Loss of back pressure

[ADK_XJ]

Hi,

I've just recently assembled a small RO setup for my backyard maple syrup production this year. To my utter surprise, once I assembled everything it did actually work to produce a thin but stable stream of concentrate out of a 3 x 150GPD membrane setup in series...I plan to add a permeate pump and possibly a pressure relief valve to better regulate pressure but it did work for about half a day of sugaring.

The issue became that I realized I was slowly but steadily losing back pressure after achieving the initial balance of about 90-100 PSI via manipulation of a check-valve on the concentrate output line. I have a couple questions for the members on this:

- some of my sap was fairly cloudy at this point, is it possible I was just trapping too much additional "stuff" along with the sugar on the concentrate side?

- my membrane housing kits came with a check-valve style elbow fitting for the permeate output port...could these possibly be impacting the efficiency / pressure of the system? Or, maybe a better question, do I need them on the permeate output at all? Should they go on the concentrate side instead perhaps?

- lastly, I am using an open-top, refillable canister style filter at the front end of the line (in front of the pump) and just jammed some filter paper in there...is there anything people find works especially well in these?

Thanks in advance...I am very, very slowly learning how all this works.

[DrTimPerkins]

You should always do a good job of filtering before the sap hits the membrane, especially with cloudy sap. "Jamming in" filter paper will not do it. Most likely what you are seeing is organic material (microbes) building up on the membrane surface and reducing flow. You will need to soap wash (RO soap, sodium hydroxide) and then rinse well with permeate to restore the flow rate. Larger machines incorporate recirculation to reduce the influence of (slow down) membrane fouling.

[ADK_XJ]

You should always do a good job of filtering before the sap hits the membrane, especially with cloudy sap. "Jamming in" filter paper will not do it. Most likely what you are seeing is organic material (microbes) building up on the membrane surface and reducing flow. You will need to soap wash (RO soap, sodium hydroxide) and then rinse well with permeate to restore the flow rate. Larger machines incorporate recirculation to reduce the influence of (slow down) membrane fouling.

Thanks, that's helpful and makes sense. Based on the color of the concentrate coming out after I had "recharged" the system from a gradual pressure loss I assumed it was in fact the heavy microbial content sap I'd been running.

Would it be fair to say I should invest in a dedicated filter housing like for a home water setup in addition to the refillable one?

[Russell Lampron]

Would it be fair to say I should invest in a dedicated filter housing like for a home water setup in addition to the refillable one?

You should get a canister type filter and use 5 micron cartridges in it. You won't need the one that you are stuffing some paper in.

[ADK_XJ]

You should get a canister type filter and use 5 micron cartridges in it. You won't need the one that you are stuffing some paper in.

Got it and, at the risk of seeming daft, if it's one that slides into a standard 10x2.5 housing that I have do I run the "permeate" line from that one into the next series of membranes and expel the remainder?

[Russell Lampron]

Got it and, at the risk of seeming daft, if it's one that slides into a standard 10x2.5 housing that I have do I run the "permeate" line from that one into the next series of membranes and expel the remainder?

You plumb that in before your membranes to filter out the fine stuff that will plug your membranes. If you're using a feed pump, plumb it in after that and before the high pressure pump. If you're not using a feed pump plumb it in before the high pressure pump. Permeate doesn't need to be filtered and should be run directly into your permeate collection tank to be saved for cleaning.

[ADK_XJ]

You plumb that in before your membranes to filter out the fine stuff that will plug your membranes. If you're using a feed pump, plumb it in after that and before the high pressure pump. If you're not using a feed pump plumb it in before the high pressure pump. Permeate doesn't need to be filtered and should be run directly into your permeate collection tank to be saved for cleaning.

Thanks, after replying earlier I realized it is a different / dedicated canister and not the same as my current membrane housing.