Let's talk RO Flow Restrictors!

[Buckeye Hydro]

The info below is intended for those interested in maximizing the efficiency of water use of their RO or RODI system.

First, check your configuration to assure you’re using only a single flow restrictor.

Flow restrictors ALWAYS go on the concentrate (aka waste water) tube of the RO MEMBRANE.

You want to use a flow restrictor that gives you the desired ratio of concentrate to permeate. Not familiar with these terms? Check this post https://www.reef2reef.com/threads/lets-talk-ro-rodi.592882/post-6007487

Figure out your feedwater hardness.
*If your water is harder (higher) than 17 ppm or 1 grain per gallon, shoot for a 4:1 ratio for a reasonable membrane lifespan.
*If your water is softer (less) than 17 ppm or 1 grain per gallon, shoot for a 1:1 or 2:1.

Flow restrictors are spec'ed based upon the flow (of concentrate) they allow in ml per min.

Assuming for example you're using a single Filmtec membrane, use this calculator to see how much your membrane will actually produce, given your pressure and your water temperature: https://www.buckeyehydro.com/calculator/

Convert this gallons/day number to ml/minute with one of the online conversion apps. For example: convert.exe.

Multiple that number by 1, 2, or 4 or other number depending upon your target concentrate flow, and match that to the nearest available flow restrictor from the table below.

Flow Restrictor Color​	Capacity (ml/min)​
Red​	125​
Brown​	189​
Black​	263​
Yellow​	368​
Green​	525​
Blue​	735​
White​	1052​
Gray​	1577​

Be aware that in most situations your winter water temperature will be colder than your summer water temperature and therefore your calculations will change seasonally. You may want to use a different flow restrictor for each. The good news here is that capillary flow restrictors cost only a few dollars, and they can be swapped out in about 30 seconds.

Lastly, as a shameless plug, always shop with BuckeyeHydro.com for all your reef, home, and commercial water treatment needs.

 

[blaxsun]

Great information!

 

[Buckeye Hydro]

One other thing this info should make apparent: you do not need a second membrane plumbed in series to "save water." And in most cases (i.e., with most untreated feedwater), plumbing two membranes in series it not a good idea if you want to get a good membrane lifespan.

 

[t5Nitro]

Great information. @Buckeye Hydro has been really helpful in helping me learn more about RO systems. Thanks a bunch. Will need some replacement parts and additions in the near future and will get them from you guys.

 

[EricR]

My source of confusion going through this exercise is:
Table provided lists restrictor by color.
On your website, I only see restrictors sold by gpd rating (of the membrane they're intended to be used with, I think).
Is there a cross-reference or something else that I missed?

 

[Buckeye Hydro]

Assuming you have factory spec pressure and temperature, then:

Flow Restrictor Color​	Flow Restrictor Capacity (ml/min)​	Membrane Capacity (gpd)​
Red	125​	10 to 18​
Brown	189​	18 to 24​
Black	263​	25 to 35​
Yellow	368​	36 to 50​
Green	525​	51 to 60​
Blue	735​	61 to 80​
White	1052​	81 to 100​
Gray	1577​	~150​

Russ

 

[EricR]

Thanks. On your website (unless I'm looking in the wrong place), I see this:

Can I assume the following to be true:
75 gpd = Blue (from table in this thread)
100 gpd = White
150 gpd = Gray

 

[Buckeye Hydro]

Thanks. On your website (unless I'm looking in the wrong place), I see this:

Can I assume the following to be true:
75 gpd = Blue (from table in this thread)
100 gpd = White
150 gpd = Gray

Roger! Assuming you have factory spec conditions

 

[Buckeye Hydro]

What if you don't have factory spec conditions? And you can't conveniently measure production from your membrane. Wouldn't it be cool if you could somehow look up what your membrane should produce given x pressure and y temperature??

You're in luck! Check out our calculator:

Reverse Osmosis Drinking Water System | RODI Systems | Home Water Filtration System - Buckeye Hydro

www.buckeyehydro.com

Russ

 

[EricR]

Roger! Assuming you have factory spec conditions

I guess I meant:
I've gone through the measurements and calculations in post# 1 and decided I want to buy the "white" one for summer (now) and the "blue" one for winter, then on your website I'd buy the "75 gpd" one (blue?) and the "100 gpd" one (white?),,, correct?

*this really started because I want to replace my BRS combo flush valve / flow restrictor with a normal flush setup from your website (where the flush valve and restrictor are separated by "T"s on both ends of the block) and also deal with the fact that I'm currently getting <2:1 waste-to-product since it's HOT right now and my source water is coming in at 76 degrees

 

[Buckeye Hydro]

I guess I meant:
I've gone through the measurements and calculations in post# 1 and decided I want to buy the "white" one for summer (now) and the "blue" one for winter, then on your website I'd buy the "75 gpd" one (blue?) and the "100 gpd" one (white?),,, correct?

*this really started because I want to replace my BRS combo flush valve / flow restrictor with a normal flush setup from your website (where the flush valve and restrictor are separated by "T"s on both ends of the block) and also deal with the fact that I'm currently getting <2:1 waste-to-product since it's HOT right now and my source water is coming in at 76 degrees

Correct! I'm not a fan of those flush valves with integrated flow restrictor you describe. We configure them a little differently so if you want to change the capacity of the flow restrictor it will cost you $4 rather than needing to buy an entirely new auto flush valve.

 

[EricR]

Thanks again for all of the info. Very informative.

Since I basically already hijacked this thread, one more educational question:
Does flow restrictor throughput (mL/min) vary much with pressure and/or temperature or are they pretty constant?
*I'm hoping close to constant for purposes of the exercise in post #1 but just wondering

 

[Buckeye Hydro]

Thanks again for all of the info. Very informative.

Since I basically already hijacked this thread, one more educational question:
Does flow restrictor throughput (mL/min) vary much with pressure and/or temperature or are they pretty constant?
*I'm hoping close to constant for purposes of the exercise in post #1 but just wondering

They do vary with pressure and temperature. The factory spec flows (ml/min) assume 60 psi and 77F

 

[Barrnone]

I have one of those BRS restrict/flush valves you don't like. I noticed my pressure goes much higher(almost double) when the flow on the concentrate line is being restricted. Which pressure are we supposed to use? When the water is flowing through unrestricted or while it's restricted?

 

[Buckeye Hydro]

The higher of the two - when the concentrate is forced to go through the restrictor, is the pressure the RO membrane sees during normal operation. The flush valve should be closed during normal operation.

 

[Barrnone]

This could explain why i'm having issues with life. I think your calculator shows me at somewhere around 125gpd with a 75 gpd membrane. My water is pretty hard around 700ppm. A 550ml/min restritor is way to small.

 

[Buckeye Hydro]

125 gpd = 329 ml/min * 4 = 1316 ml/min.

It sure is! Let us know if you want to talk about a whole-house water softener. No doubt with your feedwater TDS your water hardness is very high as well.