1986 f-150, 4.9l, carter YF feedback carb

A question for those experts on this board. What is the CPRV valve and what does it do? This valve sits in the small "vacuum size" hose that runs out of the top of my PCV valve. This hose then runs down to the larger hose off the carb. that runs to the charcoal canister. Looks like it vents the evaporative canister.

Should this valve be open at operating temperature?

 

Canister Purge Regulator Valve. The valve, at operating temp, opens allowing the vapors to be drawn from the canister into the intake vacuum.

'79 F100 300-6 A/T