求翻译：①调整好安全阀后，停止发动机运转，慢慢打开中、后轮制动贮气筒上的放污开关，使气压表指示在790千帕，慢慢拧动调压阀的调压螺钉，至调压阀的清除阀打开并开始排气为止。是什么意思？

① Adjust the good safety valve, stop the engine is running, slowly open the rear brakes put on the storage pump sewage switch, so that the barometer indicates 790 kPa, and slowly twist the pressure regulating valve of the regulator screw to pressure regulator purge valve to open and begin to exhaust

① After adjust relief valve, stop engine running slowly, rear wheel brake in open air storage tank of dirty switches on, the barometer indicates 790,000 kPa, slowly twist the regulator valve pressure regulating screws, to pressure-regulating valve purge valve opens up and begin to exhaust.