Fresh water tank vent?

[SuperSeven747]

I’m sorry but I think you are over thinking things.
The fact that an air- vent tube is fitted alongside the large bore filler tube is surely evidence that it vents to the outside, somewhere within the filler/cap system.

The above photo by @Johnny Rocket shows the inlet tube opening into the filler body ,presumably to the side of the shelf that the rubber seal on the cap seals to.
The failure to vent is probably down to a number of possible causes.
1. Oversized rubber seal on locking cap.
2. Malposition of the rubber seal.
3. Obstruction of the vent orifice.

View attachment 106814

That is an air breather pipe, and allows air to EXIT as you fill the water tank.

When the cap is closed, that pipe does not vent to the outside air (as the head of that pipe joins the plastic housing BEHIND the filler cap, so it can't be used for drawing in air when water is used and the cap closed.

 

[SuperSeven747]

I am having issues on a new Cali with air not getting into the water tank as water is drawn.
Dealer ask for details (below) and their technician is hopefully going to get back to me:

"When opening the clean water tank drain, we get just a few drops of water out. I think it is because air cannot vent into the clean water tank to replace the draining water. It you remove the water filler cap to let air it, it then drains rapidly. So that is a simple workaround, but this lack of an air vent to equalise the air pressure when water is drawn is also causing an issue when using the tap.

We ran about 2 sink fulls of water, but when trying to draw any more the tap pump started to really struggle as it fought against the reduced air pressure in the water tank, until it cut off.

At this point I tried to remove the water filler cap, but it was held strongly in place by air suction, but after forcing it off that was a sudden whoosh of air into the tank. The tap then starts working again.

So the key issue here is: “How should air get into the clean water tank as water is used via the tap or drained?”

Hence is there an air vent on the water tank, tap or the filler cap, because whatever route that is, it appears to not be working."

 

[SuperSeven747]

I'm off to the dealer this morning to pick up some injector spill line clips for my daughter's Caddy - just for a laugh I'll see if I can find a mechanic who knows how the water tank pressure is supposed to equalise with atmospheric when, say, water is being drawn - don't hold your breath though . . . !

Yes interested to know what they say, but not holding my breath as you may get a "we don't know.."

 

[SuperSeven747]

The left cap is what my new Cali has (hence a dimple, but no hole and not vented as I can't blow/suck air through it)

I ordered a replacement cap from campervanbits to try fix the issue, and the cap on the right was delivered. So has a hole and I can blow/suck through it, so is vented! But when I asked campervan bits if the cap they sell is vented or not, they said it isn't vented, but clearly what I have been sent is!

I'm just confused now..

 

[SuperSeven747]

You're of course right - the vent pipe in my photo appears WITHIN the sealing face diameter for the cap on the receptacle, so it is indeed an anti-glug vent for tank filling, whilst pressure-balancing when the cap's on and water is consumed, etc., is achieved via the small hole in the centre of the cap.
I tried sucking and blowing through mine earlier, with the inner cap body part both extended and then compressed (the latter the state when the cap is fitted), and couldn't get any flow, but this is certainly the air path - I'll investigate some more later and report! . . .

18:30 UPDATE

OK, so for the hell of it I took my cap apart today - see picture sequence below:

The little indent you see in the centre of the smaller-diameter part of the single piece white plastic 'top-hat' body is NOT a through-hole (on the reverse side view you see a blob of pink grease to lubricate the spring seat, but there is NO perforation here), and given that the water tank cap black rubber (washer) seal sits on the top face of the 'brim' of this top hat, then there appears to be no air path at all (at least via the cap assembly) from the filler neck of the tank past this top-hat body, and then out to atmosphere!

The final photo shows the filling anti-glug vent described by AA above.

So, I'm afraid to say that I now don't know where the tank-to-atmosphere pressure balance occurs, but the fact remains that with exactly this set-up, as mentioned earlier, I can happily (as can WG too) drain the tank via the sink tap with the filler cap firmly on and with no loss of flowrate as the level drops to empty.

I think we've set a hare running now . . . . !

Fingers crossed I get an answer from my dealer on Tuesday..

 

[WelshGas]

That is an air breather pipe, and allows air to EXIT as you fill the water tank.

