A pesticide spraying unit is pressurized with compressed air through an air filler one way check valve of the type having a non-puncturing depressible stem. The check valve is preferably affixed to an adapter which can be inserted between the cap and tank of the spraying unit. A pressure relief valve and a pressure gauge may also be affixed to the adapter. Optionally, a puncturing type of gas cartridge charging device may be affixed to the adapter. The spray unit includes a manual pump, and the air filler check valve and the gas cartridge charging device provide alternatives for charging the tank of the spray unit with compressed gas.