1. When any vacancy shall take place in any grade of officers, it shall be filled from the next lowest grade; provided, however, that probationary patrolmen shall serve at least six months as such before being promoted to the rank of patrolman; patrolmen shall serve at least three years as such before being promoted to the rank of sergeant; sergeants shall serve at least one year as such before being promoted to the rank of lieutenant; lieutenants shall serve at least one year as such before being promoted to the rank of captain; and in no case shall the chief or assistant chief be selected from men not members of the force or below the grade of captain. Patrolmen shall serve at least three years as such before promotion to the rank of detective; the inspector shall be taken from men in the rank not below the grade of lieutenant.

2. The boards of police are hereby authorized to make all such rules and regulations, not inconsistent with sections 84.010 to 84.340, or other laws of the state, as they may judge necessary, for the appointment, employment, uniforming^*, discipline, trial and government of the police. The said boards shall also have power to require of any officer or policeman bond with sureties when they may consider it demanded by the public interests. All lawful rules and regulations of the board shall be obeyed by the police force on pain of dismissal or such lighter punishment, either by suspension, fine, reduction or forfeiture of pay, or otherwise as the boards may adjudge.

3. The authority possessed by the board of police includes, but is not limited to, the authority to delegate portions of its powers authorized in section 84.120, including presiding over a disciplinary hearing, to a hearing officer as determined by the board.