789B Off-Highway Truck Air System and Brakes Caterpillar

(1) AUTO lube tank

(2) Air tank check valves

(3) Drain valves

(4) Primary air tank

(5) Starter relay valve

(6) Attachment shutters for the left cylinder and for the right cylinder

(7) Attachment inversion valve

(8) Solenoid valve for attachment shutters

(9) Air relief valve for primary air reservoir

(10) Starter solenoid valve

(11) Air starting motor

(12) Brake air relay valve

(13) Brake air relay valve for the Automatic Retarder Control (ARC)

(14) Air compressor with air compressor governor

(15) Air dryer with an air relief valve

(16) External air supply

(17) Double check valves

(18) Parking and secondary brake valve

(19) Torque converter and front brake cooling diverter valve

(20) Brake master cylinder (front)

(21) Brake master cylinders (rear)

(22) Air suspension seat

(23) Solenoid valve for AUTO lube

(24) Air system pressure protection valve

(25) Service brake air control valve

(26) Window wiper motor

(27) Window wiper air control valve

(28) Retarder air control valve

(29) Secondary brake air control valve

(30) Parking brake air control valve

(31) Secondary air tank

(32) Air horn

(33) Automatic Retarder Control (ARC) valve

(34) Horn valve

(35) Cab wall

(40) Brake air system pressure protection valve

(A) This is the brake air pressure sensor. The brake air pressure sensor monitors brake air pressure. The operator will be alerted to a condition of low air pressure.

(B) This is the secondary brake and parking brake pressure switch. This pressure switch is normally open. The pressure switch is closed by air pressure when the parking brakes or secondary brakes are released. When this pressure switch is open, this pressure switch signals the Electronic Programmable Transmission Control (EPTC II) to allow rapid shifts.

(C) This is the brake cylinder overstroke limit switch (overstroke switch). The overstroke switch is normally closed. The overstroke switch opens when the pistons in the master cylinder travel too far. A brake overstroke condition can result from low brake fluid level, air in the brake hydraulic circuit, leakage in the brake hydraulic lines, and master cylinder piston seal leaks. An indicator will come on in the cab and the alarm will sound. Do not operate the machine until the cause for the overstroke has been corrected.

(D) This is the Traction Control System (TCS) pressure switch. This pressure switch is normally closed. This pressure switch is opened by air pressure when the service brakes are applied. When this pressure switch is open, this switch turns off the TCS.

(E) This is the service brake and retarder pressure switch. This pressure switch is normally closed. This pressure switch is opened by air pressure when the service brakes are applied. When this pressure switch is open, the pressure switch signals the Electronic Programmable Transmission Control (EPTC II) in order to allow the transmission to perform rapid shifts. The EPTC II also indicates that higher engine rpm is needed for upshifts or for downshifts of the transmission when this pressure switch is open.

(F) This is the stop lights pressure switch. This pressure switch is normally open. This pressure switch is closed by air pressure when the service brakes are applied. When this pressure switch is closed, this pressure switch activates the stop lights.

(G) This is the Automatic Retarder Control pressure switch. This pressure switch is normally closed. This pressure switch is opened by air pressure in order to indicate that the Automatic Retarder Control (ARC) is operating. The pressure switch verifies that air pressure is being provided through the Automatic Retarder Control valve.