A disposable cartridge air/gas dryer apparatus for installation in an air/gas line delivering compressed air or gas to an air/gas-driven tool. The dryer includes a pressure vessel having first and second ends, an inlet port, and an outlet port. A disposable dryer cartridge is disposed in the pressure vessel. The cartridge includes a casing and a quantity of a drying composition in the casing. A cartridge support surface in the pressure vessel supports a first end of the cartridge. A cartridge-receiving opening is provided in the pressure vessel for inserting and removing the cartridge in the pressure vessel. A cover removably covers the opening and captures a second end of the cartridge. The dryer can be provided with a handle so that it can be easily and quickly replaced by opening the cover, pulling out the cartridge and inserting a new cartridge. To simplify the cover construction, the pressure vessel outlet port can be positioned in adjacent opposition to a side portion of the cartridge, so that the cover thus does not require any air/gas passages.