Usage:
OFF-HIGHWAY TRACTORS
ALL OFF-HIGHWAY TRUCKS AND TRACTORSProblem:
In 1980 Caterpillar began inflating tires with dry nitrogen gas on all machines shipped from its factories. Also, in that period, all Caterpillar Operation & Maintenance Manuals (OMM), and other product support documents were changed to instruct that tires on Caterpillar machines should be inflated and pressure-maintained with dry nitrogen gas. At least two (2) Caterpillar Service Magazine articles also addressed this issue. In the 20 years since these actions were taken, Caterpillar is unaware of any tire explosions occurring on tires inflated and pressure-maintained with dry nitrogen.
There are other, proven advantages to inflating and pressure-maintaining non-road tires with nitrogen. The source for the following list is tire maintenance manuals from various non-road tire manufacturers:
- * Offers improved tire pressure retention.
- * Reduces aging due to oxidation of the tire carcass and liner.
- * Minimizes rim rust.
- * There is less internal pressure variation in a tire as it goes from cold startup to its normal operating temperature.
- * Reduces aging due to oxidation of the tire carcass and liner.
Caterpillar's position is unchanged since 1980. Large off-road tires should be inflated and pressure-maintained with dry nitrogen gas. Please refer to the attached reprints of the aforementioned Caterpillar Service Magazine articles.
See also following Attachments -
October 8, 1979 Service Magazine
Warning: Excessive Heat Can Cause A Tire Explosion
4203
Earthmoving machine tires can, under certain special conditions, explode like dynamite. The explosion can expel the tire, rim assembly and other machine components for distances as far as 300 feet (91.4 m) or more from the machine. Both the force of the explosion and debris can cause personal injury or death, and property damage. Tire explosions are infrequent but due to the possible severity, all personnel should be made aware of the possibility and the actions to take to minimize the risk.
The danger of a tire explosion must be recognized as a distinct possibility whenever the smell of burning rubber or excessively hot brakes is detected. The danger is also pre-sent when a fire on the machine gets at the tire. Under such conditions, all personnel must avoid approaching the ma- chine in a manner that injury could result should an explosion actually occur. Move the machine to a remote area only if it can be done without endangering the operator or other personnel in the area. Remove all personnel from the area where the machine is located.
If it is absolutely necessary to approach a machine with a suspected tire, do not get closer than 15 feet (4.6 m) to the tire tread nor closer than 300 feet (91.4 m) directly in line with the tire. The following sketch illustrates the high risk areas to avoid when approaching the machine, although there is no absolutely safe approach.
Do not approach line within 300 ft. (91.4 m) from the side on within 15 ft (4.6 m) from the front, rear or above. 
APPROACH AREAS
Do not approach any tire on the machine if there is a brake fire, burning rubber or other indications that excessive heat was generated by the brakes on the machine. Brake-generated heat probably affects all other tires on the machine, even though the visual evidence is only at one tire.
A tire explosion is the result of excessive heat from any source (such as overheated brakes due to dragging or excessive usage, overloaded tires, machine fire, welding on tire rim with tire in place, etc.) causing auto-ignition of the gaseous mixture inside the tire. When a tire is exposed to excessive heat, the tire bead can burn due to heat transfer through the rim assembly. Deterioration of the rubber compounds in the tire bead by the heat can result in the release of a volatile gaseous mixture within the tire. Normally, the burnt bead causes loss of air and the tire goes flat without hazard to anyone in the vicinity. In a few rare instances, the gaseous mixture may reach auto-ignition temperature before the bead deteriorates sufficiently to cause tire deflation. The internal fire in the tire created by the auto-ignition of the gaseous mixture causes a very rapid increase in pressure, resulting in a violent tire explosion. The danger of a tire explosion is at its greatest after the machine stops because of loss of the cooling effect of the circulating air due to wheel rotation. The resultant explosion produces a blowout at the tire bead which reacts against the machine in most cases to expel the tire and rim assembly components, including final drives, a considerable distance from the machine. In some cases, the tire may explode without expelling wheel components.
Wheel coolant is provided in Caterpillar wheel tractor-scrapers (all except 613, 621, 623, 627) in which excessive brake application could cause burned tire beads. The coolant minimizes heat transfer from brakes through the rim and to the tire bead on these machines. The coolant must be of the recommended type and concentration be at the proper level to be effective. The recommended coolant solution is 20% mixture of ethylene glycol type antifreeze and 80% water. Oil or any other fluid other than that recommended should never be used as a wheel coolant. The coolant level should be checked at least every 1000 hours as recommended in the Lubrication and Maintenance Guides for the machines. In addition on earlier machines which require the removal of a brake drum stud to add or check coolant level, cooling system sealant should be added every 2000 hours.
December 22, 1980 Service Magazine
Tires Are Filled With Nitrogen (N2)
4203
All Tires On Earthmoving Machines
Explosions of air-inflated earthmoving tires and rim components have resulted from heat-induced gas combustion inside the tire. The heat can be generated by welding or heating rim components, external fire, or excessive use of brakes. Refer to the article in the October 8, 1979, Service Magazine, "Warning: Excessive Heat Can Cause A Tire Explosion."
Such an explosion is much more violent than a blowout. Although the risk of such failures is very low, the hazard is very great, particularly with the large tires used on wheel tractor-scrapers, large wheel loaders and off-highway trucks.
