Yes. The PCV valve serves two purposes. It regulates the flow of crankcase gasses back into the intake for burning in such a way that you don't run lean, and it acts as a one way check valve in case of an intake backfire, preventing it from reaching the crankcase. If you have a hose going from your valve cover to a manifold vacuum source, usually on the carburetor throttle plate, it MUST have a pcv valve installed in line.
Take care,
-Chris
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