Flow Restrictor Basics....

Could you please explain the difference between restrictor types and then explain the trimming of the capillary tube. There seems to be a lot of confusion on whether a shorter restrictor gives you more product water or more waste water. I get asked this question often.
Say my waste ratio is 2:1, do I trim it or should it be longer and if its the opposite and its 6:1 does it need to be shorter or longer?
Flow restrictors are used to limit (restrict) the amount of waste water that goes to drain. They are also needed to maintain a working amount of pressure in the membrane housing. If there was no FR, then ALL the water would go down the drain as that would be the path of least resistance. Also, it would not allow any pressure to be developed in the membrane housing.

To my limited knowledge, there are two basic types of flow restrctors: fixed and adjustable.

Fixed FRs are usually a cylinder of plastic with a small hole drilled through it. They too, are installed in the waste line after the membrane and allow a fixed amount (varies with water pressure) of waste water to drain. Problems arise when you don't have the working pressure (and temperature) that the fixed FR assumes you have. You can easily have a situation where you could be running at 2:1 or 8:1, not the desired 4:1 waste-to-product ratio.

Adjustable FRs are used so that you can account for your membrane, pressure, and temperature differences to get the proper 4:1 ratio. Too long or too thin, and you don't waste enough water. Too short or too fat, and you will waste too much water AND not have as much membrane pressure as you could have. We offer a different size FR for each of the membrane sizes we sell: 25, 40, 60 and 90 GPD.

We provide a very simple method for adusting the FR. With an original, full-length FR in the waste line, measure the product water for one minute in milliliters. Look at the table in the Operations Manual and determine, using the measured production rate, the proper length the FR should be to achieve the desired 4:1 ratio. Cut it to that length using a sharp blade, being careful not to crush the tiny end of the capillary tube. Re-install the FR in the waste line and you are good to go.

To answer your question, if the ratio is 2:1, the FR should be shorter; if the ratio is 6:1, the FR should be longer (tough to do - you'll need to get a new FR). In a pinch, like late on Friday night, you can put a ball valve on the waste line and adjust it (by trial and error) down to get the proper ratio.

Scott
SpectraPure, Inc.

 

preset flow restrictor

Hi Scott, so what is the ideal water pressure and tempeture that the preset F/R is looking for?

I am using a 2:1 preset green F/R with 67psi and a temp of 65 degrees,
and i get a 3.7 : 1 ratio, i'm ok just fine with that, when the weather gets hotter and my supply water heats up i switch to a preset 3:1 ratio F/R and i get it back down close to the 4:1 ratio.

Was just wondering the ideal parameters the preset F/R's are looking for so they would run true to specs.

Thank You .....Steve

 

The "ideal" parameters of 77 degF and 60 psi are mostly for comparisons of different manufacturers' production rates.

In your case, if you have the red and green FRs then you should have the hardness test strips. They are the only thing you need to determine which FR to use. If your water is too hard, you need more waste water to keep the membrane scrubbed of impurities.

Do the test, install the indicated FR, and don't worry about the actual ratio.

Scott
SpectraPure

 

Thank You