What is an accumulator and how does it work?
What is a brake bleed valve and how does it work?
What does ADD stand for and how does this system work?
accumulator - charged with nitrogen has a diaphram to seperate the air from the hydraulic fluid on the other side, it is used to dampen shock value of hydraulic surge and for aircraft brake systems allow for a reserve in the loss of hyd power.
Brake bleed valve- also refered to as a shraderdoes the same as in your car, the brake system is a one way hyd system, air can become trapped at the brake reducing performance, the bleed valve allows for venting the air/hyd fluid mix until solid hyd fluid is evident. this valve is secure and normally lockwired closed
add - an EU thing, not sure on the exact acronym but basically NEF not essential for flight. The MEL minimum equipment list is there to list the potential safety of flight items usually electronic that an aircraft can operate without for a prescribed period of time, it does not cover non safety of flight items, thus the add program.