When the cap is closed, that pipe does not vent to the outside air (as the head of that pipe joins the plastic housing BEHIND the filler cap, so it can't be used for drawing in air when water is used and the cap closed.

My cap, original from 2014, does vent . Never have a problem at altitude nor emptying using the kitchen tap or the drain tap.

 

[SuperSeven747]

I wonder if the large vent that comes from the tank to the “wrong“ side of the cap seal is just to allow air out of the tank when filling, to prevent “splash back” up the filler.

Yes, I think so

Noticed the other day that my filler cap has a very small hole in centre of the inner part, which vents through the lock. This would function as a vent when taps are on.

Any chance of a photo? Thanks

 

[SuperSeven747]

My cap, original from 2014, does vent . Never have a problem at altitude nor emptying using the kitchen tap or the drain tap.

So has a simple hole in the rear of the cap? And was there from new?

You do wonder, has VW a stock of non-venting caps they have been incorrectly fitting to recent T6.1 Cali's ?!!

 

[WelshGas]

So has a simple hole in the rear of the cap? And was there from new?

You do wonder, has VW a stock of non-venting caps they have been incorrectly fitting to recent T6.1 Cali's ?!!

It wouldn't surprise me.

 

[ArunAlec]

Yes, I think so


Any chance of a photo? Thanks

Not from a Cali but from recollection SIS is the same as fitted to Cali & Westfalia.

 

[Johnny Rocket]

Mine is STS, as shown earlier in the thread.
I’m now wondering then if those of us with unperforated caps but no problems drawing water in fact have another air leak path which (unintentionally on VW’s part) provides the air balance route?

My favourite is the donkey-dick hose which connects filler neck to tank and which very easily (if not clamped by the jubilees to the point of crush) could breathe air down the spiral whilst causing absolutely no issues with water overflow etc. since it’s high and on the outside.

For those with the issue, just do as jjp did, and drill the indent through 2mm, smile contentedly, and get on with (enjoying) life

 

[Nik_campervan]

The water pump power cable runs through a clear outer plastic hose thats a fairly tight fit but clearly not airtight. That then runs through a rubber gromet at the top of the tank, again its not sealed as such. Both likely enough to allow pressure to equalise. Could be variability in these dimensions give some vans issues.

 

[Johnny Rocket]

The water pump power cable runs through a clear outer plastic hose thats a fairly tight fit but clearly not airtight. That then runs through a rubber gromet at the top of the tank, again its not sealed as such. Both likely enough to allow pressure to equalise. Could be variability in these dimensions give some vans issues.

So basically it’s a sieve, but from time to time and for some unlucky folk, it ISN’T !?!?!?

 

[ArunAlec]

The water pump power cable runs through a clear outer plastic hose thats a fairly tight fit but clearly not airtight. That then runs through a rubber gromet at the top of the tank, again its not sealed as such. Both likely enough to allow pressure to equalise. Could be variability in these dimensions give some vans issues.

If these poor seals were acting as vents, then when the tank was filled any “overfilling” above the level of the top of the tank would result in water leaking into the van. I always “brimmed“ my tank when filling and never experienced any problems.

 

[Johnny Rocket]

Water is massively more viscous than air, so a ‘leak path’ for air is not able to pass water at the same volume flow rate. So when you brim your tank, the line of least resistance for the excess is to flood out of the filler neck and over your feet, not to track down a rather contorted capillary passage within the upper tank connections ;-/

 

[Viktorgeorge]

Thank you all who contributed on this: I just drilled my cap (I went for 2.5mm) and it now vents.

I have not had an air suction/pressure problem with the tap supply, but then I had not used much yet. Seems like an obvious thing to do anyway.

 

[Johnny Rocket]

Maybe STS supply VW with both vented and un-vented caps, and on the production line they pick from a lucky dip hopper ;-) ?!

Filler cap for fresh water or diesel | STS Oberholz

With or without ventilation ✔ Available in various colours ✔ Fits all STS, Zadi, Fawo and FAP tank filler necks ✔ Enquire here!

www.sts-oberholz.de

 

[SuperSeven747]

Thank you all who contributed on this: I just drilled my cap (I went for 2.5mm) and it now vents.

