Question about needle valves for concentrate and permeate

[Arctic Fox]

I'm rather new to RO operation and I'm wondering if any of you can offer me some guidance about using needle valves for concentrate and permeate flows.

First, is this necessary?

If so, what is/are the advantage(s)?

Are flow meters recommended?


Thanks for the help.

[jmayerl]

Yes

Increasing memebrain pressure

Yes

[maple flats]

The high pressure pump creates flow on the inlet to the membrane canister. The needle valves are after the canister and restrict the flow, that creates the pressure. The greater the restriction the higher the pressure and the higher the pressure the greater the permeate forced thru the membrane. Without the needle valve you have no way to control the amount of permeate. Without one you will get very little permeate pushed thru the membrane. You could not do it with any other cheaper type valve and get any satisfactory precision of control.
Flow meters help you know what is happening in the RO and diagnosing if anything is not right.

[Arctic Fox]

Thanks for the explanation, I think I'm understanding this better. Is it necessary to have a needle valve on the permeate outlet? It seems to me that you would want the permeate to flow freely out, but again I'm still learning.

[regor0]

Thanks for the explanation, I think I'm understanding this better. Is it necessary to have a needle valve on the permeate outlet? It seems to me that you would want the permeate to flow freely out, but again I'm still learning.Permeate needs to be free flowing.

[Super Sapper]

The needle valves used are rated for the higher pressures and have very fine adjustments. I would have a valve on the permeate side to isolate the membrane for storage but a normal ball or gate valve would work for this. During operation you want the permeate side open, restricting flow on this does no good and creates added stress on the equipment with no gain.

[Arctic Fox]

. . . Flow meters help you know what is happening in the RO and diagnosing if anything is not right.

Thanks for the response!

Is there any advantage to getting an adjustable flow meter? It seems to me the stainless needle valve on the concentrate side would be doing the adjustment for concentrate and permeate flow.

[maple flats]

Just get a flow meter to read in the range you will be. A 250 gph RO will usually have a concentrate and permeate flow meter in the 0-8 or 10 gpm range but a 0-5 or 0-6 will be even better. When you get up to a faster RO the scales will generally not be equal, with concentrate being a lower range and permeate being a higher flow range, because in use you will have at minimum 2x as much permeate and in common practice if designing it for taking 2% sap to 8% in one pass you will have 3x the permeate flow, if going a higher ratio in 1 pass the permeate goes lots higher than that. A lot there depends on the pump and the pressure you can run at.