Questions about my Homebuilt RO

[Clinkis]

So I'm building a new RO for this season. I've used a small RO built with residential membranes for the last 2 seasons and it worked great but it just won't keep up to my sap now that I'm up to 150 taps. I'm in the process of ordering everything I need and have a few questions for all the RO experts on here.

I'm using an XLE 4021 membrane (4"x21") which is 1050 GDP. Im using a shallow well for a feed pump and plan on a procon high pressure pump. Having a hard time figuring out what size of procon pump to use. Also do i want one with or without pressure relief?

For piping and fitting was hoping to use the John guest connectors and poly pipe. Will these handle the pressure?

Any suggestions or advice is appreciated

[bowhunter]

I have a system with a 2040 NF 90 membrane which handles 100 taps with no problem. I like to size the RO so that it will process a days worth of high sap flow in eight hours so I would size yours to handle 30 gallons per hour at about 70% water removal. I would go to the 40 inch membrane vs the 21 inch. A nanofiltration membrane that size would be big enough, but 4x21 XLE is probably a little tight. The reason I say that is the XLE's are rated at 100 PSI while the nanofiltration membranes are rated at 70 PSI and believe it or not that makes a significant difference in the capacity at 200 PSI.

1. Using 30 GPH as the basis you would need a 3 gpm Procon pump to handle the flow including the recycle.
2. The John Quest fittings work fine at this pressure.
3. I don't think you need a pump with the relief.

[maple flats]

Rather than a relief, just make a bypass back to the inlet to the pump. then if the pressure is too high you can bypass a little. Then you also want a valve after the bypass at the out end of your membrane to get enough pressure. On mine, a Ray Gingerich unit, it has both, a bypass and a flow restrict. I then run at 275 PSI, if I want higher sugar concentration, I open the bypass more and then restrict more to get my 275 PSI. You want less pressure, looks like 70 PSI, but the principle remains the same. My bypass is just into a 1/4" line, controlled by a needle valve, and the restriction valve is still a needle valve but it is controlling a bigger pipe/flow.

[Clinkis]

Thanks for feedback. Bowhunter I see in your profile your RO does 18 gph. Is that raw sap processed or concentrate produced? Also, according to the specs, a 2540 NF90 is rated for 520gpd whereas the 4021 xle is rated for 1050 gpd so shouldnt it process more. Thats I also understand the nf's work at lower pressure but they also pass more suger the xle's. I've kinda made up my mind I want to use the Xle but have been flipping back and forth between the 40" and 21".

[mellondome]

40" will give lot more surface. Unless you think you are done adding taps.
Have you considered using a centrifical booster pump instead of the procon?
For membranes.. the nf270 and nf90 will outflow the xle. Xle advantages only come to light with high concentrations (10%+) and cost to buy. When comparing flow ratings.. you must look at the pressures and temps used to get the flow.

[Clinkis]

Thanks for the info. So you are saying that the nf's only tend to pass sugar when concentrating above 10%? Also, could you elaborate on a centrificial pump? I've not come across any info on them while doing my research.

[maple flats]

You must also realize that the flows stated are most likely for water at higher temperatures. Temp. changes the flow considerably.

[bowhunter]

My RO processes 18 GPH of sap at about 70% water removal. The membrane will do better than this when it's absolutely clean, but I gave you a more average capacity estimate. It changes as the membrane fouls during normal operation. I use recirculation as described by Maple Flats and feed concentrate (6 GPH) directly into my little evaporator. I believe the 2540 NF90 is rated at 680 GPD of permeate. The manufacturers use different conditions to rate different types of membranes so it's a little difficult to compare them by the daily permeate flow rate. For example small house membranes are rated at 50 PSI, nanofiltration membranes at 70 PSI and XLE's at 100 PSI and on and on. Either the NF or the XLE's will work fine.

I don't think you will get any significant sugar pass through at 200 PSI with the NF's. The NF pass the same amount of water at a lower pressure than the XLE. They also pass a little more mineral content through into the permeate. The NF are more expensive so that's definitely a consideration. The NF's 270 are pretty sensitive to caustic washing and you can damage then with higher pH (above 10) during caustic washing. This can lead to increased sugar pass through. If you look closely at some of Dow early sap membranes such as Mark I's you'll see that they are NF membranes. In fact I believe the NF 270 has probably processed more sap in the industry than any other membrane.

So bottom line NF's work in sap processing and so do the XLE's. I think you will be fine with the XLE just understand that any membrane will not process nearly as much concentrate on cold sap as the rating for 77 F water. Temperature, sugar content and natural fouling of the membrane during operation have a big impact on the operation.

[Clinkis]

Thanks again for the info. I am planning on using a recirculating loop. Just curious, bow hunter, you say your RO removes 70% water. What is your usual sap suger content and your concentrate? Your maple operation seems to be comparable in size to mine. Are you happy with your RO or do you wish you had a little more capacity. I'm starting to think the 40" membrane might make more sense. The difference in price is minimal.

[BreezyHill]

The use of a procon pump will be a big factor in your design. Procon is a positive displacement pump and will give you the pressure you need to flush the membrane during operation. When the flow of your permeate starts to drop off, just increase the flow across the membrane and you will clean the membrane of lodged mater.

