Understanding Rotary Oil Pumps: Filling, Ballast, & Oil Pressure

[Myskin]

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?

 

[Bandit127]

I have no idea what experimental camera means in relation to the question.
By ballast I assume you mean offset - the rotor is offset from the centre of the pump.

Check this animation of a vane pump. There will be some vacuum crated as the pump pulls oil in. I guess this is why a low vapour pressure is needed.

The pumps I work with can change the offset of the rotor, thus increasing or decreasing the pressure it creates. Working range for mine is 15 - 200 Bar (1.5 - 20 MPa).

The pump works full. I don't know for sure about the gas, but I assume that if any comes out of solution it will quickly be absorbed as the oil becomes pressurised in the pump.