Nothing contained in the Nebraska Local Hospital District Act and sections 23-3501 to 23-3519 shall be construed to prohibit the board of trustees of any facility established under section 23-3501 or a local hospital district from establishing depreciation funds from patient or other revenue income for the purpose of replacing equipment or providing for future improvements or additions or from using such patient or other revenue income for purchasing equipment or for retiring indebtedness incurred for improvements or additions not financed by bonds of the county or direct tax levies. The limitations upon expenditures provided for in section 23-3508 shall not apply to expenditures made from patient or other revenue income or for the retiring of indebtedness or payment of other obligations from such patient or revenue income.