fuel tank over pressure

[sbend]

Good afternoon,
I am working on a new fuel tank design for 25hp off road construction equipment and am seeking information on how to prevent over pressure with trapped vapor pressure following rollover condition. The tank has a sealed cap and rollover/vapor relief valve. I have not found any information in regulations for this condition or any information on the net regarding vapor build rate, particularly at temperatures above 100 deg F. I have been studying automotive information and could not find how they deal with trapped vapor pressure following rollover or if it is an issue. My fuel temperatures would be more like 120 + deg F and produce vapor pressures over 10 psi.

Set up is: 11 gal sealed cap tank with rollover/vapor relief valve vented straight to Kohler engine. (I was told the off road application and engine size does not require carbon canister).

Any knowledge share will be much appreciated.
Thanks,
Scott

 

[decipha]

In most automotive applications the charcoal canister has a vent valve actuated by the engine controller

typically the canister solenoid will purge pressure to the engines intake on a reoccuring frequency so long as the engine isn't at over 50% load

 

[sbend]

Thank you for the reply.
Do you know if that vent valve is open when electrical power is not supplied or engine is off, in the case of a rollover?
Please let me know.
Thanks,
Scott

 

[decipha]

Its a normally closed solenoid that requires a sine wave to open, thus they are pulsewidth modulated and can be variabley opened, the flow is usually proportionate to the airmass that the engine is ingesting

in a roll over with a loss of power the solenoid will be closed

 

[Compositepro]

I think the tank vent to the charcoal canister would be under the fluid level in the event of a roll over. A floating vent tube would work but I've only seen this in chain saws that are designed to run upside down.

 

[decipha]

could you install two vents that are joined at a header with dual high points which would act as a stand pipe?

typical of a level bridle if your more familiar with pressure vessels

 

[sbend]

Thank you for the replies,
We have discussed the idea of dual vents, but have not been able to come up with a configuration to handle rollover in both directions (causing the vents to be under fluid level and float valve closed). This equipment would actually wind up on either side and probably not able to stay upside down.
Maybe three vents if I can find a location? I am going to request a test to determine the pressure build rate in the tank once it is closed.
Thanks,
Scott

 

[Meboosta]

Just an idea, if there was no power supply in the case of a rollover could you potentially trigger the canister valve open with pressurized air stored in a vacuum reservoir?

 

[mattsooty]

Gasoline Automotive applications continually & freely vent any tank overpressure through a carbon filled scrubber canister, without a 'shut off valve' (except when used for tank leak diagnosis).
This means Ptank = Pambient and, all the while the canister can hold fuel vapour, there is no HC breakthrough. When it becomes saturated the smell is obvious.
Whilst the engine is running the cannister is emptied through a controlled bleed into the intake manifold and, if turbocharged & in boost, precompressor.
Without a sufficient delta between the cannister & intake manifold/precompressor there will no flow.
Diesel engines do not require such measures as the RVP of the fuel is considered negligible.

decipha your understanding is a little misleading & your description of PWM flawed, please be sure of your facts before commenting.

ms