2 water filters for 2x the water pressure - idea and advice

Okay, I want more water pressure. I bought two separate under-the- sink water filters. Not a dual unit, but two self contained water filter units. Now I want to hook them up so that water flows separately through each, then joins back together again before exiting the kitchen faucet.
The unit is housed with 3/8" FPT (plastic) holding a 3/8MPT to 1/4 compression male (plastic). Do I have to step it down to 1/4 or can I use the 3/8" FPT? I'm wondering if putting too much pressure on the unit (by not bottlenecking it to 1/4"C) will cause it to function improperly. I don't care about the pressure in this regard. I'm getting the increase by using two units instead of the usual one. However, I do want to use less fittings.
What about exiting the units? If 1/4 C is the intake then that's the bottleneck, so at that point it shouldn't matter if I use 1/4"C or 3/8" FPT, right?
The faucet I have in mind is a single handle with standard 1/2 MPT.
Anyone know if the units themselves automatically act as a back flow preventer? If not I'd be worried unequal pressure might blow water back and forth from filtered to unfiltered water, not that I can see any terrible consequences.
advice or criticism welcomed thanks
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Jim Rainfordson wrote:

pressure will be maximum when the faucet is off, stopping down the fitting will reduce your flow. When you open the faucet the pressure will drop as the flow increases. So... if your filters can handle the pressure when there is no flow they will be fine when there is a flow. Also, the flow will balance out between the 2 filters, if one is more plugged than the other the flow though the plugged one will be less. You wont get backflow here, high side pressure will be the same on both units.You could possibly get some micro drift when the faucet is off, but who cares, its drinking water and it will only be refiltered agin when the faucet comes on. The bottleneck will be the smallest ID, try to maintain the 3/8 if you can. A short run of smaller ID has less effect than a longer run. Seems to me, either you have a filter that doesnt have a very high through-put(is it designed for this type of use?), a low pressure water supply, or a plugged faucet/aerator. Eric
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Right
No, they do not, but I don't see that it would blow water back at any point either. Where is the unequal pressure coming from? The hot water when running a blend? Not a problem.

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you can for as long as possible. Won't help much, but maybe a little.
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Sounds fine, it would be best to ensure the parallel paths are identical, same length of fittings, etc.

I would be inclined to use the unit as supplied with the 1/4" fitting. Increasing the pressure on the filter would increase the flow rate, and it is possible this could decrease the filtering efficiency. You could check with the manufacturer to see what they say.

No, that's not really true. The way fluid flow works with pipes/fittings in series with a constant pressure source is that each fitting will have a certain flow rate to pressure drop relationship. The overall flow rate will be just enough so that the sum of the pressure drops across all the fitting/pipes between the source and the faucet will just equal the pressure of the source. So adding additional lengths of small diameter tubing will cause additional pressure drop and decrease your overall flow rate.
Yours, Wayne
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