Valve

We have been putting everything into our new coach and today I put fresh water in and purged out the the oink. Also shocked the system. In doing this the plumbing is a bit different the my previous 5er. I found 3 valves for the hot water by pass. ( one was facing away from me and I missed it the first time through). I found one for allowing the pump to suck antifreeze into the system. But on the line on the input to the pump is another valve. The input to the pump is a blue hose, but as I trace back it turns t red. Color aside there is another valve in this line. I have the valve open and have used the water drawing form the tank and from the city connection. I am confused by this extra valve. I did not take down any panels but this appears to be the feed from the fresh water tank.
Can anyone shed some light on the purpose of this valve?
Thanks in advance for any help.

I may answer my own question

It came to me last night. This shuts off the line to the tank so that the pump only pulls from the jug of antifreeze.