BENDIX AH-1B Manual - Page 3

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AIR INLET

NON-APPLIED POSITION

FIGURE 4 - CUTAWAY VIEW OF RELEASED POSITION

OPERATION

Brakes Applied

During a brake application, modulated air pressure from the

foot operated air brake valve enters the actuator inlet port.

Air pressure acting upon the area of the actuator diaphragm

causes the diaphragm and push rod assembly to move

toward the master cylinder. The actuator push rod forces

the master cylinder piston to move within its bore. Initial

forward travel of the piston moves the actuating lip of the

piston away from the stem of the compensating (tilt) valve

allowing it to close due to spring force. (Refer to Figure 2 &

3.) Closure of the compensating valve shuts off the fluid

passage between the cylinder bore and fluid reservoir which

allows hydraulic pressure to build and the brakes to apply.

The amount of hydraulic pressure generated is dependent

upon the air pressure applied to the air actuator.

Brakes Released

When air pressure is exhausted from the actuator the push

rod returns to the released position due to spring force.

With the push rod load removed, fluid pressure combined

with return spring force causes the piston to return to the

brakes released position. The actuator lip of the piston

contacts the stem of the compensating valve and unseats

DIAPHRAGM

NON-APPLIED POSITION

RETURN SPRING

NON-APPLIED POSITION

PISTON

NON-APPLIED

POSITION

the valve as the piston returns. When the compensating

valve opens, the passage between the fluid reservoir and

master cylinder bore is also open. Any excess fluid

remaining at the end of the stroke due to "pumping" and/or

volume change due to temperature fluctuation is transmitted

back to the fluid reservoir as the compensating valve opens.

The push rod is used as the piston stop in the fully released

position. (Refer to Figure 4).

Fluid Level Indicator

The reservoir fluid level is reduced as the brake linings wear

due to an increase of fluid volume required in the hydraulic

brake system. The float contained in the reservoir filter cap

assembly is suspended in the reservoir fluid and responds

to changes in the fluid level. As long as the reservoir fluid

level is adequate, a metal contact plate on top of the float

stem is held away from two electrical contacts. When the

reservoir fluid level drops below the "MINIMUM" fluid level

mark on the reservoir, the contact plate on the float stem

will move and complete the electrical circuit through the

switch.

COMPENSATING TILT

VALVE UNSEALED

POSITION

HYDRAULIC

FLUID PORT