Xle-4040, not much permeate

[Cider Hill Maple Farm]

Hi guys,
I'm using a XLE-4040, and last night was the first run. After starting up I had a ton of flow in the concentrate flowmeter and about 1 GPM going through the permeate flowmeter. After tweeking the needle valves, I had the permeate valve wide open and concentrate set at 1 GPM and running at 250 PSI, the flow didn't change in the permeate. After reaching close to 300 PSI and maxing out what the membrane is rated for, the pressure vessel came apart. Besides the obvious of a plugged line or faulty needle valve, what are you able to generate for flow on the permeate side at 250 PSI? I know this question will come up so I will answer it now. This RO is homemade with two Goulds 7GB booster pumps that get me to 290 PSI without an issue. Any help would be appreciated!

Thanks in advance.

[Maplewalnut]

I start off around 3.0-3.5gpm and it drops off from there depending on how long it runs. Even after 4-5 hours I can maintain >2gpm at 250-275psi

[JRCunningham]

A couple of thoughts/questions for you.

1. Are you using PVC (Grey) or fiberglass membrane housings? I run three XLE-4040 membranes in PVC housings, and above 250PSI the ends tend to blow out of them or they crack at the bottom. I've also got a smaller RO with a single XLE-4040 membrane in a fiberglass housing, and that little bugger will take the pressure no problem.

2. Do you have a cartridge filter before the RO membranes? When I start to see permeate flow drop and need to increase pressure to keep concentrate flow rate high, I usually suspect the cartridge filter first and will change it.

3. I like to run concentrate at about 6 GPM and Permeate at 2.5GPM (again, that's three membranes and a 2HP pump)--the faster the concentrate runs the more washing effect you have on the outside surface of the membrane. My experimentation has found that running a higher concentrate flow rate at a lower pressure (like 170 PSI) is much better on the membranes and helps maintain great permeate flow throughout the season. Wash rate is good.

4. When you rinse your membranes out with permeate at the end of the day, try a fast wash rate (concentrate flow rate) and see if that helps.

Hopefully some of this is helpful. Good luck.

--J.R.

[Cider Hill Maple Farm]

JR & Walnut,
Thanks for your replies, to answer a couple of questions first. Yes I do have pre filters before the second pump, I just installed them before start up. My pressure vessel is stainless steel with clamps at both ends and rated for 300 PSI. Last night I removed the membrane from the housing and checked all o-rings on the caps and the u-cup on the membrane, checked all piping for any restrictions and found everything to be fine. Restarted RO and still could only achieve .75 GPM permeate flow at 250 PSI. On the concentrate side I could open up the needle valve and easily get 8 GPM. At 8 GPM the permeate flow showed between .75 and 1 GPM, didn't seem to matter what I tried, I could only concentrate at .25 GPM on the concentrate flow and .75 GPM permeate. I checked the concentrate and permeate for sugar and had 4% concentrate and 0% on permeate. I just don't know!! This membrane I was told should operate fine around 120 PSI, At 250 PSI it should have a better performance RIGHT? Even doing a rinse didn't seem to change up things. I have plenty of flow, plenty of pressure and no piping restrictions what the heck!!!

Thanks again,

Shawn

[RFM]

Cider Hill,

I had problems like yours with a small waterguy ro.

I found that batch processing worked better me.

I process the first batch (275 gallon for me) to where the permeate almost stops, probably about .5 gpm. ( approx 40 gallon @ 12% ) using 200 psi. (for Gould 7GB).

Then I run the next batch through which rinses the membrane (Permeate flow will increase (to about 1gpm), then decrease to .5 again.

Repeat process.

Has worked very well for me.

I agree with JR, Low pressure is better for simple RO, my 7GB will thermal out if I go below 200. I also use a 10GB with 3 membranes (XLE's) that I run at 160 psi.

Good Luck!

[regor0]

When you guys rinse and wash do you use the high pressure pump or just the feed pump or both?
Just wondering I've never seen one run before.

