one more dumb question

[Wanabe1972]

I have almost everything roughed in for my RO and I have a pressure gauge before the membrane. The question is where does the gauge after membrane go? Permeate side or the concentrate side. If it goes on the concentrate side is it before or after the needle valve? Thanks Jeff

[TunbridgeDave]

Your main pressure gauge is before the main concentrate (needle) valve on the concentrate output side of the membrane. You don't want any pressure on the permeate coming out. What are you using the gauge before the membrane for? Is it before or after the high pressure pump? The pressure between the high pressure pump and the needle valve will be the same no matter what side of the membrane it's on.

[Wanabe1972]

I guess I don't know what im using it for. I took pictures of the 600gph RO we have at work and there is a gauge right on the high pressure pump then one after the membrane. I thought maybe it was to see if the membrane was fouled but I guess you would take a reading when the membrane is new and watch it from there. Well good maybe I don't have to buy a second one. Would it be better to move this one or leave it on the pump?

[bowhunter]

Dave's right. You don't want any pressure on the permeate side. You only need one gauge right before the needle valve after the membrane. The only difference in the pressure at the pump and after the membrane would be any pressure drop in the tubing or piping. There should be virtually no pressure loss through the membrane. As the membrane fouls it will pass less permeate at the same pressure and inlet sugar content.

[maple flats]

Most have 2 gauges, one before the HP pump to show that you have pressure to feed the HP pump, the other is to read and adjust as needed the pressure in the membrane housing. While RO's can vary widely, mine at least likes to read at least 20 and sometimes up to maybe 40-50 PSI to feed the HP pump. Then I operate the RO on the HP gauge to run at about 275 PSI. Some go much higher, with different RO's. Just make sure if you plan to go higher, that all components are rated for the higher pressure. For example, my vessels that house the membranes are rated at 300 PSI with the type clamps used to hold it together, a stranger clamp may be rated at considerably higher pressure. Basically, you control that pressure by restricting the outlet flow. This then regulates how much concentrate vs. permeate you get. The more pressure the more permeate you remove.