What Flow Restrictor for New RO Membrane

[redfishbluefish]

I’m finally changing my membrane that’s somewhere in the area of 15 years old. I don’t have a pressure gauge on my old RO unit, but the TDS had creeped up from around 1-2 to 8 TDS out of the RO unit (before DI). The original membrane was a 50 gpd and I replaced that with a 75 gpd membrane. The restrictor that was there was labeled as a 550.

So I go to BRS and according to their chart I’ll need an 800 ml restrictor for a 75 gpd membrane.

I need this restrictor NOW, so I go to Amazon, and this is where it gets funky. According to their chart, a 75 gpd membrane needs a 420 cc membrane, and the 800 cc restrictor is for, are you ready, a 400/600 gpd membrane. WHAT???? That’s not even close. HERE’S the Amazon link.


I’m currently making water with the 550 restrictor with TDS at 1 prior to DI….so that’s good. But the waste water volume is up. What usually takes me 1 hour and 30 minutes is now taking 2 hours and 10 minutes to make five gallons.

Thoughts?

 

[KrisReef]

Would more restriction improve flow through the membrane? I hope you get a real answer, but I wonder if the 800 has higher back pressure than the 550? Also, since you upped your gph the restrictor should follow, and the 550/800 change is between 50 & 75 gph.

Somebody give us a real answer,bump!

 

[redfishbluefish]

Well I ordered the 420 from Amazon and it will be here tomorrow, so we'll find out!

 

[mdb_talon]

I am far from an expert but the BRS numbers match up more to what i have always known.

I think it can also depend on the incoming TDS in that the cleaner the incoming water the smaller restrictor size for that specific gpd membrane you can get away with without adversely impacting water quality or membrane life.