Fluoroplastic pumps and stainless steel pumps have vertical and horizontal structures, with self-priming, centrifugal and other forms. Fluoroplastic pumps can transmit any concentration of strong acids, strong alkalis, and strong corrosive solutions. Usually stainless steel is suitable for lightly corrosive media , Stainless steel centrifugal pump has better temperature and wear resistance, and fluoroplastic pump has good corrosion resistance. This is the advantage and disadvantage of the overall performance. So what is the difference between stainless steel pump and plastic pump? Due to the difference in performance between stainless steel pump and plastic pump, the structure design of stainless steel pump has the following particularities:
1. 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 with an impeller nut. This structure comes 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 relatively high, and the motor is strictly prohibited to reverse during operation.
2. Axial balance force
There are mostly metal parts embedded in the impeller of the plastic pump, and it is generally not suitable to balance the axial force with the balance hole. The back blade is widely used at home and abroad to balance the axial force.
3. 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 plastics is 2~6 times larger than that of steel, the operating clearance of stainless steel pumps is prone to seizure and damage the pump. Excessive clearance will reduce the efficiency of the pump and cause the imbalance of the axial force of the pump. Since the radial clearance cannot be adjusted, the axial clearance can also be considered, so that the operating clearance can be checked and adjusted without dismantling the pump. In order to prevent the plastic pump casing from falling off or cracking caused by temperature changes, consider welding tortoise shells on the pump casing Wire mesh, so that the plastic-lined pump can achieve larger specifications, and the imported pipe diameter can reach DN600.
4. Interface
The force of the inlet and outlet of the plastic pump has not yet been defined by relevant standards. It is generally requested by the design unit and determined according to the manufacturing situation of the manufacturer. For integral plastic pump casings, generally adopt a loose flange to connect to the pipeline, and the loose flange is connected to the cover plates at both ends; it can also be connected to the pipeline by integrating the flange and the cover plate.
5. Pump body lining thickness and its fixation
According to pump company standards, the thickness of the lining layer is generally 5-8mm. If the lining layer is too thin (such as 1.5~2mm), local lining defects are prone to occur during the pressing process, resulting in a decrease in the allowable temperature and service life of the pump. The possibility of falling off the base metal of the pump body and the rear cover also increases.
The fixing method of the lining layer can adopt a method of arranging a dense annular dovetail groove on the base metal, so that the lining layer is fixed firmly and the machining volume is small. The method of arranging denser small holes (or threaded holes) on the base metal can also be used. The lining layer is not as firm as the dovetail groove and is machined.
