Air compressor tanks contain pressurised air that is used to operate air tools and inflate tires. They also serve various other commercial, industrial and home-based needs. Moisture can develop in air tanks causing corrosion leading to leakages in seams and fittings. The purpose of periodic testing of air compressor tanks is to discover leaks before they become problematic and to validate the tank's condition. You can test your own air compressor tank with the proper tools, equipment and basic mechanical knowledge.
Turn off electrical power to the air compressor. Tag or otherwise mark the circuit breaker or switch to alert others of the work being done.
Open the air tank bleed-out valve to release all air pressure in the tank. The valve can be opened by hand turning the handle in a counter-clockwise direction.
Locate the air pressure relief valve on the air tank. The valve can be identified by a pull-ring inserted at the top of the valve.
Remove the pressure relief valve with a pipe wrench. Turn the valve in a counter-clockwise direction.
Close the air tank bleed-out valve.
Fill the air compressor tank with water from an available water tap.
Install the brass test coupling in the threaded pressure relief valve hole. Tighten the coupling with the pipe wrench by turning clockwise.
Attach one end of the pressure hose to the test coupler on the air compressor tank and the other end to the hydrostatic test pump. Tighten both connections with the lockjaw pliers.
Check the air compressor tank pressure rating. The tank rating can be found on the specifications tag attached to the tank.
Raise the tank pressure by operating the test pump handle up and down. Close the pump ball valve on the pump clockwise by hand when the test pressure is at the desired amount.
Determine leakage in the air tank based on dropping pressure as indicated by the hydrostatic test pump pressure gauge. Allow the test to continue for 15 minutes.
Check the area around the tank if the indicated pressure on the pump gauge falls more than 10 per cent of the test pressure within the allotted 15-minute period.
Open the moisture drain plug at the bottom of the air tank with the lockjaw pliers to release the water. The bleed-out valve can also be opened to expedite the draining.
Disconnect the pressure hose from the test coupling on the tank and the hydrostatic pump using the pliers. Remove the test coupling from the air tank with the pipe wrench.
Close the moisture drain with the pliers. Close the bleed-valve by hand turning clockwise.
Restore electrical power and remove tags.
Hydrostatic pumps have relief valves that prevent over-pressuring the air tank.
Never use compressed air to perform tank pressure tests. Testing with air over rated pressure values is extremely dangerous.