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Fuel tank vent
jos - 14/6/05 at 02:13 PM

Ive got a vent at the top of my fuel tank, presumably to allow pressure to equalise.

What is needed to make this so that grot cant get into the tank.

Photos and descriptions would be appreciated.

stevebubs - 14/6/05 at 02:50 PM

Go to www.thinkauto.com and look at tank breather valves

S

ned - 14/6/05 at 03:41 PM

you want a trl7, about £25 +vat

just fitted one myself, goes inline on 1/4" hose, i ran mine from a t-piece in the injection return line.

Ned.

rear fuel line breather return
rear fuel line breather return

theconrodkid - 14/6/05 at 06:46 PM

wrong type of hose clips there ned

Jon Ison - 14/6/05 at 06:51 PM

push bike inner tube valve, 50p

ned - 14/6/05 at 09:21 PM

conrod, explain?!

zetec - 14/6/05 at 10:00 PM

I fitted a tank vent valve from a trials bike, gives just enough both ways breathing and designed for a vehicle expected to spend time upside down when crashed! cost £5 from local shop.

SeaBass - 15/6/05 at 06:41 AM

quote:
Originally posted by ned
i ran mine from a t-piece in the injection return line


Are you sure this will work correctly ned? Won't fuel just wee out of the valve under normal conditions as well as returning to what I presume is the swirl pot on you picture? It only shuts off if it turns over right?

Clips should be fuel line clips which have a very smooth inside diameter and present uniform force all the way round the pipe. We all know jubilee types are just as good but Mr SVA won't be too happy.

Cheers

ned - 15/6/05 at 08:58 AM

JC,

The pic shows the return from the swirl pot (copper 8mm pipe) going to the return on the fuel tank. Fuel should go with gravity, so i don't expect fuel that isn't really under any pumping pressure to be getting to the t-piece and going upwards!

Am I really gonna have problems at sva with those jubilee clips? seems a bit ott to me!

Ned.

CairB - 15/6/05 at 11:53 AM

Ned,

There will be a flow induced back pressure, especially through a 90 T fitting. This may be enough to generate enough pressure to overcome the small (2psi ?) 'cracking' pressure of your vent valve and the slight amount to lift to the outlet.

This effect will be worse with increased flow especially if you've a high capacity pump for your expected power output.

Personnally I'd try to fit it in a position that was straight to the tank.

The tank vent should allow the tank to vent in both directions to allow for fuel consumption and expansion and contraction due to temperature, without allowing spillage during normal operating condiitions or 'evans forbid adnormal conditions (e.g. upside down)

Cheers,

Colin

ned - 15/6/05 at 12:01 PM

I originally brought this up in this thread:
http://www.locostbuilders.co.uk/viewthread.php?tid=26151
and no one said it wasn't a good idea! Presumably turning the t-piece round so the flat part took the flow from the return to the tank with the perpnedicular part vertical would reduce the chance of spillage?

Ned.

ps sorry for thread hijack

tks - 15/6/05 at 03:14 PM

my fuel tank hasn't got an breather on it..

and it works okay.. i have brought the breather anyway..its an TRL7 from MOCAL..

anyway NED if you think you are gonna fit an lockable fuel cap..then

there is your little vent hole....

Then another thing..

when filling the tank you have an huge hole opened there where the vapour comes out..to make room for the petrol..

also the engine is then shutdown..

then when consuming..air will entrence by the cap.. (the key hole..) or when heating up it will go out..

SeaBass - 17/6/05 at 09:22 AM

quote:
Originally posted by ned
Fuel should go with gravity, so i don't expect fuel that isn't really under any pumping pressure to be getting to the t-piece and going upwards!

Am I really gonna have problems at sva with those jubilee clips? seems a bit ott to me!


The fuel return line has a slight pressure resulting from bypass from the FPR and the bore of the pipe. I don't know if fuel will come out of your vent but worth watching out for.

As for the clips - who knows just advice I was given and followed when my car passed!

Hellfire - 17/6/05 at 11:45 AM

Ned, ours passed with Jubilee clips as have hundreds of others. SVA don't seem to be at all concerned with jubilee clips.

westf27 - 17/6/05 at 12:24 PM

so is this tank vent needed for sva as mine at present is just vented to atmosphere through 1/4" hose no valves at all.If so what is the spec req.

ned - 17/6/05 at 01:03 PM

my understanding is that the valve is there for the situation that if the vehicle evr rolls over the vlaves closes, stopping fuelling draining out of the tank all over you.

I dont know the requirements re sva though.

Ned.

Hellfire - 17/6/05 at 04:16 PM

quote:
Originally posted by westf27
so is this tank vent needed for sva as mine at present is just vented to atmosphere through 1/4" hose no valves at all.If so what is the spec req.


1/4" hose with no valves vented to atmosphere is absolutely fine. Just make sure the tube arches over and points downwards.

ChrisGamlin - 17/6/05 at 04:19 PM

If the hose comes out the top, arches up above the tank, then goes down and finishes lower than the base of the tank, then if it rolled over the fuel wouldnt come out anyway, because the top (when upside down) of the hose would be higher than the bottom (now the top) of the tank IYSWIM.

ned - 17/6/05 at 09:15 PM

be careful if looping the breather hose over as you can get a syphoning effect - just ask hicost, he was telling us once manage to empty his entire tank on a stage because of this!

Ned.

westf27 - 18/6/05 at 07:53 PM

thanks guys nice to do a job once?