Did You Adjust Your New RO Filter Flow Restrictor?

If you are one of those people that likes to figure out things on your own and only glance at instructions with your new toys - you should know that you chance damaging the membrane on your new reverse osmosis water filter. It is not obvious to the naked eye, but that waste water hose you just hooked up probably has a flow restrictor in it that may require adjusting to get the desired 4 to 1 waste to product ratio.


A Flow Restrictor from a SpectraPure ProPlus RO/DI Filter

If you run less than a 4 to 1 ratio, not enough concentrate (water) is allowed to flow past the membrane when using your RO filter and the impurities will precipitate out on the membrane surface - clogging the RO membrane.

To prevent clogging, "the Concentrate to Purified Water Ratio must be checked and adjusted in order to compensate for pressure and temperature variations that exist in all water supplies. The flow rate of the concentrate must be a minimum of 4X the product flow rate. (4X to 6X is an acceptable concentrate flow rate.)" - from SpectraPure's Installation and Operating Manual of a ProPlus RO/DI System

Determining your RO water ratio is rather easy. Simply grab that measuring cup from your kitchen and time the output of your waste water for 1 minute. (you may need to dump it quick and continue to fill and measure if you have a lot of flow - or get a bigger measuring cup)


Initial Product Output

After you determine the milliliters from your waste water, do the same with your purified water output. Then divide the waste number by the purified product number to get your ratio.

If your ratio is less than the 4 to 1, turn off your RO and let the pressure go down for a minute, it is time to adjust that flow restrictor.

Carefully remove the waste hose from the quick-connect at the membrane. You should see a tip on the end of the hose like in the first picture of this article. That tip has a small hole - that whole tip is the head of your flow restrictor that has been inserted inside the waste hose.

Now the fun part - getting that flow restrictor off. This can be rather challenging. It took this 3reefer some prying with a dull knife and a careful twist with a pair of pliers to do get it loose the first time. This process requires some delicate handling - take your time and try not to get too frustrated - you might break it.


The Insert and Capillary Tube Removed


Once loose, gently pull it out of the waste hose. You should see a long capillary tube attached to the insert of your flow restrictor.

Now get out a measuring tape and refer to the Flow Restrictor Tables that should be in your instruction manual for your RO filter.

In my case, I noted that my product water was around 154 milliliters and Restrictor Table in the manual stated that I should cut the capillary tube down to 8 inches in length.



A new razor blade is nice to have for cutting the tube - but if you just have scissors, be sure to pinch the end of the tube back to a round shape after the cut.

Now simply place the Flow Restrictor back into your waste hose, firmly inserting it all the way, reconnect the hose and retest your water ratios.

In my experience, the Restrictor Tables in the manual will get you in the ballpark, but further adjustments may be required. I had to remove mine again and cut another inch off to get to 4 to 1.


Sometimes, it pays to read the instructions!

Hope this helps...

 

Good write up.

I didn't adjust mine, I just shoved the new restrictor down the waste hose and went from there. Seems pretty easy to adjust though. Maybe if I'm not terribly lazy next weekend I'll adjust it

 

Alright.... I'll go check it...

Thanks for the push...

M

 

my unit came with 0 instructions. the hoses were pre-hooked up to the unit and coiled up. ill have to try to figure out if i have a flow restrictor

 

Most vendors do not provide capillary tube type flow restrictors but provide a fixed type restrictor with no adjustability. The advantages of the capillary tube are that with just a couple minutes time you can trim and adjust it for a perfect 4:1 waste ratio. Understand, water temperature, water pressure and tap water TDS concentrations all have an effect on how much waste you get. With the fixed type normally found you are probably not getting 4:1, many are higher thus wasting excess water, reducing pressure available to the RO membrane which results in lower GPD and lower wate rquality. Others are not wasting enough which leads to premature RO membrane failure since it is not getting flushed sufficiently to carry the accumulated solids away, you need that velocity at 4:1 to properly do so.

I would follow Matts directions in this thread and determine what your waste ratio is presently. If its close to the 4:1 you are fine. If its either higher or lower you should first determine what type of restrictor you have then determine what RO membarne you have, 50 GPD. 75 GPD 100 GPD etc. Flow restrictors will always be found on the waste line leading from the RO membarne to the drain. It may be visible as a white plastic tube with writing on it like 750mL (most common) or it could be mounted inside a 90 degree elbow where you cannot see it like Coralife and others provide. Buckeye and spectrapure are two vendors that provide the capillary tube type Matt pictured and it is the preffered restrictor if you are concerned about water quality, lifespan of your unit and wasting of a natural resource.

 

Great info. I was curious about other brands. Thank you. :thumb_up:

 

Have mine set to 2:1 for long time with no problems. Just flush it before every use.

 

2:1 will work for awhile providing you have low tap water TDS and softened water. If not again it will work for awhile them fail quickly once the membranes fabric becomes fouled and probably ruptures. Everything will be going along fine and boom so watch out for it.

 

I'm running about a 5:1 ratio. I contacted the company my unit is from and they said that would be fine as when it gets warmer I should start seeing the optimal 4:1 ratio.