Bailey with onboard water tank/pressure vessel

Why not? No harm in having one  ..... less chance of freezing perhaps 

Can't really see the advantage of a pressure vessel. Does a yacht use one maybe cos they bounce about  on the ogin? My caravan hopefully stays put on its pitch.

I expect that the chap on an adjacent pitch to me at Southport would have liked one when temperatures were down to -14c at night not above freezing all day and his aquaroll that was around half full froze solid with his pump inside! 

I think that was around 7 years ago? 

That makes sense now thanks. The pressure vessel just gives a more regular flow I think, maybe not worth the extra weight and space?

With old caravan, like many others seem to, we would have 2 water barrels on the go to avoid the "running out at inconvenient time" situations. 

Now we have onboard tank, we only take one barrel and first top up onboard tank from it, and then re-fill barrel. Same result but one less barrel to cart around. 

We have also put around 10 litres into on board tank and thus had some water for overnight stops on way to holidays. 

And yes I am aware what it would have weighed - however also happy with tow car and payload for caravan! 

we have had onboard tanks for the last two vans over 13 years, but our latest van has a underfloor 40 litre tank and even in the recent hot weather the water came out cool. Winter is ok too and we did'nt have any freezing either, together with the aqua roll we have 80 litres of cold water, which is good as my OH still thinks she is on mains water lol 

Our Bailey Barcelona does have a pressure vessel - or accumulator and it is there, as you say, to smooth out the flow, just as it does on boats.  Only difference is that the caravan version is a small plastic cylinder whereas those fitted on yachts are usually  quite large and made of steel. As for the need for an inboard tank, I wouldn't like to be without it - particularly in winter and also for when the water invariably runs out half way through a shower!  Flick of a switch and it's back on again.

If the van does not come with an accumulator, it is very easy to fit one, cost about £15-20.

Thanks for the advice, does the accumulator just go in line before splitting to hot tank?

Yes.  We have an onboard pump, the accumulator is fitted just after the pump.  All the water goes through it then to the HW tank.

We also have an onboard tank, which can be used, or bypassed, as desired, everything is controlled by 2 manual valves which are set according to where we wish to draw water from.

If you are interested in this sort of set up, I can post a schematic diagram.

Our accumulator is a Fiamma one.

https://www.thecaravanshop.co.uk/waterpumps/accessories/fiamma-tank/cat_143.html

This one