794 AC Off-Highway Truck Systems Caterpillar

Illustration 1	g06412072
View of the location of the control manifold (brake)

Illustration 2	g06327011
(1) Port for the low front brake pressure switch (2) Check valve (3) Auto apply pressure switch port (4) Supply port for the brake pressure switch (5) Check valve (6) Port to brake supply accumulator pressure gauge (7) Port to park brake pressure gauge (8) Port for the park brake pressure switch (9) Port for the low rear brake pressure switch (10) Port to park brake supply (11) Brake valve return port (12) Pilot valve return port (13) Park brake solenoid valve (14) Brake accumulator drain solenoid (15) Load brake solenoid (16) Port to the load brake shuttle (17) Port to the service brake supply (18) Check valve (19) Port to the brake control valve "P2" (20) Port from the front brake accumulator (21) Port from the rear brake accumulator (22) Brake valve return port (23) Pressure reducing valve (24) Brake accumulator drain port (25) Port from the supply brake accumulator (26) Supply port (27) Brake accumulator drain solenoid (28) Port to the brake control valve "P1"

The brake manifold assembly is a ductile iron block valve with several external hose connections ports. The brake manifold assembly is mounted inside the hydraulic enclosure box. The brake manifold serves as a centralized assembly to provide the following provisions:

• Park brake solenoid valve - dual coil, latching type, electric solenoid valve that controls the flow of pressurized oil to the park brake system to allow the brakes to be applied or released.

• Load brake solenoid - electric solenoid valve cartridge that control the flow of pressurized oil to the load brake system to allow the rear service brakes to be applied or released.

• Brake accumulator drain solenoid - solenoid operated accumulator drains with manual override feature in the event of electric failure.

• Low brake pressure switch - electric switch assembly that monitors the system supply pressure (accumulator pressure) and causes a cab dash Low Brake Pressure indicator to light.

• Park brake pressure switch - electric switch assembly that monitors the park brake system pressure and causes a cab dash Park Brake indicator to light if the pressure decreases to a level at which the park brake calipers will apply.

• Auto apply pressure switch – electric switch assembly that monitors the brake system supply pressure and causes a cab dash auto apply solenoid to shift and automatically apply the trucks rear service brakes if the pressure decreases to the level that the park brakes will apply.

• Internal pressure reducing valve – a cartridge assembly installed in an internal port designed to limit the maximum pressure available to the park brake system.

Control Manifold (Brake) Ports

Illustration 3	g06326278

Illustration 4	g06326298

There are various ports on the manifold including:

• (AL) port - not used currently.

• Rear brake accumulator (RBA) port - outlet pressure to the rear brake accumulator.

• Supply brake accumulator (SBA) port - outlet pressure to the park brake accumulator and park brake relay valve.

• Pressure (P) port - inlet pressure from the steering manifold assembly.

• Test station supply (TSS) port - outlet pressure to the gauge monitoring the supply brake accumulator pressure.

• Front brake accumulator (FBA) port - outlet pressure to the front brake accumulator.

• Test station front (TSF) port - front brake accumulator pressure switch.

• Brake switch (BS) port - mounting port for the low supply brake pressure switch.

• Auto apply switch (AAS) port - mounting port for the auto apply pressure switch.

• Park brake (PB) port - pilot pressure out to actuate the park brake relay valve.

• Park brake switch (PBS) port - mounting port for the Park Brake Pressure switch.

• Test station park (TSP) port - outlet pressure to the gauge monitoring the park brake pressure.

• Brake valve front (BVF) port - outlet port to the front brake control section of the brake control valve.

• Pilot valve (PV) port - outlet pressure to the cab-mounted secondary pedal valve assembly.

• Load brake (LB) port - outlet pressure to the load brake shuttle valve and the load brake application system.

• Pilot valve tank (PVT) port - drain return from secondary pedal valve.

• Brake valve tank (BVT) port - drain return from proportional pilot solenoid valve.

• Brake return (BR) port - outlet port from the manifold assembly to the main hydraulic reservoir.

• Brake accumulator drain (BAD) port - outlet port from the manifold assembly accumulator drain solenoid valves to the main hydraulic reservoir..

• Auto apply (AA) port - plugged-not used.

• Test station rear (TSR) port - rear brake accumulator pressure switch.

• Brake valve rear (BVR) port - outlet port for the rear brake control section of the brake control valve.

• Pressurized hydraulic oil from the steering manifold assembly enters the brake manifold through the "P" port.

The pressurized oil is routed to the three brake accumulators. The accumulators are plumbed with check valves in the manifold to maintain independence between the front and rear brake systems. Normally closed solenoid valves with manual overrides will drain the front and rear brake accumulators when energized. The supply accumulator drains through either the front or rear drain system, depending upon release rates and pressures.

The low brake pressure switch monitors the pressure in the brake supply accumulator, which will be equal to the front or rear brake accumulators (whichever is lower). The low brake pressure switch causes a dash-mounted indicator to light when the pressure in this accumulator is less than 14480 kPa (2100 psi).

The load brake solenoid (controlled by a cab-mounted switch) controls the flow of oil to the load brake shuttle valve and then on to the rear service brakes.

The park brake solenoid valve provides pilot oil to the park brake relay valve to release or apply the 4-corner wet park brakes.

The pressure reducing valve limits the maximum park brake pressure feeding the park brake solenoid valve.