Switch fuel rack or compression release?

[mbryner]

In designing my automatic start/run/stop system for my 6/1, I had planned to use a Murphy 1.5" throw solenoid to turn off and on the fuel rack.   I was going to drill the big green lever, hook a spring from above to hold the rack closed normally, and the solenoid from below to pull open the rack when energized.   Should work OK.   The solenoid can push/pull 14 lbs.

Now I thought of a different idea.   What happens if I just leave the fuel rack open and use the solenoid to manipulate the compression release lever?   Is that bad?   May be stupid question....

[Tom Reed]

Seems like that would be pretty hard on the exhaust valve. If the combustion chamber is hot enough the fuel may still burn, possible stack fire? Why not just connect the solenoid directly to the rack like they did on the SOM's?

[Bottleveg]

As you probably know, the Lister SOM opens the exhaust valve and closes the fuel rack when shutting down. If the fuel rack isn't closed then the pump carries on pumping fuel until the engine stops. Not sure if this helps with your idea?

[AdeV]

I'd say do both, like Lister did, and have a mechanical linkage between them.

The SOM decompression "lever" actually looks a lot like a Yale-type latch, sort of like this:

Code Select Expand


--------/
      /
------/


It allows the exhaust cam follower to push the lever out of the way if it happens to try to decompress while the valve is closed, but won't allow it to drop back down again. The same movement that pushes the lever in also acts through a shaft & arm to push the fuel valve shut. Springs will hold the entire unit closed in when the solenoid is off (or if it fails).

You should be able to get the principle from this picture, if you're not already familiar with it:

[mobile_bob]

go to harbor freight, and buy the largest ball valve they have
last time i was there they had either a 1.5 inch or maybe a 2 inch

put it the engine so it can cut off the intake air supply, and rig  your solenoid to close the valve

no air, no run

i don't like  the idea of using the decompressor because valve damage might result in a runaway situation

and i don't care much for rack closers for emergency shutdowns because the rack can stick and provide a real problem
for a rack closer right when you need it most.

bob g

[mbryner]

OK, thanks.   Now I know not to use the compression release for routine shutdown w/o turning off the fuel.    

The SOM suggestion is great, Ade, but it looks a little beyond my fabrication abilities for a daily use machine!

The ball valve idea is great, but you have to use a hefty solenoid to open and close it, and the all-in-one electromechanical ball valves I've seen are quite spendy.   Is there something you had in mind, Bob?

I also thought of some sort of electrical valve inline in the fuel hose, but isn't that hard on the fuel pump to run w/ a vacuum input?   Guess I'll just go back to the original plan.

I'm not trying to re-invent the wheel.   I'm just trying to figure out an easy way to start and stop a 6/1 electrically so my wife can do it.

BTW, here's the solenoid I'm using:  http://www.murcal.com/Catalog/Rack-Pullers/RP2309B-Push-Pull-Solenoid
It could be hooked directly to the rack, correct?  If it moves freely when not energized, that is.   But then one would have to energize it to shutdown (pull/push rack closed).    What if it fails and the engine doesn't shut off or overspeeds.   It would seem a de-energize to close would be more desirable.

[flywheel]

Large plastic ball valves are very cheap -  find them in the section with spraying equipment and fittings at your local farm supply store.
                               flywheel

[Horsepoor]

I also use a Murcal solenoid for emergency stop on my 6/1 amd 20/2. I took the easy route with normally open, close with over temperature trip. Everything works just fine so long as I have 12 V power. If I were to do it again, I would set a large spring to hold the rack close, manuall hold the rack open to start, then the solenoid would hold the spring back and trip closed if over temperature occurred or loss of power. Here is a short clip on my system.
http://www.youtube.com/user/rocketboy911#p/u/2/eZcW467k6Go

[mobile_bob]

you can use a very heavy spring if you set up the solenoid to pull a trigger sear like a gun
it take very little solenoid stroke or power to pull the trigger and allow the spring to do the work

the downside is you have to manually reset or recock the ballvalve to restart the engine.

detroit used this sort of mechanism on millions of engines for 50 plus years

bob g

[rcavictim]

I also thought of some sort of electrical valve inline in the fuel hose, but isn't that hard on the fuel pump to run w/ a vacuum input?  

A) Yes, it is hard on the system and will likely result in air in the fuel line and problems when you start up again

Jens,

I don't understand the logic that led you to this conclusion.  The absolute maximum vacuum you could pull with the piston sucking against a closed set of valves would be atmospheric pressure at sea level being 14.7 PSI.  In reality you would not get quite this high.  Any diesel injector is set to crack open at pressures like 1000 PSI and higher.  How are you going to get one to crack or leak with just 14 pounds of suck?

[rcavictim]

I don't understand the logic that led you to this conclusion. 

