fresh water tank capacity limited to 20 ltr

Ozzie1956

Ozzie1956

Free Member
Joined
Nov 27, 2016
Posts
9
Likes collected
14
Location
Bergen, Norway
Funster No
46,265
MH
Knaus BoxStar - Fiat Duca
Exp
Newbie
Any suggestions as to how I should understand this specification?

"fresh water tank capacity limited to 20 ltr. by overflow valve (recommended driving fill level)."

Am I correct in assuming that I should only fill tank up to 20 liters before driving to site and then fill to capacity? If so has anybody any idea how I can see if I have an overflow valve? I have a user manual, but only in German - which is not my strongest point.

Motorhome is a Knaus BoxStar Family. Thanks for any help.
 
In my old hymer, there was a lever in one of the low level external lockers.
You wouldn't have known it was there.
One way allowed you to fill the fresh water tank full. The opposite way would overflow after a lesser amount. I suppose some don't like driving with full tanks.
 
Well we go out with a full tank and when stopped and fresh water available ( preferably foc) we top up tgen when we're returning home, we empty so we can load more wine ( not in the tank but there's an idea) and beer because just saved weight equivalent for 90 litres of water.
 
EX51SSS said:
Well we go out with a full tank and when stopped and fresh water available ( preferably foc) we top up tgen when we're returning home, we empty so we can load more wine ( not in the tank but there's an idea) and beer because just saved weight equivalent for 90 litres of water.
Click to expand...
Our sentiments entirely. Works a treat!
 
From the manual -

Fresh water tank capacity limited to 20 ltr. by overflow valve (recommended driving fill level)


Fresh water tank capacity is 110 ltr. with the overflow valve closed

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Thanks - but my point (which I didn't quite get across), is that if I knew what an overflow valve looked like, I could close it before travelling and therefore carry full pot of water.
The black tap is either all or nothing. Open = dump all water ,, closed is closed, but when we arrive on site after driving, we have limited water. If I knew how to restrict water dumping before arriving, that would help.
 

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Our Laika has the same system. You have TWO release valves. One empties the tank completely and the other does the same but leaves 20 Ltrs still in the tank. If you try filling it again with the valve open you can only get 20 Ltrs in before it overflows.

Our TWO valves are built into the tank behind a small door in the garage. You just undo them. Big BLACK plastic knob.
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On my Burstner the level is controlled by the tap that is used to empty the tank. Turning it so far will let the level of the tank drop to 20lts, undoing the valve all the way will empty the tank fully.
 
If you have filled the tank on site it is obviously set to fill and any dump would be manual.

Martin

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Now I understand why we have a limited water supply / capacity when arriving. I thought it was the Truma dumping water because of low temperature. Minus 6 degrees c in Bergen Yesterday. Nube to this motorhoming thing em my bob...
 
In my Hymer also with a 20l driving recommendation there is a rotating knob on top of the water tank which directly operates the drain valve , a quarter turn drains the tank to 20l , turn fully to completely drain.
 
Ozzie1956 said:
Thanks - but my point (which I didn't quite get across), is that if I knew what an overflow valve looked like, I could close it before travelling and therefore carry full pot of water.
The black tap is either all or nothing. Open = dump all water ,, closed is closed, but when we arrive on site after driving, we have limited water. If I knew how to restrict water dumping before arriving, that would help.
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Ozzie

I have a Carthago Malibu and my freshwater tank looks very similar to that picture you attached. The rounded triangular knob to the right of the large black cap operates the drain valve and operates as @Larrynwin has described

Cheers

Trevor
 
Thanks. I would like to fill to full capacity before we leave.

As I understand it, if I close knob completely it will reserve water in tank.

If I start moving, the tank will dump down to approx 20 liters. If I am stationary the tank will remain full. I would like to fill up at home and arrive on-site with a full tanmk. Am I missing something here?
 

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Ozzie1956 said:
Thanks. I would like to fill to full capacity before we leave.

As I understand it, if I close knob completely it will reserve water in tank.

If I start moving, the tank will dump down to approx 20 liters. If I am stationary the tank will remain full. I would like to fill up at home and arrive on-site with a full tanmk. Am I missing something here?
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The one I have if filled for travelling stays full, the valve is a manual operation. The idea of the 20l limit for travelling is I believe the inclusive amount in miro.

