T&T: vent valve

[Larry N. Brown]

As I've pointed out before, it's easy to locate parts on Google or eBay . .if
you know the name of the part. I want to put a valve in one of my aft
stateroom 4" air-conditioner vent lines so I can direct AC into the head while
taking a shower. I thought I was being bright by putting 2 vents in the SR and
one in the head but the air in the head is generally wasted and the unit has
to work harder than necessary to keep the SR cool. Does such a valve exist and
where might I find one?