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Tank Vent/Newton Fuel Caps

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dmaib@me.com

Joined: 25 Apr 2006
Posts: 455
Location: New Smyrna Beach, Florida

Posted: Sat Apr 07, 2012 11:45 am Post subject: Tank Vent/Newton Fuel Caps

I have been living with this problem for quite a while and would like to solicit some ideas for dealing with the problem. 

I purchased and installed the retrofit locking caps that Van's sells for tanks that are already built. http://tinyurl.com/7fbvpyw You receive a sleeve that fits into the existing fuel cap flange. You install this sleeve into the flange using tank sealant to secure it, and then the new caps fit into the sleeve. Easy job and it looks great. The caps are manufactured by Newton and are very nice. The problem is that when tanks are filled, the fuel comes into contact with the bottom of the cap (the cap is about 1 1/2 inches deep), and, after takeoff, fuel siphons out of the key slot on the cap until the fuel level drops below the bottom of the cap. Usually, the problem stops quickly if you are burning fuel out of the tank. I also have the SafeAir1 extended range tip tanks and have installed these caps, but they do not have this problem. The tank vents are different on the tip tanks. They are a coiled aluminum tube versus the simple 90 degree bent tube on the main tanks. Both vents have the beveled opening facing forward. Could the difference in the vent lines be the key to solving this?

I was admiring a Harmon Rocket a couple of weeks ago and I noticed that it had the Newton caps installed. I talked to the owner and he confirmed that they were the same caps from Van's. He said he fills his to the top routinely and never has any fuel siphon through the key slot. I did not think to take a look at his tank vents. I am aware of several RV-10's that have these caps and, as far as I know, they all have this problem. I emailed Newton about this, but have received no response so far.

Any thoughts or suggestions, guys/gals?

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David Maib
RV-10 #40559
New Smyrna Beach, FL

Bob Turner

Joined: 03 Jan 2009
Posts: 885
Location: Castro Valley, CA

Posted: Sat Apr 07, 2012 6:29 pm Post subject: Re: Tank Vent/Newton Fuel Caps

I don't have these caps but it sounds to me as if there is a design defect, or perhaps an O ring that needs replacing.



Since the fuel caps are on the top of the wing, a low pressure area, they will siphon fuel out if they leak at all. This will also make the fuel pump work harder, especially if the normal vent can't keep up with the pressure loss out the top. And if gas can get out, then rain can get in.



Fuel caps shouldn't leak.

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Bob Turner
RV-10 QB

dmaib@me.com

Joined: 25 Apr 2006
Posts: 455
Location: New Smyrna Beach, Florida

Posted: Sat Apr 07, 2012 6:44 pm Post subject: Re: Tank Vent/Newton Fuel Caps

 	  Bob Turner wrote: 	
		  I don't have these caps but it sounds to me as if there is a design defect, or perhaps an O ring that needs replacing.



Since the fuel caps are on the top of the wing, a low pressure area, they will siphon fuel out if they leak at all. This will also make the fuel pump work harder, especially if the normal vent can't keep up with the pressure loss out the top. And if gas can get out, then rain can get in.



Fuel caps shouldn't leak. 	




I certainly agree that caps should not leak. But, all of these caps installed on RV-10's seem to do this. I can't imagine it is an o ring problem when this seems to be a fleet problem limited to RV-10's. So, I would lean towards the design defect, except that it does not seem to be a problem on other types of aircraft. (that I know of)



Interestingly enough, My airplane has had to sit out in significant rain a few times and I have never had one drop of water in my fuel samples. Ever.



I am zeroing in on the RV-10 tank vent design because I cannot think of anything else at this point. I hope somebody on the forum has some insight on this issue.

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David Maib
RV-10 #40559
New Smyrna Beach, FL

dave.saylor.aircrafters(a
Guest

Posted: Sun Apr 08, 2012 4:35 am Post subject: Tank Vent/Newton Fuel Caps

We have the Newton caps. We fill up after every flight but we leave each tank down by 2 gallons. We do this so it doesn't vent out the normal vents onto the floor. There isn't much expansion room in these tanks. 

I've heard of fuel coming out the key hole but if it happens to us it's very rare.  I very much doubt you would loose a meaningful amount of fuel.  I've  never seen any water get in. 

--Dave Saylor

1015 hrs

On Apr 7, 2012, at 23:44, "dmaib(at)me.com" <dmaib(at)me.com> wrote:

 	  Quote: 	

 Bob Turner wrote:

> I don't have these caps but it sounds to me as if there is a design defect, or perhaps an O ring that needs replacing.

> 

> Since the fuel caps are on the top of the wing, a low pressure area, they will siphon fuel out if they leak at all. This will also make the fuel pump work harder, especially if the normal vent can't keep up with the pressure loss out the top. And if gas can get out, then rain can get in.

> 

> Fuel caps shouldn't leak.

 I certainly agree that caps should not leak. But, all of these caps installed on RV-10's seem to do this. I can't imagine it is an o ring problem when this seems to be a fleet problem limited to RV-10's. So, I would lean towards the design defect, except that it does not seem to be a problem on other types of aircraft. (that I know of)

 Interestingly enough, My airplane has had to sit out in significant rain a few times and I have never had one drop of water in my fuel samples. Ever.

 I am zeroing in on the RV-10 tank vent design because I cannot think of anything else at this point. I hope somebody on the forum has some insight on this issue.

 --------

 David Maib

 RV-10 #40559

 Transition Trainer

 Read this topic online here:

 http://forums.matronics.com/viewtopic.php?p=370263#370263

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dmaib@me.com

Joined: 25 Apr 2006
Posts: 455
Location: New Smyrna Beach, Florida

Posted: Sun Apr 08, 2012 7:07 am Post subject: Re: Tank Vent/Newton Fuel Caps

Leaving the tank down enough to keep the fuel from contacting the bottom of the caps does work, but I would really like to be able to get the tanks close to full when leaving on a long cross country. 



I agree that the amount of fuel vented is not significant, but it makes a mess on the wing with the blue dye. Full tanks will definitely lose fuel through the vent tubes as fuel expands with rising temperatures. I've seen that happen on many different airplanes.



I may try modifying my vent tubes with a couple of coils, like my tip tank vent tubes. I can't see why that should make a difference, but I guess it is worth a try.

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David Maib
RV-10 #40559
New Smyrna Beach, FL

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