Autotrol
that is an autotrol, metered and on demand unit
and it is an older one...
probably about a 1993 or so.....
they are notorious for the springs and cams inside the unit weaken under high water pressure and
siphon all the resin into the plumbing system...
on the back sid e of the unit their should be a white stamped date to how old it is....
it might be better to consider a new unit....