... , chemical plants, big factory workshops etc.Negative-pressure ventilating fan series are designed scientifically. Low cost, low noise, good ventilation ... 900B1000*1000*4000.55 shutter, frame, wind set, fan blade are galvanized9FJ-1000B1100*1100*4000.759FJ-1250B1385*1385* ... style9FJ-900B1000*1000*4000.55shutter, frame, wind set , fan blade aregalvanized9FJ-1000B1100*1100*4000.759FJ-1250B1385*1385*4001. ...