[carl stanton]

I run a RO system, have done for years 40/40 wasn’t needed and my water pressure is so low even with a 40/40 booster.  Anyhoo back on track

Is there more benefit in running say two 200 gpd membranes rather than one 400 gpd membrane?

[nathankaye]

No, not really.   This is because the usual set up means that the waste from the first one is going into the 2nd membrane to produce pure from that.

The only suggestion really would be to run a booster on your 400, if you need slightly faster production. Or else, use the bigger and faster 4040 type

[Don Kee]

A 4040 membrane doesn’t produce 400gpd...it probably produces closer to 2500gpd (under the correct conditions)

I’m a little confused by the OP though.
You say a 4040 isn’t needed, but your water pressure is still low with a 4040 booster...why have you got a 4040 booster when you don’t have the membrane?

Disagree slightly with Nathan as you can run your membranes in parallel rather than in series to solve the waste fed membranes but a booster pump should always improve your productivity (as long as you have the correct one for your needs) but in theory 400gpd is 400gpd whether with one or two membranes.

If you’re desperate for more water add another 400gpd membrane and get the correct booster pump.

Or get a 4040 if you haven’t already.

[carl stanton]

A 4040 membrane doesn’t produce 400gpd...

I’m a little confused by the OP though.
You say a 4040 isn’t needed, but your water pressure is still low with a 4040 booster...why have you got a 4040 booster when you don’t have the membrane?

Disagree slightly with Nathan as you can run your membranes in parallel rather than in series to solve the waste fed membranes but a booster pump should always improve your productivity (as long as you have the correct one for your needs) but in theory 400gpd is 400gpd whether with one or two membranes.

Sorry you were confused I did say a 4040 isn’t for me with my mains water pressure as a booster for a 4040 still required a minimum input pressure from reading the data for them. Higher than one for RO set up factoring my mains pressure.

My question  was: why have two membranes of 200 so total of 400 instead of one 400 hundred? What are the real benefits?

Answer here:
https://youtu.be/BKu_e7MVLX0

I agree and have found using  the correct booster pump is a must I couldn’t run effectively without them.