THEORY OF OPERATION - CONTINUED
BRAKE SYSTEM - CONTINUED
Gear Pump (Braking and Hydraulic Fan).
Hydraulic oil flows into pump from line from tank. Oil flows from pump through check valve to shuttle valve.
Shuttle valve directs oil flow to accumulator with lowest pressure through lines to brake accumulators. Brake sys-
tem pressure sensor sends a signal to machine ECM that is proportional to pressure in brake accumulators. When
accumulator pressure rises above 2,300 ± 50 psi (15,858 to 345 kPa), machine ECM sends a signal to brake charg-
ing solenoid valve to shift brake charging solenoid valve more open.
When brake charging solenoid valve opens, pressure drop across orifice increases. When pressure drop across ori-
fice increases, brakes flow control valve opens. When brakes flow control valve opens, oil from pump is also
directed to line to fan motor. Check valve will close to prevent oil flow from brake accumulators to pump.
N OT E
Brake charging solenoid valve is a proportional valve. Amount of flow that flows through the brakes flow
control valve is proportional to the amount of flow through the brake charging solenoid valve. Amount of
flow through the brake charging solenoid valve is proportional to amount of electric current sent from
ECM to the brake charging solenoid valve.
After several brake applications, pressure in brake accumulators will decrease below 1,400 to 50 psi (9,653 to 345
kPa). Then, machine ECM will signal brake charging solenoid valve to close. When brake charging solenoid valve
closes, pressure drop across orifice decreases. When pressure drop across orifice decreases, brake flow control
valve closes to direct more oil to accumulators. This will charge brake accumulators to provide proper brake sys-