This is a basically a type of Gear Pump but
with lobes instead of gears.
The three-lobe gear pump, like the two-lobe
version, is commonly used to force high-pressure air into combustion compartments
of a diesel engine.
The output of these pumps is more pulsed than the output
of a gear pump because there are fewer teeth. The fluid is delivered in comparatively
Gases are compressible (whereas liquids basically are not),
therefore the three lobe and two lobe gear pumps work particularly well with gases,
since the compressibility helps smooth the flow.