Every position of employment, unless filled by promotion or reinstatement, shall be filled only in the following manner: The sheriff of the county shall notify the commission of any vacancy in the force of deputy sheriffs which is to be filled and shall request certification of a list of eligibles. The commission shall certify to the sheriff all those eligible from the last preceding examination held within a period of three years next preceding the date of the request for such eligibles. The sheriff of the county shall thereupon make an appointment from the eligible list certified to him.
16 P.S. § 4221.5