A little help with a little giant sump pump

[coffeesnob]

My little giant pump pumps out the water but won't shut off. Is this the diaphragm-diaphragm switch or something else. Also can you please explain why there is a air line from the inside of the pump to the end of the electric cord. Also where is a good place online to get whatever part I need? Thank you

 

[Geofd]

pics would be good but I think you could get all your answers from little giant