[convincor]

Originally Posted by Seagull81

If you have a check valve in the line, how does it relieve the fluid back to the master cylinder to release the brakes? What am I missing?

it's not a check valve, it's a residual pressure valve.
And as long as the master is above the calipers you shouldn't need one.
Exception would be drum brakes. The residual pressure is needed to keep the shoe return springs from compressing the wheel cylinders piston back into it's bore.
Wilwood Residual Pressure Valves - SummitRacing.com