Plus 2 fuel tank venting

[jono]

On my last Plus 2 I did the Club Lotus modification which worked well but was quite a lot of work, especially the filler neck connection

This time I intend to stick with the original arrangement but i'm looking at the possibility of introducing 2 way vent valves into the pipes ('Newton' valves). Has anyone done this and what did you use?

The main issue I guess is finding a valve with the correct rating in positive and negative pressure conditions.

Another question - what is the best vapour resistant tubing to use?

Cheers

Jon

[The Veg]

For tubing I don't know what the absolute best is, but I used Tygon because it is very compatible with petrol, and in a great serendipity for Lotus, it weighs almost nothing!

[john.p.clegg]

bet it cost an arm and a leg though....

John

[mbell]

The main issue I guess is finding a valve with the correct rating in positive and negative pressure conditions.

I think the main problem will be find a valve with high enough flow rates more than the pressures, I don't think the +2 needs anything out of the normal for pressures. But you need to be able to vent the tanks at rate fast enough to match the petrol station fuel pump for filling the tank. That is why the tank has two large diameter pipes.

The Newton valve is quite small and doubt it would vent at anything like the required rate for filling the tank. Even the Club Lotus setup struggles to vent when filling in my experience.

Not sure on a good solution, maybe a manual vent under the car for filling, coupled with a Newton valve for in use?

[HCA]

A Newton style vent valve does not operate during filling. It only works on a sealed tank system where it is subjected to either negative or positive pressure.

For ventilation during filling, there is a pipe from the top of the tank into the filler neck just below the filler cap seal. Ie on a +2, of the existing two tank vents - one connects to the Newton valve and the other tees into the filler neck. Make sure therubber gasket in the filler cap makes solid contact with the neck.

[jono]

A Newton style vent valve does not operate during filling. It only works on a sealed tank system where it is subjected to either negative or positive pressure.

For ventilation during filling, there is a pipe from the top of the tank into the filler neck just below the filler cap seal. Ie on a +2, of the existing two tank vents - one connects to the Newton valve and the other tees into the filler neck. Make sure therubber gasket in the filler cap makes solid contact with the neck.

Sure, I understand how they work. If installed within the existing dual vent pipe system they would come into play when filling but only once the fuel level is above the filler neck inlet on the tank. What you describe in your second para is the Club Lotus mod which I carried out on my last Plus 2 but wish to avoid on this build.

What I am trying to achieve is a means of relieving +ve pressure during filling and -ve pressure during fuel draw down and also smells being released when the car is laid up. The Club Lotus mod does that but I don't want to do it this time.

But as others have said there may not be a model of valve whith sufficient capacity to relieve pressure during filling without it being a painfully slow process.

I will speak with Newton. Otherwise it's corks!

[HCA]

Sorry, I do not know what the Lotus Club mod is. I only know how a modern sealed tank system works where the air pressure that builds up on filling is released through the filler neck. Yes you could have manual vents (not sure what you mean by corks...) but this sealed system is the accepted method.

and yes, it is schematic only - the vent pipe runs will be over the tank etc..

[jono]

Sorry, I do not know what the Lotus Club mod is. I only know how a modern sealed tank system works where the air pressure that builds up on filling is released through the filler neck. Yes you could have manual vents (not sure what you mean by corks...) but this sealed system is the accepted method.

The attachment IMG_4366.jpg is no longer available

and yes, it is schematic only - the vent pipe runs will be over the tank etc..

essentialy that is the club Lotus mod

[h20hamelan]

A modern fuel tank filler neck cap has a one way valve, allows air in.
The thickness of the edge is about the same as the original +2, and of course it fits in though without screwing. When I close the lid on the original +2 fuel door it seals it. But it wasn’t until I added the anti-slosh valve that it stopped fuel exiting around right hand corners.
The problem is atmospheric venting so you dont get vacuum.

Jono, will you be adding a anti-slosh valve to the neck like in the Miata or similar?

[alanr]

I have found the Club Lotus Fuel Vent Mod works very well in regards stopping any fuel smells. I have no fuel smells at all ever, but you do in addtion have to fit the MX5 one way valve in the filler neck hose, if you don't I found you get fuel sloshing out of the filler cap all over the rear wing when cornering hard.

Alan.

[jono]

I have found the Club Lotus Fuel Vent Mod works very well in regards stopping any fuel smells. I have no fuel smells at all ever, but you do in addtion have to fit the MX5 one way valve in the filler neck hose, if you don't I found you get fuel sloshing out of the filler cap all over the rear wing when cornering hard.

Alan.

Hi Alan,

this time I will be adding one!

It's something I never bottomed out last time and I always had fuel streaks down the rear wing after a spirited drive.

[alanr]

Hi Jon,
Yes I found you really do need to fit the MX5 on-way valve unit in the filler hose to complete the +2 fuel smell elimination excercise.
I must admit I struggled for a while to source a new MX5 non return one way valve, on back order everywhere at the time it seemed, but then I managed to find a complete secondhand MX5 filler pipe complete with a non return valve in it on ebay for just £8!

Cheers,...Good luck with completing the car,

Alan.

[jono]

Thanks Alan,

She's coming along nicely - just spent a small fortune on chrome work at Derby Plating but it's worth it as the results they achieve are truly outstanding.

I've set a high standard for this car as it's probably the last one i will do (famous last words!!)

[HCA]

With the vent to atmoshere fitted with a Newton, and the filler neck properly sealed with a good rubber washer in the cap, there should be no need for an anti return valve…

[h20hamelan]

Not to point out obvious, but, the +2 filler lid cap does have a vent, and a spring to hold the cap down from pressures of fuel slosh (insufficiency). But, is it enough, how does it compare to modern standards.
Venting to atmosphere vs venting to filler neck