SonexBuilders.net

Hi Guys,

It's been over 100 deg. in the shop for days now. So, I seem to end up in the house thinking a lot more than out in the shop doing. This evening I found myself sitting in the air-conditioning looking at this assembly and thinking about all the fuel leaks that have been reported in the past.



While opening and closing the valve it occurred to me that the root of the problem was probably the valve handle. If you imagine putting your pointer on the tip of the handle and moving it to the open position while considering what is happening at the threads going into the tank to counteract that force/torque, it's not good. One side of the threads is in compression and the other side is in tension. It's a lot like what you would do if you wanted to start a leak. Screw a pipe into the fitting and wiggle it side to side.

Now think about what would happen with a properly actuated T-handle. The only force present at the tank inlet would be perpendicular to the bore of the fitting. That is to say it would just press on the side of the fitting instead of trying to wrench it out of the tank.

Anyway, just a thought. Since I like simple, I think I'll go with a tee handle and try to get it past the DAR. I know from experience that I can remember where the fuel valve is, without looking, after just a few on/off cycles.

Wes

If that was a fitting at sea (a past life of mine) - then the valve would have to be strapped at either side to something so the torque was not transmitted to the lines - even if they are flexible. For exactly the "random" reasons you are surmising.

And here is a small fuel valve used in just about every small aircraft built in the 1940/50/60's that includes attachment lugs in the body of the valve for the same reason:

In fact the shut-off valve I have fitted to my Sonex https://www.aircraftspruce.com/catalog/appages/hbshutoff.php does incorporate attachment lugs, it's just that on the Sonex there's nothing to attach them to. If your tank incorporates the Oops fittings, it probably isn't a problem. If, as in my case, your tank doesn't have Oops fittings, you should be careful not to put too much side load on the valve.

Peter

Might consider a remote operator for that valve. A simple push pull knob and cable attached to a bracket mounted to, (clamped around) the valve will eliminate most any force pushing or pulling on the valve and its fitting to the tank, but two bigger benefits to my mind are that the valves position can be seen at all times, no question of anyone accidentally knocking it to partially closed, and it can be shut off with seat and shoulder belts kept tight in event of emergency off field landing. There have been a couple of such posted, PM me if wanting drawing and photo of what I did.

David A.

WesRagle wrote:
While opening and closing the valve it occurred to me that the root of the problem was probably the valve handle. If you imagine putting your pointer on the tip of the handle and moving it to the open position while considering what is happening at the threads going into the tank to counteract that force/torque, it's not good.

Wes

I have always suspected that could be a possible cause of a seeping original fitting. I have the same valve as Peter but have it mounted to a bracket on the firewall with an extension shaft fitted to the handle. No oops fittings yet

DCASonex wrote:Might consider a remote operator for that valve. A simple push pull knob and cable attached to a bracket mounted to, (clamped around) the valve will eliminate most any force pushing or pulling on the valve and its fitting to the tank, but two bigger benefits to my mind are that the valves position can be seen at all times, no question of anyone accidentally knocking it to partially closed, and it can be shut off with seat and shoulder belts kept tight in event of emergency off field landing. There have been a couple of such posted, PM me if wanting drawing and photo of what I did.

David A.

Thanks David but I think I'll just try a T handle. Well, not really a T but more like a giant wing nut. Lacking attach points, that seems to me to be the best answer to eliminate the tendency to side load the valve. The valves are pretty stiff so I wouldn't expect them to move in flight. The bigger hazard for me, since I'm using a float bowl carb, is forgetting to turn the fuel on and using up my bowl full of fuel on takeoff. The Zenith looks like a solid piece but lacks in flight mixture control. So, it is probably prudent to turn the fuel off after engine shutdown since it can't be pulled to idle cutoff. As I recall, my C-150 only called for fuel to be turned off in case of an emergency.

In any event, I plan to be more disciplined this time around and will use start and shutdown check lists that include checking the fuel valve. Now, if I can just figure out where to keep the check lists in a Onex :-)

sonex892. wrote:I have always suspected that could be a possible cause of a seeping original fitting. I have the same valve as Peter but have it mounted to a bracket on the firewall with an extension shaft fitted to the handle. No oops fittings yet.

Yep, those look like the fuel valves included in the old RV kits.

Wes

WesRagle wrote:The bigger hazard for me, since I'm using a float bowl carb, is forgetting to turn the fuel on and using up my bowl full of fuel on takeoff....

In any event, I plan to be more disciplined this time around and will use start and shutdown check lists that include checking the fuel valve. Now, if I can just figure out where to keep the check lists in a Onex :-)
Wes

This is where acronyms can really come in handy. The one I use anytime I'm crossing the hold-short line for takeoff is FAT PIG.

Flaps
and
Trim
Pins (canopy)
Ignition (both on)
Gas (Fuel selector and mixture)

If those critical items are always set for takeoff there isn't much else major that could go terribly wrong if forgotten. Added benefit is the chuckle I get at my silly saying, puts me in the right mindset to fly!

Flaps
and
Trim
Pins (canopy)
Ignition (both on)
Gas (Fuel selector and mixture)

Well, since I'll have carb heat, maybe a FAT COLD PIG ;-)

Wes

sonex892. wrote:

WesRagle wrote:
While opening and closing the valve it occurred to me that the root of the problem was probably the valve handle. If you imagine putting your pointer on the tip of the handle and moving it to the open position while considering what is happening at the threads going into the tank to counteract that force/torque, it's not good.

Wes

I have always suspected that could be a possible cause of a seeping original fitting. I have the same valve as Peter but have it mounted to a bracket on the firewall with an extension shaft fitted to the handle. No oops fittings yet

Where is that fuel line going from the bottom of the valve?

Rofomoto wrote:Where is that fuel line going from the bottom of the valve?

Rear removable behind seat tank.