With a built-in protector, the motor turns off automatically when overheated or when the three-phase mains loses a phase, so as to protect the motor from burning out; The gear is made of chromium-manganese-titanium alloy steel, with carbonitriding on the surface, which can prolong life span greatly; can prolong life span greatly;and stainless steel impeller are developed according to the requirements of varied usage environments and specific demands of users, eliminating the need of frequent change of impellers or painting.