We have an intermittent problem with water supply in the van when hooked up to a tap in caravan park when its playing up we get no water at the sink, Bathroom or front tap I have tried to replicate the problem at home but no luck to date

Have spoken to Jayco who told me there is a small black colour ratio valve in the water supply  line I cannot see anything that looks like what they described.

 

I have found the device shown in the attached photo and suspect it is a ratio valve bur its not small and its not Black If any of our knowledgeable and experienced members can identify this object and then tell me how to solve the problem I would be very greatfull

As a plumber I have never heard of them being called a ratio valve. They are simply a tempering valve and that means for the last few years any Hot water units installed and to be used for the purposes of human cleansing , that is to say not laundry or sink the water must be tempered.for prevention of nasty burns .Now ,thats the reason you have one. Most brands have filters that frankly are a pain in the a#$e.Remove it and clean it as best you can .Most times we find that parks have inferior water water pressure so the unit will not work to capacity .Once you return to civilisation so speak and connect to town water pressure it may work much better. They do not cost a great deal @ $65 or so it will take 10 mins ,2 shifters and some teflon.Just do it and then you have a spare Good luck.John

 I knew If I posted my problem on the forum I would get an answer, Thanks to all who have helped and to Dorian that is a very useful link I have downloaded the documents and will crawl back under the van tomorrow, I will also check behind where the hose connects to see what I can find.

Thanks everyone