No logic, just experience .... and btw, that 1000PSI is on the high pressure side and the 14 pounds of suckage is on the low pressure side so you are comparing apples and turnips.

Jens,

Now you have me confused.  I was talking about the high pressure side of the injection pump, the HP line and the injector onto which a small vacuum suck would be applied to the injector tip IF the intake manifold was slammed shut by a ball valve air shutoff.  In that scenario I cannot see how you would introduce air bubbles into or hurt the injector pump. The fuel rack can be closed, at idle or WOT.  Doesn't matter.  The engine will stop and the injection system will not lose prime nor get air bubbles in it any way that I can imagine.

What are YOU talking about?   

[sailawayrb]

For "routine shutdown" EITHER closing the normal fuel rack mechanically via an electric or pneumatic solenoid setup OR installing an electrical valve in the fuel line (i.e., on low pressure side of IP) will work very nicely.  I choose the electrical valve approach because I also needed an electrical valve to automatically switch between diesel and SVO.  Jens is correct that this is hard on the standard line/fittings that come with these engines (between where you install the valve and the IP) and I could envision how you could create air leakage at fittings.  However, I replaced the standard lines/fittings with quality high temp rated lines (since I heat the SVO), drilled and tapped the injector pump to accept better fittings, and I have not had any issues at all.

For "emergency shutdown", I would not trust the aforementioned routine shutdown approach although there are folks who apparently do and this is certainly better than not having any emergency shutdown approach at all.  I believe starving the engine of oxygen EITHER via an air inlet ball valve OR dumping gaseous CO2 into the air inlet is the only way to totally ensure shutdown.  I chose the CO2 approach because it can be accomplished automatically without human intervention and without requiring electricity, both of which might not be available when you actually need to do an emergency shutdown.

http://listerenginegallery.com/main.php?g2_itemId=351

Bob B.

[rcavictim]

Now you have me confused.  I was talking about the high pressure side of the injection pump, the HP line and the injector onto which a small vacuum suck would be applied to the injector tip IF the intake manifold was slammed shut by a ball valve air shutoff.  In that scenario I cannot see how you would introduce air bubbles into or hurt the injector pump. The fuel rack can be closed, at idle or WOT.  Doesn't matter.  The engine will stop and the injection system will not lose prime nor get air bubbles in it any way that I can imagine.

What are YOU talking about?   

The original comment was :
I also thought of some sort of electrical valve inline in the fuel hose, but isn't that hard on the fuel pump to run w/ a vacuum input? 

We were talking about a valve in the fuel hose.

Re Bob B.'s comment about using better hoses and connectors - all my hoses and connectors have been quality US/Canadian products and I still had issues. Mind you, they were hoses with hose clamps and not solid lines which you might be referring to.

Jens,

My mistake.  Yes I totally concur that trying to close the low pressure fuel suction line into the IP would be a bad idea.  This is a case where IF you had any higher volatiles mixed in with your diesel fuel, acetone or RUG for example where this fraction would likely flash into vapor bubbles in the line.  It would also promote the ingress of air as you suggest at the fuel hose fittings.  We are talking about on the low pressure, inlet side of the IP.

[sailawayrb]

Re Bob B.'s comment about using better hoses and connectors - all my hoses and connectors have been quality US/Canadian products and I still had issues. Mind you, they were hoses with hose clamps and not solid lines which you might be referring to.

Between the injector and electrical valve...I used some Teflon hose (rated for SVO and high temp) that had SS end fittings...all taken off a scrap cruise missile.  I had to drill/tap the IP to accommodate the different fittings.  I haven't had any issues shutting down the engine by cutting off the fuel at the IP low pressure suction side using my electical value.  I don't recall...which side does the standard fuel rack cut the fuel?

Bob B.

[Crofter]

Shutting off the fuel supply to the injector pump will not be quick enough to function as an emergency shut down. Leakage into the supply lines at fittings etc. should be possible to prevent but there is other leakage points (for negative pressures) in the high pressure injector pump itself that can lead to possible start up problems later as well as possible mechanical damage to the IP.
This was kicked around at great length in an earlier thread.

Normal shutdown functionally puts the injector pump (or individual injectors) delivery volume to Zero despite all components still being bathed in fuel and not placed under negative pressure.

Closing off all air intake is the only certain emergency shut down. The vacuum created will not get into either the high pressure side or low pressure side of the fuel system unless something is grossly wrong with the injector (s). Depending on how high the exhaust valve is held off the seat, the de compressor function may not stop the engine if full fuel is still being supplied normally or crankcase oil is getting in. Routine shutdown should always be by de stroking high pressure fuel delivery. You do want to idle it down anyways for the health of valves and head.  Usually routine and emergency shutdowns are by different means.