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Due to the difference in performance between stainless steel pumps and plastic/ptfe lining pump, the structural design of stainless steel pumps has the following special features.
1. Connection between impeller and shaft
The metal part is embedded in the impeller, and the metal member is connected with the shaft by a key, or the impeller and the shaft are directly connected by a key, and the end of the impeller is protected by an impeller nut. This structure is derived from a metal pump and has poor reliability due to the large number of sealing faces. After prolonged use, the shaft is easily corroded by the media.
The metal part is embedded in the impeller, and the pump shaft is screwed to cancel the impeller nut. This structure allows the shaft to be completely protected from the possibility of corrosion of the shaft. The disadvantage is that the thread processing accuracy is high, and the motor reversal is strictly prohibited during operation.
2. Axial balance force
Most of the impellers of plastic pumps are embedded with metal parts. It is generally not suitable to balance the axial forces by means of balance holes. The back blade balances the axial force at home and abroad.
3. Impeller seal and running clearance between the back blade and the pump body
Because the coefficient of linear expansion of plastics and FRP is 2-6 times larger than that of steel, the running gap of the stainless steel pump is prone to occlusion, which causes the pump to be damaged. Excessive clearance will reduce the efficiency of the pump and cause an imbalance in the axial force of the pump. Since the radial clearance is not adjustable, axial clearance can also be considered, so that the running clearance can be checked and adjusted without removing the pump. In order to prevent the plastic pump casing from falling off or cracking due to temperature changes, it is considered to weld the tortoise shell on the pump casing. The wire mesh makes the lining plastic pump can be made into a larger specification model, and the inlet pipe diameter can reach DN600.
4. Interface
The force of the take-over of the PLASTIC/PTFE LINING PUMP inlet and outlet has not been limited by relevant standards, and is generally requested by the design unit and is determined according to the manufacturing conditions of the manufacturer itself. For the whole plastic pump casing, it is generally connected with the pipe by the loose flange method, and the loop flange is connected with the two end plates; the flange and the cover plate can also be connected to the pipe in an integral manner.
5. Pump body lining layer thickness and its fixation
According to the pump enterprise standard, the thickness of the lining layer is generally 5-8mm. If the lining layer is too thin (such as 1.5~2mm), it is easy to appear partial lining defects during the pressing process, resulting in a decrease in the allowable use temperature and service life of the pump. The possibility of falling off from the pump body and the back cover base metal also increases.
The lining layer fixing method can adopt a method of arranging a dense annular dovetail groove on the base metal, so that the lining layer is firmly fixed and the machining amount is small. It is also possible to arrange a relatively small hole (or a threaded hole) on the base metal, the lining layer is not fixed firmly than the dovetail groove, and the machining amount is large.
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