ummm, thats partially correct. i dont know its true name, but it letsthe air out of the top of the head. if youll look at it, the nipple (hehe i said nipple) is at the very top of the head. now if this wasnt there it would be impossible to get all of the air out of there without some vaccuum pump or by some other means. so YES IT HAS TO BE THERE, and in working condition. otherwise you have an air pocket up there, and air only cools 1/4 as well as water.