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What are the causes of centrifugal pump vibration and its solutions?
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Centrifugal pumps belong to the subclass of dynamic axisymmetric fluid absorbing turbo machinery which transports fluid by converting the rotational kinetic energy to the hydrodynamic fluid flow. The rotational motion can be achieved either by a motor or an internal combustion engine. Centrifugal pumps are commonly used in water, petroleum, sewage and petrochemical pumping. Such a useful machine has a common problem called vibration which leads to a major maintenance costs. The causes of the vibration occurring in this pump can be generally classified into mechanical causes, system causes, hydraulic causes, operational causes and other causes. These causes of vibrations to major losses and reduced life of the pump. Engineers who came to know about the issue finally found the solutions of each and every cause of vibration which reduced the maintenance costs but did not stop the vibration. More explanation about the causes and solutions are discussed in detail in the upcoming chapters.
Keywords: dynamic , axisymmetric , turbo , kinetic energy , hydrodynamic , internal combustion engine , hydraulic.
Let us consider two identical centrifugal pumps A and B. Pump A is not optimized for vibration and pump B is optimized to reduce vibrations. It is assumed that, after 100 hours of running, the pump A will get affected in various parts like shafts, bearings, rings and impeller, seals and fasteners. But the pump B which is dampened by all aspects in vibration, will not get affected as the vibration is considered from each and every part which it originates and it is perfectly dampened. The efficiency of the pump A is very less than pump B because due to vibration, the pump A cannot work in a definite manner thereby producing less output.
In today's mechanics, and considering the centrifugal pumps, the common issue which is occurring in that pump is vibration. There are several other problems which are common are corrosion, priming, etc. But those problems can be easily avoided by changing the material of the parts or treating it with non-corrosive substance. But the vibration occurs in almost all working parts in the centrifugal pump. Also, there is no possibility of eliminating the vibration totally. But it can be dampened which reduces the vibration and not eliminating it.
This quantitative research proposal is based on the causes of vibration in centrifugal pumps and the ways to reduce it. It is highly necessary to be concerned about the vibration which outcomes from the centrifugal pump as it mainly affects the performance output of the pump. It is better if the vibration is monitored on the first time so that it can be eliminated suitable damping techniques or tightening the loosened fasteners. Some of the components which are seriously affected by vibrations are:
H.F.Black who analyzed the effects of hydraulic forces in annular pressure seals on the vibrations of centrifugal pump rotors. He said that in centrifugal pumps, the leakage path is covered with annular clearance spaces which is otherwise called as impeller seals and balance piston seals. This acts as a powerful hydrostatic bearings during turbulent flows. The author analyzed the dynamic forces acting on the rotor due to the bearings in this discussion which includes the squeeze action . Using a single mass motor which includes the estimation of amplitudes and critical speeds, the author analyzed the synchronous forces. Marcinkowskij and Karincev made a qualitative agreement found in large damping forces which was happening due to the squeeze action. The author did a simplified treatment for the fluid rotation effects which was included in the analysis of the rotor vibrations. (Black, 1969)
Rodriguez.C.G, Egusuiza.E, and Santos.F did a research on measuring the frequencies in the vibration induced by the rotor stator interaction in a centrifugal pump turbine. They said that most of the higher level vibrations in large pump turbines are generally originated from the RSI . There are some specific characteristics of vibration which can be clearly observed from the frequency domain such as, a particular relationship between their amplitudes and harmonics of a moving blade which passes frequencies. An appropriate tool which is used to determine the force and its characteristics is the CFD model. The vibration which is induced by the RSI is predicted by considering the sequence of the interaction and also different amplitudes in the interaction between same moving blades and different stationary blades. This gives a different and original interpretation about the source of the vibration characteristics. This action proposed was successful as a consequence of this new interpretation.