BENDIX LQ-5 BOBTAIL RATIO VALVE Manual

®
® ™
Bendix LQ-5 Bobtail Ratio Valve
SUPPLY PORT
1/8 P.T.
CONTROL PORT
3/8 P.T.
DELIVERY PORT
FIGURE 1 - LQ-5 ™ BOBTAIL RATIO VALVE

DESCRIPTION

™
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
chambers.
IMPORTANT: Do not replace the BP-1
portioning valve with the LQ-5
will not function properly in the BP-1
Caution: The LQ-5 ™ valve can replace the LQ-4
™
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.
™
valve delivery and the brake
™ front brake pro-
™
valve. The LQ-5
™ valve system.
™ ratio valve
1.5"
Although it is not mandatory, the LQ-5
conjunction with the BP-R1
valve, only when a customer specifies a front axle ratio valve.
™
The BP-R1
stopping distance and improve tractor control in bobtail mode.
(For more information on the BP-R1

OPERATION

GENERAL
™
valve
After an initial delivery, the LQ-5
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.
.340"
MOUNTING
HOLES (2)
STAMPED LQ-5
REPLACEMENT
PC. NO.
™
bobtail brake proportioning relay
™
valve and LQ-5 valve combine to reduce
™
valve, see SD-03-1067.)
™
valve limits front axle brake
™
valve is used in
™
1