I have not had an air suction/pressure problem with the tap supply, but then I had not used much yet. Seems like an obvious thing to do anyway.

It does seem like a pragmatic and simple solution with no obvious downsides.

I wish we could just get a simple answer from VW, hence:
"How is air meant to vent into the water tank to replace the volume of water drawn out by the tap or tank drain?"

Dealer's latest response to me is "it's an air lock", but I can only assume he has misunderstood and thinks I'm saying the tap doesn't work...

 

[Johnny Rocket]

It does seem like a pragmatic and simple solution with no obvious downsides.

I wish we could just get a simple answer from VW, hence:
"How is air meant to vent into the water tank to replace the volume of water drawn out by the tap or tank drain?"

Dealer's latest response to me is "it's an air lock", but I can only assume he has misunderstood and thinks I'm saying the tap doesn't work...

It’s quite worrying how ignorant the dealers are about the workings of the product they sell.

I went to my dealer on Saturday to pick up some bits for my daughter’s Caddy, and asked if I could look at the back side of the water tank cap on the California in the showroom (which request itself made them quite edgy!), and they couldn’t even find me the key!

 

[SuperSeven747]

UPDATE:
My dealer was a little unwilling to let me talk direct to their technician/expert on Californias, but after a couple of calls did finally hand the phone over to the technician.

He confirmed to me that there is no air vent system on the California water tank.

His advice is to occasionally remove the water filler cap to equalise the pressure or when you want drain the fresh water tank as it will drain very slowing if you do not.

I felt he was being honest and open and not trying to fob me off, so I am happy with their response.

The unofficial option B, not discussed with him, is drill a hole in the back of your water filler cap.

 

[Johnny Rocket]

Nice work. If we could get that stated from 3 different dealers I'd start to believe them!

If this is the case, then those of us with no drain / vacuum issues must just have (a) better vent passageways(s) via all the many other inevitable leak paths discussed in the course of this thread.

 

[Roger Boeken]

UPDATE:
My dealer was a little unwilling to let me talk direct to their technician/expert on Californias, but after a couple of calls did finally hand the phone over to the technician.

He confirmed to me that there is no air vent system on the California water tank.

His advice is to occasionally remove the water filler cap to equalise the pressure or when you want drain the fresh water tank as it will drain very slowing if you do not.

I felt he was being honest and open and not trying to fob me off, so I am happy with their response.

The unofficial option B, not discussed with him, is drill a hole in the back of your water filler cap.

Exactly my thoughts. Bought venting filler cap on amazon however ,wanted to see if this small hole in the cap is the only difference.

 

[marchugo]

Drilling a hole in the water filler cap, even in the back, maybe makes your drinking water tank prone to the entrance of all little open air bastards like dust and bacteria.

Taking water from the tank with the kitchen tap will create a (small) vacuum in the tank, with a suction effect for outside air.

Regards from Amsterdam,

Marc.

 

[Jabberwocky]

UPDATE:
My dealer was a little unwilling to let me talk direct to their technician/expert on Californias, but after a couple of calls did finally hand the phone over to the technician.

He confirmed to me that there is no air vent system on the California water tank.

His advice is to occasionally remove the water filler cap to equalise the pressure or when you want drain the fresh water tank as it will drain very slowing if you do not.

I felt he was being honest and open and not trying to fob me off, so I am happy with their response.

The unofficial option B, not discussed with him, is drill a hole in the back of your water filler cap.

I have a MY23 and when I fill the freshwater tank to two thirds full (The manual says "Do not over fill") I get water leaking out of the filler cap when driving (going round righthand corners). I have owned two Cali's before and not had this happen. Any ideas as to what I can do to stop this?

 

[SuperSeven747]

I have a MY23 and when I fill the freshwater tank to two thirds full (The manual says "Do not over fill") I get water leaking out of the filler cap when driving (going round righthand corners). I have owned two Cali's before and not had this happen. Any ideas as to what I can do to stop this?

Is your water cap vented or not (easy to test, just try blowing threw it from rear side)

I use the factory supplied non-vented cap when travelling with full water tank, and the swap to a vented cap when I arrive at campsite.

Non-vented cap should stop water spilling out if fitted properly