Figure 30Test Connections Multiple Trailers

Figure 28 - Brake Test Application Pressures

Figure 31 - Test Instrumentation (In-Cab)

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 Multiple Trailers The Pressure Balance and Pressure Build-up Rate Test also can be used for checking combination vehicles with multiple trailers. One duplex test gauge is installed as described in the test procedure to read brake pressures at the rearmost axles of the tractor and the first trailer. A second duplex test gauge is installed to read pressure at the dolly axle and the rearmost axle of the second trailer (Figure 30). Two additional air hoses may be required to make the gauge connections at the second trailer in order to keep both duplex gauges at one observation point. The test is then conducted as described, noting and recording the pressure differentials and build-up times obtained from the four sources - the rearmost axles of the tractor and first trailer, and the dolly axle and rearmost axle of the second trailer. Multiple-trailer combinations and their related complex- ity make it difficult to establish positive criteria. However, meeting the following guidelines should help optimize performance. For the pressure balance check, the average pressure difference between axles through the pressure range tested should fall within 28 kPa (4 psi) for optimum performance. For the pressure build-up rate check, the maximum pressure difference (lead or lag) between axles should normally be no greater than 103 kPa (15 psi) before the pressures equalize. Again, if the pressure balance and/or pressure build-up rate differences exceed the acceptable limit(s), refer to the Data Interpretation and Corrective Measures section. Torque Balance Test NOTE - If the pressure difference recorded for the pressure balance check exceeds the acceptable limit, the Imbalance must be corrected before a Torque Balance Test Is performed. However, if the pressure build-up rate indicates a problem condition, the Torque Balance Test can and should be conducted, especially if the operator’s basic concern Is that of uneven lining wear between tractor and trailer. Figure 30Test Connections Multiple Trailers CTS-4154Y - Page 31

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