO membrane housing. You start with the gate valve wide open. Once sap is circulating you gradually close the valve and watch the gauge at coming out of the high pressure pump. As the gate valve closes the pressure will start to rise. You want enough pressure to get good water flow out of the center hole of the end cap, but you do not want to exceed 250 psi. The SS membrane housings are rated to 300 psi. I once went over 300 and blew out a set of 0-rings which required replacement. You'll save 100 gallons or more of RO water for flushing the system when done. When your flush tank is full, the rest of the RO water can be discarded down the drain, or saved for consumption or plants or whatever if you prefer.

Use a food safe lubricant such as Dow Corning Silicone/Moly Lubricant to coat the O rings on the cap ends of the RO membrane housing. There are O rings on the outside of the cap and in the center hole on the inside. Once they are well coated slide the RO membrane into the housing and center it. Slide the cap ends all the way onto the membrane so that both cap ends are tightly against the end of the stainless cylinder. Use the clamps that come with the housing to hold the cap ends in place.

Step 7: Optional System Expansion. Adding Additional Membranes.

If you are prone to fits of unrestrained enthusiasm, such as I am, you may want to add capacity by adding additional RO membranes in series. It is easy to do, you just mount an additional membrane housing(s) to the Unistruts above the first.

Each membrane housing has two cap ends for the membrane housing with 1/2 in threaded holes. One in the middle and one at the periphery. The sap will flow through the holes at the periphery of each membrane. RO water will be extracted through the center hole of each membrane. On the first cap on the left just above the high pressure pump, using teflon tape to seal the threads, attach a 3 inch piece of pipe and a 1/2 pipe union to the peripheral hole. Attached the flexible high pressure hose coming out of the Procon pump to the pipe union. The pipe union makes it easy to disconnect the end cap for cleaning. Tighten very well - if you're going to get leaks, it's right here. Plug the center hole with a 1/2 pipe plug, we're going to extract the RO water from the other end of the housing.

On the right cap end of the first membrane housing, on the peripheral hole, attach a 3 inch piece of 1/2 in pipe through a barrel coupler to the second high pressure flexible hose. In the center hole attach a 3 inch piece of pipe with a garden hose fitting. The RO water from the first membrane will be extracted here. A 3 ft. piece of 5/8 garden hose (lime green in the photos) will run from the center hole to a garden hose manifold. The hose coming out of the manifold (green in the photos) will conduct the RO water to your storage tank.

Attach a second RO membrane housing parallel to the first using the 4 in. Unistrut clamps. On the right end cap of the second membrane housing attach a 3 inch piece of pipe and a 1/2 pipe union to the peripheral hole. Attach the flexible high pressure hose coming out of the first membrane housing to the pipe union. In the center hole attach a 3 inch piece of pipe with a garden hose fitting. The RO water from the second membrane will be extracted here and will run into the manifold through a 3 ft hose (lime green in the photos).

At the left end of the second membrane housing cap attach attach a 3 inch piece of pipe and a barrel fitting to the peripheral hole. Attach a third flexible high pressure metal hose to the barrel fitting. Plug the center hole with a 1/2 inch plug.

Attach a third RO membrane housing parallel to the first using the 4 in. Unistrut clamps. On the left end cap of the third membrane housing attach a 3 inch piece of pipe and a 1/2 pipe union to the peripheral hole. Attach the flexible high pressure hose coming out of the second membrane housing to the pipe union. Plug the center hole with a 1/2 in plug.

At the right hand end cap on the third membrane housing in the peripheral hole attach a 3 inch piece of 1/2 in pipe with a simple 1/2 in gate valve. Coming out of the gate valve should be a garden hose fitting. During operation you will attach a 5/8 in garden hose to that fitting that will carry the concentrated sap back to the storage tank for recirculation. In the center hole attach a 3 inch piece of pipe with a garden hose fitting. The RO water from the third membrane will run into the manifold through a 3 ft hose (lime green in the photos).

initial results from my 3 membrane system running at 250 psi on frigid sap is 90 gal of RO water (permeate) per hour.

Step 8: Testing and Operation

Before you run valuable maple sap through your unit it is a good idea to test it on 50-100 gallons of clean water.

Fill a tank with 50 - 100 gallons of fresh water. I use the gathering tank on the back of my gator.

TESTING

1) Place a fresh 1 micron 4.5x10 inch house filter in the filter housing. Don't operate the system without a clean filter. You can ruin your expensive RO membrane if you do.

2) Make sure all hoses are connected and tight. As I mentioned before. The intake hose from the tank to the low pressure pump, the low pressure pump to the filter, and the filter to the high pressure pump intake should be as short as possible and of 3/4 in hose caliber.

3) For testing purposes both hoses from the exit cap can be run to a drain. Normally, the hose from the peripheral hole would normally be run back into the tank for recirculation. The hose from the center hole would be run to the RO water storage tank.

4) Connect the switches to power and plug in the low pressure pump

5) Open the valve from the feed tank containing fresh water

6) Turn on the low pressure pump. The filter housing should fill and the pressure gauge at the high pressure pump intake should rise to 40-50 psi.

7) Once the low pressure side is pressurized turn on the high pressure pump. Water should start coming out of the peripheral hole when your gate valve is. Not much RO water will come out yet. Flush 25 gallons of water through the system. Check for hose leaks and tighten junctions where necessary.

