What are you all's PSI from your source your using? TDI?
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Temperature of water, starting TDI, PSI, theres some formulas on the website that talk about the variables.
I have 80 psi, tap tds is 88. Tds can be up to like 450 in some places. My water is low tds but high sediment, I got a fancy sediment filter after the first one only lasted like 3 months with pretty low usage. I guess sediment is like bigger chunks, so the waters dirty in a way that doesn't show as high tds. You want the sediment filters to get the big chunks so the later ones can grab tds instead of being clogged up.
Then you want your membrane to reject most of the tds, there's a proper percentage. That percentage is saying that 90% (or whatev) of the tds is getting caught be the membrane, so your di can grab the last bits instead of getting used up too fast.
Temperature affects how well the membrane does that because cold water is thicker so it doesn't go through it as easily. The 90gpd is 90 gpd at 77 degrees and 80 psi. Cold water slows it down because you are wasting water that should go through the di, but doesn't cause it's too thick for the membrane. Hot waters bad for the membrane. Low pressure slows it down because it's not pushed through as hard.
The flow restricter decides how hard the water gets pushed through the membrane. You need enough psi in the first place, but you also need the right flow (it's confusing how that's diff from psi, but it is). The flow restricter controls how much is wasted, you want enough waste to be removing the right % of tds (to keep your di healthy) but not too much or it takes forever to make water. This ratio is 3:1 or 4:1 depending on your unit. You measure how much waste water and product water you can make in a minute. If you get 400ml of waste for 100ml of product water in that time, you have 4:1.
At least, that's how I understand it from having to deal with really cold, high sediment water. Some of that infos probably wrong but I think it's the basic idea. Most people don't get this in depth with it. They just plug and play their unit. IMO if you learn what the parts do, and how to keep them running well, you can save a lot of time and money because your unit is running as well as possible.