The city employes shall, after the passage of this act, pay unto the board of pensions monthly an amount equal to not less than two nor more than five per centum of their monthly salaries or wages, as fixed by the board of pensions; in no event, however, paying at a rate greater than thirty-two dollars and fifty cents per month, which shall be applied to the purposes of this act. Payment of the monthly amount or contribution herein mentioned shall cease and be discontinued at the time the beneficiary received the pension herein provided if such beneficiary has so contributed to the pension fund during a period of twenty years. If at the time the beneficiary received the pension herein provided he or she shall not have been a contributor to the pension fund during a period of twenty years, such person shall be required to pay unto the board of pensions an amount equal to such amount as he or she would have been required to contribute had he or she contributed during such period as required by this act, until such time as his or her contributions shall have extended during a period of twenty years. If, for any cause, an employe contributing to the pension fund shall cease to be an employe of any such cities of the second class before said employe becomes entitled to the pension conferred by this act, the total amount of the contributions paid unto the pension fund by such employe shall be refunded to him or her in full without interest unless he or she has less than full pension rights under the provisions of section four of this act, and elects at once to exercise such rights by keeping such contributions in the fund and making such further payments as may be required: Provided, however, If any such employe shall have returned to him or her the amount contributed, as aforesaid, and shall afterwards reenter the employ of such city, said employe shall not be entitled to the pension designated until twenty years after said reemployment, unless he or she shall return to the pension fund the amount withdrawn; in which event the period of twenty years shall be computed from the time the said employe first entered the service of said city. In the event of the death of any such employe before the said employe becomes entitled to the pension aforesaid, the said total amount of contributions aforesaid shall be paid over to such person or persons as he or she shall have designated in writing and filed with the board of pensions as his or her beneficiary or to his or her estate.