Fuel Selector Valve

[170C]

I agree with Bruce on his comments. I seem to remember George had an incident where he found fuel all over his hangar floor one time. I know we should turn the fuel valve off each time, but rarely do so. I would venture a guess that very few high wing planes would be found to have their fuel valves turned off while in a hangar or tied down on a ramp. Probably a potential disaster waiting to happen.

[bagarre]

I agree with Bruce on his comments. I seem to remember George had an incident where he found fuel all over his hangar floor one time. I know we should turn the fuel valve off each time, but rarely do so. I would venture a guess that very few high wing planes would be found to have their fuel valves turned off while in a hangar or tied down on a ramp. Probably a potential disaster waiting to happen.

I turn mine off every time I'm not in the airplane.

I had the flexible fuel line from the gascolator to the carburetor split on me once. the fuel was off so all was well. Noticed it while pre-flighting when I turned on the fuel. Saved me a lot of gas.

Also, I can say with great authority that the gascolator holds enough fuel to taxi one airplane's length away from the gas pumps.

[170C]

David, good reason to use the OFF position! When I first got my plane I recall having the valve shut off and starting it up without realizing what I had done However, even on a private, grass strip where I could go from my hangar right onto the runway, I never got to the runway before running out of fuel. I have heard stories of some types of aircraft that might have had sufficient fuel to just get airborne before running out of fuel. I don't have any idea what kind of plane that would be.

[DaveF]

That is the case with the B models as well.

Inside the valve is a cam that 'plugs' one of the 3 inlets at a time.

Fuel Both: None of them are blocked.
Fuel Left: Right inlet is blocked. Left inlet and Outlet to Gascolator is open.
Fuel Right: Left Inlet is blocked. Right inlet and Outlet to Gascolator is open.
Fuel Off: Outlet to Gascolator is blocked but Left and Right inlets ARE open to each other and they cross feed.

There is no position that shuts off both the left and right inlets at the same time.

That's not how the selector in my airplane works! It's nothing but a manifold with two inlets and one outlet (two if you include the drain plug). There are two ball-on-O-ring-type valves, one on each tank inlet line. The cam pushes the ball off the seat to allow fuel flow. It opens one, both, or neither. When the valves are open, fuel can flow from the tanks into the selector body and to the engine and drain plug. When they're closed, they're closed, and no fuel flows to the engine or to crossfeed. There is no valve on the outlet.

[bagarre]

You're right! I mis-remembered how it was set up.
http://cessna170.org/forums/viewtopic.p ... ctor+valve

The steel ball and springs are only on the fuel inlet ports and NOT also the outlet port as I stated.

So, fuel Both Off position will not cross feed tanks with this valve.

Sorry, I should have spent a few more seconds researching vs acting off of memory.

[GAHorn]

The "late-style" fuel selector valve, as found in the serials prior to 20286 were simple "Weatherhead" brass valves with a "spigot" drilled internally to provide passageways formed as a "T".... the short tops of the T provided access from each tank in the Both position... and the long bottom of the T fed those tanks toward the gascolator. Rotating the handle, rotated the T, which allowed only ONE tank at a time to feed the gascolator...and when rotated further such that the long bottom of the T faced AFT... the gascolator did not receive fuel,... however the two wing tanks were still connected to each other and fuel could transfer between the two tanks.

The later, square, machined-aluminum fuel selector valve (as found in B-models subsequent to 20285) utilized a triangular "cam" which upsets the seat of check-balls, thereby allowing fuel to flow similarly to the earlier brass valve... EXCEPT that the common complaint of fuel transferring between tanks was eliminated, since the cam did not upset the check-balls when the valve was in the "off" position. THIS WAS THE PURPOSE of Cessna's decision to change to the machined-aluminum valve.... to end complaints of that fuel transfer while the valve was in the Off position.

UNFORTUNATELY... Cessna mistakenly illustrated the machined aluminum valve assembly in their Illustrated Parts Catalog (IPC)... and in that mistaken illustration they indicated the O-ring which provided the seat for the check-ball in an incorrect position.... which actually PREVENTED the check balls from seating correctly. This led to the popular belief that even the LATE valve would allow transfer between the tanks when the valve was actually selected to "off". (It also allowed an empty tank to re-fill, albeit at a slower rate than normal, when the valve was in any positon other than "Both".) See another thread for the descriptions of that incorrect assembly...THIS LINK is where I posted several pics and detailed description of my overhaul of my fuel selector valve overhaul...scan down the page if you only wish to view my article: http://cessna170.org/forums/viewtopic.p ... e&start=45 ....

The Cessna 172/175 models used the same valve and so anyone shopping junk yards for the later machined aluminum valve should not overlook those airplanes as possible sources.
The specific serials of those airplanes with interchangeable valves are:

C-172... SN 28000 thru 17249544
C-175... SN 55001 thru 17557002

Later 175 aircraft also have an interchangeable valve but may be accompanied with different attaching hardware SN 17557003 thru 17557119.

Hope this helps.

Let me add something which has been commented on previously...about one tank draining faster than the other while operating on "Both" (this is a paste/copy of one my previous posts)
Most high wing Cessnas, when fed from both tanks simultaneously, will actually appear to use fuel more rapidly from one tank than the other. This is because the tanks share a common vent line. Actually both tanks are feeding equally toward the engine, but one tank (the left in most 170A and B's) appears to feed more slowly because it is also being replenished by the dual-vented right tank (remember the vented fuel cap) via the vent line. In other words, a certain amount of fuel will transfer while both tanks are relatively full from the right tank thru the vent line to the left tank. This occurs for two reasons. One is: the right tank is vented not only by the vent line gooseneck, but also by a vented cap. Therefore it's head pressure is potentially higher. The second reason is because at the time of highest fuel consumption (takeoff and climb) p-factor causes the pilot to keep the airplane straight by increased right-rudder application. This keeps the fuel level in the right tank pressed against the vent line further encouraging fuel transfer toward the left tank.
Since the end result is that fuel is leaving the left tank only toward the engine, but is leaving the right tank toward the engine AND toward the left tank, the result is a right tank that empties intially somewhat faster than the left. After approximately the first hour of flight, this transfer naturally stops, and both tanks will continue to feed the engine equally, but the left tank (no longer be replenished from the right) will read higher because it is indeed containing more fuel.
I hope this explanation helps.
(I run my airplane from takeoff to touchdown on Both, and live with it.)

Let me also add that if I were the owner of a 170A model and needed a new brass valve... I think I'd make an "owner produced part" by taking a Spruce PN 05-01032 http://www.aircraftspruce.com/pages/ep/ ... hutoff.php and drill the spigot/stem all the way thu... thereby copying the original part. This might also meet the requirements of AC27-23.

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[Francis Cahoon]

I had somewhat of the same problem. I took top off value found it to be a little warped, put piece of sandpaper on top of flat car window and sanded top flat again. this stopped the leak, but i went to wreaking yard and found one reasonable, and installed it. short wrenches seem to help to get it in and out of floor. Good luck call me if you need anything, thanks. Fran