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If my one is closed fully and the tank filled it stays full when travelling

Cheers
Trevor
 
Ozzie1956 said:
I would like to fill up at home and arrive on-site with a full tanmk. Am I missing something here?
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Do you have the spare payload needed to carry maybe 100kg of water ?
My old RV had a 70 us gallon tank.....265 ltrs / 265 kg or over 1/4 ton of water.
Never travelled more than 1/8th full.
 
Fine. But the sales documentation for my MH states.

Fresh water tank, built-in (volume in liters) 20**/80***

* Please observe the information and explanations
** fresh water tank capacity limited to 20 ltr. by overflow valve (recommended driving fi ll level)
*** fresh water tank capacity is 110 ltr. with the overflow valve closed.

My manual is in German. Not my strongest point.

I am trying to find out how to find my overflow valve and CLOSE it before driving, or what a typical one looks like so I can close it before I start driving so I can arrive at destination with a full tank. I don't want it to dump water when I start driving. Answers appreiated.

I filled tank before driving yesterday... arrived destination and tank was approx one third full. Dumped water en route. I thought it was the Truma due to low temp here in Bergen , Norway... but apparently not.
 

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Hymer do this as well. All it means is that they have calculated the MIRO and therefore the payload, using only 20l of water in the fresh tank. It is a way of showing a larger payload. Not needed for mine given that I have over 800kg. Your instructions say that this is only a recommendation.

You can drive with a full tank and the overflow valve closed. We do it all the time. However you will need to make sure that you have enough payload to put that amount of water in with all your other things you carry. It will not dump water when you drive and nothing will drain out until you open the dump valve.

Edit - just seen your photo. The tank drain looks the same as in our hymer and is operated by the black wheel on the right. Turn it fully clockwise to close the valve and you will be able to fill the tank. If you want to leave just 20l in then just turn it a quarter turn anticlockwise. If you want to completely empty the tank turn it further anticlockwise.
 
It may not be as simple as payload restrictions.
Consideration must be given to construction and the effect driving with a full water tank mayhave on the tanks mountings
It could have a serious effect on safety, and or stability when cornering even the mounts giving up and loosing the tank under heavy breaking
rest assured there will be a very good reason 20ltrs is set as a driving limit, of course all and any claims will be invalid if this figure is ignored
 
According to the specs:
https://www.knaus.com/en-int/camper-vans/boxstar-600/layouts-data/family/standard-equipment/
It's GVM is 3.3 tonnes
It has a payload of 460 kgs provided the water tank only has 20 litres
If you fill it, then you only have 380 kgs payload - less whatever accessories you've got...solar, extra leisure battery, awning etc.
Also out of that amount has got to come your personal weight over 75 kgs and the weight of any additional passengers - in my case that's another 50+ kgs off the payload (I have a heavy dog!)...
Then you can consider personal effects, food, drink, chairs, ramps & all the other clutter we carry around.

Others have said above how to override the fill valve - my question is, if you do -will you be overweight?
 
Geo said:
It may not be as simple as payload restrictions.
Consideration must be given to construction and the effect driving with a full water tank mayhave on the tanks mountings
It could have a serious effect on safety, and or stability when cornering even the mounts giving up and loosing the tank under heavy breaking
rest assured there will be a very good reason 20ltrs is set as a driving limit, of course all and any claims will be invalid if this figure is ignored
Click to expand...

Sorry. but I disagree. the construction of the vehicle should be able to cope with the fact that ALL the tanks could be full. In the same way as the stability of a ship MUST be able to satisfy the rules with NO ballast or Bunkerage and why the Class societies insist on an Inclining test as part of the procedure to sign off a vessel.

I always call it "Worst case Scenario".
 
Langtoftlad said:
According to the specs:
https://www.knaus.com/en-int/camper-vans/boxstar-600/layouts-data/family/standard-equipment/
It's GVM is 3.3 tonnes
It has a payload of 460 kgs provided the water tank only has 20 litres
If you fill it, then you only have 380 kgs payload - less whatever accessories you've got...solar, extra leisure battery, awning etc.
Also out of that amount has got to come your personal weight over 75 kgs and the weight of any additional passengers - in my case that's another 50+ kgs off the payload (I have a heavy dog!)...
Then you can consider personal effects, food, drink, chairs, ramps & all the other clutter we carry around.

