Bendix LQ-2 QUICK RELEASE VALVES User Manual

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Bendix® LQ-2™ Limiting & Quick Release Valve and TW-1™ Control Valve

SUPPLY PORT

(FROM BRAKE VALVE)

SD-03-950

FIGURE 1

CUT-OUT VALVE

PORT

(FROM

TWO-WAY

VALVE)

EXHAUST

PORT

INLET
VALVE

STEM

GASKET

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LQ-2

LIMITING & QUICK

RELEASE VALVE

DELIVERY PORT

(TO BRAKE CHAMBER)

PISTON

O-RINGS(2)

SPRING

GUIDE

EXHAUST

VALVE

COVER

DELIVERY PORT (TO
LIMITING AND QUICK

RELEASE VALVE)

(FROM BRAKE

PLUNGER RETURN

SPRING

INLET VALVE

SPRING

SEAL RING

INLET PORT

VALVE)

TW-1™ CONTROL VALVE

LEVER

DIAL

EXHAUST

PORT

PLUNGER

INLET & EXHAUST

VALVE

FIGURE 2

DESCRIPTION

LQ-2™ LIMITING & QUICK RELEASE V AL VE

The Bendix® LQ-2™ limiting and quick release valve is a dual
function valve; the valve serves to limit brake applications
and is generally used on the front or steering axle of a vehicle.

The LQ-2™ valve is controlled by a TW-1™ control valve, (see
Figure 2) which is mounted in the vehicle cab within reach of
the driver. Placing the control valve in the “Slippery Road”
position will reduce front axle service application pressure
by 50%. With the control valve in the “Dry Road” position,
there is no reduction of service application pressure. In
addition, the LQ-2™ valve serves a quick release function,
releasing air directly from the front axle chambers.

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OPERATION

Reference Figure 2, the LQ-2™ limiting and quick release
valve and the TW-1
application line: one connection is to the supply (top) port of
the limiting and quick release valve; the other is to the inlet
port of the two-way control valve. The delivery line from the
two-way control valve is connected to the cut-out valve (side)
port of the limiting and quick release valve.

DRY ROAD POSITION

With the handle of the TW-1
position, the valve is in the “on” position and air is permitted
to pass through the valve.

When a foot brake valve application is made, air flows through
the TW-1™ control valve and enters the side port of the limiting
and quick release valve. At the same time, air also enters
the top inlet port; thus pressure acts upon the top and side
areas of the piston, moving the piston down, seating the
exhaust valve, closing the exhaust port. At the same time
the inlet valve opens and air is delivered out the delivery
ports, to the chambers.

When the air pressure beneath the piston (and in the
delivery lines) equals the air pressure being delivered by
the foot valve, the piston raises slightly and closes the inlet
valve. When the foot valve application is released, the air
on the top and side areas of the piston is exhausted back
through the foot valve; air pressure beneath the piston raises
it, and the exhaust valve opens allowing the air in the delivery
lines to exhaust out the exhaust port.

SLIPPERY ROAD POSITION

With the handle of the TW-1™ control valve in the “Slippery
Road” position, the valve is in the “off” position; the inlet
valve is seated and the exhaust is open. In this position air
is not permitted to pass through the valve.

When a foot brake application is made, air enters only the
top inlet port. (Air does not enter the side inlet port because
the TW-1™ control valve is “off”.) Air pressure is effective
only on the upper inner area of the piston; the piston moves
down and the exhaust valve seats and the inlet valve opens.
Air pressure in the delivery line acts on the lower area of the
piston, which is about twice the size of the upper inner area
of the piston. Thus, when the pressure acting upon the lower
area is about half of the brake valve delivered pressure, the
piston lifts and closes the inlet valve. In this position, the air
pressure in the brake chambers is approximately 50% of
brake valve application pressure.

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control valve are connected to a service

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control valve in the “Dry Road”

WARNING! PLEASE READ AND FOLLOW
THESE INSTRUCTIONS TO AVOID
PERSONAL INJURY OR DEATH:

When working on or around a vehicle, the following
general precautions should be observed at all times.

1. Park the vehicle on a level surface, apply the
parking brakes, and always block the wheels.
Always wear safety glasses.

2. Stop the engine and remove ignition key when
working under or around the vehicle. When
working in the engine compartment, the engine
should be shut off and the ignition key should be
removed. Where circumstances require that the
engine be in operation, EXTREME CAUTION should
be used to prevent personal injury resulting from
contact with moving, rotating, leaking, heated or
electrically charged components.

3. Do not attempt to install, remove, disassemble or
assemble a component until you have read and
thoroughly understand the recommended
procedures. Use only the proper tools and observe
all precautions pertaining to use of those tools.

4. If the work is being performed on the vehicle’s air
brake system, or any auxiliary pressurized air
systems, make certain to drain the air pressure from
all reservoirs before beginning ANY work on the
vehicle. If the vehicle is equipped with an AD-IS
air dryer system or a dryer reservoir module, be
sure to drain the purge reservoir.

5. Following the vehicle manufacturer’s
recommended procedures, deactivate the electrical
system in a manner that safely removes all
electrical power from the vehicle.

6. Never exceed manufacturer’s recommended
pressures.

7. Never connect or disconnect a hose or line
containing pressure; it may whip. Never remove a
component or plug unless you are certain all
system pressure has been depleted.

8. Use only genuine Bendix® replacement parts,
components and kits. Replacement hardware,
tubing, hose, fittings, etc. must be of equivalent
size, type and strength as original equipment and
be designed specifically for such applications and
systems.

9. Components with stripped threads or damaged
parts should be replaced rather than repaired. Do
not attempt repairs requiring machining or welding
unless specifically stated and approved by the
vehicle and component manufacturer.

10. Prior to returning the vehicle to service, make
certain all components and systems are restored

to their proper operating condition.

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