3/8" or 1/4" input for RO system

What are the pro's and con's for using 3/8" tubing for the input side before the RO membrane? I don't see too many people using 3/8" and I'm just wondering why

 

The only reason you would need to increase from 1/4" to 3/8" would be if you had a long distance between the tap water feed and the RO unit and had questionable or borderline pressure to begin with. If you have say 60-80 psi and raw water line is less than 25-35 feet long you will not notice any difference on a 75 GPD RO or RO/DI system. If the feed line is longer than that, your pressure is 50 psi of less or you have a dual membrane system you might want to consider 3/8" line to reduce the friction losses due to velocity in the line.
A 75 GPD RO membrane at 50-60 psi and 4:1 waste ratio uses about 1 quart of water a minute betwen the waste and treated which is no problem for the 1/4" line at normal distances.

 

Ok, thanks again good sir! I'm not running a feed line that long. As a side question, my feed pressure is 90-92 psi....is it ok for the membrane to be at that pressure or should I reduce it?

 

RO membranes are rated for 150 psi working pressure or higher, its the housings and fittings that could be a weak link. If you have a name brand system with good components 90 psi is not an issue at all. On the other hand if it is an ebay quality system I would be hesitant to go above 50-60 psi as many components, fittings and housings are cloned copies, often of questionable quality. Many visibly look the same but look for approval stamps like Uniform Plumbing Code (UPC), ANSI/NSF (American Nationals Standards Institute/ National Sanitation Foundation etc. This means the manufacturer has spent several years and invested untold thousands of dollars to submit his products for testing by recognized organizations to ensure they meet minimum standards. The imports don't do this for a reason and the quality is often inferior.

I run my personal system at 95-100 psi and have had it there for over 5 years with no problems but I trust my vendor and know the quality of their systems.

 

Last year I bought a 5 stage RO system from APEC. It works great and I have had zero issues with it so far. My only gripe is the 5 micron pre-filters that comes with it!

AZ, instead of changing the 3rd canister to DI can I change it to a polishing filter so I can get rid of the inline one that came with the system....getting rid of a stage all together sounds good to my wallet!!! Again, I don't see too many people doing it?

BTW, I cant really seem to find a forum specifically for RO drinking water. I have found, so far, the aquarium folks seem to be the guru's of this technology, correct me if I'm wrong.

 

I am not familiar with APEC so have no idea what your "stages" consist of or where they are placed.
A normal drinking water system in my opinion would consist of a sediment filter, carbon block filter, RO membrane and a final inline taste and odor GAC polishing filter so 4 "stages". You may find some vendors still use two less efficient GAC carbon filters or two high micron, low capacity carbon blocks in front of the membrane so would then be 5 "stages". There are so many possibilities.
If you plan to use this system for both drinking water and for reef water I would make sure to have a DI filter for the reef portion separated from the drinking water tank RO only circuit by a tee and check valve so it does not suffer the effects of TDS creep present in pressure or bladder tanks which eats DI resin quickly.

In this instance I would go with a 1.0 or 0.5 micron sediment filter, a single 0.5 or 0.6 micron carbon block, the RO membrane then to the drinking water pressure tank, taste and odor GAC filter and faucet. In the line between the membrane and the pressure tank you would install a tee and check valve as seen in this diagram so the DI is fed directly from the RO membrane and not the pressure tank which is for drinking water only.
http://spectrapure.com/huds/4-STAGE-DWK-RODI-NAG.pdf

This lets one RO/DI system serve dual purpose and gets you the most bang for your buck. It was very easy to justify a RO system to my wife when I showed her the cost savings compared to bottled water.

I think most if not all RO drinking water forums are vendor sites and mostly sales promotions touting their products and not RO in general.

 

For what its worth here is an excerpt from their website:

"We are proud to offer premium quality WQA Std 58 Gold Seal certified systems at affordable prices directly to consumers. Only the best systems in the marketplace will become certified to WQA Gold Seal standards.
[FONT=verdana, arial, helvetica, sans-serif]To receive WQA Gold Seal certification, a RO system must be constructed to meet strict public health standards and pass weeks of rigorous testing for material and parts safety, structural integrity, and contaminant rejection performance. In addition, the manufacturing processes, operational procedures and facility maintenance of the manufacturer are also audited annually to ensure total compliance and accountability. Therefore a WQA Gold Seal certified water system is a strong assurance of product quality, durability, and safety for the consumer."[/FONT]

The 5 stages are sediment/carbon/carbon/RO/inline polish filter. The setup I would like to have (in which I already installed most of it) is 0.2 sediment/0.5 carbon/RO/then instead of a 2nd carbon block installed a GAC 10" filter as a polishing filter in the 3rd canister, of course re-plumb the 3rd canister.

 

The WQA is a trade organization with ties to manufacturers and vendors but closely follows the ANSI, NSF and UPC codes, standards and guidelines. The other three are non biased organizations with no ties to manufacturers or vendors and set the standards along with the AWWA and WEF for water and wastewater related practices and materials.

Do you intend to use this for reef water? If so you would be better served converting the last canister to a DI filter and keep the small inline taste and odor filter. The chlorine and contaminants have already been removed by the carbon block and membrane so the taste and odor filter doesn't need to be large or elaborate and still last as long as the others since it has very little to do.

 

Wow that is great to know! On the next go around I'll most likely go with SpectraPure.

This is for drinking water only. Although, I've been lurking here lately and an aquarium would be pretty cool ;D