Can anyone tell me why my ameda lactaline pump isnt working properly?

[Newbeginning1]

I bought the pump off ebay but it doesnt seem to have the right level of suction to even stimulate my let down. I've assembled it as best i can without the instructions.

If anyone can help that would be appreciated.

Mine went like that and I changed the white thing, what's it called (diaphragm??) and was ok again.