Others have said above how to override the fill valve - my question is, if you do -will you be overweight?
Click to expand...

Which reverts back to earlier speculation about the intention of the manufacturer to be able to quote an under 3.5t figure FOR SALES AND PROMOTION PURPOSES. because of EU wide limitation on driving licences.

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Geo said:
It may not be as simple as payload restrictions.
Consideration must be given to construction and the effect driving with a full water tank mayhave on the tanks mountings
It could have a serious effect on safety, and or stability when cornering even the mounts giving up and loosing the tank under heavy breaking
rest assured there will be a very good reason 20ltrs is set as a driving limit, of course all and any claims will be invalid if this figure is ignored
Click to expand...
Water slapping about in a part filled tank IMO could make the vehicle more unstable than with a full tank which does not slop about. Tanks are fitted with baffles to try to slow this slopping. My 1992 Hymer has 120 litre fresh and waste tanks. I always fill the fresh tank to capacity. There was an overflow from the top of the tank which could lose water on corners, so I fitted a valve in this to prevent it. Open valve when filling then close it before driving. Tanks are mounted securely, so no problems of breakaway even after 25 years of which I have full timed in it for 6 years.

It is the desire to put as many goodies into a vehicle, with an all up weight of under 3500kg, that is driving this together with the restrictions on driving licences. Plain and simple.
 
Ozzie1956 said:
Any suggestions as to how I should understand this specification?

"fresh water tank capacity limited to 20 ltr. by overflow valve (recommended driving fill level)."

Am I correct in assuming that I should only fill tank up to 20 liters before driving to site and then fill to capacity? If so has anybody any idea how I can see if I have an overflow valve? I have a user manual, but only in German - which is not my strongest point.

Motorhome is a Knaus BoxStar Family. Thanks for any help.
Click to expand...
A bit of confusion with either terminology or translation, it is not an overflow it is purely the drain valve which allows you to empty the tank to 20lt for their recommended travel limit. You should always travel with the valve fully closed or you stand a good chance of losing the 20Lt you have. Like most I always travel with a full tank.
 
I have a Knaus... with the same 20/22ltr travel recommendation...

I have had the Moho 2yrs and have yet to find a valve that reduces the level..

The one thing in the outside service locker that I'd always assumed to be the valve - turned out to be the hot air winter flap for the tanks..

Being full time - I always travel with water... on avg 3/4 full mostly...

And so I have never bothered looking for said valve... which must be closed as I can retain a full tank...

As an aside.... I have not noticed anything in the inside tank maintenance hatch either!..
 
My Euro Mobil has the 20ltr warning and being the average male thought I knew better than the manufacturer and brimmed the fresh tank for first trip away.
After negotiating three roundabout's, the tortured squeal of near side tyres and the scrubbing feedback I was getting through the steering wheel quickly let me know why they had introduced a limit. On mine the water tank is under the dinnette seat, in effect a 200kg mass on the nearside of the vehicle and towards the front axle, so balance of vehicle is compromised, and no baffles installed. I appreciate that some people find they can carry a 1000 tons of water and 200 cases of beer and wine, with no sway effect whilst underway, however if the vehicle is not balanced you will feel the effect when you try to change direction with some Moho's when water tank is full.
 
Ozzie1956 said:
Any suggestions as to how I should understand this specification?

"fresh water tank capacity limited to 20 ltr. by overflow valve (recommended driving fill level)."

Am I correct in assuming that I should only fill tank up to 20 liters before driving to site and then fill to capacity? If so has anybody any idea how I can see if I have an overflow valve? I have a user manual, but only in German - which is not my strongest point.

Motorhome is a Knaus BoxStar Family. Thanks for any help.
Click to expand...

To get back to the original question, AFAIK there is no device which automatically lowers the water tank level when a MH starts to move. If you can fill the tank when stationary the 20l overflow seems to be closed, You can check this by looking underneath the MH after filling. There may be a short term syphon effect from the main overflow though. It's worth checking under the van so that you know where the various outlets are, ie truma dump valve, full tank overflow, 20l overflow and tank drain to make it easier to tell where water is coming from. Some outlets may be combined.

If you arrive with 2/3 tank full after starting full, the first thing I would check would be the truma valve.

Malcolm

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