Check Fuel Pressure Video
in 912 / 914 Technical Questions
10 years ago
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by Rob Seaton » 10 years ago
I will not tell you that you MUST do it one way or another. I guess it is a matter of opinion: what one guys sees as pure logic may look like unnecessary complication to another.
As far as metric and NPT threads go they are very similar. Try running a 10x1 tap into a 1/8NPT hole; you can barely feel any cutting taking place. Study SI-912-020 ch 79 for what it does not say: how do you install a VDO oil pressure sensor into a new engine with 10x1mm threads? Simple: screw it in. (on the other hand if you want to go the other way: Install Keller sensor with 10x1mm threads into a older engine with 1/8NPT hole you should re-cut the threads to 10x1mm so the sensor bottoms out. Why? This was found to greatly reduce the moment/vibration on the sensor.
An adaptor makes perfect sense but for aircraft use you also have to consider adding failure points, leaks, increasing weight/arm with resultant increase in moment and avoiding unnecessary parts.
I guess that is why the engineers at Diamond kept it simple and choose to install the Bosch fuel pressure switch with 1/8NPT threads into the fuel manifold. This certified aircraft has been flying for over 25 years with no manifold block/bosch switch issues. You should use thread sealant as well as not overtorque it (that will crack the manifold) this is true for any tapered thread going into aluminum (example: over torquing the VDO oil pressure sensor has cracked many oil pumps).
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by MARK JACKSON » 10 years ago
I have a new engine with a M10x1 thread in the oil pump housing. I also use a VDO oil pressure sender, but I use one with a M10x1 thread and not a 1/8NPT.
Please don't take it personally Rob, but the threads are worlds apart. You might be able to jam them together and with a bit of sealant thrown in for good measure and they probably won't leak, but on an aircraft engine I find it hard to swallow.
There is a lot higher chance of a problem doing this, and absolutely no chance of a problem using an adapter.
I know you have mentioned in the past when this cropped up about Diamond using 1/8npt and M10 threads together. but just because they have used a very poor solution to a very simple problem doesn't mean its ok.
I spent 13 years in one of the biggest engineering firms cutting every conceivable thread. I was the "King of Threads" ;-), trust me, I know what I am talking about.
I now need your help on another subject on Capacitors. Please reply to my new thread, no pun intended.
Mark
Thank you said by: Rhett Mitchell
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