Fresh Water Tank Overflow

[kelly58]

A question for my learned friends, when my tank is full obviously whilst driving along there is a loss of water from the overflow,would it be applicable to fix some plastic pipeing to the overflow outlet and then fit a small tap onto the end of the pipe.

The tap can be turned on whilst filling so as I will know when the tank is full and then turned off before transit so as the water will not wash out whilst travelling, the tap can be turned on whilst parked to allow air into the tank when in use.

I hope this makes sense because I have found that I am losing almost half a tank of water in transit especially when turning right or going clockwise around roundabouts leaving a trail of water on the road.

[mark lambert]

Hello! is there any particular reason you need to have your tank full when your driving to your destination? the van would be more stable with just a little water in your tank and it would do more to the gallon i would think. I was always told to put just a little amount in and fill up when arriving on site (?) sorry it doesn't help your problem though!

[chas]

Hi Kelvin- That is a strange one, it would appear you may not have any form of baffling inside the fresh water tank for this to happen. Can you see how far down the overflow pipe is on the tank ? I cannot see any reason why you cannot do as you suggest, as long as you do not forget to open the tank tap on filling up, to avoid blow back. My only other thought would be that the tap should be protected from road filth as there could be possible contamination back up the pipe to the water tank. Regards chas

[Derek Uzzell]

kelly58:

 

Are you certain the water is going out through the overflow? This loss-of-water experience happened to me when I bought my Hobby and I traced the problem to a poorly-seating 'cap' on the water filler. Overflow arrangements normally involve a high-mounted narrow-diameter overflow pipe, so it's not that easy for water to escape. On the other hand most water filling inlets have a wide diameter hose feeding into the tank and, if the cap's sealing is poor, when the motorhome is being driven water can exit the tank at a startling rate. If you can see water pouring out while cornering, as I could, then it may be coming from the filler (Check for tell-tale water marks on the bodywork to the rear of the filler-point).

[kelly58]

Thanks for your reply`s firstly we are going to France next week for a long tour around that is why I want to travel with welltopped water tank just in case we have to wild camp.

Secondly the overflow is at the top nearside of the tank and this is where the water is exiting so that is why I thought a pipe fitted with a small tap would help to stop the loss of water especially when cornering, but I must add not a break neck speed, the idea of the tap is to allow overflow whilst filling..

[Brian Kirby]

Kelvyn

One flaw in your scheme occurs: as you drive, the vehicle will be subject to barometric pressure, and temperature, changes.  The pressure changes in the tank due to temperature changes will probably be quite slow and small with an inboard tank.  However, the barometric changes can be quite rapid; as you go up/down mountains for example.  I would therefore be very cautious about "sealing" your tank against barometric equalisation.  It may over pressurise a joint somewhere, leading the the tank contents transferring to the interior of your van: it may do the reverse if you stop for lunch to admire a mountain view, and collapse pipework, or the tank, on the way down!

I'm with Derek, you shouldn't be losing large quantities of water as you drive.  In a number of vans, the overflow (which is not what it really is, it is a pressure relief, or "breather", pipe) connects back to the filler cap, venting just outside the sealing ring.  This arrangement tends to reduce on road losses, but it seems this is not how your installation was made.

The breather pipe should leave vertically from the top of the tank, ideally near its centre, and should not extend down inside the tank.  In short, it should always be above water level.  So positioned, because the pipe will lie above the tank water level, it will be virtually impossible for water to escape down it.  Unless the breather is obviously poorly installed, therefore, look first for leaks around the tank, or around the filler cap, as potential culprits.

If it is the installation of the pipe itself that is at fault, consider re-jigging this as above.  Block off the existing breather pipe outlet and install a new one as closely as possible to the top centre of the tank.  If unsure how to proceed, I'd suggest CAK tanks for bits and advice.

[derek500]

Our overflow is as Derek explained. We used to lose water when cornering and realised it was the filler cap not being replaced properly.

 

Where does your overflow overflow to?

 

You're not alone, we also travel with a full tank, 110 litres and another 20 litres in a jerry can.

