Small diaphragm pump with 1/4psi regulator - one line to crankcase pressure to work the diaphragm, and in/out. I think it is much the same as the pump in a gas carb in that respect.
The mystery is I believe mostly in getting the midrange correct - suction carbs tend to go rich in midrange on pressure. Hence Perry carbs and Perry pump carbs - I think the difference is just the mixture profile in the midrange, been a while since I read that bit somewhere - not on the website I could see.
Unless you mean the oscillating pump?