Voting by President and Deputy President
The President and Deputy President are in all cases entitled to a vote. When in the chair they may vote by stating to the tellers whether they vote with the “Ayes” or with the “Noes”.
Voting by the President, or the Deputy President as Chair of Committees, when in the chair, is optional. In practice this rule is extended to any senator occupying the chair. The reason for the rule is that a senator in the chair cannot avoid voting by leaving the chamber when a division is called for, as can other senators. In practice, however, the senator in the chair normally votes in a division.
When the President is present in committee of the whole during a division the President must vote. Similarly, if the Deputy President is present in the Senate when a division is presided over by the President, the Deputy President must vote.
As with the President, a senator in the chair has a deliberative vote and not a casting or deciding vote.