How to check Air System Leakage

How to check Air System Leakage in Truck and Trailer
Start the Truck Engine let the compressor fill the air and let the governor cut the air. Release Red and Yellow Valve. Then Switch off the engine But it should be in ON position (engine off) key on position and wait for gauges to stabilize and push the brake, wait for gauges to stabilize again and start your time for 2 min , should not lose more than 6 psi , 4 for the truck 2 for trailer, hold with full pressure on foot brake. If the air pressure is lost more than 6 PSI then there will be some leakage in the system.