Safety Concern with Fuel Press Sender

[rongawer]

Originally Posted by BlackhawkSP

Don:

Yes, per the plans/drawings for the RV-10, the VA 128 restrictor was installed per Drawing FF4-3. This is the same diameter orifice though, that is used for the oil pressure sensor port too, per Drawing FF1-4. I plan on calling Van's to see if there might be a different part made specifically for the fuel sensor port with a much smaller orifice port to minimize the flow rates available for a failure of the pressure sensor in this scenario. This would mitigate the fire hazard quite a bit from the current flow rates I have observed. We just need to read the pressure, so a much smaller opening would probably do to read pressure with a slight delay, while really reducing the flow rates in a failure of this type. I may just modify the one I have by plugging it with brass, and re-drilling a smaller hole.

McMaster-Carr has gauge dampers in both brass and stainless in several sizes, which includes 1/8 NPT. I have found that 0.004 works well for manifold pressure, 0.008 for fuel and 0.015 for oil. The VA-128 is shown with a 0.040" orifice for comparison. The old Kavlico's are brass, the new ones are stainless, and if you are using UMA, which I have, they are stainless as well.
https://www.mcmaster.com/3820K26

Aside from restricting flow in the event of a leak in the sensor, their real purpose is to snub pressure oscillations and provide a nice, stable read out for the monitored system, which these do well.

If you're looking for an alternative, UMA is a solid product and made in Virginia by some really nice folks with a good catalog of sensors. Most of their line is for certified aircraft, so a little more money, but it's a really small cost in the overall budget for what it does.

[Aussieflyer]

I first posted this issue in 2017. After 6 months and 80 hours operation. Garmin Australia flatly refused a warranty claim because the sender was over 12 months old having sat on my shelf during the build. There was no follow up.

I'm glad the issue has now been fixed. However they should have treated the issue more seriously in 2017. We are lucky there have been no fires. We all learn lesson along the journey.

Alan

[BlackhawkSP]

Originally Posted by rongawer

McMaster-Carr has gauge dampers in both brass and stainless in several sizes, which includes 1/8 NPT. I have found that 0.004 works well for manifold pressure, 0.008 for fuel and 0.015 for oil. The VA-128 is shown with a 0.040" orifice for comparison. The old Kavlico's are brass, the new ones are stainless, and if you are using UMA, which I have, they are stainless as well.
https://www.mcmaster.com/3820K26

Aside from restricting flow in the event of a leak in the sensor, their real purpose is to snub pressure oscillations and provide a nice, stable read out for the monitored system, which these do well.

If you're looking for an alternative, UMA is a solid product and made in Virginia by some really nice folks with a good catalog of sensors. Most of their line is for certified aircraft, so a little more money, but it's a really small cost in the overall budget for what it does.

Excellent info !!! Thanks. Dampening out the pulses definitely would reduce stress on the sensor, and have the added benefit of lower flow rates in a leak type failure.

[Lenny Iszak]

Which fuel injection servo are you guys using on the planes that had a pressure sensor failure?
Something weird is happening on this RV-7 with an Avstar injection servo. After shutdown with the mixture at ICO the fuel pressure keeps going up until it gets over 50PSI and out of the range of the sensor. Who knows how far up it goes.

This doesn't happen on my RV-10 with a Precision RSA servo. This pressure rise may have something to do with the pressure sensor failures.

Lenny

[TS Flightlines]

Lenny----thats the kind of info we need.


Tom

[Jetmart]

Originally Posted by Lenny Iszak

Which fuel injection servo are you guys using on the planes that had a pressure sensor failure?
Something weird is happening on this RV-7 with an Avstar injection servo. After shutdown with the mixture at ICO the fuel pressure keeps going up until it gets over 50PSI and out of the range of the sensor. Who knows how far up it goes.

This doesn't happen on my RV-10 with a Precision RSA servo. This pressure rise may have something to do with the pressure sensor failures.

Lenny

I wonder if the pressure increase would happen if you shut off the fuel selector for 10 -15 seconds before going to ICO. Not long enough for it to use all the fuel in the line. Might be worth experimenting how long it would take to run with the fuel off to not get an increase.

A 2nd question do most shut off their fuel after shutdown?

[Pilot135pd]

I never shut off my fuel selector.

[bkervaski]

Originally Posted by Pilot135pd

I never shut off my fuel selector.

+1 (same here)

[TShort]

+ another. I never shut mine off.

I did the Garmin SB Saturday; I have the exact numbers written down (not in front of me), but shutdown was around 23PSI, it went up 0.1 or 0.2 PSI in the first couple minutes then steadily trended downward after.

[TimO]

While I don't have that particular sensor, myself, to piggyback on Lenny's comment, I have the Avistar on my IO-390 and I do know that it holds in fuel pressure with the mixture at idle cut-off. I also have the andair fuel pump. If I park while hot, and I move the mixture off of cut-off, I can hear fuel squirt into the injectors. (when hot, of course) So I know the pressure builds and is retained in that pump-to-servo section of the fuel system.

I haven't ever had an issue, but like I said, I'm using a higher pressure stainless steel sensor. I just never heard the same thing on my IO-540 with a precision system and AFP pump.