Potable water tank 'vent' position

[BruceM]

Simple question. I have an A Class Dethleffs with a potable water tank manual control tap which according to the manual has three positions;

 

1. Open – to empty the potable water supply tank

2. Closed

3. Vent

 

I’m uncertain as to what is meant by ‘Vent’. My initial thought were either to allow the air pressure to vent out during filling (in which case it doesn't do a very good job of it) or to allow an empty tank to have some air flow and stay dry during a lay over.

 

Can anyone enlighten me

 

Many thanks

[Derek Uzzell]

I’m guessing that the “vent” setting causes the contents of the tank to be drained to a specific level (say 20 litres) prior to the motorhome being driven.

 

It’s commonplace nowadays for motorhome converters to specify two fresh-water tank contents values. One value indicates the tank’s maximum capacity (say 100 litres), while a second (much smaller) value indicates a ‘when driving’ capacity. It’s an infuriating ploy that allows the motorhome’s payload value to be artificially inflated.

[monique.hubrechtsgm]

I think the vent means an intermediate overflow position to the underfloor drain tube. contained in the drain valve itself. I have it on my burstner either you filled it up to `120 ltr max cap, or put that drain manually to intermediate as described in your manual to half, being 60 ltr. Air cushion in the tank H/ L is regulated by the filler cap. Put off the filler cap when draining, it goes faster than whit the cap on. In belgium, but no one is interested anymore according Derek, it has no legal effect on the Miro. This is my last post on begian rules.