Air Shutdowns for 6v92's

[mikfin]

I've got some old 425HP low profile twin dry turbo Covington 6v92's. They have a manifold on top of the blower which collects the air from the turbos, but no air shutdown mechanism. Does anyone know the approved solution for stopping the engines from a runaway condition? Is it to fire the CO2? Is anyone aware of a part or modification which can be bought/made to serve as an air shutdown?

[Genesis]

Those are the same engines I have, but at a lower HP rating.

There is no air door option possible on them due to the way the turbo is set up - it would not close if fired.

Those engines have spring-loaded racks which should not be able to stick. My recommendation is to make damn sure there's a fuel shut-off where you can get to it quickly, and pay attention to blower seal condition.

[MikeP]

The use of a CO2 fire extinguisher to stop runaway diesel engines is a age-old solution. Whether it's a GOOD solution, as Genesis pointed out in another post, is another issue. As a maintainance office in a US Army Tank Battalion, I saw it used on more than one occasion and it worked very effectively. I have to admit that I never saw it actually create a problem but that doesn't mean it couldn't. But, as Genesis also suggested re fire, the possible result of a runaway diesel is way worse than the possible damage the CO2 might cause.

[Genesis]

There are three potential sources of runaway on a Detroit:

1. Stuck rack. Not possible on a spring-loaded rack as more than an annoyance, and in any event, can be dealt with so long as you are in gear by shutting off the fuel with the shut-off valves. Just DO NOT take the engine out of gear!

2. Lube oil pullover. God help you if this happens. The only realistic way to have it happen on a Detroit is a blower or turbo seal failure. This is NOT a sudden occurance; you have plenty of warning. If you are burning a LOT of oil (more than a gallon a day of running time) figure out WHY. Pay attention to blower and turbocharger condition and fix oil consumption issues before you lose the seals entirely. If you have such a thing happen, its your own fault.

3. Improper maintenance, particularly to the governor, which locks it up at full-fuel on a start. This is solved by NEVER allowing the governor to control ANY initial startup on an engine that has had the valve covers off for any reason whatsoever, and always checking rack travel before attempting a start. You do it with your HANDS, holding the rack at NO FUEL with the valve cover off. If it even HINTS at trying to overrule your hand, your finger comes OFF the start button instantly. Only once the engine is spinning and you KNOW you are in control do you manually allow the rack to advance and the engine to start. In this fashion you eliminate this (very real!) risk. BTW since this is an "out of gear" event you have no prayer of dealing with it if it happens - so prevention is the order of the day!

IF you have such an occurrance, your only hope is to either shoot a big CO2 extinguisher down the intake OR to stuff something solid that can't be ingested through the turbo airhorn in it (that is, that cannot contact the blades.) Neither is simple, and both assume the runaway happens IN GEAR. In both cases you do not have much time to deal with it if lube oil is involved, as it will quickly be consumed to below the pickup level, and when it is, your engine is toast. Both require getting way closer to the engine than I prefer in such a situation. Realize that a full-on runaway can literally explode, ejecting engine pieces in random directions with enough force to hole not only the boat but YOU.

A flooding system (e.g. fixed CO2 system) which is manually fired is a potential solution - if you catch it in time AND can get to the pull before it goes "bang".

For a fuel-fed runaway, the best (zero damage) option is to close the fuel supply valve.

A runaway out of gear will leave you with ZERO time to deal with it though.

A runaway that occurs IN gear can be dealt with PROVIDED YOU DO NOT TAKE THE BOAT OUT OF GEAR AND you are able/willing to get close enough to the engine to deal with it. Note that manual CO2 dump pulls are usually closer to the engine (e.g. in the salon) than is safe in such a circumstance.

The air shutdown system isn't on lots of these engines because it can create its own problems, particularly if tripped accidentlaly, and isn't a damn-foolproof solution to the problem in the first place. It was pretty much required on the two-screw solid rack engines as a binding injector rack on ONE injector could lock the engine at full-fuel - and that DOES happen. The newer spring-loaded control tubes don't have that problem - a stuck rack can lock the single injector at full-fuel, but not the entire engine. When the spring-loaded rack showed up the airdoor became something that was omitted on a lot of DD engine configurations.

[mikfin]

Thanks for the replies, proper MX is always crucial.