Electric stop solenoid - why?

[BadDog]

This is just to satisfy my curiosity.

I've read a fair number of post recently with folks somewhat fixated on a stop solenoid, adding or repairing. My B2150 came with one, but the relay is burned. It appears there was a small electrical fire there in the past, and other required systems were repaired, abandoning the stop timer-relay. Solenoid is still in place, and would probably work, but I don't really care enough about it to invest time in replacing wire/plug/timer-relay. The pull rod operates the same lever and it's a lot less failure prone. I like simple and direct, particularly on tools like a tractor. I'm also more familiar with the tractors of decades past where only gas burners turned off with a key (in my limited experience anyway).

Anyway, with specific interest in this showing up repeatedly on the board, it makes me wonder if there is something more than simple convenience at play. Why would a tractor manufacturer even add a more expensive and failure prone system, particularly when the parallel simple system must be maintained for the inevitable primary failure? Is there some common problem that this electric off switch avoids? Or is it really just to make it act more consistent with the gas burners and cars? I'm quite content with the pull-to-kill rod on both my 7100 and 2150. I wouldn't remove it if it worked, but I wouldn't spend 10 minutes and $10 to fix it when (not if) it failed. Is "key off" really just about relatively trivial convenience?

 

[Daren Todd]

The simple answer is safety. They can add switches to the seat, pto, transmission and such so if the operator gets tossed, it will shut down. Can't be started if someone leaves the pto engaged or the transmission in gear.

 

[BadDog]

Ok, that I totally understand, and that makes sense for why it was added by manufacturers to new tractors going into safety focused markets. You fall off the seat, it shuts the tractor down, and then you need additional mechanisms so you can allow off tractor seat work when required, and round we go with more and more points of failure both for normal operation and fail-not-safe surprises.

And I don't think this applies to the "can't be started" angle. That is usually done on the starter lock-out, just like the clutch depression switch.

But these older tractors (like the 7100 and my much later 2150, and like some mentioned in the posts that prompted this one) don't have the gaggle of safety switches that folks are always having trouble with (often accompanied by "my tractor won't crank" or "my tractor keeps dying" posts. I think the only safety switch on either of mine is the clutch starter lock out. So putting a shut-off solenoid on these wouldn't have the multitude of safety switch inputs to justify it for safety (or so I assume?).

 

[Daren Todd]

It would be fairly easy to add extra safety stuff to one that has a fuel shut down solenoid. All it would be is running the power for the selonoid through another relay. Older ones like mine where there isn't a shut down solenoid then it could be quite a chore. We've entered into the day and age of protecting people from themselves

 

[sheepfarmer]

I'm trying to make the correlations between this tractor in your discussion and mine, which may have a solenoid or something that shuts off the fuel with the key? It does have a lever associated with the water/fuel separator that can be closed. It doesn't seem to have anything like a decompression lever, and I am wondering if any tractor has something to shut off the air supply? It sounds like that might come in handy given the number of tractors lately that have been running after the key is turned off.

 

[BadDog]

Both of my Kubota's and all the older Diesels I've operated had a mechanical kill device that shut off the fuel. Pull rod, lever with rod, some just push the fuel throttle lever all the way forward to kill. And it eliminates fuel, not air, so a run away due to leaks and such providing fuel continues to be unaffected. I've never seen a practical air cut-off on a diesel.

And the kill solenoid I'm speaking of is nothing more than a simple electric solenoid that actuates the same fuel shut off lever as the mechanical kill operation. And other than potential "protect me from myself" (well put) safety devices, the only value I see is that you just turn off the key and it dies just like a car or gas burner. To make this work, they include a timer so it only holds for some number of seconds until the it dies, and then de-energizes to save the battery. I suppose they could also reconfigure it as so it has to energize to hold the fuel shut off in the run position, but then an electrical issue would disable the tractor leading to generally lower reliability. My B2150 is supposed to have a timer.

