Fuel Selector Valve - Both Tanks Option?

[jsharkey]

I fly C172s and am used to having a "Both Tanks" option.
The Van's valve doesn't seen to enable this.
Am I correct in this assumtion - and is there a reason?
Is it a low wing versus high wing issue?

Jim Sharkey
RV6 - getting there!!!

[Mel]

With a high wing, you have gravity helping you. If one port is uncovered, gravity will cause the other to feed. Not so with a low wing. If a low wing port is uncovered, the pump will cavitate and NOT feed from the other wing.

[Kevin Horton]

Anyone who can't understand why a Both selection wouldn't work in an RV should do a simple experiment. Buy some clear plastic tubing and a T fitting. Put a piece of tubing on each end of the T. Put two ends in glasses of water, and suck on the other end. This is the situation when both tanks have fuel. Now, empty the water out of one of the glasses and try again. Now all you suck is the air from the empty glass.

On a high wing, gravity feed fuel system, a Both position can improve safety, because you don't have the risk of engine failure if you forget to change change tanks. On a low wing, suction feed fuel system, a Both position would decrease safety, as the engine would quit when either tank ran dry. Yes, you could simply change to the tank with fuel to get a restart, but first you have to figure out which tank is the good one. At least with a Left - Right fuel selector, if you forget to change tanks it is obvious which tank you need to switch to.

[Greg Arehart]

Along those same lines, I dislike the Vans fuel selector because it doesn't have a clear "stop" at each position (sure, its there, but only if one is very sensitive). Seems to me this might easily allow one to put the valve in a slightly "off" position. Of course, it would probably be noticeable as soon as the engine sputtered and stopped but... I have been considering a couple of alternatives. One is to put a manual stop just CCW of the L tank position and another just R of the R tank position, thereby allowing me to turn the valve to exactly the correct position. Downside is that there would not be an "off" position. An alternative is to put a single on-off valve on each tank line, with a T just engine-side of the valves. This would necessitate turning two valves to change tanks, plus an additional connection (i.e., leak potential), but at least I could be certain of valve positioning. Comments on other aspects of this that I have overlooked would be welcome, including other options for the fuel selection.

greg

[Mel]

Fuel systems need to be as simple as possible.
Just use a different valve if you are uncomfortable with Van's.
BTW, I can't remember the last time I certified an airplane with Van's valve.

[FrankK90989]

Originally Posted by Greg Arehart

Along those same lines, I dislike the Vans fuel selector because it doesn't have a clear "stop" at each position (sure, its there, but only if one is very sensitive). Seems to me this might easily allow one to put the valve in a slightly "off" position.

greg

Place a thin clean mark on the valve stem and one for each position (L-R) on the plate and just line them up, no need to feel.

[L.Adamson]

Originally Posted by Greg Arehart

Along those same lines, I dislike the Vans fuel selector because it doesn't have a clear "stop" at each position (sure, its there, but only if one is very sensitive). Seems to me this might easily allow one to put the valve in a slightly "off" position. Of course, it would probably be noticeable as soon as the engine sputtered and stopped but... I have been considering a couple of alternatives. One is to put a manual stop just CCW of the L tank position and another just R of the R tank position, thereby allowing me to turn the valve to exactly the correct position. Downside is that there would not be an "off" position. An alternative is to put a single on-off valve on each tank line, with a T just engine-side of the valves. This would necessitate turning two valves to change tanks, plus an additional connection (i.e., leak potential), but at least I could be certain of valve positioning. Comments on other aspects of this that I have overlooked would be welcome, including other options for the fuel selection.

greg

Either exact markings, as mentioned. Or just get an Andair valve, and problems will all be solved, including the "off" position.

L.Adamson --- RV6A/Andair fuel valve

[Greg Arehart]

Mel, so what are people doing for fuel valves?

greg

[L.Adamson]

Originally Posted by Greg Arehart

Mel, so what are people doing for fuel valves?

Andair from Van's or other sources.

Note; Link didn't go where I wanted. Look under cockpit and airframe accesseries. Then fuel valves.


http://www.vansaircraft.com/cgi-bin/...1195402699-94-

[Mel]

Originally Posted by Greg Arehart

Mel, so what are people doing for fuel valves?
greg

Most people opt for the Andair valves.