Petrol tanks

[Andrew Way]

I’m after some advice on petrol tanks for my HF3000. I want to baffle and foam fill the tanks which is no problem. I’m unsure what to do about the breather & fuel rail return. Do I need a valve fitted to the breather or just vent to atmosphere? I’m thinking two separate 6mm pipes at the top of both tanks (one breather, one return) so I can divert the returned fuel to either tank in case ever want to remove the opposite tank, temporarily. Ideas / comments appreciated.

Cheers.

[colin artus]

The original car had a valve fitted to the breather system that was connected to both tanks. The valve was mounted at the top middle of the rear screen. And what valve was it? Yes! the Beta non return valve that you forgot to take off your donor car. Perhaps someone has a spare?


Colin

[Andrew Way]

Doh!

[guy mayers]

Hi Andy, here's how it should go!

There is an outlet at the bottom of each tank that need to be joined together to allow the fuel levels to equalise. Using a T piece in this line is the usual place to fit an external fuel pump. With an Alfa installation the pump should be prefiltered, a coarse one will do, and there should be a normal fuel injection one between the pump and the fuel rail. You will also need a return pipe from the fuel rail to one of the tanks. This can go to either of the two pipes on the top of either of the tanks. There should also be a link pipe between the two tanks with the valve Colin mentions set into a T piece. The purpose of this is to allow the tanks to vent properly. The valve shuts when it is inverted so it has to be fitted the correct way up. It's real function is to stop fuel leaking out if the car is overturned in an accident. This leaves one unattached pipe on the top of one tank. This needs another pipe that runs down the side of the tank to below the bottom of the tank. This is an overflow pipe in case you ever overfill the tanks. (This can happen if the balance pipe becomes blocked and the return from fuel rail puts excess fuel into one tank only) Without the pipe the excess fuel will come out on the top of the tank rather than below the car where it is less likely to cause damage! Also, should you manage to overturn the car this pipe will allow fuel to leak unless it's lower end is below the botttom of the tank.

And that's the basic layout. There are some further options to consider at this point. You can use the Alfa fuel pump and swirl pot in the nearside fuel tank with a little careful work. In this case there will be an outlet and return pipe in a cap set into the top of your tank just like it was in the Alfa. The advantages of this are less possibility of overflows as fuel is fed from the same tank to which it is returned. There is no fuel pump exposed in the engine bay with less connections to work loose and less chance of fuel vapourisation due to heat build up. (Although this is a remote possibility because the fuel is constantly circulating and cooling it all down). The downside is that working on the pump is much harder! You could also consider installing taps to the bottom balance pipes to make tank removal easier.

Finally, please remember that this is a high pressure installation so you must use the correct type hose for the injector rail connections to the filter and back to the high pressure side of the pump. Aeroquip is very pretty but it won't allow you to see the rubber degrading underneath. Always use good quality clips to secure the pipe to the chassis and the best clamps to secure the hose to the rails, pump and filters. and a plumbed in fire extinguisher is recommended just in case. Finally, always be careful starting up the car after working on the system. Let the pressure build up onthe ignition and check for leaks before starting the car.

End of sermon!
Guy

[Andrew Way]

Guy, thanks for the detailed tank set-up explanation. One question, what is the breather system with the valve doing that the overflow isn't? The top of the tank (air) has to vent to atmosphere to allow for thermal expansion / contraction and the tube in the tank needs to be bent through 180deg to prevent sloshing fuel poring out of the overflow.

[guy mayers]

ermmmm good question. Is fuel vapour lighter than air so the only way it could vent safely is up?
Guy

[roger001]

I only have the vent with the one way valve. I cant see the point in having an open breather as well, in addition i dont think a scrutineer would be too happy with an open vent/breather.

[Sando]

Originally posted by guy mayers
ermmmm good question. Is fuel vapour lighter than air so the only way it could vent safely is up?
Guy

Guy
I always thought that petrol vapour was heavier than Air? But I'm not 100% - I'll ask a Fireman!
I always thought that replacing the vacuum caused by using the fuel is one of the main reasons for the vent. (as well as the expansion/contraction) I found this out the hard way on a motorway once many moons ago with a blocked breather........

cheers
Rob:cool: