I closed the valve so the water would go stright into the tank to which it does but i have no psi when I open the valve....
I have a 4040 ro & was told your not supposed to close it all the way, it needs to filter the waste.
Secondly, if you open the valve all the way there isn't any back pressure to give a psi reading, the water is flowing freely down the drain.
I might be wrong but that is how I understand it anyway.
Best of luck.