The right tool for the job. The guys at Classic Auto Air use a specialized wrench to undo the valves. This shot is an example. You should have your gauges hooked up before you do this. The tool prevents the flats on the valve from being damaged. If you've used the wrong tool and chewed up the threads on the high-pressure hose, Classic Auto Air has the correct valves to replace them. Just be sure that you evacuate the system before replacement.