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Old 05-03-2014, 12:03   #1
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Engine safety shutdowns, do you or don't you

Due to a recent post on this forum regarding a fuel problem on a 50hp Perkins, the question came up regarding safety shutdowns controlling the shutdown solenoid and whether the solenoid would be Normally Open and require power to close or be Normally closed and require power to open.

Also wondering what the typical installation for any safety shutdowns would be (if any) as I am not aware of any boat that has such devices installed. I would have thought that the last thing you would want is for your engine to quit at the worst possible time such as maneuvering in a marina or other confined area as a result of a faulty temp or oil pressure switch. Any boat that I have ever seen will have warning devices installed but no capability to shut down the engine automatically. On all the boats that I have operated the engine will run once started even with the power shut off as the shutdown solenoid requires power to close off the fuel.

Just curious
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Old 05-03-2014, 12:17   #2
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Re: Engine safety shutdowns, do you or don't you

I was on a boat with a 6-71 fitted with a low oil pressure shut down in the form of a air flap that would snap closed over the air intake when the oil pressure got below a pre set level. This was solenoid controled though I don't recall which engergy state it was. This is a good thing because if your oil pressure fails, your engine is not going to run long enough to get you out of trouble anyway.
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Old 05-03-2014, 12:23   #3
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Re: Engine safety shutdowns, do you or don't you

Called Murphy switches, usually used on engine that run un-monitored like irrigation systems, aircraft auxiliary power units etc., in those kind of applications they require power to allow operation, that way in the event of a broken wire / open circuit the engine just shuts down.

Personally I don't want any Murphy switches on my single engine boat, I'd rather have an alarm, that way I'm in the decision loop
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Old 05-03-2014, 12:25   #4
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Re: Engine safety shutdowns, do you or don't you

Thanks for posting.

These Detroit engines were installed in a prolific amount of equipment and not just marine. they were especially popular in railroad equipment till the end of the 80's. If I recall correctly, the air intake shutdown would not trigger until the oil pressure fell below 7psi. Not much and you would probably notice on the gauge well before unless it was a catastrophic failure somewhere in the engine anyway.

Also, the air intake did not actually shut the engine right down as the engine would still run at a low idle with lots of black smoke due to the rich mixture. Not worth a damn really.
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Old 05-03-2014, 19:30   #5
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Re: Engine safety shutdowns, do you or don't you

This is interesting, as I always thought the air intake flaps/stoppers were to shut the engine down in case of a runaway. Stopping the air is the only way to stop a runaway. A fuel injector shut off, just like your normal shut off solenoid would be better to stop the engine if oil pressure got too low. Just a thought. _____Grant.
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Old 05-03-2014, 20:27   #6
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Re: Engine safety shutdowns, do you or don't you

This one shut it down right now. This was on the gen set, and when you went to power down and let the revs down to idle after a good hard run the "murphy switch" killed it good.
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Old 05-03-2014, 20:49   #7
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Re: Engine safety shutdowns, do you or don't you

Many fire trucks and emergency apparatus are equipped with air intake shut downs but is generally for use if the vehicle is in a hydrocarbon rich environment. In this case, it is a possibility that there would be enough vapors in the intake air to cause the engine to continue to run even after shutting down the fuel system.
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Old 05-03-2014, 21:10   #8
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Re: Engine safety shutdowns, do you or don't you

Some sail and power boats have shut downs tied to engine room fire suppression systems. If the fire suppression system is engaged either automatically or manually the shut down solenoid is also engaged to stop the engine. The air inlet duct may have a damper that closes to help starve the fire for O2. Most solenoids are normally open so power is applied to block fuel flow.

The vast majority of propulsion engines only have a buzzer or bell that goes off when engine oil pressure or coolant temp is unsafe. It's considered better to let the operator decide if it's safe to shut down or keep going a bit longer.

Nearly all gen set engines will auto shut down when oil or coolant is unsafe.
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Old 05-03-2014, 22:57   #9
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Re: Engine safety shutdowns, do you or don't you

My brother works for the Calif Highway patrol as a cummunications engineer. They coordinate with CDF which is the state fire service. He used to work for a fire department, and tells me ( in a recent conversation) that new computerized fire trucks are creating a problem, in that when the onboard computer decides that something like an air filter or fuel filter is overdue for change, it shuts the engine down. This has happened on emergency runs and is creating a dangerous situation for emergency responders. This goes along with automatic shut downs for boat engines (not generators) being dangerous in any situation. Maybe I am a control freak , but I want to be in charge, if the choice is burning up my engine or hitting another boat or person. Alarms are essential, but shut downs are dangerous. My highly biased opinion. _____Grant.
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Old 11-03-2014, 04:13   #10
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Re: Engine safety shutdowns, do you or don't you

Glad to see that I haven't lost my marbles out here on the sea as I couldn't imagine a scenario (except maybe fire in the engine room to shut off the fuel supply at the source) that would cause me to want the engine to decide to shut down on it's own.

Yea those computers are getting fancier and fancier but let's hope that nobody ever decides to put automatic safety shutdowns in the system on marine engines.
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