westcost1
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| posted on 22/2/07 at 12:46 PM |
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efi fuel system dose it need a breather ?
Hi all
Im finally getting to the stage where the car is showing signs of life turned it over from the ignition last weekend . Im fitting the fuel system at
the moment I have fitted the tank and filler cap. flow and return lines and pump will be going in at the weekend. The question is dose the tank need
a breather to release the vacuum produced as the fuel is used? The engine is a mk5 1600 cvh efi xr2i/3i I seem to remember that air was sucked into
the tank when I used to fill up the escort I think ( was 2 1/2years ago now) which would indicate a sealed system but that was with a plastic tank
would the vacuumed be able to crush the ally tank? Or make the pump work harder?
Thanks Nick
[Edited on 22/2/07 by westcost1]
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mookaloid
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| posted on 22/2/07 at 12:56 PM |
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I would have thought a breather would be neccessary
- however I have never understood how cars which give a whoosh of air into the tank when you take the filler cap off work any way as the tank must be
operating as a vacuum which must make it hard for the pump to get fuel out.
So I dunno maybe someone who really knows will tell us
Cheers
mark
"That thing you're thinking - it wont be that."
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Agriv8
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| posted on 22/2/07 at 12:56 PM |
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Yup.
The Fuel out of tank needs to be replaced by somthing.
regards
Agriv8
Taller than your average Guy !
Management is like a tree of monkeys. - Those at the top look down and see a tree full of smiling faces. BUT Those at the bottom look up and see a
tree full of a*seholes .............
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macnab
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| posted on 22/2/07 at 01:01 PM |
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wrap the breather pipe right around the outside off the tank, so that if the car ends up inverted, fuel will not pour out the pipe
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Phil.J
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| posted on 22/2/07 at 01:54 PM |
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Definitely needs a breather in the top, preferably with a non-return valve fitted
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fesycresy
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| posted on 22/2/07 at 01:57 PM |
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I've a Mocal one way vent.
If you do vent it down the side of the tank, don't take the pipe too low 
-----------------------------------------------------------------------------------------------------
The sooner you fall behind, the more time you'll have to catch up.
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westcost1
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| posted on 22/2/07 at 02:11 PM |
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Ok thanks I have had a look at the fuel tank breather valves on dimon tweeks how do they fit to the tank is it welded on or bolt in? and what dose it
mean by medium high and max flow?
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tks
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| posted on 22/2/07 at 02:46 PM |
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mhhh
i have fitted a Locking cap
and no breather (still have on in case i need one- a red one from mocal-)
Anyway i guess air is sucked in by the hole in the cap as far as i know the woosh is over pressure not untherpressure in a cars sytem..
Tks
The above comments are always meant to be from the above persons perspective.
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RazMan
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| posted on 22/2/07 at 03:02 PM |
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If your fuel system is airtight without a breather it will gradually implode as the fuel is pumped out. You need a breather to prevent this but most
of the best ones are two-way valves which will allow air in and out but not fuel out, using two ball bearings of different weights (not quite sure how
they work) This allows for expansion of the air on a hot day but still prevents fuel draining out in an 'upside down' incident.
The simplest ones (which I used) are often used on Motocross bikes. These let air in easily but also a small amount out (for expansion) Fuel is still
prevented from flowing out as the exit path is very small.
You can fit in-line jobbies but ideally you need to weld a stub on top of the tank. Alternatively you could put a stub into the filler neck or cap.
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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westcost1
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| posted on 22/2/07 at 03:21 PM |
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Thanks raz man didn’t think about expansion on hot days. The tank has a pipe for a breather on top but this means i will have to put an extra one on
for the return line.
Found this on how stuff works could explain the rush of air.
Fuel tank vent
Since the advent of emission controls, tanks are equipped with a control system to prevent fuel vapor from being discharged into the atmosphere. A
vent line in the tank is connected to an activated carbon or charcoal filled canister in the engine compartment. Vapors from the tank are stored in
this canister, until they can be purged later for combustion in the engine. On many carbureted engines, the float bowl is also vented to this
canister.
 
Rescued attachment 191.jpg
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westcost1
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| posted on 22/2/07 at 04:23 PM |
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thanks fesycresy who has pointed me in the direction of www.thinkauto.com for the valve lots of good stuff there
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