help with RODI system.

[cst0215]

Hello all.

I am stumped with my BRS 4 stage 75gpd system.

I am getting very high tds readings after the water leaves the membrane.water

I have isolated the plumbing so that the unfiltered water goes into my sediment filter, than the carbon filter, then directly into the RO membrane and then to the drain line and final water collection bucket (bypassing the DI filter completely).

I have plumbed my dual sensor TDS meter so that it is reading the water directly as it enters the RO membrane housing and leaves the RO housing.

I was already getting high rejection rate, so I have installed a new membrane rated at 75 gallons per day and as far as I can tell, the membrane is fully seated in the housing with the stem even with the top of the housing threads.

Even with the new membrane I am getting readings of 358 incoming and 127 outgoing. This is a rejection rate of 64%

I have a flush valve installed on the waste line that has 550 marked on the side.

This is a used system that sat for approx 6 weeks before I recently started getting it installed. I was told that all of the filters were recently replaced before I got the system and the sediment filter is completely white.

Any help and advice would be greatly appreciated

 

[Asm481]

Are you giving it a good 10-15 minute run before judging the tds? Most times the meter is after the membrane and after di canister. Hope it works out for you.

 

[chrizo]

Isn't the tds meter supposed to be after the membrane and the last one after the DI stage?

 

[Hammy]

64% rejection is definitely way too low, especially with a new membrane. Since you already changed the membrane and checked that it’s seated correctly, I’d check the waste-to-product water ratio and the pressure going into the membrane next. Also make sure the flow restrictor actually matches the 75 GPD membrane. If pressure and waste ratio are good but you’re still seeing 127 TDS after the membrane, I’d start looking at the membrane housing or seals/O-rings for bypass

 

[UncommonSense]

Along with the good advice above, I’m curious about the RO membrane itself!

Is this a direct factory replacement Dow Filmtec 75GPD membrane?

 

[cst0215]

Yeah. It’s an Amazon membrane which I’m reading is suspect in itself. It is also slightly shorter than the original (I thought they were a universal size?).

My pressure is about 60 lbs, this is being read between the carbon chamber and ro housing.

I have let it run for over an hour with no improvement.

The reason I temp installed the 2nd tds sensor after the membrane instead of after the di. Is I wanted to isolate it to only the ro membrane. Right now the di resin housing is completely disconnected. Can anybody verify that the 550 flush valve is correct for a 75 gpd system?

 

[UncommonSense]

It is also slightly shorter than the original (I thought they were a universal size?).

This is suspect… there are different lengths of membrane for different form factors of filtration systems… (under-sink drinking water filters, for example)

The reason I temp installed the 2nd tds sensor after the membrane instead of after the di. Is I wanted to isolate it to only the ro membrane.

this is fine, it’s a great way to troubleshoot the system, in fact!

Can anybody verify that the 550 flush valve is correct for a 75 gpd system?

It’s in the right range!

I’m unsure if BRS changed flow restrictor sizes over the years, but my 150GPD dual membrane “water saver” RODI initially came with the same flow restrictor! (Your tap water TDS is around 2x mine, so 550 is well sized for your application)

 

[Tangdora]

I would pull out the membrane and check its condition. Being told the filters were replaced is one thing. Replacing the filters and the membrane is another as the membrane are replaced an a far less frequent basis. He may have had spare filters laying around and never touched the membrane

 

[EricR]

I agree with earlier comment to check the waste-to-product water ratio.
Just run for a bit collecting both waste output and product output in separate containers and compare volume measurements.

Those BRS combo flush/restrictor units seem to get some "flak" from users sometimes but I never had a problem with mine.
*I use 800 cc restrictor in summer and 550 cc in winter on 75 GPD unit so your current one seems reasonable if it's working correctly

I'm also curious how much shorter the RO membrane is.
Any chance "that" is allowing some water to pass around the membrane and not all through it?

 

[cst0215]

Here is a photo of the 2 to membranes. The top membrane is the new unit from Amazon the overall length is the same, but the rolled membrane is different.

 

[EricR]

I'd assume that as long as the seals on both sides actually seal, the rest of the differences aren't likely a problem.
*was worried that maybe you meant the overall length was different

 

[cst0215]

I'd assume that as long as the seals on both sides actually seal, the rest of the differences aren't likely a problem.
*was worried that maybe you meant the overall length was different

I reinstalled the original membrane and TDS as it leaves is still around 88. I’m at a loss here.

Water goes into the sediment, then into carbon, then into the membrane, then to drain and collection bucket. 300 plus going into the membrane and mid 80s coming out. Don’t understand why the rejection rate is so poor. I guess I will by another membrane ( bulk reef supply this time) and see if it improves.

 

[Tangdora]

One other small thing to throw out there. Make sure the tds probes are position correctly to eliminate false readings. The two prongs should be perpendicular with the line not parallel. Other than that. Would reseat the membrane and lower the psi down to 40 to start let it flush for 10 mins after.

 

[cst0215]

I reinstalled the original membrane and TDS as it leaves is still around 88. I’m at a loss here.

Water goes into the sediment, then into carbon, then into the membrane, then to drain and collection bucket. 300 plus going into the membrane and mid 80s coming out. Don’t understand why the rejection rate is so poor. I guess I will by another membrane ( bulk reef supply this time) and see if it improves.

Also just to check the tds sensor I filled a glass with distilled water and it reads zero. Also filled another glass with tap water and it reads high tds so I don’t believe the sensor is defective

 

[cst0215]

Also just to check the tds sensor I filled a glass with distilled water and it reads zero. Also filled another glass with tap water and it reads high tds so I don’t believe the sensor is defective

How do I lower the input pressure?