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elbow for oil press switch

JDA_BTR

Well Known Member
I want to install an oil pressure switch at the sender mount fitting. (see page 43-04). I think that I can leave off the 1/8 pipe plug below the oil pressure sensor and use an elbow. The sensor is too fat to just screw right in.

Is an AN914-1D the right thing to use? Anybody tried this and found trouble?
 
Just curious what you plan to use the switch for? Traditionally they are often used to run the Hobbs, but G3X (and presumably all the other EFIS systems) will track engine hours without needing the switch. This eliminates a couple pieces of hardware and a potential failure point that could result in dumping all your oil overboard...
 
While you are at it add a pressure switch for a back up idiot light on the panel. If your screen goes dark sometime at least you will know oil pressure is good to go.
 
spacer

If you put a spacer behind the Van's manifold you will be able to screw the oil pressure switch into one of the side ports on the manifold.
Bill Brooks
Ottawa, Canada
 
This may sound a little odd, but when I designed my panel, I installed a Hobbs meter before I knew that the Skyview system tracked engine time, etc. I didn't want to install an oil pressure switch to run my superfluous mechanical Hobbs meter, so I just hooked it up to the alternator field switch power. If the engine is running, the alternator is running, so the Hobbs meter is running. It tracks the Skyview Hobbs meter exactly.
 
Just curious what you plan to use the switch for? Traditionally they are often used to run the Hobbs, but G3X (and presumably all the other EFIS systems) will track engine hours without needing the switch. This eliminates a couple pieces of hardware and a potential failure point that could result in dumping all your oil overboard...

I also wanted an independent means of tracking time. My RV already had a Hobbs meter in the panel but was unfortunately wired to start running whenever electrical power was turned on ( ie battery turned on). You can imagine the difference in ?hours? that quickly developed. When I bought the RV from its builder the ?tach? time was around 160+ however the Hobbs read over300.

When I checked the log book sometimes tach time was used, sometimes Hobbs and sometimes both. You could literally see the disparity grow over time. I decided to bring them back together. I purchased a new Hobbs meter, an oil pressure switch, ran the Hobbs to match current tach time, and installed both new switch and new Hobbs. Of course I noted in my log book the changes.

Now after a year and a half, time tracking difference is again occurring but it?s less than two hours difference for over 100 hours of use. This difference is due to how both are powered. Tach time begins at 650 rpm and Hobbs begins at sensing of oil pressure. For most Flight tracking I use Hobbs because it?s visible after engine shutdown. For log book entry I use both. However when someone else logs work on my RV I?ve noticed that they usually only record Hobbs - which incidentally was what occurred when the builder owned it. At least now when that happens the two are close to each other and time differences are immaterial.

I also discovered during this process that ?Tach Time? could be changed by just an EIS entry. Hobbs time changes take a lot more time and effort (see above). That?s one reason complete tracking of work in a well maintained set of log books is important. Not all owners keep good log books. Not all aircraft mechanics will turn on power to check tach time when they see a Hobbs meter.
 
Funny I was just thinking about the same thing. I want an low oil pressure idiot light so I want to use the Van's pressure switch. I was also thinking about using the elbow approach. I was also curious whether there would ever be a need to take a manual oil pressure measurement. It that case I might want a Tee instead of a 90. At the moment I'm leaning toward the just using the 90 but I was also wondering if this would separate the oil pressure sender on the manifold and the switch on the 90 far enough apart. I can't really tell without buying the parts.
 
There are plenty of reasons to want it....
But is that elbow the one I want?

I did like the spacers idea. but then its hard to get under/behind the switch for connections.
 
I don't think that elbow is going to space the switch far enough away from the pressure transducer. I think you need a nipple and a female elbow., but I don't have the parts yet to confirm.
 
A little too much time commuting on the train I guess to think about future steps. I realize this is slightly off topic, but not too far.

Do these transducer lines that are connected to the manifold need to be purged to get rid of the air? It seems like they should be, but then I was wondering how that was done if you need to put the plug into the manifold with thread sealant.
 
A little too much time commuting on the train I guess to think about future steps. I realize this is slightly off topic, but not too far.

Do these transducer lines that are connected to the manifold need to be purged to get rid of the air? It seems like they should be, but then I was wondering how that was done if you need to put the plug into the manifold with thread sealant.

Good question..... Pressure is pressure.. It doesn't matter if it's water, gas, oil or air. They do make the transducers compatible with the product being measured. But an oil pressure transducer will measure air with no problem. It will compress, but only to the same pressure applied.

Actually, air trapped in the line will cushion pulses from pumps and that's a good thing for longer transducer life. Also, the next time you remove the fitting, you will have a clean disconnect.
 
Another approach, which I did not develop but used and has been shared here on VAF in other posts in the past, can be found here:

http://rv-14a.blogspot.com/2016/12/avionics-oil-pressure-switch.html

IMG_8374.JPG
 
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Good question..... Pressure is pressure.. It doesn't matter if it's water, gas, oil or air. They do make the transducers compatible with the product being measured. But an oil pressure transducer will measure air with no problem. It will compress, but only to the same pressure applied.

Actually, air trapped in the line will cushion pulses from pumps and that's a good thing for longer transducer life. Also, the next time you remove the fitting, you will have a clean disconnect.

Wont happen you will have oil the air will go away over time and be replaced with...??..OIL.
 
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