Dual Vacuum Check Valves?
 

'86 305 Silverado.
I don't see these vacuum devices on my hood diagram. I removed them, really can't see the need for them, or is there?
They look factory, under what conditions would these operate and why 2? They are identical, flow is from green to black (green side is connected to distributor.)

Attachment 671523

Re: Dual Vacuum Check Valves?
 

Those are trash, someone likely pulled them from another vehicle. You do NOT want checkvalves going to the distributor.

Sometimes they are used to hold ventilation doors open...etc after the vehicle is shut off.

Good thing you removed them, if they were holding vacuum on your distributor, it was likely staying at full advance all of the time..should run a bit better now, or accept a better time.

Re: Dual Vacuum Check Valves?
 

I knew what trouble they were causing, my confusion was with the OEM look of the valve configuration, even for HVAC two valves seems an overkill. Out of curiosity, I was hoping someone had run across them in there designed use, whatever that could be.