 

[ShaunRH]

Practical air cut off on a diesel is a decompression system. If you have small enough air intakes, you can put a ball valve with a rod attached to it on the intake if you really fear runaway's but they are rare on normally aspirated diesels. They happen most often on turbo charged units where the oil seals on the intake side fail and even with fuel off, it feeds the engine it's own oil as fuel. They can happen with a certain type of blow-by on the rings but that's not common either.

Mechanical fuel shut offs work fine. There are ways to make them so they work as fail-safes as well. It requires spring loading the rod to shut off and then a clip which is tied by a lead to you or your belt. The clip is pulled if you fall or jump off and the rod closes by spring action. This is old school type stuff and was never really used for much more than demonstration/gadgety purposes.

Modern electrical ones have a lot of purposes, most have already been stated but it's also to save the engine if the computer detects an issue with the tractor. It can stop the motor and throw an error code.

 

[sheepfarmer]

The thing that got me curious about all this is the recent posts for L3301 and L3309's in which the engine kept running after the key was switched off, one until the oil was all gone and out on the ground. Seems like after Kubota gets done with replacing a few engines that they might engineer in something simple the owner could do to shut the air off. Levers are nice in an emergency, skip the computers! The air intake on mine requires lifting the hood to get to it, and is not comfortably accessible on a running away engine.

 

[Daren Todd]

You could rig up a flapper hooked to a choke cable on the are flow. But would probably be easier to just put a ball valve with a nipple on each end and splice it in an easy to get to location on the fuel line. If fuel gets shut off, the motor dies very quickly. Especially if it's a tight seal.

 

[BadDog]

The point of my original post wasn't for more modern computer controlled tractors with more computational power than Apollo 11. Neither of my tractors have computers, nor do the tractors in the threads that prompted me to make this post. Obviously if a computer is controlling things, or you want to have electronic CYA switches shutting down the motor, then the stop solenoid makes perfect sense in every way.

But my question is targeted at the older tractors like my B2150 that have VERY limited electronics, yet someone decided it needed an electric stop solenoid tied to the key complete with requisite timer; and for no good reason that I can discern. I also saw recent a thread where someone is adding a stop solenoid to a B7100 (IIRC), and there are other similar comments about adding/fixing them on older tractors that I've run across in my forum trawling (searching and reading). And so far I've heard nothing that indicates it was anything other than convenience and familiarity of "key shut off" in the general population. Later model electronic tie-ins not withstanding...

Regarding air shut-off, a determined fellow could probably rig some sort of butterfly damper or gate shut off (such as used on dust control systems) to eliminate/restrict air supply. It wouldn't be too hard to at least limit air supply sufficiently such that the motor doesn't actually "run away" until you can find a solution to get it shut down. And if placed before the breather, you wouldn't have to worry about it allowing unfiltered bypass air. But as others pointed out, for the most part, it's unlikely to pay off on the effort for the simple/older NA tractors.

 

[North Idaho Wolfman]

For me installing or repairing the stop solenoid system was 3 fold.
#1: Convenience, shut the key off and it dies.
#2: Safety, Me, Wife or anyone else knows to shut off the key to kill it, they might not know to pull a lever.
#3: Required, when I changed my B7100 from a D750 to a D950 the linkage to throttle changed, it went from a single lever to twin lever, so stop ended up on a different lever, it was easier to just keep the solenoid shut down setup than to change it lever. Now that model does not have a passive timer controlled solenoid it has an active setup, Key to start activates solenoid.

 

[BadDog]

That all makes sense and generally fits with my expectations, thanks.

I was close with the common place convenience thought, but hadn't quite got to considering the "everyone knows how to turn it off" safety angle that follows. Very valid.

And the active (no timer) 2 lever system is certainly a game changer supporting the solenoid use, but I haven't seen a system like that, so new information there.

Given the cost of Kubota parts (need timer/relay at a minimum), I doubt I'll fix my stop solenoid on my B2150, but at least I now have a reasonable answer for why it would exist based on your answer #2 (#3 obviously doesn't apply).