1.High entire pressure 2.Big wind,low noise 3.Low engery consumption,run ... and close, windproof, rainproof and dustproof.5Newly punch forming fan blade, reasonable angel and reach the max. air flow, ... process: noise test, vibration test .concentric performance test, fan blade turning speed test, input air teat and vehicle efficiency ... type B,thicker and durable ,double life time Industrial Exhaust Fan