Fresh water tank ventilation

[DrunkenDuncan]

Just fitted a filter on our G600L for drinking water and came across an issue that may or may not pose a problem when filling the fresh water tank with one of these:

On inspection (and discussion with dealer) I established that the tank was vented from a pipe from the top of the tank to the top of the filler here:

Now the issue I have is that when filling with the adaptor, the pressure in the tank was so great that there was water and air being forced out of the water level sensor on top of the tank until I released the pressure by opening the inspection cap (which was considerable; making me wonder about the ventilation of the tank in the first place)
I had of course assumed that the tank would be vented and that filling with an adaptor designed for the job would not be a problem, but it appears that the adaptor seals the filler recess (as does the lockable cap when it is on) so it would appear that the tank is not actually vented at all when either of these are used.
Am I missing something here or is this is by design and I need to fill up the old fashioned way by sticking the pipe down the filler neck so that the air replaced by the water going in can come out past the pipe?

 

[WillH]

My tank vents through an overflow fitted direct from the tank top. I use a watering can to top up though so venting isn't a problem. Does your tank not have an overflow?

 

[pappajohn]

Does your tank not have an overflow?

I would say having that breather the filler IS the overflow.
Once full via a hose etc water will simply emerge from the full neck.

 

[Manic]

That filler should have come with two seals, one for vent tanks and one for unvented tanks, this one has castlations so it can breath.
I also fitted a piece of pipe to mine to stop water coming out of filler.

 

[WillH]

On the rare occasion I have filled my tank it overflows under the van, not from the filler. There is a proper overflow arrangement. The waste tank has a series of holes drilled in its sides just below the tank top as an overly.

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[DrunkenDuncan]

I would say having that breather the filler IS the overflow.
Once full via a hose etc water will simply emerge from the full neck.

Seems reasonable as the overflow pipe (attached to the red connector near the very top of the tank on the side) is the one connected to the vent hole on the filler.

 

[DrunkenDuncan]

That filler should have come with two seals......

Only came like this:

Guess I could attach a tube to it like yours and drill a hole in the seal to let it vent - what could possibly go wrong!!

 

[Manic]

Only came like this:
View attachment 364271
Guess I could attach a tube to it like yours and drill a hole in the seal to let it vent - what could possibly go wrong!!

Looking at yours maybe not so easy to attach a pipe, mine has a spigot on the back that’s just the size of hose pipe. Mines a Heos filler.

 

[Gooney]

Great avatar Dunc?

 

[TheBig1]

there are vented and non vented filler caps available, the one you have appears to be non vented

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[Landy Andy]

it would appear that the tank is not actually vented at all when either of these are used.

The tank must be vented some way whilst the standard cap is on, otherwise you would not be able to get water out of the tank.

 

[gus-lopez]

Does your tank not have an overflow?

With that type filler assembly the Op's picture shows the vent .It vents from tank top back in to filler neck

The tank must be vented some way whilst the standard cap is on, otherwise you would not be able to get water out of the tank.

It does the actual cap allows air in to the vent pipe.
To the op why do you need the fancy filler cap to fill ? I just poke the hose down exactly the same type of filler & fill at whatever the potable water pressure is & which is usually around the 90-100psi.

 

[Landy Andy]

With that type filler assembly the Op's picture shows the vent .It vents from tank top back in to filler neck
It does the actual cap allows air in to the vent pipe.

That is my point about their statement “it appears that the adaptor seals the filler recess (as does the lockable cap when it is on) so it would appear that the tank is not actually vented at all when either of these are used.”

 

[DBK]

Ours has a similar vent in the neck but the lockable cap doesn't block it. You can tell this when you drain the water tank and hear the air rushing in around the cap.

Have no problem with a Heos filler.

 

[gus-lopez]

(as does the lockable cap when it is on)

No it doesn't as DBK said the locking cap allows air in

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[DrunkenDuncan]

Thanks everyone. I have confirmed that the locking cap does actually vent and drilled a hole in the blue filler adaptor which has fixed the problem. Happy days