Concentrate restriction valve

[Minnesota Tapper]

Been running a home build ro for the first couple runs this year. Procon 660 with 2- 4x40s. If I open my concentrate restrictor valve all the way open, I can't run the ro. Pressure goes to 250+ on start up and unit will just shut itself down. I have a 3/4" needle valve to adjust pressure. The passageway inside this valve (3/8" or smaller) is too small for my pump to flow sap through without building high pressure. Ive been able to use the ro by cracking open my recirculation line which allows me to run as low as 180psi.

Its obvious to me the issue is the needle valve not being large enough. So my question is what type of valve is best suited for setting pressure in my situation. A gate valve seems like if would have the most flow through capacity. However I read they arent meant to adjust flow but are meant for on or off purposes.

I worry a globe valve wouldnt flow enough as they also typically have a somewhat smaller passageway inside them. Similar to my current needle valve. Anyone else had this issue? I'm leaning towards the gate valve at this point.

[hunterhunter111]

I used a gate valve, seems to work OK so far

[Bricklayer]

I had the same problem. So I plumbed a bypass into my system.
It still needs some tweaks. But it cuts down system pressure on startup big time. Increases flow as well.
From my concentrate out line from membrane I put a 4 way cross fitting.
1 line to needle valve
1 line to recirc needle valve
1 line to bypass.
I then put a ball valve on the bypass line and ran a line to a T fitting at my concentrate flow meter.
It works great. I was originally had pressures of 150-175 with my needle valve wide open.
But get around 75 now. But I’d like to even bring that down.
So I plan on isolating the bypass.
I’m going to use a 3/4” cross fitting. And a 3/4” line from membrane concentrate out. 1/2” line to everything else
And a separate flow meter 3/4”. This should stop all restriction and reduce pressure hopefully.

[maple flats]

The main issue is that a Procon 660 essentially pumps 660 gpm. That is far too much without creative plumbing on 2- 4x40 membranes. That would be good for 1- 8x40 or 4 - 4x40's

[Bricklayer]

It’s definitely an oversized pump for a 2X40 system.
The 660 procons are 1” discharge so
I’m sure if you installed a 1” tee and ball valve right off the pump before membrane with a 1” or even 3/4” hose on it and have it run back to the feed tank. This would reduce pressure big time and to start concentrating you slowly close it and then start closing your needle valve.

[maple flats]

Ideas like that are what I mean when I say "creative plumbing" Maybe even a 1/2" bypass with a ball valve, going back to the source tank. The size of the bypass and how much if any to restrict it are the question.

[Minnesota Tapper]

I know its oversized but the plan was to start big with the pump and motor so I can grow the system as needed. Plus I got the pump brand new on auction under $200. I like the adjustable bypass between the procon and membranes idea. So simple not sure why I didn't think of that! The rest of the system is designed to run 660 gph without building pressure. All my stainless piping,hoses,and end caps are 3/4" or 1". Its just the needle valve that bottle necks the flow. Going to order fittings for a bypass. Once again, thanks

[maple flats]

You may even want a gate valve for regulating the bypass flow. Once set it might not need further adjusting. Try it.

[bowhunter]

If you could send me a sketch of your set up I might be able to help. Send it pm in case I don't check the forum that often. I'm finishing my season and cleaning up. Generally speaking you should use a needle valve or globe valve to regulate flow or pressure. A gate or ball valve will work but they are better suited for on or off operation not flow modulation.The recirculation line should have a needle or globe valve in it. It's the line you use to adjust the pressure. It does sound like your valves may be too small but I haven't had time to check the sizing.