A small number of rotor pump shaft failures are caused by metallurgical and manufacturing process defects, such as undetected pores in the base material and uneven hardness caused by improper heat treatment processes. Some other failures are due to substandard shaft machining accuracy or insufficient design margin, which cannot withstand the torque, fatigue and corrosion loads under normal working conditions. For cantilever-structured rotor pumps, the shaft flexibility coefficient ISF=L³/D⁴ is the core design index, where D is the shaft diameter at the mechanical seal sleeve (mm), and L is the span between the rotor outlet centerline and the radial bearing (mm), which intuitively reflects the deflection degree of the shaft under radial force when deviating from the design working condition.

-Bonve Pumps Cam-type Twin Rotor Pump-

Operation away from the best efficiency point (BEP) is the primary cause of rotor pump shaft breakage. When the pump operates outside the allowable flow and pressure range, it will generate severe unbalanced radial forces, causing the shaft to bend multiple times per revolution. Taking a speed of 255 rpm as an example, the shaft will produce 510 bending cycles per minute. This high-frequency alternating load is extremely easy to cause tensile bending fatigue failure. Only when the deflection strain is small enough can the shaft withstand long-term cyclic loads.

Substandard straightness of the shaft itself will produce the same fatigue effect. The total indicator reading (TIR) tolerance of high-quality rotor pump shafts should be controlled within the range of 0.0254mm to 0.0508mm. Rotor imbalance is another high-incidence inducement. During the meshing operation of twin rotors, tiny imbalances will be amplified, leading to periodic shaft runout. Even if the pump shaft is completely straight during static inspection, it will still bear continuous bending loads during operation.

Fluid property changes have a particularly significant impact on rotor pumps. If a pump designed for low-viscosity fluids is used to pump high-viscosity or high-specific-gravity media, the shaft load will be greatly increased; jamming of media containing solid particles will also generate instantaneous impact torque. At the same time, corrosive environments will sharply reduce the fatigue strength of shaft materials, and corrosion-resistant shafts should be preferentially selected for corrosive working conditions. Moreover, torque is inversely proportional to speed during variable speed operation.

Improper use will significantly shorten the service life of the shaft. The intermittent torque of engine drive and the additional radial load of belt drive will increase the fatigue load of the shaft, and rotor pumps are not suitable for direct belt drive. Even extremely slight misalignment between the pump and the driver will generate bending moments, which usually lead to bearing failure first and then shaft breakage. In addition, abnormal vibration caused by cavitation, critical speed, etc., improper assembly of rotors, couplings and keyways, and operation beyond the allowable speed range will gradually lead to fatigue failure of the shaft.

Bonve pump always adheres to the philosophy of "Wholeheartedly Making Good Rotor Pumps," committed to providing global customers with customized conveying and mixing solutions. If you have technical inquiries, selection needs, case references, or other cooperation intentions related to Bonve rotor pumps, please feel free to contact us.  

Service Hotline: 0574-87588986 13586591794  

Official Website: www.bvpumps.com  

Business Email: market@bonvepumps.com  

We look forward to working with you to drive efficiency and innovation in industrial fluid transmission with precision technology.