After failing to keep to the advice "shiny side up, greasy side down" on a CCV trial, I have discovered that Tiggrr will leak fuel from its tank if the angle of dangle is extreme enough. The leak is through the breather pipe, and I need a non-return valve to allow air in, but not fuel out. The pipe is rubber, about 1/4 inch ID. Anyone know of a source for these? Haven't seen any about locally. It would need to be OK with petrol, so the type that goes in the windscreen washer tube to prevent water flowing back may not be suitable.
First off, Merlin motorsport, Demon Tweeks and Mocal all sell flap or ball valves for just this purpose. These are normally open but close when they are inverted. The problem with these is that they still allow spillage at intermediate angles which can be an issue. They are more designed for circuit racers which tend to be on their wheels or upside down.
The second option is the old school rally technique. This involves wrapping the breather pipe around the tank a few times with some of the coils being at 90 degrees to the others. In this way, no matter which direction you roll in the fuel always has to go against gravity to escape. These do tend to leak a little as, over time, fuel will work it's way to the end of the pipe. I believe that you can also get problems with the system managing to prime itself as a syphon which can defeat the object somewhat :-)
The third option is the most complex but has the advantage of being cheap (if you can use second hand LR parts) and will not leak fuel in any circumstances. If you look at a classic Range Rover with an expansion tank in the wing you'll see it has a number of valves. (Or a Disco/Defender with a charcoal canister) One of these valves is designed to open when there is a vacuum behind it, another is designed to open when there is positive pressure behind it. By splitting your breather pipe (either run two breathers from the tank or put a T piece in) you can run one pipe to one of the positive pressure valves and the other to a vacuum valve. On the other side of the vacuum operated valve you run a pipe upwards as this is your air intake for the tank. On the other side of the positive pressure valve you run a pipe downwards as this is where the pressure and vapours will be released. On Discos and Defenders this is normally fed into a charcoal canister and you could do the same if you wanted but it's a bit unnecessary IMV as it's only releasing small amounts at a time.
With a good fuel cap seal you'll find that this last option leaves your tank somewhere between a negative and positive pressure at all times ( you get a hiss when you open the cap). This confirms that the fuel system is sealed (no breather in the fuel cap for example) and you won't get any fuel spillage no matter what angle you put the vehicle at. I've been running this system in my competition vehicles for just over 2 years now without any issues. Those that know the kind of event that I compete in will realise just how much testing at silly angles it's got in that time :-)
Strangely I find on an EFi equipped like this the tank seems to spend more time pressurised than in vacuum, especially in the UK. European fuel seems to contain less butane so doesn't froth as much, doesn't pressurise the tank and gives me more MPG.
If you want the part numbers for the valves I can dig them out for you.
...it lets the air through the wrong way, right? To let air into the tank, but not allow fuel out, you would have to mount it wrong way round, top end in the pipe and screw fitting outside. Or have I got it wrong?
Twas 13 Oct 2004 06:30:38 -0700 when snipped-for-privacy@yahoo.co.uk (Richard Brookman) put finger to keyboard producing:
for aquariums you can get inline rubber valves which will let air through one way and stop any liquid going the other way. fits inline in the same bore plastic tube as screen washer pipe. just a thought. they are dead cheap.
I sell a ball valve type in-line non return assembly. It will let a bit dribble out if you happen to be at the critical angle of confusion but in real terms if you have the pipe off the top of it extended up a bit this is not likely to happen. It is fitted with -6jic unions either end to be used with braided hose and unions but I could find some unions to adapt these to 'push on' bayonets.... Best way to fit them is to weld a -6 male boss into the top of the tank and fasten the valve direct to the tank then run hose off it to wherever you want....
Not cheap but bloody good ( good enough for NASCAR regs. anyway! )
Twas Wed, 13 Oct 2004 18:10:03 +0000 (UTC) when "Richard Brookman" put finger to keyboard producing:
that I have no idea about, I think the valve itself is a synthetic rubber.
formatting link
down to non-return valves.I'm sure I have a couple kicking around here somewhere, I'll drop onein the post and you can try it if you like, I'll have a hunt aroundtonight.
MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.