Unknown parts under hood!

[76chev454]

I have looked through 3 chev off-the-shelf manuals and have been unable to id to vacuum valves under my hood.  Both are on passenger side of firewall.  One is under the hood.  It is about 3" in dia and 3" high.  It has a vacuum line running to it from the carb.  What is it and what is it supposed to do and/or be doing?  I feel real stupid even asking.  The second valve is a metal one located directly beneath the passenger side windshield and in hangs in the space where the windshield wiper rods are located.  It has a vacuum line going through the firewall.  I have not taken the dash apart to determine where it goes.  Anybody help this lost character?      

[ccb]

Not sure what year truck you have I think your talking about the plenum valve above the heater lets air in you truck. the other one sound like the round vacuum tank, that has a line running  to provide vacuum to the main control block.

Craig  

[roundedline]

Can you get us a picture of the items in question?  

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project