Nuevo Fresh Water tank capacity

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Post by gassygassy on Tue Aug 27, 2019 7:03 pm

When looking at a new / used motorhome, after Mrs Fragrant has decided that there are enough roof cupboards inside, I find out what the fresh water tank capacity is. Less than 100 litres means I am going to have to stop for water more often than I would like and that might mean paying an English camp site £20 just to fill up with water. I wouldn't want that, would I? We have just got back from 4 days away and the filled up tank did last that long without getting down below 25% so I guess it might last a week if we just have full washes instead of showers.
Today I drained the water tank, closed the tap, recorded my house water meter reading and filled the tank. Thankfully it took 100 litres, which is what the book says it should. Next thing I need to know is the volume of water left when the tank level meter reads 75%, 50%, 25% and crucially how much is left when it gets to 25%, and is there any left when it gets to 0%? This will determine what lengths I need to go to, to find a tap somewhere.
Using a National Physics Laboratory calibrated Builder's bucket ( hugegrins ) with some capacity mouldings on it, the results were as follows, with the leisure battery reading 12.8v:
Drained 22.5l and gauge shows 75%
Drained a further 12.5l and gauge shows 50%
Drained a further 36.5l and gauge shows 25%
Drained a further 2.0l and gauge shows 0%
Then I removed the bucket from under the drain tap outside the van and used the internal water pump to drain the remainder which was a further 14l.
Then the pump was just sucking air and no water from the tap.
I then put the bucket under the outside water tank drain tap and coaxed another 3 litres of fresh water from the tank.

For those of you with a mathematical brain you might think that these numbers don't add up to 100l. You would be wrong. Either that or my NPL calibrated builders bucket is a bit off and needs re-certifying.

But what it does mean is that I have to do a couple of things:
1) See if I can fit a better, more accurate with more readings meter to the van if I want to know more accurately how much water I have got left
2) Remember that there are still 3 litres of water left that I can get, even if the pump won't suck it out.
It also means that the system, whatever it is, for displaying the tank's contents is badly out of symmetry. There is 36.5% (i.e. 36.5 litres) between 50% and 25%, and only 2l between 25% full and 0% full, both of which are lies.
I'll contact CAK tanks and see if they have any ideas. I think that a variable resistance probe (if it exists) stuck in the top of the tank feeding an analogue meter would do the job. I think some fuel tanks use an ultrasonic transducer fitted to the top of the tank. That would be nice, but probably costs 3p more than whatever A/S uses at the moment.
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Post by PLOUGHLIN on Tue Aug 27, 2019 7:17 pm

Your figures above. Do you mean you drew off water until the gauge showed 75/50/25/0, and those are the quantities resulting. Or do you mean you drew of the quantities then looked at the gauge and read the %s?

The 2 l between 25 and 0 doesn't look right, there should be roughly 25 l between each change except from 100 to 75 which only requires a small amount.

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Post by Dbvwt on Tue Aug 27, 2019 7:51 pm

Blimey, I might have had a couple of glasses of wine to cool me down this evening but I’m well lost smile!
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Post by gassygassy on Tue Aug 27, 2019 10:26 pm

PLOUGHLIN wrote:Your figures above. Do you mean you drew off water until the gauge showed 75/50/25/0, and those are the quantities resulting. Or do you mean you drew of the quantities then looked at the gauge and read the %s?

The 2 l between 25 and 0 doesn't look right, there should be roughly 25 l between each change except from 100 to 75 which only requires a small amount.
Yes the first method is right ploughlin. I drained off the water till firstly the readout changed from 100% to 75%, and measured the water in the bucket. The bucket has moulded-in marks at 2.5litre intervals, and of course there was a small discrepancy between me looking at the readout and running round the side of the van to see what the water level was in the bucket. Not a lot though, maybe one litre would flow in the time it took. I agree the 2 l from 25 to 0 is obviously not right and that is partly my point, you have no idea how much water you have got left when it reads 25%, and of course the less you have the more important it is to know how much. I suspect that the old fashioned analogue meters might be more accurate, if they are truly linear.
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Post by PLOUGHLIN on Tue Aug 27, 2019 11:07 pm

I am surprised. On my display, reads 100%, quickly reduces to 75% as you use a couple of litres, a day later 50% shows, a day later 25% shows, a day later 0% shows, a day later water runs out ie pump can't pick up. So all seems fairly proportional.

