Hyundai HL955, Manual

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4-14
Purpose Purpose
The purpose of the brake valve is to sensitively increase and decrease the braking pressure
when the brake pedal is actuated.
Ready position Ready position
When the braking system is ready for operation, its accumulator pressure acts directly on ports
(P1, P2) of the brake valve. A connection is established between ports (A1, A2) and ports (T1,
T2) so that the wheel brakes ports (A1, A2) are pressureless via the returns ports (T1, T2).
Partial braking Partial braking
When the brake valve is actuated, an amount of hydraulic pressure is output as a ratio of the foot
force applied.
The spring assembly (21) beneath base (28) is designed in such a way that the braking pressure
changes depending on the angle. In the lower braking pressure range, the machine can be
slowed sensitively.
When the braking process is commenced, the upper spool is mechanically actuated via spring
assembly (21), and the lower spool is actuated hydraulically by spool. As spools (11, 8) move
downward, they will first close returns (T1, T2) via the control edges, thus establishing a
connection between accumulator ports (P1, P2) and ports (A1, A2) for the wheel brake cylinders.
The foot force applied now determines the output braking pressure. The control spools(11, 8)
are held in the control position by the force applied (Spring assembly above the spools and the
hydraulic pressure below the spool (Balance of forces).
After output of the braking pressure, spools (11, 8) are in a partial braking position, causing ports
(P1, P2) and ports (T1, T2) to close and holding the pressure in ports (A1, A2).
Full braking position Full braking position
When pedal is fully actuated, end position of the brakes is reached and a connection established
between accumulator ports (P1, P2) and brake cylinder ports (A1, A2). Returns (T1, T2) are
closed at this point.
When the braking process is ended, a connection is once again established between brake
cylinder ports (A1, A2) and return ports (T1, T2), closing accumulator ports (P1, P2).
The arrangement of spools in the valve ensures that even if one braking circuit fails the other
remains fully operational. This is achieved by means of the mechanical actuation of both spools
and requires slightly more pedal travel.
Failure of a circuit Failure of a circuit
In the event of the lower circuit failing, the upper circuit will remain operational. Spring assembly
(21) will mechanically actuate spool. In the event of the upper circuit failing, the lower circuit will
remain operational since the lower spool (8) is mechanically actuated by spring assembly (21)
and spool (11).
Installation requirements Installation requirements
Return lines (T1, T2) must be connected directly to the tank.
The connecting lines must be installed is such a way as to permit proper bleeding.
(1) (1)
(2) 2)
(3 (3)
(4 (4)
(5) (5)
(6) (6)