A pump has a casing, a rotating device and a switch valve. The casing includes an enclosed space, an inlet and first and second outlets. The device includes an impeller. The valve is in the shape of a circular arc. The valve is configured to turn on the pivot so as to: close the second outlet side to form a first volute around the central axis of the impeller inside the valve if a rotation direction of the impeller is a first direction, and also close the first outlet side to form a second volute around the central axis of the impeller inside the valve if a rotation direction of the impeller is a second direction. The first volute becomes gradually wider from the second outlet to the first outlet. The second volute becomes gradually wider from the first outlet to the second outlet.
