AIR BRAKES - GENERAL INFORMATION - cont

AIR BRAKES - GENERAL INFORMATION - cont - TM-5-3820-256-24-4_103

OPERATIONAL CHECKS OF SPLIT AIR BRAKE SYSTEM

TM-5-3820-256-24-4 Drilling System Well Rotary Truck Mounted Air Transportable 600 Feet Capacity Model LP-12 NSN 3820-01-246-4276 Manual
Page Navigation
62

AIR BRACKERS-GENERAL INFORMATION Figure 21 - Power Divider Lock Air Shift Control With Separate Spring Brake and Tractor Protection Control Valves BRAKE AIR PRESSURE DISTRIBUTION VALVE Prior to the introduction of FMVSS 121 (March, 1975), front wheel limiting valves could be used on trucks and buses with air brakes. This would permit full brake valve delivery pressure to front wheel brakes when operating on dry roads, or at the option of the operator, reduce the pressure delivered to the front wheel brakes by 50% when operating on wet or slippery roads. Since the introduction of FMVSS 121, Federal Highway Administration, Department of Transportation, Subchapter B, Federal Motor Carrier Safety Regulation states that, "Manually operated devices to reduce or remove the front wheel braking effort must not be installed in a bus, truck or truck-tractor manufactured after February 28, 1975." The regulation, however, does permit an automatic type device to reduce front wheel braking up to 50% of normal braking with certain specific limitations. It should be noted that this is a constant function and is not controllable by the driver. There is a valve made available (code 04567) for special requests. It, however, is not a true front wheel limiting valve but a brake air pressure distribution valve. This valve only limits full front wheel braking during light brake applications regardless of road conditions. However, in a hard or panic brake application, the driver obtains full front wheel braking (full braking potential). Figure 22 - Power Divider Lock Air Shift Control With Modular Control Valve For Spring Brakes and Tractor Protection Control Valve There are other considerations which one should be aware of with the installation of the air pressure distribution valve. They are: Increased Rear Axle Brake Wear The vehicle’s brake wear balance, as designed, Is equal on front and rear brakes. During normal brake stops with the installation of an air pressure distribution valve, air pressure to front axle brakes is half of that applied to rear brakes, resulting in abnormal wear of rear service brake linings. Glazing and Noise During continued light brake applications glazing, poor burnish and noise problems could increase. The air pressure distribution valve reduces front axle braking work by about half. CTS-4154Y - Page 19

Privacy Statement
Press Release
Contact