Here's a pretty colourful picture drawn on a computer. More than anything, just drawing the picture made the biggest difference as it cleared thoughts and made working out a layout in the van and measuring a lot easier.
This isn't exactly how it ended up, but how we set out. Two things were taken out, the stop cock to the toilet when there wasn't room to turn it, and the non-return valve which didn't seem to want to run either way at any reasonable rate.
The coldwater is held in the fresh water tank, and fed to the system via a stop cock. This was included as feel good safety factor, if we started to get a leak, we could turn off the supply!
From the stop cock to the pump. The pump is an electric 15psi diaphram pump from Whale. This gives a good flow for showering and sink filling but not quite 'mains' like pressure. It's buffered by a surge damper which does gives constant flow and also seems to enable quick runs of water without the pump turning on. The pump has it's own internal pressure switch so other than a supply of water and electricity doesn't need any other controls.
Fitting the pump was a pain for one reason, instead of running straight across, the feed and outlet pipes end up at right-angles to each other.
One thing not clear is that as part of the pump is a filter to remove coarse particles which may be in the tank and may damage the pump if they are sucked through. I'm told that if you buy a pump without a filter then it's a good idea to get one seperately.
The cold water supply has to feed four items, the kitchen sink, the bathroom sink/shower, the toilet and the hot water heater.
The bathroom shower/sink is a straight forward feed to a mixer tap with built-in shower head. Similarly, the feed to the toilet is just a pipe to it's solenoid controlled valve.
For the kitchen sink we fitted an inline Whale water filter. This has pushfit fittings so while it need changing regularly, it's not much of a problem to do so. This does cut the flow a bit, but the odd effect is that it does appear to aerate the water quite a bit so you end up with semi-fizzy drinks. We did look at the more sophisticated all in one 'filter anything' units but decided we would stick to tap water and avoid water of dubious quality.
The last cold water supply is to the hot water heater. This was also combined with a drain cock to dump the contents of the system out the bottom of the van if needed. We've got into the habit of doing this regularly and always in winter. This didn't appear to be much of a problem, but I've put more details in the problems section!
Finally there's an overflow pipe, which runs from the top of the fresh water tank in case of overfilling, and also takes a feed from the hot water heater to accomodate expansion in the hot water tank. This runs out through the van floor.
The hot water feeds run from the top of the water heater to the kitchen sink and bathroom sink/shower, probably the most straight forward of all!