Couple RO questions. (Flow Restrictors) , 1 or 5 micron replacements?

I just picked up a used 4 stage RO/DI unit that is in great condition.

However over the last month that I've used it i've noticed the TDS to go from around 4ppm to about 20ppm using the inline TDS meter that came with my unit. It seems to operate at about 50 psi when I dont have the backwash line open and am producing product water.

My RO/DI unit has (what I think) first a sediment cartirdge, then a carbon block, then a refillable DI resin container. And on top is the RO cartridge? I think. Its the one with the o-rings on the tip.

How do I determine the flow rating/gpd of my unit? What are the purpose of flow restrictors? (although I dont have one, was just wondering).

Also, im trying to order replacement sediment and carbon cartridges, how do I determine if mine are 1 or 5 micron spec? What do I need? 5 Micron/Sediment then 1 Micron/Carbon?

I plan to buy one of those refill kits from BRS if anyone cares to know.

Thanks for the help.

 

If you have 50 psi and your water is anywhere close to 77 degrees F you should be seeing about 6 ounces of treated water per minute. Colder water or lower pressure will produce less.

You do have a flow restrictor or else the RO membrane would not function. If you have a flush kit the valve you open is bypassing that flow restrictor. The restrictor should have a number on it like 550mL or 850 mL or something like that and it will be matched to the RO membrane output. A 550 goes with a 50 GPD system and a 850 goes with a 75 GPD system.
You won't see a micron rating on most filters, they will look pretty much the same. When replacing go with no larger than a 1 micron prefilter and a 1 micron or better yet 0.6 or 0.5 micron carbon block. They are there to protect the RO membrane and have little to no effect on TDS, they remove large particles like sediment, particulates and chlorine not dissolved solids which are in the 0.0001 micron range and the job of the membrane and the DI resin.

 

Thanks for the great answers AZDesertRat you cleared up a bunch for me.

Tell me, do you have any insight why BRS only sells 1 and 5 micron cartridges? I was hoping to go with your suggestion and replace with a 1 mic/sediment, followed by a .5 mic/Carbon.

 

I don't know.
SpectraPure Water Purification Products and www.buckeyefieldsupply.com both sell them though and Spectrapure sells a 0.5 and 0.2 micron absolute rated rather than nominal rated prefilter which is what I use to protect my carbon blocks and membranes. More expensive but worth it.

 

dont you think a 1 micron would stop up pretty quick? Wouldnt you want some larger prefilters in front of a 1 micron filter to extend the life of the smaller rated filters?

 

I use a 0.2 micron and get 18 months out of one filter with only a 2 psi drop.
Unless you have sediment, particulate or colloidal material problems in your tap water a 1 micron works fine. Places like Spectrapure and Buckeye have been selling them for years and years and they are two of the most trusted names in the business. If they didin't work they wouldn't be using and recommending them on their best reef quality systems.