Technical Using the on board water systems van when its below 7 C

[Nenagh52]

The " auto water dump valve" on the van opens at 7 C and empties the cold water tank.
Want to use the van this week for work temps will not get above 3 C all week and will be -2 C or so at night.
So its looks as if I wont be able to use the cold water tank for the week.
Thanks for any insights

 

[rayc]

Do you intend keeping the interior of the van below 8 degrees ?

 

[Nenagh52]

Thanks: No, I have the gas keeping it at 9 C as don't have a power hookup and will be 18 C when living in it.

 

[rayc]

Thanks: No, I have the gas keeping it at 9 C as don't have a power hookup and will be 18 C when living in it.

You need to get the temperature up to about 10 degrees at the dump valve to allow it to be reset. Can you run the gas heater to enable this to be done and then continue to use as normal? [Note that the cold water will lower the temperature at the dump valve as it flows through it so if you have just refilled the tank try to get the temperature at the dump valve a little higher to compensate and stop it dumping.]

 

[HughJampton]

As you mention 7 degrees, I assume you have one of the newer blue/grey frost control valves and a Truma Combi.

These are designed to dump water from the combi boiler under frost conditions, though a by-product of this might well be to drain the cold water tank, depending on water system design, especially if the pump is switched on.

The valve is designed to dump at around 3 degrees, and can't be reset until it is above 7 degrees.

If it's mounted near to the boiler, and the heating/water heating is on, then this is usually sufficient in UK conditions to overcome any risk of dumping by maintaining an ambient temperature of above 3 degrees at the valve. (not guaranteed though if it is really cold). When away from the 'van I would use space heating only (no water heating) just in case the water does dump.

The older series of (red) valves were electrically operated (rather than the current "passive" operation). As such, the valve wouldn't dump if the heater was switched on, being held by electric current. If you are concerned about dumping, and have enough occasions when you think it might, you could consider retro-fitting the Truma accessory that effectively replicates this on the newer valves (it also assists with getting the valve up to temperature to refill). It applies heat to the valve when the combi is in heating mode.

Truma Frost control Element | Truma Combi heaters + Spare Parts | Leisureshopdirect

Buy a Truma Frost control Element | Truma Combi heaters + Spare Parts | Leisureshopdirect

www.leisureshopdirect.com

 

[Nenagh52]

Thanks for all this, lots to learn, Hugh, its the blue/grey one, will post a picture later showing where it is. in relation to the combi.
Going out to wash it now!

 

[Nenagh52]

Okay, learning update:
van washed and at 9 degrees, went to take the picture of the auto dump valve and it is as warm as toast so the heating is keeping it warm.
Will fill the cold water tank tomorrow and see does it hold

 

[Nenagh52]

Mission update

I have no way of knowing when that pull cord is on or off but anyway when heating is on, the blue black valve gets warm.

I loaded up with 90 tires of water and headed off for a 200 km trip with gas heating at 9 degrees, and outside temp minus 3
Van of course got heated from the cab so got to 20 degrees and c half the water got dumped on route.

 

[rayc]

I loaded up with 90 tires of water and headed off for a 200 km trip with gas heating at 9 degrees, and outside temp minus 3
Van of course got heated from the cab so got to 20 degrees and c half the water got dumped on route.

So had the frost valve operated and dumped the water?

 

[Nenagh52]

So had the frost valve operated and dumped the water?

It didn't dump it all, just about 40 litres

I suppose the issue here is that the dump valve is outside the conditioned apace so its going to be chilled at 100 kms/hr at minus 3 if cabin is at 20 and heat set to 9

 

[HughJampton]

Much depends on the construction of the 'van and the location of the services.

If the dump valve trips, the it will certainly dump the contents of the boiler, and most likely the contents of the fresh water tank if the pump is running (that's more likely with a pressure-switched pump than microswitched). It is also possible that the fresh water gets syphoned, but that depends on the piping geography.

It's not common (IMO) for the dump valve to trip in a heated vehicle on the move (but see first sentence above).

I've just been away for four nights in the 'van in sub-zero temperatures. External taps on the campsite froze solid overnight, but I had no problems leaving heating on at 10 degrees. It was -2 this morning when I left, and is still 0 degrees here after a four hour journey. No water problems.

The corded Truma arrangement is for a "diverter" that will pass space heating to the fresh and/or waste tanks to inhibit freezing. I'd have bet the other way round, but web research indicates that with the string slack, flow is enabled, and it can be closed by (carefully) pulling the string tight and latching it in the clip.