## Increasing dynamic pressure in a pipe

I'm starting a project involving a venturi and water, and for the venturi, I need the water pressure to be around 7-10 psi. This means for my water pump, the head height must be around 15-20 ft. Most pumps that fulfill this requirement are either too expensive or are too powerful for my application. I'm looking for a 300-500 gph pump that can give me the 7 psi (most pumps are in the thousands of gph by this point, or are hundreds of dollars). I'm wondering if there is a way to convert flow (gph) into psi (head height) by changing the shape or diameter of the piping. I know if I make the piping smaller, it will reduce pressure (Bernoulli's) but at what point would increasing the diameter of the pipe stop helping me?
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 What is the reason for this, how long do you need to flow for? The very cheapest way to get 20 feet of head pressure, is to build a reservoir 20 ft up. This of course limits the amount of time you will get the desired flow rate depending on how big you can make the tank. You can then use a cheap pump to repump this up to the top. Although to be honest a couple of hundered pounds/dollars for a pump isn't really that much (it's certainly not silly money) and that would be by far the best way to achieve the goal.
 Okay, I'll go through what I actually need to do... I am using a venturi (mazzei injector) to pump co2 into my fish tank for the plants (I know.. nerdy) and am also supplementing macro/micronutrients. For the venturi to work properly, it needs between 5-10 psi of pressure (when the venturi goes through the narrow part, it speeds up, agitates itself, and when I inject the co2 at this point, the absorption rate goes way up, near 100%. The problem with the water supply 20 ft up, is getting the water up there. This will need to be a closed loop (meaning I'm not going to be filling the reservoir with the faucet and end up draining the water from the fish tank into the drain), so then the pump still needs that 20 ft of head height, and I might as well just connected the pump directly to the injector. Since this is a small project (30 gallons) the 1500gph that I would get with the normal water pumps would totally destroy my tank (fish getting sucked up, plants getting uprooted). If I had something like a 75-125 gallon tank, I would probably go with the \$150 pump, but I'm hoping I won't have to.. :) I was thinking a weak well/sump pump might work, but I'm worried about noise, and that it will be running 24/7, unlike the ones in your home.

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