Beta 16 pressure in fuel tank

[webcraft]

I discovered our Beta 16 in Avy-J somehow creates pressure in the fuel tank when running when I tried to top it up mid-passsge. Never had the same problem with the Beta 14 in Fairwinds.

The problem came to a head on our recent 2-day passage when I filled the tank right up before setting off.

Heavy seas at night deck work required and super-slippy diesel everywhere, from the breather tube apparently.

This must not happen again, how I didn't kill myself falling overboard or down the companionway remains an obscure miracle.

What could be causing this over pressure in the tank?

 

[Sea Change]

Definitely pressure rather than the motion of the boat?
Could you fit a one way valve in the breather tube?

 

[garymalmgren]

RE I filled the tank right up before setting off.
diesel everywhere, from the breather tube apparently.

Ok. If it were gas pressure it would move through the liquid and vent out as a gas.
If it were liquid pressure it would push liquid out of the vent.
However, I cannot see how you would end up with move liquid (fuel) in the tank than you started with.

My guess is that tank was "filled right up" and the motion of the boat sent it out the vent.
Even a small spill can seem like a lot when it is spread out.


One other point is that most small boats will have the vent below (and leak into the bilge).
Are you sure you have a vent on deck. I mention that because it could be a leaking filler cap.

gary

 

[ridgy]

Sounds like you've had a difficult time but once you've had a good night's sleep you will realise how irrational your suspicion is.

 

[Boater Sam]

If the tank is completely full, running the engine will warm the return fuel up and cause it to expand. Simply do not overfill the tank!

 

[webcraft]

If the tank is completely full, running the engine will warm the return fuel up and cause it to expand. Simply do not overfill the tank!

Total logic but fuel will simply not run out of the filter funnel and into the tank when the engine is running, even when the tank is less than half full.

The breather spillage issue is different, violent motion and too much fuel in a stupidly shaped tank. But I doubt positive pressure would help.

 

[RunAgroundHard]

Was the pressure detected when you opened the cap to fill up mid passage i.e. there was an outrush of air? It might have been excessive foaming in the tank. Sourceof the foam comes from air being entrained when the filler at the pump is shoving in a lot of fuel, that can also happen when you fill up from a can, but to a lesser extent. Agitation of a tank that is not full, such as your high seas could also cause foaming, aided by the excess fuel return to the tank. So you now have a few conditions: diesel that will foam, a full tank that may have foamed when filling, agitated tank contents and returning hot fuel contributing to foam. Expanding foam could eject out the vent causing the diesel spill. Why the pressure? The foam expands and can't escape fast enough out the vent, especially if the vent hose is kinked, partially blocked or restricted in any way, the hot air in the foam, the heat from the pump, expands causing a slight pressure increase.

You might just have add a bad combination of events.