Structure difference between metal and non-metal pump

Due to the difference of performance between non-metallic and metallic materials, the structural design of non-DU metal pump has the following particularity.

1. Operation Dao clearance between impeller seal and back blade and pump body

Because the linear expansion coefficient of plastic and glass fiber reinforced plastic is 2-6 times larger than that of steel, the running gap of metal pump is easy to be occluded, which will damage the pump. If the clearance is too large, the efficiency of the pump will be reduced and the axial force of the pump will be unbalanced. Since the radial clearance is not adjustable, the axial clearance can also be considered, so that the running clearance can be checked and adjusted without dismantling the pump.

2. Connection form of impeller and shaft

① The embedded metal parts in the impeller are connected with the shaft by key through the metal parts, or the impeller is directly connected with the shaft by key, and the end of the impeller is protected by the impeller nut. This structure comes from metal pump, because there are many sealing surfaces, the reliability is poor. After long-term use, the shaft is easy to be corroded by the medium.

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

3. Thickness and fixation of pump body lining layer

According to the standards of foreign pump enterprises, the thickness of lining layer is generally 3-5mm. If the lining layer is too thin (such as 1.5-2mm), it is easy to have local lining defects during the pressing process, which leads to the decrease of the allowable service temperature and service life of the pump, and the possibility of the lining layer falling off from the base metal of the pump body and back cover is also increased.

The lining layer can be fixed by arranging a dense ring dovetail groove on the base metal, so that the lining layer can be fixed firmly and the machining amount is small. It can also be used to arrange more compact holes (or threaded holes) on the base metal. The lining layer is not as secure as the dovetail groove, and the machining amount is large.

In order to prevent the non-metal from falling off or cracking from the pump shell caused by the temperature change, it can be considered to weld the tortoise shell wire mesh on the pump shell, so that the plastic lined pump can achieve a larger specification and model, and the maximum inlet pipe diameter can reach DN600.

4. Axial balance force

The impeller of plastic pump is mostly embedded with metal parts, so it is generally not suitable to balance the axial force with the method of balance hole. Back blade balance axial force is widely used at home and abroad.

5. Interface

At present, there is no relevant standard to limit the stress of the connecting pipe at the inlet and outlet of the non-metal pump, which is generally required by the design unit and determined according to the manufacturing situation of the manufacturer. For the integral non-metallic pump casing, the looper flange is generally used to connect with the pipeline, and the looper flange is connected with the cover plates at both ends; the flange and cover plate can also be made into an integral way to connect with the pipeline.