Apparently the valve in question was a turbopump valve. I don't know how the turbopumps work in the Falcon 9, but they are a fairly interesting topic in general. For example, in the German V-2 rockets the turbopumps were steam driven. The steam for this was created with hydrogen peroxide and a catalyst; almost like a little miniature rocket engine inside of a larger one. I think this highlights just how much complexity we can forget liquid fuel rockets have.
The turbo pumps for the Space Shuttle Main Engines generate about the same horsepower as the engines of a Supercarrier -- all in the volume of a trash bin.
A quick google suggest at least one supercarrier has 280,000hp split across 4 engines. I'd love to read up on something that makes 70,000hp in the volume of a trash bin.
"The HPFTP is a three-stage centrifugal pump driven by a two-stage hot-gas turbine. It boosts the pressure of the liquid hydrogen from 1.9 to 45 MPa (276 to 6,515 psia), and operates at approximately 35,360 rpm with a power of 71,140 hp. "
I'll keep hunting for dimensions. Thanks for the tip-off to another interesting Sunday nights trawl through the internet…
The main difference to air breathing engines is that both your fuel and oxidizer are dense liquids so their volume is a thousand times less than comparable ambient air (never mind the nitrogen). Still, if you think that's a lot of power, only a few percent of the propellant is burned to run the pumps. Something like 20x burns in the main chamber, the aim being to accelerate the exhaust gases. The power of that jet can be gigawatts, though it's relatively meaningless.
