# Creating a constant flow system [closed]

I've been asked to create a system that will output a constant flow of liquid (water) even when the input pressure is variable.

I can't use gravity filtration because the system is for a straw filter (diameter of 1-2cm). It's a system that should take in the water when sucked by a person, send it through a filter with a constant flow rate and be available for drinking. The final straw would look something like this

So far I haven't been able to think of any design that's possible for a straw. I'm starting to wonder if it even is possible considering the dimensions involved.

## closed as off-topic by Emilio Pisanty, Jon Custer, ZeroTheHero, Qmechanic♦Aug 29 '18 at 18:55

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• why is a constant flow rate necessary in this application? – niels nielsen Aug 29 '18 at 17:56
• I actually don't think it is, but the PhD student I'm helping wants a system like that. I'm thinking a filter that works at the maximum expected flow rate would be easier to build and fit into the design. – user43334 Aug 29 '18 at 23:13

When the flow increases, the difference between $P_1$ and $P_2$ increases, which pushes the disc to the right and restricts the flow.