running RO system unattended to concentrate 4:1

[SapTsunami]

I have a 50 gallon barrel of sap I'd like to concentrate by 4:1 while I'm at work tomorrow. I'll be gone about 10 hours.

I built the Roseum system with 5x 400 GPD membranes: https://www.roseummaple.com/2020/01/diy-2-stage-portable-hobby-ro.html

I do not have a bypass line. So I can recirculate and make two passes at 2:1, or I can set the permeate to 4:1 and do it in a single pass.

Which do you think is a better idea?

Also I have no idea how long this will take (my sap is just barely above freezing) but it should be done before I get home.

Is there any harm to the system leaving it running beyond the point at which it can pass any permeate? Will it permanently foul or damage the membranes?

Or do I just need to flush it with permeate before my next batch?

[82cabby]

It’s not going to take long to get through 50 gallons of sap. I run the exact same set up except with the bypass/recirc line plumbed in and it does 25 gallons of very cold sap per hour condensing from 1.4% to 5% at 110psi with the recirc dialed in.

[SapTsunami]

so set it for 50/50 to get a 2:1 concentration and allow it to recirculate?

will it be OK if it only takes a couple hours to process the sap then the pump keeps trying to work for the rest of the day until I get home to turn it off?

[82cabby]

If it were me and I had to leave it for the day, I would run the sap from the source barrel, through the RO and output to a second receiver barrel. Do a single pass. It probably won’t hurt the pump to run dry for that long afterwards but if there is any way someone can swing by and shut it off for you mid day that would be better.

Everyone else feel free to correct me!

[red/one]

Hook up a pressure switch to shut the pump off when the sap runs out.

[DRoseum]

Even better - use the GRL8-02 level controller. Put the wire probes at the level ypu want it to go down to (1/4 of total barrel height for example). I use these controllers to start ROs, stop them, sense when my head tank is too low and evaporator should shut off...they are great.

[82cabby]

Even better - use the GRL08-2 level controller. Put the wire probes at the level ypu want it to go down to (1/4 of total barrel height for example). I use these controllers to start ROs, stop them, sense when my head tank is too low and evaporator should shut off...they are great.

I actually have one of those kicking around and have yet to wire it up to something…. An RO shut off sounds like a good idea!