How often do diesels "run away"?

[Rock knocker]

I've been around diesels most of my working life, and have never seen it happen, or heard of it. But it seems like a persistent concern here. I have a old JD 950, and to choke off the machine from air would be a real project.

It's a totally mechanical system, are they safer or more prone to run-aways than solenoid machines?

 

[Egon]

The Diesel engine can "runaway" if there are combustible vapours entering through the air inlet. The diesel has no air restrictions.

What can be done is put a valve that can be closed inline on the air system. This is usually a clip gate type valve. There are various means of operating the valve.

Many refineries or similar type plants have a air shut off requirement for diesels. :

 

[phcaan]

I've been around diesels most of my working life, and have never seen it happen, or heard of it. But it seems like a persistent concern here. I have a old JD 950, and to choke off the machine from air would be a real project.

It's a totally mechanical system, are they safer or more prone to run-aways than solenoid machines?

I don't have any experience with tractors but in the 80's I owned a Diesel VW Rabbit. On a trip from Wyoming to California the rabbit began to run on it's own crankcase oil and I could not shut it down. Luckily it was a standard transmission and I was able to put into 5th gear and use the brakes to kill the engine. No fun and I would never care to relive the experience.

 

[JimRB]

The scary joy of an old Rabbit is a 50-65 HP Diesel Rabbit engine you could kill with the right gear and brakes. Not so sure if that would work with the more modern 90-120 HP VW 4 cylinder I have and I have no hope if my 300 HP 600 lb/ft Cummins ran away. By the way that old Rabbit was mechanical fuel injection not unlike my Jetta. Cummins has little injectors under the valve cover I think running of the camshaft. I never removed the valve cover on the Cummins but it is quieter than the old Cummins that used the same style pump my Jetta uses.

 

[jaydee325]

I would say modern diesels today, never.

Back in the day when I was in fuel injection class at Ferris State, we were learning how to adjust the fuel rack on a 6-71 Detroit Diesel. When my buddy got the rack adjusted, the instructor suggested we hook a battery up and fire it up in the lab. He had the rack adjusted to tight on one of the injectors and as soon as the engine fired, the rack stuck at full fuel. The lab filled with a roar and thick smoke. We all dove for cover. Fortunately, my buddy stayed with it and tripped the emergency trip, which was basically a spring loaded clapper valve over the inlet of the supercharger.

When the smoke started to clear, we hear the instructor laughing! He said, I saw 15 students run away but only one diesel. We all got a pretty good laugh out of that.:laughing:

Bob

 

[phcaan]

I would say modern diesels today, never.

Back in the day when I was in fuel injection class at Ferris State, we were learning how to adjust the fuel rack on a 6-71 Detroit Diesel. When my buddy got the rack adjusted, the instructor suggested we hook a battery up and fire it up in the lab. He had the rack adjusted to tight on one of the injectors and as soon as the engine fired, the rack stuck at full fuel. The lab filled with a roar and thick smoke. We all dove for cover. Fortunately, my buddy stayed with it and tripped the emergency trip, which was basically a spring loaded clapper valve over the inlet of the supercharger.

When the smoke started to clear, we hear the instructor laughing! He said, I saw 15 students run away but only one diesel. We all got a pretty good laugh out of that.:laughing:

Bob

A several years ago I was the manager for an oil company and one of our delivery drivers was delivering gasoline to a bulk plant, the engine of the truck ran the pump to transfer the fuel, and the fumes from the gasoline were enough to run the diesel in his truck and there was a runaway. The driver was killed. Since that time all the truck engines have been equipped with a flapper system that will completely block off the air supply to the engine.

 

[Ivan49]

When I was in the Army in the early 70's all of the heavy equitment we had that had a Detroit Diesel engines we run with the air intake cap loose so it could be flipped over in case of a run away engine. I saw one run away in a trenching machine and in a 20 ton trk mounted crane. I was in the cab of the crane at the time and I can tell you it is enough to make you fill your pants having to go in the back to flip the intake cap over. I have seen the results of an engine that sucked all the oil out of the crankcase also. The newer equitment that came thru the shop had the flap valve in the intake.

 

[Egon]

I would say modern diesels today, never.



Old or new when they get an unlimited fuel supply through the air inlet they will just keep on revving up.

In most cases the same Diesel engine only runs away once!:thumbsup:

Diesel Engine Air Intake Shutoff Valves
Model RDS5 High Temperature Electric Swing Gate Valve
Overview
If flammable gas or vapor is present in the atmosphere surrounding a diesel engine, it can be ingested into the engine and become an ungoverned fuel supply. This ungoverned fuel can result in runaway engine overspeed, potentially leading to dangerous mechanical failure or an explosion.
The Roda Deaco RDS5 Swing Gate Valve is a positive spring actuated air intake shutoff valve that provides emergency overspeed shutdown of a diesel engine. The RDS5 Swing Gate Valve can be triggered to close, which starves the engine of air and shuts down the engine.
Model RDS5
High Temperature Electric Valve



Reliable protection from
diesel engine overspeed
During operation of industrial and marine engines, combustible vapors present in the operating envelope of the engine can be drawn into the air intake. This provides an additional source of fuel. Intake of this va- por can result in loss of engine control. Loss of control can also be the result of a failed drive train or sudden loss of a coupled load. Attempts to shutdown the engine by standard control systems such as normal fuel shutoff will not stop the runaway condition and prevent serious engine damage, personal injury or catastrophic results.

 

[powerpace]

Years ago when I was in the Fire Department we had a area that was served by Portland, Or., TRIMET bus lines. After having a emergency on one of the buses we were given a quick what to do/not to do class a few weeks later. The first thing the mechanic said was flip the air shutoff if there was a fire or engine problem. The second was "do not crawl or reach under the coach. It seems the frame may go within a few inches of the ground if the airlines are compromised.

 

[psj12]

I was a diesel mechanic most of my life and only had one true runaway. It happened in 1972 on a WW II vintage landing craft that belonged to some researchers from Hawaii University who were stationed on Christmas Island in the Pacific. I was in the Coast Guard and we were there to work bouys around their small harbor and our captain said we would repair the LCM as a favor to them. The Landing craft was rusting away and had holes in the hull everywhere. When we finally got one of the old Grey Marine (later to become GM then Detroit diesel) 6-71s to fire up it had a bad blower seal and started running away on lube oil. The old Grey Marines had no emergency air cut off so I slapped a clipboard to the blower intake and then dove for cover. As soon as the rpm dropped the vacuum holding the clip board in place dropped and so did the clipboard. Then it really ran away until it tore itself up. Rods, pistons and crank all broke. We then used the LCM as a barge. Later that night it sank from all the rust holes in the hull.