Centrifigal pumps can move large volumes at lower pressures; since when the pressure reaches an elevate point the impeller starts to cavitate in fluid as it is unable to push the flow away.

Then factor in the small Hp that is needed to run a procon and you can setup secondary pump with an additional pump to get even more water removal.

My unit is a dinosaur 1982 Memtek. It has a centrifugal pump to filter the sap and supply the 3 cylinder piston pump that is rated for 600 psi. The unit is designed to run at 500 psi with 2 4"x40" membranes Last season I installed 2 new membranes and vessels. XLE's . They cut the working pressure way down to achieve the same permeate passage as the unit had on the other membranes.

The problem is the pumps put out to much flow for just two of these membranes. In the future I will be adding an additional pair of xles to split the flow since my flow is over twice what is recommended for the membranes.

Procon pumps can be found at very reasonable prices all set up and ready to go...and they are relatively easy to rebuild if they fail.

Be very careful of plastic hoses...when they fail they ave very dangerous so have a power disconnect way from the unit that can be thrown to cut the power. My unit only has plastic on the low pressure side. Copper on the high pressure. A friends DIY RO has plastic all around and he has had failures; but they are easy to fix. His is in a wood cabinet that is insulated; with power off out side of cabinet.


Good Luck!

Ben

[mellondome]

Multistage centrifical pumps are what all commercial units use for their pressure pumps.

Not saying that procon pumps aren't a good way to go, but there are advantages to using multistage pumps. You will still be able to get all the pressure you need on the membrane. With a miltistage, you will not need a wash tank heater. They aren't positive displacement pumps which do have drawbacks with pressure increases. positive displacement pumps also create micro pulse waves, which in the long run might not be good for the membrane.


But , to each their own. Good luck with your build which ever way you chose. Nothing beats boiling concentrate.

[bowhunter]

My sap averages about 2.5% sugar so my concentrate averages about 8%. I would probably make mine a little bit bigger if I had it to do over again, but my system handles 100+ taps comfortably with 6-7 hour boiling days and a 1/2 pint evaporator. I can always go longer if needed. I have a little more capacity on my evaporator so I can run a little faster on the RO with lower water removal if needed. Once you decide to go with a 4 inch membrane I think I would go ahead and use the 40 inch vs. 21 inch. Both membranes require the same minimum concentrate flow, but the 40 incher is about double the permeate capacity. As a good rule of thumb, the permeate capacity of a membrane will be about 40% of the rated or published capacity for these small systems. So a 1000 GPD membrane will remove about 400 GPD of permeate from maple sap.

As far as pumps go. I think the ProCon is pretty hard to beat. It's simple, inexpensive, and reliable. If you decide to build a larger system other pump options would probably be a better choice, but for your system they are an excellent choice. It's also not that expensive to keep a spare ProCon pump around in case you wreck the pump.

Hope this helps.

[Clinkis]

Thanks again for all the feedback. This is why I'm asking these questions now before I start so I can learn from everyone's knowledge, success's and failures.

So, I'm going to go with with the XLE 4040 membrane and a procon pump. I think I would rather have a little extra capacity then be wishing I had more. So now that's settled, which procon pump do I want? Series 3 or 5? 1/2" or 3/8"? Should it be stainless or is brass ok? How many GPH?

I'm planning on getting everything in the next couple weeks so I can get it built and have some time to get the bugs worked out before the sap starts which won't be all that long!

[bowhunter]

The pump depends a little on how fast you want to process. For 25 GPH of sap feed you will need about 150 GPH on the pump and for 30 GPH you need about 175 GPH pump. I would go to the larger pump because a 150 GPH is a little light for a 4 inch membrane. You'll need a 3/4 or 1 HP motor. It would be better to use stainless steel, but my brass pump works fine. It's generally recommended to avoid brass as much as possible in maple syrup production. I believe this is a series 5 pump with 1/2 fittings.

[Clinkis]

So I order a 190 gph procon pump and motor, an xle4040 membrane and stainless steel housing. Parts should be in this week. Now I am in the process of planning and collecting all the plumbing. My plan was to feed procon pump with 1/2" pex. Do I want 1/2" or 3/8" pipe for high pressure lines to feed membrane? I also plan to plumb in a simple recirculating loop. What size should that be? I don't expect to ever use more then one membrane.

[bowhunter]

I believe the fittings on your pump and membrane housing are 1/2 inch so I would plumb everything in 1/2 inch. It they're 3/4 inch then use 3/4 inch. The recycle line will flow about 80% of the total flow through the pump and membrane housing so I would stick with 1/2 inch for the recycle as well. You should get good results using 1/2 inch needle valves. In any case make sure you use a needle valve on the recycle line and concentrate. A gate valve or ball valve won't offer fine enough flow and pressure control. My entire system is 3/8 inch (including the needle valves) which is the same as the fittings on the membrane housing and the ProCon pump and everything works fine.

[Clinkis]

Ok thanks. Yes fittings on pump are 1/2". Not sure about membrane housing. Yes I was planning on using needle valves. Do I need a check valve on recirc loop?

[mellondome]

Are you using a supply pump before your filter?
Fastest way to destroy the pump is to cavitate it.

[Clinkis]

Yes, using shallow well pump with low pressure shutoff to protect procon pump