Not drawing from the right hand tank

[Mel]

There is nothing unsafe about the BOTH position of this valve. It MAY become unsafe if it is used but even then the airplane won't fall out of the sky.
There are a number of switches in every aircraft that create an unsafe situation if used in flight. Guess what happens if the ignition switch is moved to OFF or the mixture is pulled to OFF? Placards are even not required for these obvious unsafe situations.

Apples to oranges.

The pilot of this aircraft is lead to believe that the aircraft will function normally using a both position on a fuel valve. This is not normal.

The pilot of any aircraft is lead to believe that the aircraft will function normally if the ignition switches are left "on". This is normal!

If you bring an aircraft with a modified fuel system to me for inspection, you must prove to my satisfaction that your modifications are feasible.
If you think that a "both" position on an otherwise standard RV fuel system is feasible, then you shouldn't bring your aircraft to me for inspection.

 

[David-aviator]

Apples to oranges.

The pilot of this aircraft is lead to believe that the aircraft will function normally using a both position on a fuel valve. This is not normal.

The pilot of any aircraft is lead to believe that the aircraft will function normally if the ignition switches are left "on". This is normal!

If you bring an aircraft with a modified fuel system to me for inspection, you must prove to my satisfaction that your modifications are feasible.
If you think that a "both" position on an otherwise standard RV fuel system is feasible, then you shouldn't bring your aircraft to me for inspection.

With all do respect Mel, you do good work, but there is nothing normal about any experimental aircraft. That's why the FAA requires the warning to passengers that the aircraft has not been built to FAA standards.
This airplane was certified by someone who pulls their pants on just like everyone else here. I simply vote to give them a break.

 

[Toobuilder]

And to add, I'm convinced that adding a "both" position to an RV is going to increase pilot workload rather than reduce it - but properly managed (i.e., don't use the "Both" position), it is not "unsafe".

There are plenty of single engine certified aircraft with far more complex and difficult to manage fuel systems than an RV with a "Both" position. Some older Beech products and even the PA-22 with an aux tank comes to mind. Just about every Rocket has you pass through "OFF" every time you switch tanks - a very specific "Fail" in todays aircraft design philosophy.

Best to add the proper valve, but going so far as to ground an aircraft owned and flown by an aware pilot until that happens... a bit much.

 

[Bevan]

I'm STILL a DAR. I have certificated over 800 aircraft. and like Gary, I would never sign off an RV with a "Both" position on the fuel selector.

It is my understanding that the Andair two position valves have a "common" position that technically feeds fuel from both tanks. This is so that fuel is not interrupted from one tank before it begins to flow from the other tank (when switching tanks). If true, it is a safety feature. The difference with the OP's valve is that it may simply be labeled with a "both" position. So in this case, it may be prudent to simply order a new face plate or somehow cover/delete the word "both", and leave the valve itself as is. Best to check directly with Andair and post the findings back here for future reference.

Bevan

 

[Bevan]

Here's an alternate test rig. I recommend Stella Artois for test fluid, but this guy looks like a Bud man:

Stick this hat on the fan sitting in front and slightly below you (tell him it's a science project) with one cup empty. See what happens after you begin to suck...if you even get that far.

Bevan

 

[rv7charlie]

It is my understanding that the Andair two position valves have a "common" position that technically feeds fuel from both tanks. This is so that fuel is not interrupted from one tank before it begins to flow from the other tank (when switching tanks). If true, it is a safety feature. The difference with the OP's valve is that it may simply be labeled with a "both" position. So in this case, it may be prudent to simply order a new face plate or somehow cover/delete the word "both", and leave the valve itself as is. Best to check directly with Andair and post the findings back here for future reference.

Bevan

Ding!

Some variation on that theme likely applies to most selector valves. If the label says 'both', it *implies* it's ok to operate there, but if it just says 'left-right-off', the pilot should pick one.

A friend sold an -8 with the current 'stock' valve; 45 degrees L & R for tanks. Buyer had fuel starvation in flight with fuel in the tanks; later said that he thinks he might have aligned the handle either fore/aft or in line with the spar because he'd previously owned an RV with one of the old style valves. Nothing wrong with the valve or the label; he just didn't select a labeled position.

To the OP:
If you don't find a blocked vent, is it possible that you finally found the right conditions for the plane to draw from only one side with the selector in 'both'? Even a high wing Cessna will feed unevenly when running on 'both', though it's difficult for it to suck air (unlike low wing planes).

As a FWIW, on my -4, with less than ~1/2 tanks I can disconnect the line from the tanks to the (stock) Van's selector valve without fuel flowing.

You can check for actual flow by selecting 'off', and disconnecting the fuel line at the engine or gascolator, as others have recommended. If you use a tank leak test setup (balloon on one leg of at T fitting, or a manometer tube on the T), you can select a tank and pressurize the tank through the vent. If there are no blockages, you can easily move fuel through the valve and out the line in the engine compartment. Then select the other tank, & repeat. The balloon or manometer tube will protect the tank from over-pressure, & still allow enough pressure to move the fuel through the open valve & line to the firewall area.

Charlie

edit: You won't get 'bubbles' in the fuel by blowing in the vent, unless you have the tank completely full & that wing is 'low'. The vent is (or should be) at the highest point inside the tank.

 

[BobTurner]

I'm with Mel here. As an A&P his finances are at risk here.
(Can you see the widow's lawyer in court? He'll hold up THIS thread, and say that if ordinary people thought this was bad, then an A&P should surely have known...)

 

[Toobuilder]

Are we still talking about the OP and this one specific instance of troubleshooting, or are we off in the twilight zone again?

 

[Mel]

You are correct. It is experimental and you can do what you wish. But when an airplane goes down because the pilot was flying "on both" and one tank became too low, it goes against all of us flying these homemade airplanes."

You may have the last word.

Please don't call me for an inspection.

 

[David-aviator]

You are correct. It is experimental and you can do what you wish. But when an airplane goes down because the pilot was flying "on both" and one tank became too low, it goes against all of us flying these homemade airplanes."

You may have the last word.

Please don't call me for an inspection.

If I do, it will be right.

Bottom line here is the RV's are a LEFT-RIGHT fuel system.

 

[RV7A Flyer]

It is my understanding that the Andair two position valves have a "common" position that technically feeds fuel from both tanks. This is so that fuel is not interrupted from one tank before it begins to flow from the other tank (when switching tanks). If true, it is a safety feature. The difference with the OP's valve is that it may simply be labeled with a "both" position. So in this case, it may be prudent to simply order a new face plate or somehow cover/delete the word "both", and leave the valve itself as is. Best to check directly with Andair and post the findings back here for future reference.

Bevan

Well...sort of true. The L-R-Off valve has a sort of detent at each position, but it will flow (some) fuel when it is between positions, by design (IIRC). I believe the L-Both-R-Off valve has detents at all *four* positions. Flowing fuel while switching tanks is, as you say, a safety feature, but shouldn't be relied on, obviously.

Would be really unusual if a L-R-Off valve was shipped with a L-Both-R-Off faceplate, or would be *very* bad construction if the builder swapped out the correct faceplate for an incorrect one.

ETA: http://www.andair.co.uk/wp-content/uploads/2014/02/fuel_selectors_FS20.pdf

The data sheet for the valves in question talk about the detents at each position.