1, bad welding: Welding very ears and pole piece; very ears and cover Weld. 
2, electro-hydraulic too few: too few liquid injection quantity is not accurate; when the intensity is too large seal extrusion, extrusion electro-hydraulic. 
3, the assembly dysplasia: no close contact between the pole pieces; various points of contact area is too small. 
4, material problems: the conductivity of the lug and the housing; electrical conductivity liquid; conductivity graphite and carbon powder.