Front cover of impeller： ductile cast iron（ASTM A-536 GR 60 －40－18）
Shroud: Nodular Iron (ASTM A 5536 GR 60-40-18)
Diversion device modification：
1、Special metal layer adhesion to cope with erosion and corrosion;
2、The original material was cast iron, which is completely corrosion-resistant；
3、Epoxy coating or PTFE coating is prone to damage and peeling off；
