1. The running clearance between the impeller seal and the back vane and the pump body

Because the coefficient of linear expansion of plastic and glass fiber reinforced plastic is 2~6 times larger than that of steel, the operating clearance of metal pump is prone to seizure and damage the pump. Excessive clearance will reduce the efficiency of the pump and cause an imbalance in the axial force of the pump. Since the radial clearance cannot be adjusted, the axial clearance can also be considered, so that the running clearance can be checked and adjusted without disassembling the pump.

2. Connection form of impeller and shaft

① The metal parts are embedded in the impeller, and the metal parts are connected with the shaft with a key, or the impeller and the shaft are directly connected with a key, and the end of the impeller is protected by an impeller nut. This structure is derived from a metal pump, and its reliability is poor due to its many sealing surfaces. After long-term use, the shaft is easily corroded by the medium.

② Metal parts are embedded in the impeller, which is connected with the pump shaft by thread, and the impeller nut is eliminated. This structure can completely protect the shaft and avoid the possibility of the shaft being corroded by the medium. The disadvantage is that the thread processing accuracy is high, and the motor reverse rotation is strictly prohibited during operation.