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The article Mr. Carter refers to mentioned the possible requirement by the Va. Board for Towing and Recovery Operators requiring the use of Grade 80 chain for recovery work. In the article I used the phrase "chain of failure" which engineering wise is similar to the terms "pre-engineered failure", "sacrificial link", sacrificial part", "engineered failure mode" and "shear pin" as well as others. Engineers design parts to fail under stress in a specific chain of events in order to prevent more serious damage. For example, a 30 amp fuse is used in an electrical circuit so if the circuit is exposed to an unusually high load, the fuse will blow out and protect the more expensive parts of the circuit from burning out. Obviously, the blown fuse can also prevent a fire that could destroy the entire vehicle. A "shear pin" is used in a winch so that if the operator uses the winch on a load that is so great that the it could break or explode, the shear pin will snap first. This prevents an accident that could destroy the winch and possibly kill or injure persons nearby. Power companies use explosive fuses so that when lightning strikes a wire, pole, transformer, etc. the explosive fuse will not just blow out and break the circuit but also throw a damaged wire away from other wires so that shorts will not be caused in other circuits. Automobile manufacturers use "sacrificial parts" that are designed to wear faster than other parts. For example, a bronze bushing in a door hinge will wear out faster than the hinge or hinge pin so they are not damaged. It is cheaper to replace a bronze bushing than the entire hinge mechanism which is costly and welded into place.
The article about grade 80 chain was intended to point out that a tow operator should only use the materials or equipment called for by the manufacturer. If for example you decided to replace a shear pin with a stronger pin, you might avoid a situation when the pin might break and cause you to lose a recovery job, but the stronger pin could allow you to put excessive stress on the winch and cause serious damage. Manufacturers recommend certain equipment for their tow trucks and usually include those items with the original sale. If the item is not included when the tow truck is initially purchased, the manufacturer will make recommendations to you at a later date if you decide to buy a certain item.
We know that the safe working load for a wire rope used on a light duty tow truck is 3,000 pounds. The safe working load for the winch is normally 8,000 lbs. Obviously, there is a considerable difference in the load carrying capacity of the two tools; the wire rope and the winch. The engineers intend for the wire rope to break before the winch. If a tow operator decides to install a stronger wire rope such as one with a load capacity of 10,000 pounds, he could easily overload the winch. Because some people will actually do such things, the manufacturer of the winch installs a shear pin that will break sacrificially rather than allow the winch to break. In the event the genius we are discussing here decides to go for a heavier wire rope and shear pin, the manufacturer installs the winch to the frame of the wrecker with a specific grade of bolt so that if the load is really great, the winch will come off the truck without ripping the wrecker off the chassis. I have actually known tow operators who decided replace a bolt that kept breaking with a heavier one rather than learn a better way of winching. Manufacturers usually in the maintenance or owner manuals state that parts should only be replaced with equivalent parts.
I honestly believe that a tow operator should buy recovery hooks, chains, etc. from the truck manufacturer at the time of original sale and then replace those parts as they wear out with the same parts. Use of a Grade 80 chain that has not been recommended by the wrecker manufacturer may cause damage somewhere up the recovery chain of events that could cause catastropic failure of a part and possible injury or death. I have nothing against heavy duty equipment as long as it meets the specifications of the equipment it is to be used on. I do not believe that the Commonwealth of Virginia should be specifying equipment parts; I believe the specifications should be designed by the engineers who design the wrecker assembly and they are the parts that the tow operator should use. It might be appropriate for Virginia to require an 8 ton or 10 ton wrecker, but it is not appropriate for the state to then decide what components should be added to it; leave that to the engineers who design the equipment and the manufacturers build it. Certainly, if the manufacturer offers two or more quality levels in accessories, you should buy the better one.
Dave, perhaps I did not explain myself in the article as well as I should have but I hope this explanation will clarify the issue. I appreciate your confidence and hope that my credibility is restored. Trust me when I say that I believe fully in safe operation and safe equipment and I would never suggest that someone cut corners on maintenance or parts, but I am concerned when original manufacturers recommendations are not followed.