Consider the following statements pertaining to centrifugal pumps:

1. The inlet to the impeller of a centrifugal pump is always axial, while the outlet may be radial or inclined.

2. The impeller may be shrouded on both sides with an eye at the center and vanes curved backward.

3. Impeller of double-entry type has a balanced radial thrust.

4. Un-shrouded and part-shrouded impeller are used only where high efficiency is unimportant.

Which of these statements are correct?