Brake Circuit; Service Brake Circuit Operation - Komatsu 830E Shop Manual

The 830E truck is equipped with hydraulic actuated
disc brakes. The front brakes have three calipers
applying braking effort to a single disc on each wheel.
The rear brakes have two (armature-speed) discs with
one caliper per disc. Each rear outboard disc also
contains a parking brake caliper.
The fundamental function of the brake system is to
provide an operator the control he needs to stop the
truck in either a slow modulating fashion or in as short
a distance as reasonably possible.
Outlined below are the functions that are necessary for
safe truck operation:
1. Warn the operator as soon as practical of a
serious or potentially serious loss of brake pres-
sure so proper action can be taken to stop the
truck before the secondary system is exhausted
of power.
2. Provide secondary brake circuits such that any
single failure leaves the truck with sufficient stop-
ping power.
3. Automatically apply service brakes if low pressure
warnings are ignored and pressures continue to
decrease.
4. Wheel brake lock to relieve the operator from
holding the brake pedal while at the dump or
shovel.
5. Spring applied park brake for holding, not stop-
ping, the truck during periods other than loading
or dumping.
6. Brake system that is easy to diagnose and per-
form necessary service.
The following brake circuit description should be used
in conjunction with the hydraulic brake system sche-
matic, refer to Section "R".
The brake system consists of two major valve compo-
nents; the dual circuit treadle valve (heart of the sys-
tem) and brake manifold. The dual circuit treadle valve
is the only component located in the operator's cab.
J02032

BRAKE CIRCUIT

The remainder of the system, including the brake
manifold, circuit accumulators, and electrical compo-
nents, are located in a weatherproof cabinet behind
the cab. This cabinet is accessible for diagnostic and
service work.
The brake manifold contains dual circuit isolation
check valves, accumulator bleed down valves, and
valves for brake lock, park brake and automatic apply
functions. All of these components are screw-in car-
tridge type valves.
In the 830E truck, there are two independent means
of brake actuation, the service brake pedal and brake
lock switch.

SERVICE BRAKE CIRCUIT OPERATION

This portion of the system provides the operator the
precise control he needs to modulate (feather) brake
pressure to slowly stop the truck or develop full brake
effort to stop as quickly as possible. The heart of this
circuit is the treadle operated dual circuit brake valve.
This valve enables the operator to control the relatively
high pressure energy within the brake accumulators
directly to the brakes. The only element between the
operators foot and the actual brake fluid is the dual
circuit treadle valve.
As the pedal is depressed, each valve within the dual
circuit treadle valve simultaneously delivers fluid from
its respective accumulator to the wheel brakes at a
pressure proportional to both pedal position and force.
The further the pedal is depressed, the higher the
brake force, giving a very positive feel of control.
Brake accumulators have two functions; storing en-
ergy for reserve braking in the event of a failure and,
provide rapid oil flow for good brake response. Depres-
sion of the brake pedal actuates the stop light pressure
switch, which in turn actuates stop and service brake
indicator lights and propulsion interlock. The stop light
switch (12, Figure 2-1) is located on the junction block
(10) inside the brake cabinet.
Brake Circuit J2-1