Upgrading RO, need thoughts on flow and plumbing.

[Mark B]

So I built a homemade with an 8852 pump last season. The pump was undersized for the 3 x 400 gpd membranes. This year I bought a procon rate 100 gph and I am planning to pair it with 4 x 400 gpd membranes. Just need thoughts on if this is a good pairing and thoughts on plumbing. Thxs, Mark

[bowhunter]

The pump size depends on the configuration of the membranes. I assume you are using 2 1/2 inch membranes? This set-up will probably work fine if you split the flow between two banks of two membranes in series. There are three flow parameters to worry about to get optimum performance and membrane life. The maximum flow through a 2 1/2 inch membrane is 6 gpm to prevent mechanical damage to the membrane. The minimum recommended flow rate is 1 gpm on the outlet concentrate flow to minimize fouling. And then you need to keep the recovery close to 15%. Your system will work outside these parameters but it may not perform as well. With this configuration and 100 gph pump you would have 50 gph of flow through each side. If you run once through without concentrate recirculation you may have to reduce the pressure to keep the permeation rate down so that the concentrate flow doesn't drop too low coming out of the second membrane. There is no absolute "right" way to set it up but some ways work better than others.

[Mark B]

These are 3x12 400 gpd from membrane solutions. The 400 gpd from membrane solutions are rated max 2 gpm (120 gph) with a max pressure of 300 psi. I was told the membranes optimally run at about 140-150 psi. I will have 4 of these membranes. I was thinking I would plumb each pair in series and the plumb the two pair in parallel.

I came back here to get thoughts on the best way to plumb this. I guess I could do all 4 in series based on the above. Just looking for thoughts from folks here that know way more then me. Thxs all.

[bowhunter]

I'm not familiar with that membrane but I agree with your plumbing plan. I wouldn't do all four in series. The concentrate flow will be very low out of the last two membranes when they're all in series and they may not perform as well longer term due to premature fouling. The maximum flow of 2 gpm is a mechanical limit that you don't want to exceed because it can damage the membrane. Dow limits the flow through their 2 1/2 inch membranes to 6 gpm, so that where I got that number in my first post.