Urgent: Fuel Venting Problem
Discussion
I’m hoping someone can help with this…
When the tanks are brimmed the fuel tanks pressurize and then fuel overflows through the vent/roll over valves (previous ones and the new ones I’ve just installed a I thought it was the valves) and into the catch bottle which then over flows. Mess and danger of fire!!
The vent / roll over valves are situated at the top of the bulkhead (well above the tanks), the vent line then runs along the roll bar to the catch bottle which is at the very back and lower point of the engine bay.
The vent line to the vent valve is at the top of the tank.
The problem seems to have started after I tightened the screws around the fuel cap surround and plugged the holes in the rubber connection to the fuel cap surround as it was spilling fuel out and wasn’t controlled/safe venting.
When the tanks are brimmed the fuel tanks pressurize and then fuel overflows through the vent/roll over valves (previous ones and the new ones I’ve just installed a I thought it was the valves) and into the catch bottle which then over flows. Mess and danger of fire!!
The vent / roll over valves are situated at the top of the bulkhead (well above the tanks), the vent line then runs along the roll bar to the catch bottle which is at the very back and lower point of the engine bay.
The vent line to the vent valve is at the top of the tank.
The problem seems to have started after I tightened the screws around the fuel cap surround and plugged the holes in the rubber connection to the fuel cap surround as it was spilling fuel out and wasn’t controlled/safe venting.
Hi Tony
I suspect the problem is that the fuel comes out of a cold tank in the ground and warms up in your tanks. If you brim them, as the fuel warms it expands and if the tank and system is sealed it will pressurise the tank and expand up the vent pipe as you have experienced.
I never bother to completely brim my tanks for this reason.
Paul
I suspect the problem is that the fuel comes out of a cold tank in the ground and warms up in your tanks. If you brim them, as the fuel warms it expands and if the tank and system is sealed it will pressurise the tank and expand up the vent pipe as you have experienced.
I never bother to completely brim my tanks for this reason.
Paul
Storer said:
Hi Tony
I suspect the problem is that the fuel comes out of a cold tank in the ground and warms up in your tanks. If you brim them, as the fuel warms it expands and if the tank and system is sealed it will pressurise the tank and expand up the vent pipe as you have experienced.
I never bother to completely brim my tanks for this reason.
Paul
+1I suspect the problem is that the fuel comes out of a cold tank in the ground and warms up in your tanks. If you brim them, as the fuel warms it expands and if the tank and system is sealed it will pressurise the tank and expand up the vent pipe as you have experienced.
I never bother to completely brim my tanks for this reason.
Paul
It happens when static (just a warm day or environment) but also when running. I can open the cap and release the pressure and it just builds back up again.
The tanks are separate and I've check the "return" system is operating correctly.
I have had a have a thought that as the catch bottle is lower than the fuel level that it is siphoning, but that still doesn't explain why the tanks are pressurising with proper vent valves.
I was thinking about installing a catch tank up high on the roll bar / bulkhead and then having a vent line down to secondary catch tank........
The tanks are separate and I've check the "return" system is operating correctly.
I have had a have a thought that as the catch bottle is lower than the fuel level that it is siphoning, but that still doesn't explain why the tanks are pressurising with proper vent valves.
I was thinking about installing a catch tank up high on the roll bar / bulkhead and then having a vent line down to secondary catch tank........
Toni
Not sure about the catch tank. Is it normal to have a catch tank on a fuel tank vent?
I understand the thinking but it suggests your catch tank is not large enough for the fuel expansion.
I have linked tanks, so unless you are happy to spend a looooooooong time brimming the tanks you never completely fill them.
Paul
Not sure about the catch tank. Is it normal to have a catch tank on a fuel tank vent?
I understand the thinking but it suggests your catch tank is not large enough for the fuel expansion.
I have linked tanks, so unless you are happy to spend a looooooooong time brimming the tanks you never completely fill them.
Paul
Swiss_Toni said:
It happens when static (just a warm day or environment) but also when running. I can open the cap and release the pressure and it just builds back up again.
The tanks are separate and I've check the "return" system is operating correctly.
