Usage:
NOTE: This article has specific information and recommendations for prevention of fires on hydraulic excavators. However, many of the recommendations apply to all machines and engines, and can be used by all personnel performing repairs, lubrication, maintenance, or inspection of machines.
During the past few years, Caterpillar has received reports of fires on excavators (and other machines). Normally, it is not possible to determine the exact cause of a fire on an excavator that has destroyed the hydraulic hoses, fuel line, and electrical wires. This article summarizes information observed from several on-site inspections of excavators. We urge you to discuss with users the need for good house-keeping, cleanliness, and maintenance of all excavators to prevent fires or reduce the damage if a fire does occur. Your main theme should be fire prevention resulting from cleanliness and scheduled maintenance.
Keep The Machine Clean
Excavators working in forests, road construction, and housing developments are more apt to accumulate debris than those working in open areas. Nothing burns faster than oil soaked pine needles, leaves, and twigs. See Illustration 1. Users of excavators in these environments must spend more time on cleanliness, and even minor leaks or electrical malfunctions should be fixed as soon as possible.
Preventing Hydraulic Hose Inteference
High pressure or low pressure hoses can rub sheet metal, firewalls, frame members and posts, as well as other hoses and tubes. Why?
Illustration 1. Trash and rags create a potential hazard.
... If the clamps are missing, loose or improperly positioned, this can allow a hose to move and wear everytime it is pressurized.
... Field-fabricated hoses with stems or elbows installed at wrong angle.
... Sometimes hoses are not installed or routed correctly after field repairs.
Hose interference can sometimes be corrected by loosening the flanges or fittings and turning the hose slightly, or repositioning the clamps. When new hoses are installed, be sure they are routed the same way as the old hoses. Start the excavator and operate it in all positions and cycles to see if interference occurs, particularly during pressure surges. See Illustration 2.
Illustration 2. A hose rubbing the clamshell attachment.
Illustration 3. A missing clamp may allow vibration to wear a hole in these tubes.
Illustration 4. Damage in these areas can force the hydraulic tank and hydraulic lines out of alignment.
Some excavators are equipped with other manufacturers' auxiliary equipment, such as hydraulic hammers, grapples, mowers, and logging attachments. The additional hydraulic lines must be properly routed and clamped to prevent interference. You should make the user aware of good installation practices where you do not perform the installation.
Keep Hydraulic Tubes Tight And In Alignment
Loose tube clamps causes wear and eventually leaks.
A few tubes were observed where the flange had been welded or brazed to the tube because the joint had loosened and leaked. If a joint leaks, find and correct the cause to prevent a subsequent failure.
All tubes flex a small amount due to pressure fluctuations and they are designed to withstand this without being overstressed. This is accomplished by swedging the flange around the end of the tube. However, if the joint is prestressed too much because the tube is not aligned when installed on the machine, the additional stresses from pressure fluctuations can cause the joint to fail. Thus, when a tube is installed, be sure both ends are correctly aligned and tightened before any clamps are tightened.
Correct alignment of the flanges may be difficult if the tube has been bent or if the components connected to the tube have been forced out of alignment. Remember to install all clamps. See Illustration 3.
Component Misalignment
Excavators working around trees or large rocks sometimes have damage to the outside of the house, particularly the right rear corner. Illustration 4 shows typical minor damage. Sometimes the blow is severe enough to bend the outer channel and the hydraulic tank outrigger of the upper frame. Such damage also can bend the posts supporting the walls and sheet metal, as well as clamps and tubes. Evidence of this damage requires a thorough inspection for leaks and hose and tube interference.
Illustration 5. Former return lines to tank.
On early 225 Excavators such damage can cause misalignment with the suction tubes (2 per pump) between the pumps and the tank. Also, misalignment can exist in the return tubes/hose connection between the oil cooler bypass housing (on filter) and the tank. Illustration 5. When any of these tubes are misaligned, the connecting hose is overstressed. These suction tubes and return tubes have been replaced by XT-3 hoses less sensitive to misalignment. The Service Magazines of November 4, 1974 and October 16, 1978 give you retrofit details for the suction lines and return lines, respectively.
A 160 mm (6.3") length of hose connects the two former return tubes between the oil filter and tank. This short hose, particularly if oil soaked is more easily damaged by fire than the new XT-3 hose. If the hose is damaged by fire, oil flows to the ground and fuels the fire. The new parts listed in the October 16, 1978 Service Magazine should be installed whenever convenient. Do not use the 5P1260 Bulk Hose in this application.
Maintenance Of Electrical Wires And Harness
Check wires and harness for worn insulation. Worn insulation causes a short circuit when the bare wire touches the steel tubes or frame, and increases the chances of fires. Illustration 6. Keep all clips tight, and replace any that are missing. Replace or tape securely all worn or damaged harnesses.
Pay particular attention to the wiring harness and cables that go through sheet metal openings. Inspect batteries to assure that the battery retainers are in place and tightened, and that the batteries and compartment are clean.
Illustration 6. Check wiring and cables for worn areas.
Keep Fuel Lines Tight And Check For Wear
It is always a good practice to periodically inspect fuel lines. Tighten leaky fittings and look for signs of wear or interference with tubes or hoses. If a steel fuel line is replaced, be sure to use a new steel line.
Illustration 7. Casual inspections inside the house can help detect early leaks and accumulation of trash.
Summary
Several changes have been made to excavators since first production to reduce hydraulic leaks, improve wiring harness protection, and provide better insulation around the muffler and engine compartment. Specific suggestions regarding further improvements are always considered. It is very important that all fires, no matter how small, are reported to Service Engineering. Use Incident Report Form No. 01-735-82918. A knowledge of minor fires often enables Caterpillar to determine the specific cause because the contributing factors have not been destroyed.
When dealer service people visit an excavator, they should take a few minutes to open the house doors for a minor visual inspection inside the machine. Observe and note any suspect problems and discuss them with user personnel.
We recommend that users and operators, for their own safety and for maximum service life of the excavator, make a thorough walk-around inspection and check under and around the excavator for such items as loose or missing bolts, trash buildup, oil, fuel, and coolant leaks before starting the engine. Most accidents, no matter where they occur, are caused by someone's failure to observe and follow simple and fundamental rules or precautions.