New Recommendation:
Caterpillar now recommends using dry nitrogen (N2) gas for both tire inflation and pressure adjustments on all current and past production machines. Nitrogen is an inert gas and will not support combustion inside the tire. The same inflation pressure used with air should be used with nitrogen. However, proper nitrogen charging equipment and training in the use of this equipment is necessary to avoid over inflation. Because initial nitrogen cylinder pressure is approximately 15 000 kPa (2200 psi), a tire blowout and/or rim failure could occur if the equipment were not used correctly. Information about a nitrogen charging kit appears later in this article.
Tires on most U.S.-built Caterpillar machines (except lift trucks) produced after September 1, 1980, are inflated with nitrogen at the factory. These machines have a tag attached to the steering wheel identifying and briefly describing this change. To denote nitrogen fill, the tires are branded with an "X" or an "N" directly below or in front of the first letter of the tire supplier's name of the outside sidewall. Plans to institute nitrogen fill on earthmoving machines manufactured outside the United States will be announced at a future date. Caterpillar Beadless Tires have been filled with nitrogen since 1977.
In addition to reducing the risk of an explosive-like failure, using nitrogen instead of air to inflate tires lessens the slow oxidation of the rubber and the accompanying gradual tire deterioration. This is especially important for tires that have a long service life (4 or more years). It also reduces the corrosion of rim components and the resultant disassembly problems.
Safety Procedures
The danger of a tire explosion must be recognized as a distinct possibility whenever the smell of burning rubber or excessively hot brakes is detected. The danger is also present when a fire on the machine reaches the tire and wheel area. Under such conditions, all personnel must avoid approaching the machine in a manner that could result in jury should an explosion actually occur. Move the machine to a remote area only if it can be done without endangering the operator or other personnel in the area.
DO NOT WELD OR HEAT ON RIM COMPONENTS.
For several years Caterpillar and some tire manufacturers have warned users never to weld rim components with the tire mounted on the rim. The gases that build up inside the tire during arc welding or heating on rim components may ignite, resulting in one of these explosive-like failures of the tire and rim. Caterpillar now recommends scrapping the part if heat is necessary to repair any rim component.
If there is evidence of a brake fire or the smell of burning rubber, don't go near the machine. FIGHT THESE FIRES FROM A REMOTE LOCATION. (Too often, the immediate response to a fire involving tires or brakes is for everyone in the vicinity to grab a hand-held fire extinguisher and rush up close to the machine in an effort to control the blaze.) Stay away from the machine until it is cool. Allow at least eight hours for the tires to cool before approaching the machine.
If it is absolutely necessary to approach a machine with a suspect tire, approach only from the front or the back. Stay at least 15 meters (50 feet) from the tread area. Keep observers out of the area and at least 460 meters (1500 feet) away from the tire sidewall. See Illustration 1. When fighting a fire, approach only at the front or the back of the machine and use a large dozer as a shield.
Do not approach tire in shaded area.
Illustration 1. Approach Area.
Inflating With Nitrogen
The 6V4040 Nitrogen Tire Inflation Group is available to inflate tires with nitrogen. The 9S5477 Charging Group for accumulators is not recommended for tires due to the higher pressure available and increased line flow restrictions.
The 6V4040 Inflation Group has a 0-1379 kPa (0-200 psi) Regulator (6V4037) and a 1137 kPa (165 psi) Safety Relief Valve (6V4039) that will restrict working pressure to that comparable to an air system. The regulator can be set just above the recommended tire pressure for various size tires.
Remember, initial nitrogen cylinder pressure is approximately 15 000 kPa (2200 psi). A blowout could occur if the equipment is used incorrectly. Be sure to adjust the regulator to a pressure no more than 140 kPa (20 psi) above the required tire pressure, then adjust the pressure with the tire gauge in the usual manner.
The 6V4040 Nitrogen Tire Inflation Group can be used to inflate conventional and Beadless tires with standard and large bore valves. Super-large valved tires have standard or large bore valve stems. The group connects to compressed gas cylinders of nitrogen available from local suppliers. Standard Bore (6V4038) and Large Bore (1P3551) Clip-on Chucks are provided for the two sizes of valve stems used on tires. The chucks connect to an 8.1 m (26.5 ft) hose with quick disconnect fittings. The gauge at the regulator allows you to monitor inflation pressure, yet stay away from the tire, by backing down the regulator or valving off the cylinder.
The 6V4040 Nitrogen Tire Inflation Group comes assembled. (See Illustration 2.) It is made up of the following parts. (See Illustration 3.)
Illustration 2. The 6V4040 Nitrogen Tire Inflation Group, assembled, is shown below. A Storage box (2P8292) and Tool Holder Block (2P8289), above, are available separately for storage.
Illustration 3. Refer to the chart to identify the parts.
SMHS7867, is available. The Special Instruction gives information about the parts in the group and the procedures for the use of the group for tire fill and pressure adjustments.
Inflation pressure and volume determine the amount of nitrogen needed for a given tire size. Scrapers 621 through 657 require from .5 to 1.5 cylinders per tire. The cylinder size is 22.9 cm (9") in diameter by 129.5 cm (51") high containing 6.4 cu m (225 cu ft) dry nitrogen. Trucks 769 through 777 require from .5 to 1.0 cylinders per tire. Requirements for large wheel loaders 980 and up are similar to that of scrapers. Smaller loaders, skidders, and motor graders use a fractional part of a bottle for inflation.
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