[JRCunningham]

I rinse out exactly as I process--both pumps, I pump permeate through and of that all of the concentrate goes back into the concentrate tank and measure the sugar in the concentrate line, stopping the rinse when the sugar is 0%.

As for having better performance at 250PSI than you do at 120PSI, not necessarily. What's key is the concentrate flow rate. Having less pressure and more concentrate flow rate can actually increase your performance, as you're moving more liquid across the surface of the membrane and you're continually "washing" the membrane with the concentrate. I've found that my RO units have a "balance" point at around 170PSI with a concentrate flow rate of about 6GPM is great to start. As my permeate rate slows down, I'll increase concentrate flow rate (which decreases pressure), and this will rinse the membrane pretty effectively.

I often find myself mentally viewing RO as a "filter", which it really isn't. Pressure from the pumps is simply being used to overcome osmotic pressure of water, causing it to pass through the membrane. Too much pressure and you start forcing sugar into the membrane. One way (of many) to destroy a membrane is to force the sugars from sap into it at high pressure without maintaining an effective "wash rate" of concentrate flow over the membrane. If you lower the concentrate flow rate too much, your permeate rate will be very high and fall off rapidly--this can indicate a clogged membrane.

RFM's batch method is an excellent way of keeping membranes healthy. I do something similar, I capture the permeate in a 100 gallon tank, and after each batch I run the permeate through the system, washing the sugar out of the pre-filters (which I have two, a 20" bag filter and a 20" cartridge filter).

I hope this is helpful. I feel for you--now's not the time a guy wants to be messing with this stuff. Hang in there.

[Brent]

You say you have a filter but don't say what the rating is. A course filter will allow a lot of crud to get through
onto the memebranes. I think the standard is a 5 micron pre-filter. Also if you are letting the sap sit around a while
before starting to run it through the RO the crud (microbes) will multiply and the problem will get worse fast.

Any chance you've got the membranes flipped end for end ????

[Cider Hill Maple Farm]

You say you have a filter but don't say what the rating is. A course filter will allow a lot of crud to get through
onto the memebranes. I think the standard is a 5 micron pre-filter. Also if you are letting the sap sit around a while
before starting to run it through the RO the crud (microbes) will multiply and the problem will get worse fast.

Any chance you've got the membranes flipped end for end ????

Brent,

I have two 5 micron filters in series before the pressure pump. After running for four hours this past weekend, I need to change out the filters because I had a bid differential pressure difference. As far as the membrane being flipped, not sure, that was something I meant to check before I ran again, THANKS FOR REMINDING ME. The u-cup was already on the membrane when I opened it up, being in a hurry I nevev checked see if there was a flow arrow or not(I'm BAD).

Thanks,
Shawn.

[Brent]

mine did not have a flow arrow
the removable stems on each end are interchangeable if I recall correctly so
the U cups are you clue which way is which.

[markct]

I had no idea membranes were directional. Why do they have a groove for the u cup seal on both ends then?

[wiam]

I had no idea membranes were directional. Why do they have a groove for the u cup seal on both ends then?
They are not directional. You can run them either way.

[JoshStamp]

I suspect you're getting full rated capacity on your xle's. I have two and tend to get around 1.4-1.6 gpm. They're rated to make 2400-2600 (depending on what you read) per day at 70 degrees. You have to adjust for temp- the charts (google will find then) only go down to 50 degrees, but I bet your sap is a lot closer to 32. If you divide the 2400 gpd out you realize you should be getting 100 gallons an hour or about 1.6 gpm of permeate. Then start looking at temperature. At 50 degrees you divide that by 1.7. So, 50 degree sap would yield .9 gpm. The charts don't go lower, but I'd say .7 at 32-40 degrees seems right in line.
I'm planning to add 2 more membranes to my system this winter because I want more permeate flow. Sounds like you're getting exactly what Dow says you should, so maybe another membrane is in your future too?