RODI problem

[unkel j]

I bought a new spectrapure rodi maxcap. The tds from my tap fluctuates from 130 to 160. At first the tds coming out of the membrane was 0. Now that my container is full, the tds coming out of the membrane seems to always be 20 less than tap (right now its 157 from tap and 137 after membrane) and coming out of the first di is now 1 instead of 0. So it seems like the whole system is exhausted after making only 1 batch. I feel like I paid $300 for 30 gallons of water.

Spectrapure is closed and I've been busy all week. That's why I'm posting here.

Any opinions?

[jefnalyssa]

Do you have a flush valve for the ro membrane? It might be open? What is your water pressure?

[whosurcaddie]

Might be water pressure. It could also be that the membrane isn't seated correctly. I'm just grasping at straws here. You didn't run hot water through it did you.

Some ro units have pressure gauges on them it should read in the 45 75 psi range or higher.

[dkeller_nc]

You have one of three problems (or perhaps all of them): The most likely is that a pressure fluctuation has displaced the seals between your RO membrane and the interior of the housing, the second one is that your carbon pre-filtration is exhausted and the chlorine/chloramine in your tap water has destroyed your RO membrane. The third possibility is that you simply received a defective RO membrane.

The second issue is very unlikely - it generally takes more time for chlorine/chloramine to destroy an RO membrane.

Here's what I would do: go to the home store and buy some silicone grease. Make sure that it's 100% silicone and isn't mixed with lithium - the home stores sell this in little containers in the plumbing section. Dissassembly your RO cartridge (one end will screw off). Carefully extract the RO membrane, noting whether the o-rings are in-place and not torn or deformed. Put a very small amount of silicone grease on your fingers and run them around the o-rings on your membrane. There should be no visible grease on the rings, just a darker appearance to the rubber. Carefully clean the inside of your RO housing to ensure there's no debris or scaling that will cause the o-rings to catch or become displaced when you insert the cartridge.

Re-assemble the unit and measure the TDS coming out of the product side of your RO membrane. It should 10% or less of the incoming tap water after running for about 10 minutes. If not, use a measuring device and a stopwatch to calculate the volumetric ratio of the product water to the waste water. It should be about 4:1 to as little as 8:1 waste to product. If it's less than 4:1, then either one of the o-ring seals is torn, or the membrane is defective.

[unkel j]

Thanks for the replies everyone.
No its not hooked up to hot water.
The flush valve is closed.
The psi is 55.

dkeller, I will check that out and get back soon.

[unkel j]

Okay, I'm back. Everything appeared clean and in order in the membrane housing. I greased the o rings with silicone grease (already had some). When I run the end product line into a bucket, the product side of the membrane will drop slowly to 0 and stay there while the water is running. Once the unit is stopped, the tds slowly starts to creep up again. It is already at 5. This means crappy water goes into the di when the unit first starts to make water so they are both about done for I'm sure.
I sure hope Spectrapure will send all new filters or return the unit because this sucks.
FYI This is a 2:1 membrane and I have two duel tds meters.

[dkeller_nc]

Actually, it's normal for the water on the product side to come up a bit when the unit isn't running, though when you turn the unit on, the total amount of high tds water going into your DI should be quite small (perhaps 100 mL or so).

It's also normal for perhaps 1 canister volume of water coming from the DI when the water is first started up to be considerably higher in TDS than the water coming from the unit at a running steady-state. That's why I usually dump the first 1/2 gallon or so, then start collecting it. Industrial systems actually have a pumped loop that maintains high quality water at all times. One could conceivably do this on a hobbyist scale, though there would be no point unless one had the RODI unit directly plumbed to an ATO.

[unkel j]

You are right, there was very little water in the bucket when the reading dropped to zero. The reading after the first di has dropped back to zero now. When it jumped to 1ppm I panicked. At one point the tds after the second di was 3ppm but is now 0. Maybe I am just over reacting and shouldn't read into the meters so much. I did cut in a tee and valve just before the float to drain a little first like you said.
Everything set aside, The end result is 0 tds. I just want the DIs to last.

Thank you dkeller!

[Buckeye Hydro]

So it sounds like your RO water is now 0 ppm, rather than 137, right? What caused the difference - did you measure it differently?

The increase in TDS on the product water side of the membrane that occurs when the feedwater pressure is off is called "TDS Creep." This is normal, typical for RO technology. Here's some data from a couple of bench tests with a 75 gpd membrane. When you measured 137 ppm permeate, were you measuring immediately upon start up?



Russ

[Buckeye Hydro]

Originally Posted by unkel j

FYI This is a 2:1 membrane...

There is really no such thing as a "2:1 membrane."

Given your pressure and your temperature, the ratio of concentrate to permeate (waste water to RO water) is controlled by a little $4 part called a flow restrictor. Change out your flow restrictor and you can change that ratio to whatever you'd like. Be careful however in that if you go below 4:1, you may shorten the life of your RO membrane.

Russ

[unkel j]

There are two flow restrictors that come with the unit. One says 2:1 and the other says 3:1. The directions say to test the hardness of my tap water and if it is less than 180ppm to use the 2:1 restrictor and if it is 180 or more to use the 3:1 restrictor. So I guess I worded it wrong when I said "2:1 membrane".

The tds meters are in line in the system so I can watch the number drop when I use it and creep up when I stop. After it sits for a day it reaches a high number and then when I open the float valve it drops just like your chart.

I guess I just didn't know that tds could creep through the membrane.

[mpjones]

Check out the link I posted below. It talks about reduction in your DI consumption along with TDS Creep (I copied link from my iPhone).

http://m.youtube.com/watch?trk_conta...Dbrstv_110813o

[unkel j]

that doesn't seem to work

[Buckeye Hydro]

Originally Posted by unkel j

There are two flow restrictors that come with the unit. One says 2:1 and the other says 3:1. The directions say to test the hardness of my tap water and if it is less than 180ppm to use the 2:1 restrictor and if it is 180 or more to use the 3:1 restrictor. So I guess I worded it wrong when I said "2:1 membrane".

That sounds right - the harder the water, the more likely it is to deposit scale in the membrane, and the more flushing of the membrane is needed.

Does the unit have a automatic flush valve on it?

Russ

[unkel j]

My hardness was <50ppm however, I just changed the restrictor out to the 3:1.
It has a manual flush kit.
I shut off the main supply valve and relieved the pressure to the unit hours ago and the post membrane tds has not moved at all (2ppm).

[dkeller_nc]

Originally Posted by unkel j

My hardness was <50ppm however, I just changed the restrictor out to the 3:1.
It has a manual flush kit.
I shut off the main supply valve and relieved the pressure to the unit hours ago and the post membrane tds has not moved at all (2ppm).

If your total hardness out of your tap is <50 ppm consistently, there's really no need to waste the extra water by putting in a 3:1 restrictor. Perhaps Russ could comment on this, but with a total hardness that low, you could probably use a 1:1 restrictor and produce less waste.

Watch out, though. Many places in the Western US change the source of their water from winter to summer, and the water in the summer is much, much harder.

[unkel j]

That's interesting. I don't think my area does that but I will find out for sure and test again in summer. I'm going to change back to the 2:1.
Thanks for all the help.