Help with RO/DI plumbing

so what is the purpose of the gauge then?

 

To let you know what kind of pressure is coming in the R/O unit. It is also a great indicator if your R/O tubing is clogged too. My unit needs a min of 60psi to work properly.


Luna

 

So i used a test kit and tested the water and it came back pretty nasty. Where can I get new filters for that unit and what kind of filters should I get?

 

Its not the TDS that tells you when to replace filters either.

Lets start from the beginning with some basics. The prefilter and carbon block are there to protect the RO membrane, not to remove TDS (total dissolved solids) but to remove TSS (total suspended solids, particulates and sediment, much larger than TDS) and chlorine. They have very little to absolutely no effect on TDS, its the RO membrane that is the workhorse and removes 90-98% of the TDS.
The prefilter and carbon block should be changed every 6 months like clockwork. This is a rule of thumb but usually worlks out well. You can also go by pressure drop and chlorine breakthru but these require monitoring with additional pressure gauges and a low range chorine test kit so 6 months is the easier way to go. At the same time you replace the filters always disinfect the system while you have it down to reduce the possibility of virus or bacteria growth in the housings and filters.

Now TDS does come into play when we are talking about the RO membranes condition and the DI resin condition. You need three TDS readings so a handheld TDS meter is the best choice here. Get your tap water TDS, RO only TDS before DI and finally the RO/DI or final product water TDS.

The RO membrane should be removing 90 to 98% of the TDS all by itself before DI depending on which membrane you have. The DI should be removing the final TDS for a reading of 0 TDS. If not its time to do some troubleshooting to see where the problem lies.

Define "pretty nasty". What did you test for and did you use a TDS meter, the only real way to test RO/DI water?

 

Good post by the Rat Man.

Also - assuming your pressure gauge is mounted in the correct location (which it should be if installed by the manufacturer of that particular system), check what the gauge reads when your 2 prefilters are new, and then keep an eye on the gauge over time. There is no hard and fast "rule" as to how much pressure drop is too much, but certainly don't let the pressure go below the spec on the membrane (50 to 65 psi depending on the brand of membrane), and remember that the higher the pressure (within reason), the better the membrane will work.

Russ

 

now, can you run these straight into a auto top off system for your tank or do you need some kind of holding tank past this?

 

It's not recommended. A stuck float valve or solenoid could turn your marine tank into a freshwater tank.

 

or in the case of our tanks at my office, the tubing they had running to it blew apart and sprayed all over the place. thankfully it was a brand new setup and some how didn't change the SG so we were good but yeah... def risky.

 

Its best to run it into a holding container of some sort which then feed the ATO system. I use a 23 gallon Rubbermaid rectangular recycling can myself which was a perfect fit for the space I had. I also use float switches and a solenid for more positive control versus a simple float valve. Float valves can stick, we all know this from the running toilets we have at home and they also give you a very limited range between on and off so lead to a problem called TDS creep. TDS creep occurs every time a RO membrane first starts up, you get a spike of high TDS water until it smooths out. Capture this in a ATO reservoir or feed it to your DI resin frequently and it can lead to high final TDS and premature resin exhaustion. By moving my start and stop float switches several inches apart I have to drop 11 gallons before my RO starts again so I get long, less frequent runs for best filtration and minimal effects from TDS creep.

 

+1 good idea if it's doable with your setup