 

That usually lasts two nights/three days.

 

[Mel E]

Kelly,

 

We have done exactly as you propose and for exactly the same reasons. And it works a treat! And to answer all the other replies you have had:

 

1. We have only a conservatively small tank (about 45 litres) so we really don't want to lose half of it. (We have a space designated for a second tank to double water capacity, but haven't felt the need to install it yet.)

 

2. Yes, all the seals are fine and yes, the tank has baffles - but only up to about one-third of the way from the bottom, and they are only aligned front-rear so do not stop a 'slosh' developing when accelerating/braking or on steepish hills up/down.

 

3. The overflow is near the top at the front corner of the tank. Hence we lose water both as in 2 above and also when cornering with a full tank.

 

4. As Brian says, many tanks do not have overflows but only a drain cock with tap and an air vent to the roof. The overflow is effectively the filler cap and you stop filling when water shoots back out. If you do have an overflow,

 

So we have fitted a tap to the overflow pipe which works fine. We have put the water filler cap key on its own ring with a tag attached warning you to open the overflow tap before using.

 

For once I think the usually extremely erudite Brian has got it 'in error' (I don't want to appear rude by suggesting he's wrong) about pressure differences. First, the tank can vent air through the filler cap - it's certainly not completely air-tight. If it was, then the water pump would stop pumping water as the pressure dropped inside the tank. Also the screw cap on top of the tank is also not completely airtight. Secondly, the pressure changes with altitude occur very slowly in a motohome - unless you drive off a very high cliff - say, the 7,000 foot Grand Canyon - when you will be more concerned with other problems! Pressure falls with altitude at an average rate of just 3 millilbars per 100 feet; 1 psi is approximately 70 millibars, so you would have to change altitude by 2300 feet to get even a 1 psi difference, and if your water tank cannot withstand that, then, once again, you have much bigger problems . . .

 

So go ahead and do it!

 

Mel E

====

[Brian Kirby]

I defer to Mel's gently expressed superior knowledge of barometric pressure changes, he's the fly guy!  Also, I concede I'd forgotten the filler caps, at least mostly, can breathe through the keyholes. 

I was responding, rather unthinkingly I'm afraid, to a remembered experience from some years back when I had stowed an empty water container under the driver's seat of a car, where it was a nice snug fit, while ascending the Pyrenees.  After a few miles the seat felt a bit funny and the pedals seemed further away.  As my ears were popping regularly, it suddenly struck me the discomfort of the seat might be connected to the water container, which I knew had the cap screwed tight, so I fiddled with this on and off, while doing the hairpins!  Interesting road from Bourg Madame to Ripoll!  Eventually the cap loosened, accompanied by a loud hissing, and my head gradually retracted from the roof, where it had been parked!  Not many psi, I guess, but an enduring demonstration of barometric pressure.

[Mel E]

Brian,

 

You must have noticed the same effect in reverse when flying if you take a plastic bottle of water on board with you - I always try to on long-haul flights to prevent dehydration. When you land, the bottle is sucked in because you last opened it, in effect at between 6,000 and 8,000 feet - the normal pressurisation altitude of a passenger jet. Open the screw cap and there is a hiss of entering air.

 

It was even more marked recently when we flew from La Paz where the airport is at 13,600 feet, to Buenos Aires, where it's at about 60 feet!

 

But it takes a long time for a motorhome to lose/gain 6,000 feet.

 

Mel E

====

 

 

[kelly58]

Thanks to you all for your comments it seems I have the same external tank system as Mel E 45 ltr capacity the overflow pipe is in the same location, on the inside of the offside locker where the filling pipe passes through to the tank beneath the floor on the sidewall or as you may say the outside wall the filler cap attatchment has a small air breather as part of the unit to prevent blowback I would say the filler cap is about 18 /24 ins above the tank

[Brian Kirby]

Mel E - 2007-05-04 3:49 PM  But it takes a long time for a motorhome to lose/gain 6,000 feet. Mel E ====

Provided you keep it on the road, of course!  :-)

[Tomo3090]

Just be aware that if your "water trail" caused an accident, then you might be liable for a vehicle with an "insecure" load.

