Operating Instructions - Section 30 03/13 OM3040 Page 30-14 SUDDEN LOSS OF ENGINE POWER If the engine suddenly stops operating, stored hydraulic pressure in the brake and steering accumu- lators enables temporary operation of the steering and brake functions. Accumulator oil supply is lim- ited, however, so it is important to stop the truck as quickly and safely as possible after the loss of engine power. When pressures drop to a pre-determined level, the "low brake pressure" and “low steering pressure” warning lights will illuminate and a buzzer will sound.
If the brake pressure continues to decrease, the "auto-apply" feature will activate and the service brakes will apply automatically to stop the truck. DISABLED TRUCK DUMPING Sometimes it is necessary to dump a load from the body of a disabled truck when the hoist system is inoperable. The following instructions describe the use of a "good" truck to provide the hydraulic power required to raise the body of a "disabled" truck to dump the load. Figure 30-4 shows the quick disconnect fittings on a hoist manifold for connecting the hoist circuits between trucks. Hookup Be certain there is an adequate, clear area to dump the loaded dump body.
Bring the truck to a safe stop as quickly as possible by using the foot pedal to apply the service brakes. If possible, steer the truck to the side of the road during braking. Apply the parking brake as soon as the truck comes to a complete stop. Turn the key switch OFF and notify maintenance personnel, immediately. 1. Safely park the good truck as close as possible to the disabled truck. When the good truck is in position next to the disabled truck, shut off the engine. If the truck becomes disabled in a high-traffic area, mark the truck with warning flags during daylight hours, and flares at night. 2.
Bleed pressure from the brake accumulators, steering accumulators, and hydraulic tanks on each truck. 3. Attach a hose from the power up quick discon- nect on the good truck to the power down circuit on the disabled truck. (Hoses must be rated to withstand 19 305 kPa (2800 psi) or greater pressure. Emergency Steering And Braking The steering and brake systems each have accumu- lators that store energy and provide capability to steer and stop the truck in the event of an unex- pected engine shutdown or pump failure. NOTE: The power down circuit uses a smaller diameter hose (tube) than the power up circuit.
As part of the routine maintenance of the vehicle, one requirement to ensure proper operation of each system is to maintain proper accumulator nitrogen pre-charge. Refer to the shop manual for proper pro- cedures when charging the accumulators. 4. Connect another hose from the power down quick disconnect on the good truck to the power up circuit on the disabled truck. Raising the Body Audible and visual warnings will alert the operator if accumulator pressures drop below the preset values during operation. 5. Move the hoist control lever on the disabled truck to the HOLD position. Leave the lever in this position during the entire procedure. 6.
Adjust the power down relief setting on the good truck to the maximum setting. On HD1500-5 trucks, the power down relief valve (1, Figure 30- 4) is located on pilot valve (2) which is inside of the brake cabinet on the lower RH side. Gently, turn the adjustment screw clockwise, until it bottoms out. (Count the exact number of turns that the adjustment screw is turned, and note for later adjustment.) 7. Start the engine on the good truck, and adjust the engine speed to 1000 rpm.