Bendix Commercial Vehicle Systems AH-1B AIR HYD INTENSIFIER 4/04 User Manual

®

Bendix® AH-1B™ Air Hydraulic Intensifier

ELECTRICAL FLUID

LEVEL INDICATOR

CONNECTION

RESERVOIR

CAP

BRAKE FLUID

DELIVERY PORT

MASTER

CYLINDER

SD-11-1326

BRAKE FLUID

RESERVOIR

AIR
INLET
PORT

ACTUATOR

MOUNTING

BRACKET

NON-PRESS

PLATE

CLAMP RING

AIR INLET

PRESSURE

PLATE

DIAPHRAGM

PUSH ROD

FIGURE 1

RETURN

SPRING

BOOT

O-RING

DRAIN HOLE

DESCRIPTION

The AH-1B™ air hydraulic intensifier is a hydraulic brake,
power booster which utilizes compressed air for its power
assist. Its function is to convert air pressure to hydraulic
pressure for use in the brake system.

The AH-1B™ intensifier consists of three major component
groups; a specially designed type 30 air actuator is bolted
to a single piston master cylinder which incorporates an

ELECTRICAL

CONNECTOR

SEAL

PISTON

MOUNTING

BRACKET

INDICATOR

SWITCH

FILLER CAP

ASSY.

RESERVOIR

FLOAT

COMPENSATING

VALVE

HYD.

DELIVERY

PORT

RETURN

SPRING

PISTON

ACTUATOR

LIP

integral brake fluid reservoir. A bracket installed between the
actuator and master cylinder provides a means for mounting.

A float actuated, low fluid level, on/off electrical switch is
incorporated in the reservoir filler cap assembly. A two
“prong” connector is provided to permit the installation of a
vehicle electrical cable assembly . Switch actuation occurs
when the reservoir fluid level drops below the “minimum”
level marking on the reservoir.

1

HYDRAULIC

PUSH-PULL VALVE

DISC BRAKE

™

AIR OVER

AH-1B

HYDRAULIC

INTENSIFIER

BRAKE

VALVE

AIR DRYER

RESERVOIR

COMPRESSOR

FIGURE 2 - TYPICAL AH-1B™ AIR HYDRAULIC INTENSIFIER SYSTEM

SPRING BRAKE

ACTUATOR

RELAY
VALVE

AIR APPLIED

POSITION

DIAPHRAGM

APPLIED

POSITION

COMPENSATING

TILT VALVE SEALED

HYDRAULIC FLUID
BEING DELIVERED

PISTON APPLIED

POSITION

RETURN

SPRING

COMPRESSED

FIGURE 3 - CUTA WA Y VIEW OF APPLIED POSITION

2

AIR INLET

NON-APPLIED POSITION

DIAPHRAGM

NON-APPLIED POSITION

COMPENSATING TILT

VALVE UNSEALED

POSITION

HYDRAULIC

FLUID PORT

PISTON

NON-APPLIED

POSITION

RETURN SPRING

NON-APPLIED POSITION

FIGURE 4 - CUT AW A Y 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

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.

3