Not exactly scam, but depends on who and how they sell it. The permeate pump is certified, made of harmless material, and won't fall apart, but it is the magic bullet as claimed in the manufacturer's Aquatec website? No. But since they only sell it to distributors, they give you no specification and they are not responsible how you use it. But now these companies know that nothing can stop people selling things to individuals on eBay, they are a bit careful on their website, in order not to develop a scandal.
Many pumps are sold to retrofit existing systems. But notice the 75 psi feed input on the main diagram on their website. If you haven't got that pressure, it very doubtful it will work well. And if you got all that pressure, it's doubtful if you need a pump to get good results.
Standard main water pressure depends on water district, but should be 50 psi, which is the value for sprinkler specification. You may get higher pressure if you live uphills in individual houses, where the water pressure gradually decrease downhills to 50 psi for houses at the bottom. In this case you need a pressure regulator, which is usually factory preset to 50 to 60 psi, with 75 psi as the absolute rating. So basically, now that the permeate pump isn't new anymore, Aquatec is basically saying you need a booster pump without admitting it. A booster pump cost twice as much and gives you a lot of improvement if your feed is just 50 psi. It's crazy if you use a booster pump plus a permeate pump. Since I have 75 psi without the need for a booster pump, I'm OK. It wouldn't work well for 60 psi, and I can prove it.
When the tank is empty, that is, no back pressure to the membrane, the membrane sees the full pressure of about 70 psi. The pump is supposed to maintain the back pressure to at most a few psi so the full 70 psi pressure is maintained at all times. With the right flow restrictor, there should be enough pressure and flow in the brine/concentrate to do that. But I found out that the recovery rate have to be high at about 25%. Which means that the drinking water to waste water ratio is 1:3. This is far from the usual 1:4, or 20%, and far from the specified Filmtec membrane recovery of 15%.
But all is not lost. At 70 psi, even 25% recovery gives 98% stable rejection, which is the same specified rejection at 50 psi and 15% recovery. So with a virtual booster pump, and a permeate pump, I can't get better rejection but I waste half the water, 1:3 recovery instead of 1:6 recovery.
It won't work if you don't have 75 psi main feed. Say at 60 psi feed, you have about 50 psi across the membrane, and clearly at this pressure, you need 15% recovery to achieve anywhere near 98% rejection. 25% recovery is far off.
It's doubtful if you need any pump when you have 75 psi pressure. A 75 gpd membrane becomes 110 gpd which is a hell lot of water. But since the pressure is constant across the membrane, it's easy to design your system, and the performance is guaranteed under all circumstances. In other words, peace of mind.
In pumpless systems, basically the water is excellent when the tank is empty. Then the water tend to get worse as the tank fills up, or you waste a lot more water without realizing it, that's what Aquatec is trying to market their pumps. With typical usage, the system works most often when only a few cup or a kettle of water is being drawn from the tank. The water is worse or wasting most water when the pressure across the membrane is often 50% to 33% of an empty tank.
Actually I would like to write software to design residential systems. Dow has free software but far too complex and did not give out parameters for the residential membranes. So I couldn't do anything but to use 75 psi main pressure. The pressure is constant and everything is constant so it's easy to design.
And now the cutoff valve. It's not cheap at 1/3 of the pump price. But does it worth it? Nobody claims that it's necessary but say enough that you will buy it. I was surprised to find out that the valve don't cutoff at 90%, but about the same as the old valves about 66%. I talked to the distributors and manufacturer and it seems that they are well prepared. The distributor send me over to the manufacturer, who promise to test it and replace it if it's defective. But I am not to expect 90%, but 85% depending on pressure.
I almost sent it off when I realized that now the cutoff pressure of my tank will be the main pressure of most people, at 50 psi. It will be crazy to increase that to 65 psi. I don't need that and the pump may not work at that pressure. Also, the valve turn back on at 30 psi, giving 20 psi of hysteresis so the system won't turn on and off whenever people drawn a glass of water or a kettle of water. I don't know if my old valve do that. But since the new valve has JG connectors that are easy for me to measure things, and that the tubings are fitted already, I rather not go back to the old one.
Previously I have doubts about measuring pressure when water is flowing. But I find that it's very accurate, the dynamic pressure into the tank equals exactly the static pressure when the tank is isolated. After all, what else can it be? Now I left the pressure gauge dangling in a T piece somewhere in the water path. And since I needed a tank shutoff valve as an adapter for the standard gauge, I can shut off the valve so the gauge isn't in contact with potable water when not in use.