aquasafe ro/di pressure guage...
 

so i've been running this unit for several years now but i have no idea what to do with the pressure guage that it came with. i was hoping someone could let me know where it goes and what it indicates. :)

i would be very grateful,

I think it is to check the pressure of the water going into the unit. If it is too low then you need a pump. The pumps are expensive. I think most city water pressure is adequate so a pump isn't needed. If you have a well maybe you wouldn't have enough pressure? If you have been using the system for years without any problems I would forget about the gauge as long as your system is working properly (they never make as much purified water as they are rated for).

isnt it to check the output pressure of the R/O to check if the pre filters are clogged?

It is a diagnostic tool. You should have used it during the install to ensure that you had adequate pressure for the unit, and then probably won't ever use it again unless you write Ed and ask a question about why something is the way it is. Then he'll have you putting the guage on every tube in the system, and from that data, he'll offer a solution. Worked a wonder for me...

i don't mean to steal your thread but i also have an aqua-safe. anyone know when to change the filters or membrane? i've probably ran about 2,000 gallons through it by now.

Easiest way to tell is when your TDS level starts rising