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Post by inspiredron on Tue Aug 27, 2019 11:17 pm

Your sensors are placed very differently to mine. I have 5 studs - 1 very near the bottom,, 1 near the top and e others reasonably equally spaced. The indicator tells you that you have at least x% left so as has been said after draining a litre or two it shows 75%. As soon as the level drops below ¾ it shows 50% a d I know that when the alarm sounds at 0% I have around 20 or 25 litres left. I've had the same "accuracy" in both my vans and never had an issue. Nor do I feel it necessary to worry about the accuracy.

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Post by inspiredron on Tue Aug 27, 2019 11:19 pm

Your sensors are placed very differently to mine. I have 5 studs - 1 very near the bottom,, 1 near the top and e others reasonably equally spaced. The indicator tells you that you have at least x% left so as has been said after draining a litre or two it shows 75%. As soon as the level drops below ¾ it shows 50% a d I know that when the alarm sounds at 0% I have around 20 or 25 litres left. I've had the same "accuracy" in both my vans and never had an issue. Nor do I feel it necessary to worry about the accuracy. I fill up at 0% or sooner if that may be cutting it fine.

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Post by gassygassy on Wed Aug 28, 2019 8:38 am

Yes that is a point I forgot to mention. As soon as the water level drops below the sensor it will show the next level down. I.E. Suppose it is in theory 3/4 full and the display shows 75%, then if you use half an inch of water the display will show 50% but that doesn't mean it is only half full, it means it is a bit less than 3/4 full.
I've now found some collapsible portable water containers in the shed so I could do with learning how to use the external filler pump. It looks as if you have to turn it on at the control panel. Harrumph. That means reading the instruction manual and being a bloke, one doesn't like to have to resort to such things.
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Post by marconi on Wed Aug 28, 2019 11:28 am

That is a very dedicated study of the levels well done.

I have found that all the gauges on various vans have been similarly hit and miss but you get the feel for them.
What they are is Boolean Algebra NOT gauges  smile!  75% is NOT 100%, 50% is NOT 75%, 25% is NOT 50% the last sector depends on how long its been since the pesky Alarm first went off. Of course it all varies with the level of the van too.

I find the Nuevo water gauge quite good compared with some we have owned. I did try the Auto 50% fill on one occasion and found that it indicated 75% when it stopped but it soon went to 50% after not much use.
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Post by steamdrivenandy on Wed Aug 28, 2019 12:31 pm

I remember the builders of our first campervan explaining that they didn't fit water gauges because they hadn't found any accurate or robust enough. It sounds like things haven't progressed all that much since then. There probably are gauges/systems that will provide accurate percentage full readings but they'll be v expensive and require accurate calibration.
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Post by steamdrivenandy on Thu Sep 26, 2019 4:40 pm

Seeing this thread on the Newsletter has reminded me of an issue with my van.
The original owner had the supplying dealer modify the van to accept a large cassette wheelchair lift under the van, to serve the side sliding door space. The cassette was about as wide as the doorway and went right under the van, almost to the offside. 

Trouble was that the original CAK Tanks fresh water tank protruded below the level of the cassette, so the dealer had a replacement tank made. He still wanted the same 45 litre capacity and the only way to go was to make the tank less deep, but longer fore and aft. It also wasn't fitted with the overflow vent nozzles that all CAK tanks use. The result of the lack of vents is that it has to be filled very slowly or a gush of water flows back at you as the displaced air tries to get out. It also means that when full it doesn't overflow from the top of the tank, but out of the filler opening. Several pairs of soaked shoes attest to these issues.

