yakplt(at)yahoo.com
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 Posted: Sat Oct 03, 2009 12:22 pm Post subject: Oil Shut off valves |
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In a previous post to the YAK LIST, I mentioned putting in an oil shut off valve so that you would not have to pull the prop through before every start. I mentioned that a valve was available from Kevin Kimball. What I did not do was to go into explicit detail on the many places one might PUT such a valve. This let to a little bit of misunderstanding.
On the M-14 there is a SUMP. This sump has it's own return oil pump, and that pump is the reason why shut-down procedures call for "running the engine up" for some period of time before shutdown. The reason for this is because, at idle, this aforementioned pump is not turning fast enough to keep up with the oil coming in, and it simply fills up. With it full, more oil coming in as time passes will be more likely to get into engine cylinders after the engine is shut down.
So, the shut-down procedure calls for you to run the engine up, thus turning the sump oil pump fast enough to pump MOST of the oil (not all, but most) out of the sump. Now the engine is shut down.
Now here is where we come to the oil shut off valve. The oil shut off valve location *I AM TALKING ABOUT* is located between the oil tank, and the oil pump. It will typically be located on the LEFT SIDE, but it is possible to put it anywhere you want, in the oil line that runs from the oil tank to the oil PUMP. This is the main SUPPLY LINE to the engine. With it shut off, the oil tank simply can not supply any more oil to the engine. Period.
This leaves residual oil.
Residual oil is that oil contained in the engine at shutdown, and the oil that is in the line already between the newly installed shut off valve and the oil pump.
MOST of that oil is going to slowly drain down into the oil sump. If you ran up your engine properly before shutdown, the oil sump should be able to have this additional amount of oil added without becoming "full" (per se). If you do NOT run up the engine, then you are not following proper procedures, and thus other things can of course happen.
A small amount of residual oil might eventually run down the cylinder walls past the engine rings and into the cylinders combustion chamber. This would allow a very very small amount of oil to remain in the lower cylinders if both engine intake and exhaust valves are closed.
Thus, using common sense, after you install such a shut-off valve, and follow the above procedures, one should before trusting that everything is working as advertised, pull the prop through as normal. One should also leave the existing intake drains open with a collection bottle to see how much oil comes out. One should look at the engine exhaust pipes while pulling through to see how much oil comes out there as well.
After following this procedure for say 20 or more flights, and you see that a pattern develops, as in.. there is no more oil coming out of the engine when pulling though, and there is very little if any oil coming out of the intake drains, then one can start feeling confident that the system is working as it is supposed to.
If large amounts of oil continue to come out of the engine, then something is not right, and should be investigated.
Oil shut off valves located OTHER than at the main intake line are obviously not going to afford the user with the same amount of protection as one installed IN the main shut off line. So knowledge of what you are doing, how you are doing it, and what you should expect after you have done it are required. Obviously someone not well versed in engine oil lines, fittings, and installing new valves should not take this on as a "first project".
If after having this done, it makes anyone feel more comfortable to keep pulling the prop through, especially during priming, where doing that still helps a lot, is of course welcome to do so. Nothing wrong with that.
That said, with a thoughtful approach to this method, one will typically find that the amount of oil coming out of the exhaust and the intake drains is so small that a hydraulic lock is pretty much impossible. Which is the whole reason of putting it in there in the first place.
The oil SUMP will ALWAYS have some oil left in it, even with this valve located in the proper place, as described here. Having some oil left in the oil SUMP is not dangerous at all.
This discussion is directed only at this particular shut off valve located on this particular oil line, on the M-14 engine series. Nothing else.
Thanks,
Mark Bitterlich
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