Vacuum applies the heat riser. (closes the butterfly valve)
Thanks, it comes off tomorrow. So when cold, the therm switch in the water neck is open, allowing vacuum from the manifold through the switch, then pulls in the vacuum piston. Once the water temp warms up, the switch closes off the vacuum, I suppose the switch also has a vent to release the vac as well?
Thanks for the info. I now know which way to tie it off until I install the headers.