8) Slowly start to close the gate valve at the exit of the peripheral hole of the membrane housing. Watch the high pressure gauge at the exit from the high pressure pump. As the valve closes the pressure should increase and RO water should start flowing out of the center hole. Adjust the valve so you have good flow. Do not exceed 250 psi of pressure. Check the connections in the high pressure circuit between the exit from the Procon pump and the intake into the membrane housing for leaks. If you're going to have leaks it will be here in the high pressure circuit. Note any leak points so you can come back and tighten the leaking joints.

9) Run another 25 or more gallons through the system.

10) Before you run out of water, open the gate valve, turn off the high pressure pump, then turn off the low pressure pump. Close the valve coming out of the feed tank.

11) Your test is complete

OPERATION

Many of the steps are the same as for testing

1) Place a fresh 1 micron 4.5x10 inch house filter in the filter housing. Don't operate the system without a clean filter. You can ruin your expensive RO membrane if you do. I generally will use a new filter each time I run sap through unless I am going to have multiple runs in a day. If you have a clear filter housing you can see if the filter is getting contaminated and needs replacement.

3) Place the exit hose from the center hole on the exit cap into a 100 gallon or more tank to collect RO water (permeate). The hose from the peripheral hole coming from the gate valve should be placed back into the sap tank for recirculation. Make sure the gate valve conducting concentrate out if the membrane is wide open.

4) Connect the switches to power and plug in the low pressure pump

5) Open the valve from the feed tank containing your maple sap

6) Turn on the low pressure pump. The filter housing should fill and the pressure gauge at the high pressure pump intake should rise to 40-50 psi.

7) Once the low pressure side is pressurized turn on the high pressure pump. Sap should start coming out of the peripheral hole when your gate valve is. Check to make sure sap is recirculating back to the tank. Not much RO water will come out yet.

9) Monitor the sap volume in your sap tank. If you are starting say with 100 gallons, your goal should be to take the volume down to 40-50 gallons thus producing 50-60 gallons of RO water. You can test your sap concentrate with a refractometer and stop when the sugar content reaches 8%.

10) Once you have hit your target volume/sap concentration open the gate valve, turn off the high pressure pump, then turn off the low pressure pump. Close the valve coming out of the feed tank. Remove the end of the recirculating hose going back to the sap tank. Remove the end of the hose going to the RO water tank.

FLUSH AND CLEAN THE MEMBRANE

After you have processed a batch of sap you need to flush the membranes to prepare for the next batch.

11) Remove the dirty sap filter from the filter housing and put a clean filter in. Once you are in season, you can save your wash filter in a large zip log bag and reuse it to save money. Attach the low pressure pump to your RO water (permeate) tank. Run both the recirculating hose and RO water hose to a drain or let drain outside onto the ground. Open the valve to the RO water tank and turn on the low pressure pump. Wait for the pressure gauge at the high pressure pump intake to rise to 40-50 psi.

12) Turn on the high pressure pump and run 50-100 gallons of RO water (the more the better) through the membrane housing. Leave the gate valve wide open while flushing.

13) Turn off the high pressure pump. Turn off the low pressure pump. Close the valve to the RO water storage tank.

14) Remove your wash filter from the filter housing and save in a large zip lock bag.

15) You are ready for the next sap run

Step 9: Cleaning, Off-season Storage and Next Season Start-up

Cleaning Between Batches. End of Season Cleaning and Next Season Start-up

CLEANING AFTER USE DURING THE SEASON

After you process a batch of sap flush the membrane(s) with 50-100 gallons of RO water - the more the better. That is all you need to do. If more than 2 days go by without processing the next batch some membrane manufacturers recommend that you flush with an additional 50-100 gallons before processing the next batch although I generally have not done this and I haven’t had any difficulty with membrane life.

PVC ENCLOSURE

After season end cleaning you will place your membrane in a white PVC tube in a preservative solution. Take a piece of 4 inch white PCV pipe and cut it to 44 inches. On one end cement on a cap to seal it. At the other end cement on a cap with a threaded removable plug. You will need one enclosure for each membrane you have.

END OF SEASON CLEANING AND STORAGE

At the end of the season it is good practice to clean the membranes with a cleaning solution, then rinse them and store them in a preservative solution until next season. The cleaning solution used is actually a strong NaOH (sodium hydroxide or lye) solution. Food grade sodium hydroxide is available on Amazon or eBay quite inexpensively. It is EXTREMELY corrosive with a pH of 11 or so. You must use gloves, protective clothing and eye protection while using it. BE CAREFUL WITH THIS STUFF, if it gets on your skin, it will cause a nasty chemical burn!

CLEANING

Use a 15 gallon plastic tub to mix the sodium hydroxide solution. Add ½ cup of NaOH to 10 gallons of hot water. Place the intake hose from the lower pressure pump and both discharge hoses in the plastic tub. Start the low pressure pump, then the high pressure pump with the gate valve at the exit of your last membrane wide open. Recirculate the cleaning solution for 10 minutes, then shut off the pumps and let sit for 10 minutes. Repeat these steps for 3 cycles. Rinse the membranes with 100 gallons of RO water or fresh water.

PRESERVATIVE

The preservative is food grade Sodium Metabisulfite. This is a common preservative used in wine and beer making. It is the solution used in the air locks on wine carboys. You will need 2 gallons of solution for each membrane you are storing. Add ¼ cup of sodium metabisulfite to 2 gallons of RO water or fresh water. Place the clean membrane in the PVC storage container you have made. Pour the sodium metabisulfite solution into the tube with the membrane until full. Screw on the cap. Store the cylinder upright in a cool place where it will not freeze.

NEXT SEASON START UP

At the start of the next season remove the membrane(s) from the storage container and dump out the preservative solution. Assemble the RO unit. Flush 100 gallons of clean water through the unit. It is ready for use.