User manual BENDIX LQ-3 LQ-4 FRONT AXLE RATIO VALVE

[. . . ] An example would be: 65 psi delivered to the supply port results in 65 psi out the LQ delivery port. 1 SD-03-951 E-6TM/E-7TM BRAKE VALVE BRAKE CHAMBER BRAKE CHAMBER LQ-3TM VALVE TEE LQ-4TM VALVE E-6TM/E-7TM BRAKE VALVE MODULATOR OR RELAY VALVE BRAKE CHAMBER RESERVOIR BRAKE CHAMBER RESERVOIR TYPICAL LQ-3TM FRONT AXLE RATIO VALVE INSTALLATION FIGURE 2 - TYPICAL INSTALLATIONS TYPICAL LQ-4TM FRONT AXLE RATIO VALVE INSTALLATION SUPPLY Note: The pressures used here are examples only. Both the LQ-3TM and LQ-4TM valves may have been supplied with initial hold-off pressures of either 4 psi or 10 psi and equalization pressures of 60 or 65 psi respectively depending upon the vehicle installation and manufacturer's specification. The LQ-3TM valve hold-off pressure depends on the inlet-exhaust valve spring installed. The LQ-4TM valve by whether or not a hold-off spring is installed under the lower piston. OUTER PISTON OUTER PISTON RETURN SPRING INNER PISTON INLET & EXHAUST VALVE RETURN SPRING INLET & EXHAUST VALVE OPERATION -- BRAKE APPLICATION OF 40 PSI OR LESS When a service brake application of less than 40 psi is made, application air enters the LQ valve supply port and exerts a force over the surfaces of the outer and inner pistons. [. . . ] (See Figure 5. ) The delivery volume air exhausts both through the brake valve and out the exhaust port. SUPPLY OUTER PISTON OUTER PISTON RETURN SPRING INNER PISTON OPERATION -- SERVICE BRAKE APPLICATION 40 PSI OR GREATER When a service brake application of greater than 40 psi is made, air entering the supply port forces the outer piston into contact with the inner piston against the resistance of the outer piston return spring. Because of the added surface area of the outer piston, delivery pressure from the LQ valve will DELIVERY EXHAUST INLET & EXHAUST VALVE RETURN SPRING INLET & EXHAUST VALVE FIGURE 6 - LQ-3TM FRONT AXLE RATIO VALVE* BRAKE VALVE APPLICATION AT 60 PSI OR GREATER. The 50% reduction will occur while supply line pressure is between 0 and 40 psi. COVER (1) 4. When the supply line pressure exceeds 40 psi, but is below 60 psi, observe that the delivery line pressure is no longer one half and that the delivery line pressure is "catching up" to supply pressure. When supply pressure exceeds 60 psi note that the delivery line pressure is approximately equal. O-RING (6) INNER PISTON SPRING (9) OUTER PISTON (4) O-RING (7) Note: The pressures stated here are examples only. Various piece numbers of the LQ valves may have different pressure settings. For information on a specific installation, consult the vehicle handbook. LEAKAGE CHECKS OUTER PISTON SPRING (5) INLET EXHAUST VALVES (10) O-RING (8) INNER PISTON (3) BODY (2) HOLD OFF SPRING (11) Make and hold a service brake application. Apply a soap solution to the exhaust port and around the seam between the cover and the body. If the LQ valve does not function as described above or leakage is excessive, it is recommended that it be returned to the nearest Bendix authorized outlet for a factory remanufactured valve under the Exchange Plan. If this is not possible, the valve can be repaired with genuine Bendix parts, in which case the following should prove helpful. Note: Maintenance kits for the LQ-3TM and LQ-4TM front axle ratio valves are available from any authorized Bendix outlet. FIGURE 7 - LQ-4TM FRONT AXLE RATIO VALVE PREVENTIVE MAINTENANCE Important: Review the Bendix Warranty Policy before performing any intrusive maintenance procedures. A warranty may be voided if intrusive maintenance is performed during the warranty period. No two vehicles operate under identical conditions, as a result, maintenance intervals may vary. Experience is a valuable guide in determining the best maintenance interval for air brake system components. At a minimum, the valve should be inspected every 6 months or 1500 operating hours, whichever comes first, for proper operation. Should the valve not meet the elements of the operational tests noted in this document, further investigation and service of the valve may be required. REMOVAL Apply the vehicle parking brakes. Identify and disconnect the supply and delivery lines of the LQ valve. Remove the two mounting bolts securing the LQ valve to the vehicle. DISASSEMBLY 1. Prior to removing the four Phillips head screws and their lockwashers which secure the cover to the body, mark the relationship between the cover and the body. Carefully separate the cover (1) (Figure 7) from the body (2) and remove the inner (3) and outer pistons (4). (The cover is under approximately 30 pound load from the outer piston spring. ) 3. Remove the large (8) and small (7) diameter o-ring from the inner piston. [. . . ] 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. 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. 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. [. . . ]