RO Pressure Remains High During Initial Cleaning / Flushing Procedure

[fireant911]

I finished my first run of sap through my home built Reverse Osmosis machine. I was very pleased with the results - raw sap was at 2.6% sugar and the concentrate was at 5.6%! I adjusted the needle valve and ran the system at 92 psi. A total of 44 gallons of sap was processed on this first run that yielding 17 gallons of concentrated sap. Like many of the other systems, mine has a five-micron sediment filter and four 150 gpd filters. Upon finishing this run, I referred to the instructions from the 'Mattatuck Madness' website and replaced the five-micron filter element while flushing / recirculating the system with permeate with the needle valve wide open. With the needle valve wide open, the system pressure would never drop to less than approximately 56 psi with both the permeate and concentrate line were flowing??? Something is amiss (I think) but the ONLY change was replacing the five-micron filter.

I doubt that the RO filters would be clogged at this early stage as the filters were brand new and this was my initial run. Why would the system pressure remain this high? Additionally, I have seen NO decrease in pressure while flushing the system. Does anyone has any suggestions on what may be the issue? I do have RO Soap and Citric Acid on-hand but my novice mind tells me that is too early for any of that sort of cleaning to be required. Any help and / or guidance would be greatly appreciated!

[ecolbeck]

I don't think this is necessarily an issue. The pump may be able to create backpressure even with the needle valve fully open. My system creates about the same amount of pressure under the same conditions.

[sweet spot maple addict]

The internal diameter of the needle valve might be so small that even when fully open a restriction is applied
on the membrane generating that residual pressure.
If you feel like it , you could plumb a bypass, T out before the needle valve, T back in after the needle valve, and insert a gate or ball valve in this loop.
When concentrating you close the ball valve and use the needle one.
When washing/ rincing you close the needle valve and fully open or so , the ball valve.
On the long term your system will greatly benefit from it, since washing and rincing are best perform at a lowest pressure

[fireant911]

ecolbeck,
my worries dropped by 50% after reading your reply! Since I am really, really new to RO as this is my very first season and only my second season for syruping, I may be fretting over nothing. This was my first attempt at flushing and was not knowing what to expect - that is why I found the somewhat high system pressure troubling. Now, I am mostly at ease. Thanks!!!

Pierre,
Just as you stated so eloquently, it was my understanding as well that the lower pressures would aid in releasing the sugars and other trapped materials from the filters. After repeated attempts at flushing, I am not seeing any decrease in the pressures with the needle valve open fully. Your suggested bypass solution makes great sense and I will get this plumbed in and test this out!

I certainly appreciate all the help and guidance here!!!

[fireant911]

Well, I bypassed the needle valve completely yet the pressure remained unchanged. We have experienced some recent ice, more snow, and colder temperatures which has delayed any subsequent RO processing. Hopefully, all will be well when that time comes!

I ran an interesting experiment yesterday that really surprised me. I have read varying statements about sugar content in the frozen portion of the sap in the bags. Given that our bags are mostly frozen now, I took a sample of liquid sap and frozen sap from the same tree. I brought these samples inside and covered them. After allowing them to melt, as applicable, and stabilize to the room's temperature, I used my 0-10% refractometer to look to see if there was any difference in the sugar content. WOW!!! The sample derived from the frozen ice showed a sugar content of 1.1% while the liquid sap sample yielded a much higher sugar content of 5.9%. Earlier, I had pulled a sample from the tree and saw that this was at 2.6% sugar. Is something falling out of the solution at the point the sap freezes? Granted, this was only done on one sugar maple tree and on one sap bag but I was amazed at what I saw!

[DrTimPerkins]

I ran an interesting experiment yesterday that really surprised me.

Dozens of threads on MapleTrader.com about this already. https://tinyurl.com/yjy785h4

When a sugar solution freezes, the pure water component freezes, but the sugar does not. Poor Man's RO. If the sap is less than 50% frozen, dump the ice, keep the liquid. If more than 50%, keep both. You may lose a tiny amount of sugar, but you also eliminate a LOT of boiling.

Also used in some places to concentrate the alcohol in wine, cider or other spirits, although technically illegal for those uses.