I have a drawing from Airstream showing the plumbing layout of a 31' trailer that someone passed on to me some time ago.
The drawing is dated 1997 - but updated to 2005 - I'm not really sure if it matches what is actually on my 2005 Classic 30, but it is probably pretty close.
In looking at the drawing today, I see there is a one way check valve on the city water inlet line - and I understand the need for that, i.e. so that you don't loose water out the city inlet when running from your fresh water tank and 12v
However the check valve is shown with a manual bypass valve around it and i am wondering what the purpose of that would be?
The only thing I can think is that it may somehow be related to winterizing if you use plumbing antifreeze - i.e. a quick open/close of the bypass valve would flush out the city water inlet line.
But doing so could still leave a "slug" of water on the trailer side pipe leading away from the check valve which could perhaps not get diluted with antifreeze and could freeze.
I suppose the safest way to ensure the check valve is protected in winter is to both blow the system with compressed air, and then fill the system with antifreeze.
That is what I do most years, but a couple of times, I have winterized the trailer away from home with no access to a compressor so I just used plumbing antifreeze and still didn't encounter any freezing problems - maybe i was just lucky?
Anyone know if there is any other purpose for the check valve bypass valve?
At least reviewing the plumbing schematic explains one thing to me. When winterizing our trailer, I had noticed one extra valve down in the general area of the three valves used to bypass the HW tank.
I always wondered what it was and I now suspect it must be the check gave bypass.