 

It might be worth a phone call to your local police station traffic office to clarify this point, but I am certain that is the position.

 

It is the same for anyone who's diesel tank does the same.

[Brambles]

Hi, to pick up ona few points mentioned.

The top (access cap) should not leak and shoud be water tight.

The 'overflow' pipe is actually a vent pipe for when filling. If you can re-route to connect to vent pipe boss on filler cap. If not then see if possible to raise outlet of pipe to a higher position. You could always bung it and drill bung with a 1mm Dia Hole so it can still 'breath' but water loss will be remarkably reduced (bear in mind your filer cap should breath anyway). However filling tank quickly might splash back at you and also if using a hose which is a close fit to inlet pipe you wil pressurise the tank too much.

The other option is to extend the pipe inside the tank into the center top position (seems a bit of a awkward job).

Personally I would go for connecting the pipe to the Filler vent boss, even if it means having to drill a hole through floor and sealing pipe through floor. Just follow next to route of filler pipe, or get a repair workshop to modify for you. (make sure tank access top is water tight and screwed on properly so if tank is overfilled water will not leak out.)

The difference a full tank versus an empty tank is small compared to overall weight of vehicle and will make no noticeable difference to fuel consumption, or speed going up hill.

Jon.

[Brambles]

Tomo,

Lorries carrying wet goods, be it sand, stones, or a freezer lorry finished deliveries and defrosting freezer trailer leave trails of water all the time, and have never heard of an accident being caused by such.

Then there are animal Lorries with animal pee running out the back...

Water flooding on road from leaked pipes - and again a claim agianst whoever is responsible would not stand up in court as you should have seen the water.

Diesel is a different catagory all together as it contaminates your tyres and you can skid easily.

J.

[Tomo3090]

Brambles, I used to be in the fire service and there was an example where a fire engine left a water trail and a motorcyclist skidded at a roundabout. The witnesses at the time told the police and the driver was going to be prosecuted but the tank design on fire appliances in the 1980's was such that the tanks weren't sealed, and the FBU successfully defended thre driver. Following this case and others the design was changed and tanks are now sealed. There are cases where fire engines do leave trails, as do other road vehicles, but if someone witnesses this and a crash happens then I am just warning that a prosecution would follow.

 

The roads get very slippy when it rains following a dry spell because of all the oil and fuel on them already, so it doesn't need much water to cause a problem.

 

I agree the chances are VERY slim that it could be proved to be YOUR water that caused this, and highly probable you wouldn't get done, but it can happen and I don't think it would stop an insurance company or some individual taking on the case.

 

Don't forget "Where there is a blame there is a claim!" Sadly!

[flicka]

Kelly

Just a thought,

Could airflow across the end of the overflow pipe be creating a syphon effect ?

Repositioning the end or connecting another section of pipe may solve your problem.

Others on the forum might have some more knowledge than me on the subfect.

 

Flicka

[Derek Uzzell]

Flicka:

 

On my Hobby, all the breather/overflow/drain hoses for the water tanks and the Combi heater that extend below the floor are cut off at an angle with the resultant oval 'hole' facing towards the rear of the vehicle. Aerodynamically this should encourage the below-floor slipstream to suck from the hoses rather than blow into them. In practice, because of the relatively low speeds at which motorhomes travel, the suction effect will be tiny and the primary reason for angling the hose-ends rearwards is to minimise the risk of road dirt clogging them up.

 

A water-tank vent hose that extends below the tank's water level shouldn't enter the tank itself. If it did then the water would indeed have the opportunity to siphon out when the hose became full. I'm sure that 'slipstream suction' on the end of the hose wouldn't be sufficiently powerful to initiate siphoning but, once siphoning commenced, I suppose it might increase the water-loss rate.

 

In Kelly's case (as has already been suggested) I expect it would be possible to re-jig the present arrangement so that a shut-off tap is not needed, but, for now (and as Mel E has proved that fitting a tap is effective) that's probably the simplest way to go.