I have had a have a thought that as the catch bottle is lower than the fuel level that it is siphoning, but that still doesn't explain why the tanks are pressurising with proper vent valves.
I was thinking about installing a catch tank up high on the roll bar / bulkhead and then having a vent line down to secondary catch tank........
Then your vent is lower than the top level of the fuel in the tank.The tanks are separate and I've check the "return" system is operating correctly.
I have had a have a thought that as the catch bottle is lower than the fuel level that it is siphoning, but that still doesn't explain why the tanks are pressurising with proper vent valves.
I was thinking about installing a catch tank up high on the roll bar / bulkhead and then having a vent line down to secondary catch tank........
Also are your vent valves fitted in the right direction?
This likely to be the case but the vent line and the valve (the correct way around, but good point) is approx 40cm above the tank and 15 to 20 cm above the fuel cap. It is very much the highest point in the system.
Another thought I had is that the "outlet" side of the valves (one for each tank) are joined by a "T" then run with a common vent line to the catch bottle at the back end of the car (it's not a reservoir, it's just to catch any fuel that may come out, which is the problem), and the pressure of one tank is closing the other valve and letting the pressure build up and then vice verse????
What do other's do for venting?
Another thought I had is that the "outlet" side of the valves (one for each tank) are joined by a "T" then run with a common vent line to the catch bottle at the back end of the car (it's not a reservoir, it's just to catch any fuel that may come out, which is the problem), and the pressure of one tank is closing the other valve and letting the pressure build up and then vice verse????
What do other's do for venting?
Edited by Swiss_Toni on Thursday 3rd April 05:36
Swiss_Toni said:
This likely to be the case but the vent line and the valve (the correct way around, but good point) is approx 40cm above the tank and 15 to 20 cm above the fuel cap. It is very much the highest point in the system.
Another thought I had is that the "outlet" side of the valves (one for each tank) are joined by a "T" then run with a common vent line to the catch bottle at the back end of the car (it's not a reservoir, it's just to catch any fuel that may come out, which is the problem), and the pressure of one tank is closing the other valve and letting the pressure build up and then vice verse????
What do other's do for venting?
Where does the vent start from?Another thought I had is that the "outlet" side of the valves (one for each tank) are joined by a "T" then run with a common vent line to the catch bottle at the back end of the car (it's not a reservoir, it's just to catch any fuel that may come out, which is the problem), and the pressure of one tank is closing the other valve and letting the pressure build up and then vice verse????
What do other's do for venting?
Edited by Swiss_Toni on Thursday 3rd April 05:36
The problem as I see it is not where the line and valve finish or where the catch tank is, it would seem to be where you are tapping the system in the first place.
This must be below top fuel level to pick up fluid and not vapour.
I haven't looked at my set up but I thought there was a small vent/hole right at the top of filler neck of the tanks a couple of centimetres or so from the fuel cap.
You can get vents with a float in that seal when the tanks are full:
http://www.demon-tweeks.co.uk/motorsport/fuel-tank...
http://www.demon-tweeks.co.uk/motorsport/fuel-tank...
I've already got the proper vent/roll over valves, it looking like, as Tony and others have mentioned, the fuel level is above the the vent fitting I'm using in the tank.
I've ordered some fittings to do a mod on the fuel fill pipe to correct this.
Fingers crossed it works.
Thanks all for the input.
I've ordered some fittings to do a mod on the fuel fill pipe to correct this.
Fingers crossed it works.
Thanks all for the input.
Just to follow up.
Problem solved, as mentioned the fuel tank vent was at the top of the tank and not the top of the system (fuel tank fill hose).
I installed the below adaptor (from SAMCO hose) with a dash 6 adaptor into the fuel fill hose then to 2 separate fuel vent / roll over valves (above on the bulkhead) then down to the catch bottle and vent.
No pressure or over flowing fuel!
Problem solved, as mentioned the fuel tank vent was at the top of the tank and not the top of the system (fuel tank fill hose).
I installed the below adaptor (from SAMCO hose) with a dash 6 adaptor into the fuel fill hose then to 2 separate fuel vent / roll over valves (above on the bulkhead) then down to the catch bottle and vent.
No pressure or over flowing fuel!
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