RO housing full of sap?

[MarquisVII]

When I pulled my membrane out of my single 4040 to put it in storage, the housing was completely full of spoiled sap. I rinse/was/rinse after each use. End of season I had flushed, washed twice, flushed again with another 200 gallons permeate. 0 TDS permeate coming out concentrate and permeate lines. What's going on that the housing is totally full of milky sap but the membrane itself is flushed completely clean? I rinsed the exterior of the slimy sap and stored it in SMBS but I'm wondering if I have an issue. I don't remember this happening in the past.

[BAP]

When I pulled my membrane out of my single 4040 to put it in storage, the housing was completely full of spoiled sap. I rinse/was/rinse after each use. End of season I had flushed, washed twice, flushed again with another 200 gallons permeate. 0 TDS permeate coming out concentrate and permeate lines. What's going on that the housing is totally full of milky sap but the membrane itself is flushed completely clean? I rinsed the exterior of the slimy sap and stored it in SMBS but I'm wondering if I have an issue. I don't remember this happening in the past.
How much water are you using to rinse it with? It takes a lot of water to rinse thoroughly.

[Bricklayer]

You may of had a leak at some point with your membrane u-cup seal that ended up sealing once pressurized or had it in backwards. But I think you would notice a backwards seal. If font was a real slow leak then it would have taken a lot of permeate to rinse it out.

[MarquisVII]

Hmmm. I did insert the membrane "backwards" at the start of the season, meaning the inlet side was pushed all the way through the housing. I tested that method and found there's not enough play in that o-ring for it to curl or not seat properly, so I lubed it with silicon lube and went for it. Wonder if that could've been the issue and it was corrected with pressure, as you suggest.

Worked flawlessly all season. Permeate always reads 0 TDS and I rinse it long past the concentrate line reading 0 TDS. Plus washing after each used and then rinsing again... Not that it should matter but this is a MES membrane.

[Bricklayer]

TDS isn’t really a good way to check your permeate when running sap. I think Dr Tim explains that in a post on here somewhere. Havnt came across it in a while but it’s here somewhere.
I would get to the bottom of this before you have to deal with it next year in a rush and end up with the same problem again.
Your feed side of your membrane housing where the sap comes into the housing from the prefilter is the outside fitting. Not the middle one. That is permeate. This is where your membrane u-cup seal should be.

[maple flats]

Did you build the RO or is it a manufactured commercially sold RO?. If you built it, check with the membrane MFGR, if bought, contact the RO MFGR. They should be able to solve the issue.
On my deer run RO, there is a U shaped seal and the open part of the U needs to face the inside or pressure side, (face the open U towards the opposite end) that way, as soon as there is pressure in it, the pressure forces the sides of the U shape to form a positive seal.

[Bricklayer]

Exactly what I just explained

[Waynehere]

Funny, I just pulled my Deere Run 250 apart and have been having this same problem for a few years. Doesn't seem to degrade the sap or hinder the performance of the membranes. I know they say you only need a seal at the pressure end of the housing. The way I understand how the flow works is it enters the end of the membrane around the center. Then when you restrict the flow going through the membrane the water is squeezed into the center and is your permeate. The concentrate then goes through the 2nd membrane and repeats.

What I don't understand is with no seal on the opposite end, what stops the sap from going down the outside of the membrane inside the housing? That seems to be where this sap gets stuck all season as it can't circulate. Then you end up with spoiled sap. Or is the end cap supposed to seal against the end of the membrane? My guess is it doesn't and thus why you need the seal. What would happen if you put a seal at both ends? Wouldn't that keep the sap from going between the membrane and housing?

Would love to solve this as well