BENDIX BW2598 Scheda Tecnica

The pressure 

under the piston 

equals the 

pressure above.  

The piston lifts 

slightly  - the 

exhaust remains 

closed.

The driver 

releases the 

brakes. The 

piston in the relay 

valve moves 

up, closing the 

delivery, and 

opening the 

exhaust. 

See Figure 5.  When the driver releases the brake pedal, air 
pressure above the relay piston is exhausted at the brake 
valve exhaust.  At the same time, air pressure beneath the 
piston lifts the relay piston and the exhaust seat moves 
away from the exhaust valve, opening the exhaust passage 
at the base of the relay valve.  With the exhaust passage 
open, the air pressure from the brake chambers passes 
to the Antilock Modulator Valve exhaust port, releasing the 
brakes, and air pressure between the relay valve and the 
modulator is released at the relay valve exhaust port.

The ABS Controller monitors the driver’s accelerator 
application, as well as the vehicle’s motion using wheel 
speed sensors.  When the vehicle is stopped, or moving 
at any speed up to 25 mph and the Controller detects 
wheel spin, for example where one wheel is slipping on 
an icy patch, the ABS Controller will intervene to assist the 
vehicle’s traction.  

The ABS Controller obtains braking power for the traction 
intervention by energizing the Control Solenoid in the 
ATR-6

™

 valve.  This causes the traction piston to move to 

its secondary position, allowing the supply air to operate the 
relay piston and supply air pressure to each of its Antilock 
Modulator Valves as shown in Figure 6.

The Controller then operates (opens and closes) the 
solenoid valves in the individual Antilock Modulator Valve 
for each spinning (slipping) wheel to slow that wheel.  As the 

The small piston moves to its energized 

position. The arrow indicates the direction 

it moves. The antilock traction Controller 

energizes the solenoid, applying  full reservoir 

pressure to the antilock modulators.

The Controller 

selects the 

antilock 

modulator to 

deliver air to the 

brake chamber

spinning wheel slows down, it forces the vehicle differential 
to drive the other stationary, or slowly-turning wheel on that 
axle, aiding the vehicle in gaining traction.  Note: in some 
vehicle arrangements a single modulator valve may control 
air delivery to more than one brake chamber.