Fresh water tank ventilation | MotorhomeFun | The Motorhome Support and Social Network

Fresh water tank ventilation

Oct 30, 2018
29
9
Brize Norton
Funster No
56,991
MH
Pilote G600L
Exp
Not enough!
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:
IMG_7757.jpg

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:
IMG_7755.jpg

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?
 
Feb 9, 2008
3,302
3,578
SW Scotland
Funster No
1,453
MH
LP Coachbuilt
Exp
Since 2008 after caravanning for 20 years
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?
 
Nov 4, 2011
2,781
7,523
Uk
Funster No
18,763
MH
A class
Exp
2001
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.
C97EC1BC-722C-485A-9289-5C05EB7036BE.jpeg
 
Feb 9, 2008
3,302
3,578
SW Scotland
Funster No
1,453
MH
LP Coachbuilt
Exp
Since 2008 after caravanning for 20 years
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.
 
OP
DrunkenDuncan
Oct 30, 2018
29
9
Brize Norton
Funster No
56,991
MH
Pilote G600L
Exp
Not enough!
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.

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Nov 4, 2011
2,781
7,523
Uk
Funster No
18,763
MH
A class
Exp
2001
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!! :p
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.
 

TheBig1

LIFE MEMBER
Nov 27, 2011
13,391
21,888
Dorset
Funster No
19,048
MH
A class
Exp
many many years! since I was a kid
there are vented and non vented filler caps available, the one you have appears to be non vented
 
Aug 18, 2014
14,208
49,005
Spain
Funster No
32,898
MH
Transit PVC
Exp
6 years since restarting
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.

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Apr 22, 2018
1,587
2,350
Herts.
Funster No
53,503
MH
Adria Coral lowline
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

LIFE MEMBER
Jan 9, 2013
15,206
31,949
Plympton, Devon
Funster No
24,219
MH
PVC, Murvi Morocco
Exp
2013
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.
 
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