The Gen III has a gerotor pump with a spring. I really don't understand how it works, but there's a spring and a sort of valve. Maybe that's the bypass valve?
Yep that's the bypass. You can put a stiffer spring in it to make more peak pressure.
It's kind of like the Wankel of pumps. The rotor blocks and unblocks the inlet and outlet ports as it turns. Each lobe is a little chamber that fills up with oil as it passes the inlet, then as it rotates it gets pushed over to the other side and squished out the outlet.