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Old 01-12-2019, 02:49 PM   #1
Skoolie
 
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Positive Air Shut-Off

Anyone have any knowledge or experience using positive air shut-off valves (especially on a DD 6-71TA)? They are also known as ASOV, AISV, ESD or emergency shutdown valves. These air intake shut off valves are systems that allows for emergency over speed shutdown and protection for diesel engines. They do this by cutting off an uncontrolled fuel source to the engine and air that is required to keep the engine running. Supposedly, they are the most efficient systems used to prevent engine runaway today.

My understanding is that they are not fool-proof but in most situations do a good job. I am considering installing one later but would like to know more about them and get some recommendations etc.
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Old 01-12-2019, 02:58 PM   #2
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Years ago I worked at a quarry that had a number of 2-stroke Detroit powered dump trucks. They had a so-called "butterfly" shut-off that served this very purpose. When closed, it was *VERY* effective at choking off the air supply and stopping the engine (it did nothing for the fuel supply). We would sometimes leave these closed overnight, as some of the Detroit engines were said to restart spontaneously (such as the engine would stop at a perfect equilibrium point for an injector to spray as the engine cooled or some-such. Never actually witnessed this myself, so who knows?)


Normally these engines had a fuel-supply shut off that we were supposed to use for shutdown. The butterfly valves were more for emergency run-away shut-offs.
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Old 01-12-2019, 03:00 PM   #3
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Any of the DD two strokes are well served with an emergency shutdown.

The intake restriction is how they they typically work.

Normal engine shutdown is controlled by the fuel solenoid. If the seals in the blower fail the engine will start pulling engine oil into the intake. The engine will run on the oil making the fuel solenoid useless.

At that point shutting off the air to the engine is the only way to shut it down.

Google "Detroit runaway " and you will see what I am referring to.
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Old 01-12-2019, 04:11 PM   #4
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In the older units there was a lever with a red knob on the the end to close a damper on the blower intake. Later someone wiser added a cable to the inside of the cab labeled EMERGENCY SHUTDOWN. Us mechanics always kept a phone book close to cover the blower intake when we were working under the hood.When I first started as an apprentice mechanic the yard I worked at had a fleet of Hendrickson's with 238 Detroits the senior drivers, after the bosses' went home would run them upgrade in a highgear at idle until the engine died if you did that correctly as the engine died and it started to roll backwards it would start to run backwards.Then they would take them out in the yard 13sp reverse 1 forward sp and drag race them backwards it was quite a sight as the exhaust was pulling in clean air and the exhaust was coming out of the air cleaner they were way down on power which was a good thing as the were going backwards and full of adult beverages. Gene
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Old 01-12-2019, 06:17 PM   #5
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Our 2 stroke dirt bikes would run just fine backwards, air goes into the intake, exhaust out the pipe. The SC500 Yamahas were notorious.
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Old 01-13-2019, 10:53 AM   #6
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Quote:
Originally Posted by 2kool4skool View Post
Our 2 stroke dirt bikes would run just fine backwards, air goes into the intake, exhaust out the pipe. The SC500 Yamahas were notorious.



Naturally aspirated 2 strokes run ok in reverse Detroits need a blower to run well and running backward negates the usefullness of the blower how hair standing was 5sp reverse 500 cc ride???
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Old 01-13-2019, 02:46 PM   #7
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Quote:
Originally Posted by PNW_Steve View Post
Any of the DD two strokes are well served with an emergency shutdown.

The intake restriction is how they they typically work.

Normal engine shutdown is controlled by the fuel solenoid. If the seals in the blower fail the engine will start pulling engine oil into the intake. The engine will run on the oil making the fuel solenoid useless.

At that point shutting off the air to the engine is the only way to shut it down.

Google "Detroit runaway " and you will see what I am referring to.
Yes, I have heard of DD runaway and that the fuel solenoid does not prevent runaway if there is some other fuel source (oil etc.). One would think that an emergency air shutoff valve would be standard equipment on a DD 2 stroke given the dangers of a runaway.
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Old 01-13-2019, 04:52 PM   #8
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All of the DD (about 12) that I take care of do have the emergency air shutoff. By the way this should only be used in an emergency, as it can cause the oil seals in the blower to fail if used on a regular basis to stop the engine.And of course if the oil seals in the blower fail guess where all that oil is going...in the intake ready to run away.
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Old 01-13-2019, 05:09 PM   #9
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I personally got a 6-71 detriot running backwards once, only the older truly mechanical ones will do it, the blower just runs backwards and sucks the exhaust out of the cylinders which pulls fresh air through the exhaust valves so it runs, the piston type fuel pump does not care which way it spins, still pumps fuel to the injectors
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