Hi everybody. I'm studying this kind of pumps right now but i'm finding a few difficulties trying to understand how it works... First of all i know it needs to be filled with oil, right?but totally or partially filled? When we start the pump the rotor starts spinning so it starts to evacuate our experimental camera from the gas...this gas cause of the spin of the rotor goes inside the pump...but does it flow THROUGH the oil or what else? Can someone explain me what's the utility of ballast? Why does it need a kind of oil with a low vapor pressure?