Comment by cfallin

> DC/DC step-up/down voltage regulators

Interestingly, there is actually a hydraulic mechanism that's the equivalent of a boost converter with inductor, diode, and switching element:

https://en.wikipedia.org/wiki/Hydraulic_ram

It translates a low-pressure fluid with continuous flow into periodic high-pressure impulses. The inertia of the fluid is the hydraulic equivalent of the inductor, and a switching element (valve) closing suddenly causes a spike in pressure as the water decelerates suddenly, equivalent to a voltage spike as an inductor "wants to keep the current flowing".

But it usually operates with water, which has much higher density (hence inertia) than air, so it might not be very efficient (or might require much higher flow rate) in a pneumatic version.