For the variable-frequency combustion-supporting fan in the gas annealing furnace, should the vent valve remain open at all times?

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A problem was identified: the continuous hot-dip galvanizing annealing furnace in the workshop is equipped with a 120kW variable-frequency combustion aid fan; during inspection, it was operating at 46Hz while the pipeline vent valve was open； I asked the operators and equipment managers; some said they were worried that high pressure might damage the fan, so the vent valve remained open ； Some say it’s not necessary to open it; it only needs to be opened when starting up and shutting down ； Some say that variable-frequency fans experience surge when the frequency is too low, and it cannot be lower than a certain value; however, the air volume generated is greater than what is required by the gas furnace, so the vent is opened ； I hope the experts here can help answer my questions. Thank you! Does it need to stay on all the time, and for how long? How can we determine it?