求助一句话的理解? slag tapping is in "manual-run" mode, all burner double-block and vent valves are powered-up and shut with their vents open with the exception of the nitrogen double-block and vent system ( which is open, )as is the main air/nitrogen flow control valve, fc4380.(已标出状-主-谓-补结构,自己再根据上下文去理解) double-block and vent valves 双切断阀加放空查看更多