The water take-off to the pump is set as low as possible on the side of the tank, at the back. However what I've discovered is once the top of the take-off hole is exposed to air, the supply starts spluttering and just a short while later the water stops pumping completely as the pump prefers to pump the thinner air from above the water surface. This means that it stops pumping whilst there is still an inch or so of water throughout the tank, if level. If the van is nose down then the water moves towards the front but still stops pumping when the take-off reaches about an inch left. So that can mean substantially more water left in the tank, but inaccessible, unless you use the tank drain.

Because the tank is longer and not so tall as the original it means that whereas the original tank hit such issues when there were 5 to 10 litres left, in my case this now happens with between 15 and 20 litres left inside. That means that between 30 and 40% of the fresh water can't be pumped to the tap. I guess it's an example of unintended consequences.

The wheelchair lift was removed 18 months ago before I even saw the van and I've lived with the issue for that time and learned to keep the tank topped up via a watering can that's used very gingerly to avoid splashback. It would be great to buy a proper CAK Tanks replacement and get a usable 40 litres instead of a miserly 25 litres and avoid the risk of wet shoes but I can't really justify the price of the tank and fitting on an 11 year old van.
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Post by raymondo on Thu Sep 26, 2019 5:13 pm

than I would like and that might mean paying an English camp site £20 just to fill up with water. I wouldn't want that, would I?



camping and caravan club will allow members to fill and empty (and have a shower, use washing machines etc) for a payment of I believe £7

I am recently returned from 8 weeks wild camping never had to pay for filling or emptying so it can be done  a tank lasts me about 3 days (two showers)

most (perhaps all) moror way service stations have free showering facilities which ekes out the water supply!

I agree however that both the fresh and grey tanks are a little small
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Post by marconi on Fri Sep 27, 2019 5:44 pm

gassygassy wrote:
PLOUGHLIN wrote:Your figures above. Do you mean you drew off water until the gauge showed 75/50/25/0, and those are the quantities resulting. Or do you mean you drew of the quantities then looked at the gauge and read the %s?

The 2 l between 25 and 0 doesn't look right, there should be roughly 25 l between each change except from 100 to 75 which only requires a small amount.
Yes the first method is right ploughlin. I drained off the water till firstly the readout changed from 100% to 75%, and measured the water in the bucket. The bucket has moulded-in marks at 2.5litre intervals, and of course there was a small discrepancy between me looking at the readout and running round the side of the van to see what the water level was in the bucket. Not a lot though, maybe one litre would flow in the time it took. I agree the 2 l from 25 to 0 is obviously not right and that is partly my point, you have no idea how much water you have got left when it reads 25%, and of course the less you have the more important it is to know how much. I suspect that the old fashioned analogue meters might be more accurate, if they are truly linear.

I wanted to know how much water is left in the Nuevo Fresh Water Tank when the less than 25% alarm sounds.
With the 'van nice and level in both directions, today I pumped out gradually via the basin tap into a 3 Ltr calibrated jug and measured 21 Ltrs at which the pump started to struggle with minimum flow. I then opened the blue drain tap on the cold tank with the jug below, nothing came out.
I then replenished the tank with 25 Ltrs, measured, of water, the gauge showed 25% full ie. 25% but not 50% with no alarm.

I find this result quite reasonable, particularly the fact that almost all of the available water was pumped out.
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Post by steamdrivenandy on Fri Sep 27, 2019 5:59 pm

To get all the water out usually needs a take-off in the centre of the bottom of the tank, preferably with the tank bottom sloped towards that centre. Then water will always collect around the take-off, until the tank is empty. However as soon as the water take-off is even slightly open to the air in the tank, the pumped quantity will reduce as the pump needs the suction on water to perform properly. If even a tiny air gap is present it destroys the suction

For motorhomes bottom take-offs often present a problem as the take-off pipe and the hose from it will reduce ground clearance and both will be easily damaged over rough ground.
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