... structure sea. Butterfly Valve Main FeaturenThe raw material of BD series butterfly valve is steel or alumininum. Aluminum butterfly valve sealing ... utilizes the mechanical sealing structure.nThe locking cover of the series butterfly valve has three structural types shown in the pictures ... .2Φ2502502683003508-M20390Steel46fig.2Structure Drawing Butterfly Valve for Transformer, BD series, D50~D250