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christhjesus 
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 Topic: RO Pressure Gauges
Posted: April 08 2016 at 2:25pm |
I have been wanting to add some pressure gauges in strategic locations in my RODI system and I discovered something that is bothering me. Pressure gauges in RO systems come in direct contact with RO water. From what I have discovered is most pressure gauges have a copper tube inside that expands and contracts with the pressure differences giving the pressure reading.
Am I just reading into this too much or could our RO system gauges be leaching cooper into our RO water (if that gauge is after the RO membrane)
PS Most of the fittings on gauges are brass also which could leach some copper also.
Edited by christhjesus - April 08 2016 at 2:28pm
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Mark Peterson
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Posted: April 08 2016 at 3:45pm |
Yes, we certainly don't want copper in constant contact with RO or saltwater, but contact with tap water causes no problem. I just assumed, maybe incorrectly, that the inside of the copper is coated with a polymer. To be honest, I have seen many RO units with pressure gauges but have never understood, nor had the need to check pressure for my RO systems. I've owned probably half a dozen of them. Maybe I need to be educated.  Aloha, Mark 
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christhjesus
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Posted: April 08 2016 at 11:39pm |
I have looked further into gauge placement. As far as I can tell most systems have the gauge before the membrane or on the waste side of the membrane so there is no contact with product water. I was wanting to do this to see exactly how high/low the pressure is coming off of the product side of the membrane (I love to monitor stuff). I suppose there might be a reason no one monitors pressure on the product side of a membrane and I don't think it will be worth the difficulty finding a special gauge.
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Mark Peterson
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Posted: April 09 2016 at 8:08am |
Yes, it really helps to learn how it works. Basically, the pressure on the waste side of the membrane, which will be pretty much the same as city pressure is what pushes the pure water through the membrane. That's the principle of reverse osmosis. While the unit is running, the pressure of the pure product water is nil. When any pressure occurs on the pure water side it begins to push back against the pure water that is trying to come through the membrane. Understand?
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christhjesus
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Posted: April 09 2016 at 9:42am |
I do understand how a RO membrane works. If there is no pressure coming off of the membrane then a tank would never get filled. However, a permeate pump will allow the membrane to not "see" the pressure so there is no back pressure fighting against the membrane thus increasing the overall efficiency of the membrane. I thought about it a little longer and decided I could get a good round number of product water pressure if I were to check the tank pressure once they are full. I am also going to assume the product pressure is only going to be what the shut-off is set to (mine is adjustable) but I don't know what it is exactly. I suppose I could temp install a pressure gauge to dial in the shutoff switch and just remove it once I get pressure dialed in so there is no possibility of cooper leaching from the gauge. I like to have gauges so I can see filter performance at a glance and know when there might be a problem arising. I also have inline TDS meters.
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Mark Peterson
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Posted: April 09 2016 at 8:28pm |
I guess you know a lot more about RO membranes than I do. It's been my understanding that the purpose of a Permeate pump is to allow the membrane to work a little longer to push about 25% more water into the holding tank. The pressure in a holding tank is zero at first, but as the bladder fills the back pressure rises to something like 12 psi and that's where the auto shut-off valve automatically closes to stop the source water. The purpose of the auto shut-off is to stop the unit sending waste water down the drain 24/7 when no product is being produced. That's how I understand it.
Aloha, Mark
Edited by Mark Peterson - April 09 2016 at 8:44pm
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