A portable NPWT system includes a dressing assembly for positioning over a wound to apply a negative pressure to the wound and a canister assembly. The canister assembly includes a control unit having a vacuum source and a controller and a collection canister in communication with the dressing assembly operable to receive fluid from the wound. The collection canister has ports to introduce a vacuum from the vacuum source into the collection canister. A ball float is provided to substantially close the suction port in response to one of collection of a predetermined volume of exudate in the collection canister, tilting of the collection canister beyond a predetermined angle of orientation or inversion of the collection canister.