BENDIX BW1625 User Manual download pdf

SD-03-953

Bendix

LQ-5

™

Bobtail Ratio Valve

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.)

OPERATION

GENERAL

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.

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

™

valve delivery and the brake

chambers.

IMPORTANT: Do not replace the BP-1

™

front brake pro-

portioning valve with the LQ-5

™

valve. The LQ-5

™

valve

will not function properly in the BP-1

™

valve system.

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.

FIGURE 1 - LQ-5

™

BOBTAIL RATIO VALVE

3/8 P.T.

SUPPLY PORT

1/8 P.T.

CONTROL PORT

1.5"

.340”

MOUNTING

HOLES (2)

STAMPED LQ-5

REPLACEMENT

PC. NO.

3/8 P.T.

DELIVERY PORT

1 2 3 4 5 6 7 8

Summary of Contents

Page 1 - Bobtail Ratio Valve

1®SD-03-953Bendix® LQ-5™ Bobtail Ratio ValveAlthough it is not mandatory, the LQ-5™ valve is used inconjunction with the BP-R1™ bobtail brake proporti

Page 2 - TRACTOR-TRAILER MODE

2TRACTOR-TRAILER MODEBrake Application—LQ-5™ Valve LimitingDuring tractor-trailer operation, the trailer supply valve (redoctagonal button) is depress

Page 3 - VALVE HOLDING

3BALANCED BRAKE VALVE APPLICATION - LQ-5™VALVE HOLDINGThe forces acting on the proportioning piston are equal whenair pressure beneath the piston is a

Page 4 - BOBTAIL MODE

4FIGURE 8 - LQ-5™ BOBTAIL RATIO VALVE MODEFIGURE 7 - LQ-5™ BOBTAIL RATIO VALVE BLENDINGBACK: TRACTOR-TRAILER MODEBRAKE APPLICATION—LQ-5™ VALVEBLENDIN

Page 5 - LEAKAGE TEST

5bobtail mode. Upon brake valve release, delivery air pressureflows back through the LQ-5™ valve, to the brake valve andout to atmosphere. Air from th

Page 6 - DISASSEMBLY

62. Make and hold a full brake application and apply a soapsolution to the exhaust port and around the cover whereit joins the body. The leakage shoul

Page 7 - ASSEMBLY

75. Make certain all air channels are clear and free ofobstruction.6. Inspect all pipe threads and make sure they are cleanand free of thread sealant.

Page 8