01-08-2010, 02:51 PM
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Ok, I apologize for the delay in this, but I have it now...
I am going to copy/paste my husband's response below. I hope it helps. "Most RO units are pretty similar as the RO membrane has a somewhat universal standard that is followed when manufactured. There are two types of membranes available CTA (Cellulose Triacetate) and TFC (thin film composit). CTA isn’t as available as it used to be. Because it is susceptible to bacterial breakdown, CTA membranes must be used with water that has chlorine or chloramine in it. TFC is synthetic and is not broken down by Bacteria. The only time Bacteria will damage a TFC membrane is if it sits unused and moist inside the RO system for months and anaerobic bacteria grow in it and clog it up. TFC membranes can be used on any water source. If Chlorine is present in the water then carbon must be used before the membrane to remove it as Chlorine will destroy a TFC membrane. There are both standard 3 stage RO systems that have a prefilter, a carbon cartridge, and an RO membrane as the last stage. This unit is fine for most cases as it will block (or reject) anywhere from 95% to 100% of any dissolved solids that tries to go thru it (100% rejection is very rare however). It is considered acceptable for up to 5% of dissolved solids to pass thru it. The 4 stage RO/DI system is designed to remove 99.9% to 100% of all dissolved solids that remain in the water after the RO membrane. This allows you to get almost pure water that you can manipulate however you want to by using chemical additives/salt additives. Although they all perform similarly, there is a difference in hardware quality such as compression fittings and canister housings. I prefer JACO or John Guest fittings as they are “beefier” than other brands of fittings. The Kent Marine RO and RO/DI (Maxxima) systems use JACO fittings and the lower cartridge canisters are double the thickness of most of the brands out on the market. They can handle much more pressure than most other RO systems. As a result, they cost a bit more but are worth the money. When deciding to use an RO or RO/DI system, you will want to check to see what your home’s water pressure is at. RO systems are designed to run on 40 PSI or higher. 75 PSI is the maximum for most brands of units. The Kent unit can handle around 100 PSI but the membrane cannot (really high water pressure will damage the RO membrane), so 75 to 80 PSI is the recommended max. If someone has well water with pressure less than 40 PSI then they will want to invest in a RO system booster pump which will drive the pressure up to 65 to 75 PSI (depending on brand). If you try and run an RO with low water pressure without a booster pump then your rejection rate gets really poor. The membrane will not swell up properly and it may only block 60% of the dissolved solids. How the membrane works is that when water enters the membrane housing it tries to go thru the waste line but hits what is called a flow restrictor. The restrictor has a small hole in it so only so much water can go thru it at any given time. This creates back pressure on the membrane forcing water thru the ends of the membrane. The membrane swells up (the higher the pressure the more it swells) and water is forced thru most of the pores in the membrane giving you better dissolved solid removal. Once misnomer is that RO and DI water should have a neutral pH, but this is not always the case. RO membranes are not able to remove dissolved gases and neither are DI resins (for the most part). The carbon is what removes most of the dissolved gases. CO2 can get thru the system and will cause the water to have an acidic reading when testing for pH. This water has no buffering ability so you can easily aerate the water to vent out any residual gasses and adjust the pH to what ever you want it. It is a good idea to invest in a TDS (total dissolved solids) meter to be able to tell if your RO system is performing up to specs. Almost all test kits such as ammonia, nitrite, nitrate, phosphate, etc will give false readings (usually on the positive side) when testing RO or DI water. TDS is the only true test for it. If the TDS comes up as zero then the water is pure even though a test kit says there is phosphate (or what ever other compound you try to test for) present. TDS meters are available anywhere for about $39 on up and are generally digital. An RO system can be used for drinking water or icemakers as well, but DI water should not be used for drinking. If in the event that an RO membrane blocks 100% (or close to it) of dissolved solids then you will not want to drink it as it will strip your body of electrolytes (it also tastes funny)." If you have more questions, please feel free to ask.