Quote Originally Posted by Swingpure View Post
How many gallons of concentrate will two 400 gpd membranes produce per hour?
It is highly dependent on the sugar level in your sap, how high you're concentrating to, and the sap temperature.

As long as you flush the membranes after each daily use, is that all you have to do to maintain them during the season?
No...membranes should be periodically "washed" with RO sap (a strong alkaline solution) to reduce/remove microbial buildup and restore high flow rates. Other conditions may dictate an acid wash (much less common).

You'd probably benefit from reading the section on RO concentration in the Third Edition of the North American Maple Syrup Producers Manual. Lots of general info in there on ROs, how they work, how to operate them, and how to clean them.