BENDIX BW1625 Manuel D’Utilisation

®

Although it is not mandatory, the LQ-5

™

 valve is used in

conjunction with the BP-R1

™

 bobtail brake proportioning relay

valve, only when a customer specifies a front axle ratio valve.
The BP-R1

™

 valve and LQ-5

™

 valve combine to reduce

stopping distance and improve tractor control in bobtail mode.
(For more information on the BP-R1

™

 valve, see SD-03-1067.)

After an initial delivery, the LQ-5

™

 valve limits front axle brake

pressure during normal tractor-trailer operation. The LQ-5

™

valve has two spring-loaded pistons: a blend back piston
and a proportioning piston. The “stepped” proportioning piston
determines actual air pressure reduction and the blend back
piston allows the valve’s delivery pressure to “blend back”
and reach a 1:1 ratio during high pressure brake applications.

The LQ-5

™

 bobtail ratio valve is used on the front (steering)

axle of tractor air brake systems to reduce brake applica-
tion pressure during normal tractor-trailer operation. It is
designed for tractor systems only and replaces the existing
front axle limiting valve. It is not to be used on straight trucks
or towing trucks. Also, a quick release valve must be in-
stalled between the LQ-5

™

 valve delivery and the brake

chambers.

Caution: The LQ-5

™

 valve can replace the LQ-4

™

 ratio valve

on tractors. The LQ-5

™

 valve control port must be connected

to the trailer supply line. When the tractor is disconnected
from the trailer, bobtail tractor braking performance is improved
because full brake valve pressure will be applied to the
steering axle brakes.

3/8 P.T.

SUPPLY PORT

1/8 P.T.

CONTROL PORT

.340”

MOUNTING

HOLES (2)

STAMPED LQ-5

REPLACEMENT

PC. NO.

3/8 P.T.

DELIVERY PORT