purpose of vacuum hose?

I have a 1993 Cherokee with a 4.0 six. The vacuum hose located at the rear of the valve cover pan is broken. I just noticed it recently and ordered a new one. I asked the person that works in the parts dept at the dealer and he did not know what it is for. Does anyone know what this does? I never noticed any difference in the way it runs since it has been broken.

Are you talking about the PCV hose?

Part of the PCV system, Postive Crankcase Ventilation system.

This is the crankcase vent hose, as others have pointed out. It's the hose through which (we hope) crankcase fumes will be sucked into the engine's intake. The big hose in front, which might look like the vent hose, is actually the one through which atmospheric air is supposed to enter the crankcase. When the little hose clogs, leaks or otherwise goes bad or missing, it's common for the system to work in reverse and send oil vapor into the air cleaner box.

Upshot: you did well to replace it.

Thanks MC, I couldn't figure out what it did by looking at it but I knew it was put there for a reason. Thank you for the explanation.

Actually it's a CCV. No "valve", just a metered orofice.