Flow restrictor size

[plecocicho]

Hi,
i wll be building my own reverse osmosis unit out of cheap chinese parts. I will connect two 100 gpd membranes, so the waste will go into another membrane. What size should flow restrictor be in ml?

[DJW]

Flow restrictors are sized in milliliters per minute. You would use a single flow restrictor of 750 to 1000 ml/m. I would base it partly on the TDS of the source water. If the water is already fairly soft, you could get by with 750 ml/m but with harder water (>250ppm) the membrane will last longer with a 1000 ml/m restrictor.

When you force a better waste-to-product ratio with a smaller flow restrictor you are shortening the life of the membrane, so its a balancing act between the cost of replacing membranes and the cost of your water.

http://www.purewaterproducts.com/articles/flow-restrictors

Are you going to use a booster pump, or do you already have good pressure in the line?

[plecocicho]

Pressure is quite good and i will use flush valve, which will prolong the life of the membranes. Hm, conductivty of my tap water varies quite a lot, but its max around 380 microS ish i think.

[DJW]

380 μS is roughly 190ppm of TDS... not that hard. Flow restrictors are cheap, you could get a couple different sizes and see how it does with less waste.

I don't have much water pressure so I'm working on a way to move the booster pump out into another building where I can't hear it. It sounds like there is a Panzer rolling through the house.

[nc0gnet0]

Hi,
i wll be building my own reverse osmosis unit out of cheap chinese parts. I will connect two 100 gpd membranes, so the waste will go into another membrane. What size should flow restrictor be in ml?

If your building your own, go with larger membranes.

http://www.ebay.com/itm/400-gpd-Reverse-Osmosis-Membrane-TFC-3013-400-RO-Membrane-Water-Filters-/272354759040?hash=item3f699bd180:g:v38AAOSwAoRXFdF e

[plecocicho]

I saw a 1500 ml/m flow restrictor, for how big (in gpd) two membranes would that suffice?. The problem is that i would have to buy also a very long line for the waste water, since i dont have a drain near the faucet for the osmosis unit.

[DJW]

A very long drain line would be restricting the flow somewhat, from friction, so I'm not sure which membrane would match, especially with a larger membrane. You could use larger diameter tubing to reduce the effect of the length. I have a valve on my drain line so that I can throttle it down toward the waste-to-product ratio I want. Getting it right depends a lot on your pressure.

[nc0gnet0]

Pressure is quite good and i will use flush valve, which will prolong the life of the membranes. Hm, conductivty of my tap water varies quite a lot, but its max around 380 microS ish i think.

What is your psi? Many people think they have good pressure, until they put a gauge on it. Booster pumps are quite a good investment, and help prolong membrane life, as well as increase output to waste water ratio.