On Nov 4, 8:03*am, "Pintlar" wrote:
*I am assuming
this piston would have a reed type (ball type?) valve built into it so the
fluid could only go one way, towards the caliper.

Your assumption may be incorrect.

Most master cylinders I've worked with have a simple bypass port
drilled just below the rest position of the piston for fluid transfer
by gravity from the reservoir. A millimeter or 2 of movement blocks
off this port during use. If the brake cylinder has been installed
with the piston already compressed then this port is covered and fluid
will not pass from the cylinder to the reservoir, acting like a one
way valve of sorts. This feature is handy when working on the wheel
end of the system to prevent loss of fluid. Just depress the master
cylinder enough to cover that port and then you can remove downstream
components and the fluid stays in the reservoir.

Some brake systems do have check valves, to retain residual pressure
in the lines, but these are normally installed down stream of the
master cylinder.
===================
Leon McAtee