[martinj]

As I understand it the flow restrictor creates back pressure on the membrane and its rating should be about 4 times the gpd? If its less then 4Xgpd you get faster production/ less waste and shorter membrane life and the opposite is true.
So if you upgrade a 100 gpd system which has a flow restrictor rated 400 by adding another 100gpd membrane do you need to swop the flow restrictor for one rated 800 to avoid killing the membranes?

[Spruce]

Good question.
Look at Ro-Man's site and look for a flush kit for your specific upgrade.
My personal opinion is that each restrictor, although having a water to waste ratio of 3:1 will have a different size orifice. If it was a one 'size fits all' then they wouldn't list a different flush kit for each R/O combination.

In the early days RoMan also had a 5:1 restrictor which they recommended for those who are a hard water areas, but I don't see them listed on their site any longer.

Spruce