Figure 28 - Brake Test Application Pressures

Figure 26 - Test Connectlon8 - Single Trailer

Figure 30Test Connections Multiple Trailers

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
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AIR BRAKES - GENERAL INFORMATION respectively, as shown in Figure 28. As each pressure increment is reached at the tractor’s rearmost axle, note and record the pressure reading for the trailer’s rearmost axle. Repeat this step three times. IMPORTANT - When applying the brakes, air pressure must be Increased steadily and maintained at each step. Any slight decrease In pressure will affect the accuracy of the gauge readings and must be avoided. Note and record the pressure only after all gauge recordings are stabilized. Figure 27 - Test Gauge Hose Connection (At Service Brake Chamber) Figure 28 - Brake Test Application Pressures Under normal conditions, the average pressure vari-ance between axles through the pressure range as test-ed should not exceed 28 kPa (4 psi) for optimum performance. (See Data Interpretation and Corrective Measures.) 4. Check pressure build-up rate as follows: While observing the duplex gauge, apply the service brake control moderately to at least 207 kPa (30 psi). The moderate rate of application should simulate that used in day-to-day braking under normal operating conditions. Observe and record the pressure difference between the hands on the test gauge dial (Figure 29). The dual pressure readings give an indication of the timing difference between the axles. If the pressure build-up in the trailer brakes leads the tractor brakes, the gauge reading should be recorded as a positive (+) number. If the pressure build-up lags, the reading should be re- corded as a negative (-) number. Release the service brakes. Repeat this step at least three times and record the average of the total readings. Figure 29 - Gauge Reading - Pressure Balance Check Initial pressure difference (lead or lag) between axles should normally be no greater than 69 kPa (10 psi) for single-trailer combinations before the pressures begin to equalize. NOTE - Since pressure lead and lag derived from using a duplex test gauge are estimates only, pressure build- up rate tests involving large fleets of vehicles can be performed more easily and accurately using pneumatic timing devices. These Instruments are available from electronic laboratories and air valve manufacturers. The above check, however, will provide an indication if slow pressure build-up rate Is a cause for compatibility complaints. 5. If pressure balance and/or pressure build-up rate differences between axles exceed the acceptable limitis1. refer to the Data Interpretation and Corrective Measures section. CTS-4154Y - Page 30

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