Any machinery or equipment requiring an experienced operator shall be rented or hired only under the supervision of an experienced employee of the county or township. It shall be hired or rented only at such times as it is not being used by the county or township in its own work. The charges for the use of said machinery or equipment shall be sufficient to defray the expense of the county or township employee operating said machinery or equipment, and the cost of operating said machinery or equipment, together with any charges for additional insurance that the county or township may be called upon to pay for the additional liability assumed. The charges shall be the same to all persons for the use of said machinery and equipment under similar circumstances.