RO expansion advice

[MillbrookMaple]

Probably should put this in the RO section but I really want the tinkerers to look at this post.
I have an old EcoChem RO that a few years back had the head seal go on the membrane vessel and leaked profusely when it ran and finally killed the pump motor on the top of the vessel. Tried having a local machine shop replace the motor and fix the seal with no luck. (it leaked worse and I stopped using it before I ruined another motor) Since the unit was older, and finding replacement parts was impossible, I decided to scrap fixing the vessel and sits unloved on the frame. Being low on cash, We purchased a couple of codeline vessels and filmtec membranes from EasternRO. I put them in series and we are currently getting 8-9GPM Permeate with 4GPM of Concentrate first run with the PSI between 250-300 depending on Temp and sugar % of sap and how long it has been since I ran a wash. This is higher capcity than the old vessel could ever do. My High Pressure pump is a 7.5 HP. Recirulation is achieved by a needle valve that plumbs output back into input side of Vessels. I do multiple passes and try to get my sap between 12 and 15% before sending it to my saphouse head tank. I want to maximize the potential of my HP pump and increase my processing speed while still being cost conscience.

I have 2 Questions.

#1 Should I get a maple industry post to put after my current pair or Should I just double what I Already have?
I'm not sure even what new maple industry posts are going for now but for about $2500 I can get 2 more vessels and membranes from EasternRO. I am guessing doubling what I have should increase my permeate flow to around 13-14GPM total first pass.

#2 Those of you that think I should buy 2 more Non-industry membranes and vessels, should I run them in series or parallel with my current ones?
Series would be higher flow rate thru all membranes. Parallel would be less extreme conditions on the last 2 in the line which would have them all clog more evenly.

Just an FYI I've been thinking about how to do the plumbing. My plan is if I do them all in series I would make it so I could reverse the flow each time I run a load so the first becomes the last in series each time flowing in the opposite direction. If I do parallel I will put shut offs before and after each leg so I can isolate them to rinse and clean each pair with maximum flow thru them.

[bowhunter]

Not quiet enough information to give you any advice but a couple of points:
1. The filmtec membranes are fine in sap service.
2. When you change either the pump capacity or membrane capacities or configuration you can end up with all kinds of problems like low flow fouling the membrane or very high recovery. The pump needs to match the flows required for the particular membrane and configuration you're using. You can also do mechanical damage to the membrane if you significantly exceed the maximum flows through the membranes with a larger pump. Deciding to go series or parallel is a really big change as far as flow rate or velocity through each membrane.
3. Almost any combination will work and remove some water but, the membranes may not last very long or may foul quickly.

[MillbrookMaple]

Bowhunter thank you for responding! I'm guessing since it was originally built with only one membrane the flow rate is within spec for normal maple membranes. I was told that it could support 3 posts though. By putting 2 in series like I did the thru flow rate should be close to the same and again if I put all 4 in series flow rate would be the same for the first few membranes then decreasing as you head towards the last one decreasing by the permeate output of each vessel prior to it. I'm not sure how to calculate flow rate since I have no internal flow gauges, only ones that measure the flow of sap and permeate out of the system and with sap recirculating total concentrate and permeate out per minute do not equal flow thru the membrane. I am guessing I'm safe on not having too much flow thru the membranes but may run into a problem with not enough depending on my configuration. Also since the original post had a recirc pump on it as well I am running lower flow volume than was occurring previously. I am not sure who to talk to that could tell me what the actual flow rates would be in either scenario or even currently. Since I'm dealing with non-industry parts I was hoping that someone here may have some advise on my situation because most times industry people tell you to use industry parts.