when the peddel is up the fluid is at atmosperic pressure to alow for expansion.
so the fluid has a open path from the res to the calipers.
when foot pressure is applyed the hole to the res is blocked off buy the piston and fluid has no where to go so pressure in the system is created.
when i used to work in the garage i would just leave the nipples open with pipes attached after workin on the hyd system ago and do a diffrent job keeping an eye on the fluid level and let gravity do the workwhen no bubble come out lock up the nipples one at a time.
worked 80% of the time with no pumping needed
