A cartridge seal for centrifugal pump comprises a shaft tube assembly attached to a structure. A shaft tube of the shaft tube assembly receives a shaft of the centrifugal pump. A shaft collar of the cartridge seal attached to a second end of the shaft tube is in communication with a second end of the structure. A chamber tube of the shaft tube assembly and the shaft tube collectively define a chamber that contains compressed gas. A spring is located in the chamber of compressed gas. The compressed gas and the spring cause the shaft tube assembly to substantially prevent movement of fluids between the shaft and the structure in the centrifugal pump.