increases blood flow, engourges the area / clit.
I can't recommend a pussy pump because I bought a smaller one just designed for my clit for solo play that was just "so so"... the review is linked off my profile.
Because that experience was not the best I am not super sold on investing more in a larger pump. Personally I was just looking to increase sensativity to my clit during solo play which I can also do with a blam or the like.