Any of the candidates for nomination or election at a primary may withdraw his name as a candidate by a request in writing, signed by him and acknowledged before an officer empowered to administer oaths, and filed in the office in which his nomination petition was filed. The withdrawal, to be effective, must be received in the office of the Supervisor of Elections or his deputy not later than the ordinary closing hour of such office on the fourth Wednesday in May in the election year. No candidate may withdraw any withdrawal notice already received and filed, and thereby reinstate his nomination petition.